From 25a18f478323f274163dac615b225f403da3eaf5 Mon Sep 17 00:00:00 2001
From: Mike Taylor These were large, often huge predators. Some
-of the carcharodontosaurines are the largest known carnivores ever to walk
-upon the Earth, even larger than A recent find of a group of differently-aged carcharodontosaurines (the
-genus is yet to be publicly named) in association with each other suggests
-that these enormous carnivores may have hunted in packs. Interestingly,
-the largest known land animals of all time,
-such as There are some cranial similarities
-between carcharodontosaurines and , another
-group of Gondwanan (Southern Hemisphere) carnivores. This may be due to
-convergence, but some have proposed that carcharodontosaurines are not
-, but more
-closely related to abelisaurs. But other characteristics, such as the
-three-fingered hand (neoceratosaurs have four fingers), cast doubt on this
-idea. This recently discovered group has
-proven difficult to place. The original member, The discovery of Alvarezsaurs were small, terrestrial animals with
-long legs. Their niche is far from certain. Since their stubby forearms
-were built so powerfully, it has been suggested that they used them for
-digging. (In fact, some think that their sterna were keeled as a digging
-adaptation, similar to moles, and that they evolved keeled sterna
-separately from birds, which evolved it for flying.) The overall body plan
-of alvarezsaurs is not that of a burrower, but it has been suggested that
-they might have fed on colonial insects, ripping into nests with their
-single-clawed hands. Anapsida is a clade of of with no fenestrae
-(openings) in the back of their skulls. It includes large herbivores like
-pareiasaurs as well as modern-day turtles. During the , "The Age of Reptiles", turtles grew to great
-sizes. Some, like In traditional usage, Anapsida included all
-without antorbital fenestrae. It has now been restricted to those sharing
-more recent ancestry with chelonians (turtles) than with other extant
-amniote groups. Membership is mostly the same, but excludes basalmost
- (e.g. ) and
-basal romeriids (e.g. ).
- Within Reptilia, anapsids are probably the most distant relatives of
-. Among Earth's enormously vast array of animals, belong to the clade,
-which is characterized by the possession of a backbone. Ankylosaurs include the most heavily armored
-dinosaurs of all, the "tanks" of the . The
-entire back was covered with bony plates, studs, and spikes. So was the
-head, right down to the eyelids! (Bony eyelids have been found in Some nodosaurids bore very large spikes along their sides, the largest
-often sprouting from the shoulders. These may have been used as defense,
-weapons in rivalry, or both. These animals are known from all
-continents except South America and Africa. They were most prevalent in
-Laurasia (the northern supercontinent). A large club at the end of the tail
-distinguishes ankylosaurines and shamosaurines from the more primitive
- They probably used this club to give
-crippling blows to potential predators. A similar structure existed in the
- Polacanthines were once classified as
-nodosaurids, but are now recognized as a distinct clade closer to the
-Ankylosaurinae. It was recently thought that they had small tail clubs,
-but this has been refuted. Shamosaurines had narrow snouts, especially compared to the very wide
-snouts of ankylosaurines. This may reflect different niches. Many ankylosaurines had complex, looping nasal passages, possibly to
-enhance their sense of smell. Archosauromorpha includes all with
-four-chambered hearts, an evolutionary innovation that permitted them
-higher activity levels and terrestrial dominance throughout the . The forms shown here were once all included in
-Archosauria in the "grab-bag" taxon "Thecodontia" -- any archosaur that
-wasn't a , a , or
-a . This form of classification was abandoned
-once knowledge about these animals increased. The non-archosaur archosauromorphs, or "protoarchosaurs", show fairly
-wide diversity, from small hunters with insanely long necks like The two major groups of Archosauria proper are rather poorly named.
-Pseudosuchia means "false crocodiles", yet it includes true ones.
-Ornithosuchia was named after the creature Pseudosuchians became the dominant
-terrestrial animals after the demise of the two previous "dynasties" -- the ""
-and the non- . They
-diversified into many niches: armored herbivores (aetosaurs), big
-carnivores (rauisuchians), tiny sprinters ( But by the end of the they had been
-outcompeted by their fellow archosaurs, the ornithosuchian . Dinosaurs and pterosaurs would continue to
-dominate terrestrial and aerial niches until the end of the , far longer than any previous or subsequent
-terrestrial "dynasty" (and they still dominate aerial niches!). Of
-all the pseudosuchians, only the aquatic crocodylomorphs survived beyond
-the . Birds evolved from small, possibly "sickle-clawed"
- probably sometime during the (some have suggested the ),
-as did their close relatives the . The
-earliest known definite bird is the European Pygostylian birds are characterized by a
-pygostyle, a fusion of the vertebrae at the end of the tail. This trait
-seems to have evolved convergently in at least one ( Ornithothoracean birds, a large subset of pygostylians that includes
-, have a "modern-style" thorax and an alula,
-or "bastard wing" -- a group of feathers associated with the first finger
-that aids maneuverability in flight. Unlike the other two groups of
-flying , and
-, the hindlimbs of birds are not in any way coupled with
-the wings, and remain free for running. Due to this and other pieces of
-evidence, some dinosaur researchers argue that birds did not evolve from a
-tree-dwelling ancestor, as the other groups are thought to have. Recent
-studies suggest that But many disagree with this idea, arguing that flight in birds evolved as
-it seems to have in bats and pterosaurs -- from the "Trees Down".
-They hold that bird ancestors were scansorial coelurosaurs which leaped from
-tree to tree, then evolved into gliders, and from there to fliers. The
-facts that As of now, the fossil evidence does not clearly favor either the
-"Trees Down" or "Ground Up" hypotheses of the evolution
-of flight in birds. The hypothesis that birds descended from
-dinosaurs has been around for a long time. Thomas Huxley (a.k.a. "Darwin's
-bulldog") proposed such a relationship based on similarities between
- Heilmann's view was finally dispelled by the discovery that some dinosaur fossils (such as those of A more recent objection to the dinosaur-bird link is the claim that
-embryological evidence shows the digits in the hands of modern birds to be
-II-III-IV, not I-II-III as in coelurosaurs and other . In fact, the story may be quite a bit more
-complicated. It is not certain that the element that has been interpreted
-as a vestigial digit I is in fact digit I. Furthermore, other studies show
-that frame shift can cause some birds to have digits aligned differently
-than in other birds, even with the same species. Opponents of the dinosaurian theory of bird origins have yet to
-propose an explicit alternate theory, generally stating that birds
-evolved from basal of some kind. They
-also have yet to explain why such an enormous degree of convergence
-would appear between birds and terrestrial
-when they represent separate niches. The taxon Carnosauria once included all large , from large to to . More recent
-research shows that most of these are more closely allied to other groups.
-Today, only the allosaurids and their relatives are considered true
-carnosaurs (The precise definition: all animals sharing a more recent
-common ancestor with Many carnosaurs bore crests atop their heads.
-The primitive forms Carnosaurs did not survive to the end of the
-. They may have been out-competed by and . But in
-their heyday they included the largest known land predators of all time.
- One of the two main lineages of ceratopsids (a.k.a. horned
-dinosaurs"), most centrosaurines bore large horns on their noses. Unlike
-most members of their sister group, the ,
-their neck frills tended to be relatively short, although often
-accentuated by two large spikes at the top, or spikes all along the rim of
-the frill as in The advanced pachyrhinosaurins had a large, blunt bony growth in place
-of the nasal horn. This may have formed the core of a horny pad in life,
-or possibly the core of a gigantic nasal horn. This group of herbivores contains the frilled , including the horned dinosaurs. Like many other
-groups of dinosaurs, they inhabited only Asia and North
-America. The creatures on this page were all bipedal. From such as these came
-the quadrupedal . Coronosaurs were generally
-larger, although at least one bipedal ceratopsian ( (See for a discussion on the "s" in
-Ceratopsia). Unlike their sister group, the ,
-ceratopsines (a.k.a. chasmosaurines), placed more emphasis on brow horns
-than the nasal horn, to the point that some barely had a nasal horn at
-all, hence names like Their neck frills were longer than those of centrosaurines, except in
-the lineage leading to There has been some disagreement over the name of this group and all
-other groups named after the genus Coelurosauria once included all the small .
-It was the sister group to , which included
-all the big theropods. This system of theropod classification has become
-very much outdated, but the original names are still kept for certain
-actual groups. If the more primitive forms of the old Coelurosauria are
-excluded and a few other forms are added (including ), they do form a monophyletic group. Interestingly,
-this group that once contained only small theropods now includes Coelurosaurs are an enormously diverse group. They include , , , , , and the incredibly varied birds. Skin impressions are known from several coelurosaurs.
-A partial impression, possibly from the tail of a
-shows scales like those seen in other dinosaurs. All other
-coelurosaur skin impressions, such as those of The advanced coelurosaurs make up
-Maniraptoriformes. All
-maniraptoriforms sharing a more recent ancestor with Arctometatarsalia originally included ,
-avimimids, tyrannosauroids, troodontids, and ornithomimosaurs. It was
-named for the arctometatarsalian foot of these animals, wherein the
-middle metatarsal is pinched at the top. This trait, an adaptation for
-running, is now thought to have evolved separately in caenagnathids
-and possibly in all five of the groups.
-have an extreme version of this feature. This group includes all of the quadrupedal . Coronosaurs tend to be larger and have larger
-neck frills than more primitive ceratopsians. There has been much dispute
-as to whether the front limbs of coronosaurs were held fully erect or
-sprawling to various degrees. An intermediate posture seems most likely. The most primitive coronosaurs, like the well-known The function of the neck frills in these and other ceratopsians is not
-certain. They may have borne colorful displays, protected the neck from
-predators, anchored powerful cheek muscles, or performed a combination of
-these functions. In Hailing from the very latest stretch of
-the , ceratopsids were the pinnacle of
- evolution. They included some of the very
-largest , such as the mighty Skin impressions are known from both centrosaurine ceratopsids ( The genera listed here, plus other
-were once grouped in the family Protoceratopsidae (=Protoceratopidae),
-since they all had claws instead of hooves. Most now consider this a
-paraphyletic (and hence invalid) grouping. There may, however, be a
-monophyletic (hence valid) group of basal coronosaurs which would be
-termed Protoceratopsidae. Crocodylomorphs originated around the same time as the . They were the only
-to survive the , and survive to the present day
-in the form of crocodylians. Of all living animals, crocodylians are the
-closest relatives to dinosaurs (excluding ,
-which are dinosaurs). Unlike other living (except for birds), crocodylians have a
-four-chambered heart and a semi-upright stance. Some "primitive" crocodylomorphs may have been more active and agile
-than today's crocodylians, which have evolved a relatively sluggish
-lifestyle. The attack strategy of a dromaeosaurid was possibly to leap at its
-prey, feet and arms extended. This posture would be balanced by the long,
-stiff tail. The dromaeosaurid would grab onto its prey with cruel,
-grasping hands, then tear out the unfortunate creature's throat or guts
-with the eviscerating foot-claws. The energy and quickness needed to carry out such a maneuver is one
-piece of evidence used in the debate over whether were cold-blooded or warm-blooded. These dinosaurs may have hunted in packs, as shown by one find where
-three Dromaeosaurids were probably very close to
- ancestry, as shown by their bird-like hip arrangement
-(unusual for non- ),
-extremely stiffened tails, and their similarity to the feathered, flying
- "'Raptors" were one of the major stars of the blockbuster movie
-Jurassic Park. Although this movie and its sequel, Jurassic Park
-2: The Lost World boasts the most accurate dinosaurs in the history of
-movies, there are a significant number of errors, especially with the
-"'raptors". The most obvious problem is that they were much too big. Real
- The reason for this is probably as follows. Michael Crichton wanted to
-use a fierce, approximately man-sized predator. For the movie they decided to bump the size up. They also gave it a
-more Interestingly, while the movie was being made, a new dromaeosaurid was
-found which was even larger than the movie's "'raptor". The discovery of
-this new dinosaur ( So the "'raptor" in Jurassic Park is probably a decent
-approximation of a real, undescribed dromaeosaurid (not a There are three major types of dinosaur.
-includes all of the carnivorous dinosaurs, as well as their modern-day
-descendants, the . consists of long-necked herbivorous dinosaurs,
-including , the largest land
-animals of all time. The third group, ,
-contains many diverse forms of beaked, herbivorous dinosaurs. Although the major groups of
-dinosaurs are clearly recognized, there
-is some debate about their relationships to each other and to the
-ancestors of dinosaurs. About the only thing that can be confidently
-stated about early dinosaurian/ evolution is
-that the following evolutionary lineage occured:
- are thought to have split off from this
-lineage probably before The confusion about dinosaur ancestry leads to the question "What is a
-dinosaur?" The original definition of Dinosauria, as stated by Sir Richard
-Owen in 1842, was a group of large (which he
-considered a type of ) consisting of Dinosauria was traditionally divided into the orders Ornithischia
-("bird hips" -- a misleading term) and Saurischia ("lizard hips"). For
-much of the history of paleontology, the status of Dinosauria as a real
-group has been considered dubious -- Ornithischia and Saurischia were
-separated from each other and sometimes were themselves split up. More
-recently, however, cladistic analysis has reaffirmed Dinosauria as a
-natural group. It is defined as the most recent common ancestor of (which are now considered saurischians) and
- This definition has lead to some disagreement as to whether certain
-primitive ornithodirans are dinosaurs or not. Some include all of the
-genera shown in the above lineage in Dinosauria, whereas others don't even
-consider to be true dinosaurs. On these
-pages But a minority claim that early sauropodomorphs show more similarities
-to early ornithischians than to theropods. They classify Sauropodomorpha
-and Ornithischia in Phytodinosauria ("plant dinosaurs") as a sister taxon
-to Theropoda. Diplodocids included some of the hugest creatures to walk upon the
-Earth. These animals have been the focus of several computer-assisted studies
-in biophysics. One study suggests that diplodocids could actually crack
-their tails like whips, causing loud sonic booms. Another study, focusing
-on the other end of the animals, suggests that they could not hold their
-heads very high, and thus may have fed on low-growing vegetation. This
-goes against previous thought that evolved their
-long necks to reach into the trees. Recently a diplodocid was found with non-bony dermal spines along its
-back. Since non-bony structures are rarely preserved, it is not certain
-how widely throughout this feature
-existed. Members of this group had long, whip-like tails
-(possibly used for defense), peg-like teeth, and high vertebral spines.
-The extremely long spines of some diplodocimorphs, such as
- Some of these animals, like the dicraeosaurids, made it into the
-Cretaceous, but not to the end of the Mesozoic Era. There is a possible diplodocimorph named Enantiornitheans were a large group of which
-evolved alongside modern-style birds, or ,
-during the . Their name ("opposite birds")
-refers
-to the articulation of the scapula with the coracoid, opposite to that of
-modern birds. Like neornitheans, advanced enantiornitheans were toothless.
-These two lineages, along with ,
-, and ,
-represent the five known lineages of toothless
-. Enantiornitheans achieved a fair degree of
-diversity, beginning as
-small, perching fliers, with some developing into shorebirds. They
-ranged from sparrow- to vulture-size. Although apparently more plentiful than their neornithean cousins
-during the Cretaceous, enantiornitheans, like all non-neornithean
-dinosaurs, became extinct at the end of the Cretaceous. Why neornitheans
-survived while they did not remains a mystery. These "duck-billed" were mostly non-crested,
-although some, like Before the discovery of The old genus These are commonly known as the "duck-billed" dinosaurs, since their
-beaks bore a superficial resemblance to those of ducks. They were the last,
-largest, and most numerous of the . More "primitive" hadrosauroids like Hadrosaurids are divided into two subfamilies, the generally non-crested
-hadrosaurines and the lambeosaurines, which developed large hollow crests
-on their heads. At least one scientist considers them to be two separate families,
-with It was once thought that the duck-bills, like their namesakes, were
-aquatic. This notion seemed to be supported when a fossilized "mummy" of a
-hadrosaurid was discovered, showing what appeared to be webbed fingers on
-the hands. The hollow crests of the lambeosaurines were supposed to be for
-air storage, since they connected to the nasal passages. This theory is largely out of favor now. The "webbed" fingers, upon
-closer scrutiny, more closely resemble desiccated hoof pads. The crests
-could not have functioned as air storage, since they were rigid and
-inflexible. Air sucked out of them would have created a vacuum. And the
-rugged teeth of the hadrosaurids strongly indicate that they ate rough, woody
-plant material, not soft seaweed. The teeth in the jaw were aligned in great
-"batteries", so that if one wore out there was another one behind it to
-replace it. Some hadrosaurid jaws contained as much as 2,000 teeth! It seems that duck-bills led a largely terrestrial life. They would walk
-primarily on all fours, as shown by the hoof-like nails and supporting pads
-on the hands, but were easily capable of switching to bipedal locomotion. These are the only known marine of the
-! Hesperornithiforms had adapted to life in
-the oceans of Laurasia, and are best known from the
-North American interior, which was covered by a large sea during much of the
-. Unlike the major modern-day group of marine birds (penguins),
-which have flipper-like wings, hesperornithiforms propelled
-themselves with large, (presumably) webbed feet, like loons
-and grebes. Their wings had atrophied to tiny, useless things, and their
-feet were set so far back that walking must have been extremely awkward.
-Thus, they probably spent very nearly all of their time in the water. Heterodontosaurids were a group of small, primitive
-
-from the . They
-were all fairly similar to each other. Some species, such as
- Heterodontosaurids were traditionally considered primitive
-, although they bear a number of similarities to
- as well. Despite their name, ichthyosaurs were neither nor
-, but
-a group of uncertain origin that evolved into
-completely marine forms. Like sharks, they had dorsal fins and a tail
-fin that swept side-to-side. Ichthyosaurs arose during the , but did not
-make it to the end of the . They were gone
-before the K/T Extinction, which killed off other large marine
- and the non-
-.
- Unlike all other advanced , ichthyosaurs
-had more than five digits. It was once thought that they might be related
-to very early tetrapods like The major characteristic of these medium- to large-sized herbivores is
-a spiky thumb, possibly used for defense against predators. When
- The animals listed here cover the transition from early,
--like iguanodontians to the medium-sized
- These "duck-billed" bore large, hollow
-crests on their heads. The crests of The lambeosaurine crests may have been used as sexual displays. For many
-lambeosaurine genera, there are two forms known, one with a smaller
-crest, one with a larger crest. These were originally classified as different
-species, although in some cases they may just be different genders. In addition to visual display, the tubular crests, which connected to the
-nasal passages, may also have been used as giant trumpets, allowing the
-lambeosaurines to let out great, deep, resonant bellows across the
-prehistoric landscape. Another idea is that the crests enhanced their sense
-of smell, allowing them to detect giant predators. Lepidosauromorphs include all with
-overlapping scales. Two types of lepidosauromorph remain alive today:
- During the late , there were huge, marine
-squamates known as mosasaurs. They went extinct at the end of the
-, along with all non-
-. The name Macronaria ("large nostrils") refers to the enlarged nasal
-openings of this group. Like all , their nostrils
-were situated atop their head, nearly above the eyes. Macronarians
-had crests of varying sizes formed by high nasal bones. In some
-specimens, these bones were not completely preserved, leaving the skull
-looking rather low, like those of . For this
-reason, many were once classified with them. Basal (non-titanosauriform) macronarians, or
-"camarasaurs", were fairly typical sauropods of small to average size.
-They had boxy skulls and spatulate teeth. Embryonic "camarasaur" material
-indicates that some laid eggs with diameters of 24 cm. Most of the animals listed above as
-non-titanosaurian titanosauriforms have been included at some time in the
-family Brachiosauridae, but their exact relations to one another are
-poorly understood at this time. Among these animals are some of the
-largest land animals of all time, such as It was once thought that the large crest of "brachiosaurs" was a
-snorkeling device. Since then it has been shown that if a
- Mammals originated around the same time as the
-, but remained in their shadow throughout the
-. After the K/T extinction, they diversified to
-fit the niches that the dinosaurs left empty, as well as many other niches.
-Go us! Dinosaurs may be cool, but who's on top of the food chain now, eh?
-I have to go eat some . These were mostly medium-large predators which displayed some primitive
-characteristics, such as four manual digits, one of which was lost in
-the more "advanced" , the other great branch of
-. Although never quite as diverse (or numerous) as the
-tetanurans, neoceratosaurs had some variety. Most were medium-large
-predators, but there were also tiny ones like
- Neoceratosaurs were generally robust with "tall" heads. Some had a small
-opening in front of the antorbital fenestra, similar but probably
-convergent to the maxillary fenestra of tetanurans. Neoceratosaurs had six
-or seven fused sacral vertebrae, more than other theropods. During the , neoceratosaurs inhabited the southern, or Gondwanan,
-continents. If, as a few suspect, the mighty
-are abelisauroids, they may have even been the dominant Gondwanan predators
-(although it seems more likely that they are
-). Neoceratosaurs persisted to the end of the
-. This group contains all modern, toothless .
-They are divided into paleognathans (ratites and tinamous) and neognathans
-(all other modern birds). Beyond that, classification gets tricky --
-there are about as many schemes as there are scientists studying avian
-phylogeny. Neornithean systematics is highly volatile at the moment, so
-don't be surprised if you see changes here. When all the other died
-out at the end of the , neornithean
-birds made an attempt to fill the empty niches left by the large predatory
-. In South America, large, ground-dwelling,
-carnivorous phorusrhacids evolved and lasted until fairly recently. But
-today, with few exceptions, birds are aerial, not terrestrial. In the skies, however, these last descendants of the mighty dinosaurs
-still reign supreme. They beat out in the
- (in the smaller niches) and today they keep
- from flying during the day. There are over
-twice as many living species of bird as living species of mammal. They are
-the last vestige of the dinosaurs' dominion. Apart from certain , ornithischians were the only
-beaked dinosaurs. They were all herbivorous (save for a few possible
-omnivores, like ), and included a very wide
-variety of forms: ,
-,
-, , and
-. The earliest ornithischians were small, bipedal plant eaters, like
- Ornithodira ("bird necks") is divided into two major sections.
-Dinosauromorpha includes and their early
-ancestors, the "lagosuchians". These ancestors were very small, about
-1.5 to 3.5 feet long. They were probably carnivorous or insectivorous. The other group, Pterosauromorpha, includes ,
-the so-called "flying " (although
- are also considered reptiles under the cladistic
-system). There are two possible non-pterosaurian pterosauromorphs:
- Some do not consider pterosaurs to be close relatives of dinosaurs:
- All ornithodirans walked
-with a fully upright stance, like that of most .
-The group is named for the S-shaped neck found in most members. The only living ornithodirans, birds, are highly endothermic (or
-"warm-blooded"), but there is still debate as to the metabolic rate of
-extinct ornithodirans. The idea that they were endothermic has gained
-much acceptance in recent times, but some still maintain that they were
-ectothermic (or "cold-blooded"). Others think that they may have had
-intermediate metabolisms, or alternate types of physiology. But everyone
-agrees that the upright stance of ornithodirans indicates a high level
-of activity, regardless of metabolic rate. It has been suggested that the fur-like integument seen in some pterosaur
-fossils and the feathers seen in some dinosaurs (fossil and living) might be
-homologous. These are commonly known as the
-"ostrich mimics" or "ostrich dinosaurs" (although, technically,
- are dinosaurs -- and if you think about
-it, isn't it ostriches who are ornithomimosaur mimics?). They were possibly
-the fastest of dinosaurs, with conjectured running speeds of 40-50 1.
-They all had very large eyes, like their possible relatives the
-. A peculiar feature of the ornithomimoids is the toothless, beaked mouth.
-This may indicate that they were one of the few groups of
-non- to abandon a
-predatory lifestyle, possibly assuming an herbivorous or omnivorous mode of
-life similar to that of modern-day ostriches. Early ornithomimosaurs such as
- Ornithomimoids were all fairly similar. They had lost the first, inner
-toe, a dewclaw in most theropods. The ornithomimids are especially difficult
-to distinguish from each other, and for this reason some feel that they
-should all be lumped into one genus, Ornithomimosaurs were fairly similar in size, from the most primitive ones
-at 2 meters long to the advanced ones at 3.5-4m. The exception is the giant
-ornithomimoid This group has at various times included nearly all bipedal
-. By now many forms once included here have
-been recognized as primitive members of other largely quadrupedal groups
-( It was once thought that the animals listed on this page formed a clade:
-Hypsilophodontia, sister clade of . But newer
-studies indicate that this group was paraphyletic. The only definite
-hypsilophodont is The animals on this page were small or tiny bipedal runners which may
-have lived lifestyles similar to those of such modern-day
- as deer, gazelles, and kangaroos. From creatures
-such as these came the larger, semi-quadrupedal iguanodonts. Ornithurans include modern birds () and
-their relatives. Except for neornitheans, ornithurans retained small
-teeth in their jaws, except at the front of the upper jaw (premaxilla). Four main types are known: the flightless patagopterygiforms,
-the aquatic , the seaside-dwelling
-ambiortimorphs, and the extremely diverse neornitheans. All lived in the
-, and all except neornitheans died out at the
-end of the Cretaceous. This group includes the oviraptorids and the caenagnathids. The latter
-are a somewhat poorly known group, known mainly by hands and feet, which
-are fairly -like. Oviraptorids were a very peculiar group of .
-Their mouths were entirely toothless, forming beaks. They were sometimes
-classified with the , another group of
-toothless theropods. However, they lack the arctometatarsalian foot of
-the ornithomimids and other
-theropods. One oviraptorid specimen was found huddled atop a nest of its own eggs,
-its wing-like arms spread over them. Apparently it was protecting its brood
-when a sand avalanche buried and killed it. (The head of the
-specimen is missing, so it is not certain which type of oviraptorid it is,
-although it may well be It is not certain whether oviraptorosaurs made it to the very end of
-the . There is no evidence of them from very
-late sediments, so they may have died out
-right before the K/T Extinction. But some dinosaur groups are only known to
-have died out in the K/T Extinction because their teeth have been found from
-that time. Since oviraptorosaurs had no teeth, and teeth preserve better than
-other remains, they may have made it to the end but not left any evidence
-that we have yet found. This was an odd group of , characterized by an
-extremely thick skull roof, often lined with small bumps and spikes. The
-most commonly accepted explanation for these thick "bone-heads" is that
-they were used to butt heads in mating displays similar to those of
-bighorn sheep. Pachycephalosaurs were once classified as ,
-mainly because of their bipedal stance. But they seem to be more closely
-related to the , due to similarities such
-as a ridge along the back of the skull, which evolved into a frill among
-the ceratopsians. The genera listed here were the "flat-headed" pachycephalosaurs. They
-were sometimes grouped into the family Homalocephalidae, although this is
-probably paraphyletic. Pachycephalosaurs, known only from the northern hemisphere
-(with few possible exceptions), are fairly
-rare, leading some to theorize that they may have inhabited environments
-that were not conducive to fossilization, such as mountains. Pachycephalosaurids were the "dome-headed" pachycephalosaurs. Their skull
-roofs were immensely thickened to create a large dome of solid bone on the
-top of their skulls. The dome was adorned by bumps and spikes, which grew
-quite long in Pterodactyloids included the largest flying animals of all time. Giants
-like These short-tailed came in a wide
-variety of forms, from the forceps-beaked Pterodactyloid diversity declined throughout the
-. By the end there were only a few giant
-forms, the smaller niches having all been taken over by
-. This last remnant went extinct at the end of the
-, as did all
-save for . Although they were the only other flying ,
-pterosaurs were not closely related to . Their
-wings had a very different structure. Birds support their wings with their
-second finger (or possibly third, if the frame shift hypothesis is true),
-while pterosaurs used the fourth. Additionally, pterosaurian
-wings were largely made up of skin membranes strengthened by fibers, while
-avian wings consist mainly of feathers. Pterosaurs originated at about the
-same time as the
-. They began as small, long-tailed forms,
-sometimes called "rhamphorhynchoids". From these came larger,
-short-tailed forms, which make up the group
-. There is a recent theory that pterosaurs were not archosaurs, but
-derived from some type of basal .
-For more:
- Pterosaurs were unique among in that at least some
-of them were covered with hair, similar but not homologous to
- hair. Although in some cases fibers in the wing
-membrane have been mistaken for hair, some fossils such as those of
- Sauropods were giant, long-necked plant-eaters.
-All sauropods were quite large. Even the smallest ones were about as big as
-the largest members of other dinosaur groups. Early sauropods like The eusauropods shown here were often grouped together in Cetiosauridae,
-but it is probably a paraphyletic grouping. Vulcanodontidae, consisting of
-the non-eusauropod sauropods, is also probably paraphyletic. There is a wide variance
-of opinion about this group, if it is a group. Some hold that the
-club-tailed Sauropodomorphs were the long necked, herbivorous, lizard-hipped
-, including the largest land animals of all
-time. The primitive sauropodomorphs listed
-here are commonly called
-"prosauropods". These were semi-quadrupedal herbivores from the
- and with large,
-hooked claws on their feet. They were once thought to be omnivorous, since
- teeth found with them were often mistakenly
-thought to be the teeth of the prosauropods themselves. Instead, they were
-the largest herbivores of their day (although primitive ones may have been
-omnivorous). It is not certain whether "prosauropods" gave rise to the larger
-, or if they are just the sister group to
-Sauropoda. No cladistic analysis has yet been done to test "prosauropod"
-monophyly. All to date have simply assumed monophyly based on the
-fact that prosauropods lack a digit that sauropods possess, lack of a digit
-usually being a derived trait, not a primitive one.
-The taxon Brontosauria was originally designated for a group containing
-Sauropoda and Prosauropoda, considered paraphyletic by its author. Here
-it has been cladistically translated as the node containing Sauropoda
-and Prosauropoda (sensu Wilson & Sereno), although this definition
-has not yet been used formally, to my knowledge. Sauropsida is one of the two great lineages of
- (the other being ,
-which includes ). All sauropsids, except for
-primitive forms like mesosaurids, belong to the clade Reptilia. Reptilia was once a "grab-bag" taxon for every amniote that was neither
-a nor a mammal. It was divided into four sections based
-on the number and alignment of certain holes in the back of the skull
-(temporal fenestrae): Anapsida (no holes), Synapsida (a low hole),
-Euryapsida (a high hole), and Diapsida (two holes -- includes
-). Reptilia has since been re-defined as a clade: all the descendants of the
-most recent common ancestor of the four living groups considered reptiles:
- (turtles), The groups Anapsida and Diapsida are still used as clades within Reptilia,
-slightly modified from their traditional meanings (Anapsida now excludes
-the most primitive sauropsids; Diapsida now includes birds). "Euryapsida",
-which included marine reptiles such as and
-, is now recognized as an unnatural grouping of
-various aberrant diapsid lineages which lost their lower temporal
-fenestrae. The is often called "The Age of Reptiles"
-because of the reptilian dominance during most of that era. Dinosaurs ruled
-the land, ruled the skies, and a great variety
-of marine reptiles , plesiosaurs, ichthyosaurs,
-etc.) ruled the oceans. Most of these creatures died out in the K-T
-extinction (ichthyosaurs died out earlier; champsosaurs, a freshwater
-lineage, later). Sauropterygians were a group of marine reptiles of uncertain origin. At times
-allied to or , they are probably
-, possibly a basal lineage of either
- or . Their limbs had evolved into
-flippers, which they used to swim through the
- seas. The advanced sauropterygians, plesiosaurs,
-came in two main body forms. Pliosaurs had long, large heads, and short necks,
-similar to the distantly related . Plesiosauroids
-had extremely long necks with tiny heads, looking something like a cross
-between a and a .
-All sauropterygians were carnivorous. Placodonts may or may not have been sauropterygians. They were
-large, probably sluggish creatures somewhat similar in form to today's
- and
-(manatees and dugongs). Their broad teeth splayed outward from their mouths.
-It has been suggested that they used them to crush
-shells. Sauropterygians died out at the end of the ,
-along with all non- .
-There have been reports of modern-day populations of plesiosauroids, but
-these have either turned out to be other animals (rotting basking shark
-carcasses) or deliberate hoaxes (the Loch Ness monster). Spinosauria once included all theropods with tall vertebral spines. Some
-of these creatures, such as Spinosaurs all have -like conical teeth. Their
-long snouts have kinks like those of and some
-early . It is thought that they used these for
-fishing, possibly in conjunction with other carnivorous activities. Baryonychines have more teeth at the end of their lower jaw than
-spinosaurines. Spinosaurines are characterized by straight, unserrated
-teeth. These primarily herbivores had two rows of
-plates and/or spikes going down the back. Although the spikes, which were usually found on the tail, were certainly
-used for defense, the exact purpose of the plates is unknown. They could
-not have made very effective armor, since they left the sides completely
-exposed. Perhaps they performed a similar function to the sails of
- Stegosaurs did not last to the end of the ,
-but died out during the , possibly due to
-competition from other herbivores or from a
-change in flora (the transition from gymnosperms to angiosperms) which they
-could not adapt to. One creature which was thought to be a
- stegosaur ( Once called -like ,
-the animals shown here are no longer considered reptiles. Instead, they were
-the non-mammalian members of a separate lineage. Their skin was
-not scaly like true reptiles. Synapsids were the first terrestrial vertebrates to truly dominate the
-landscape. There were two main "waves", the "pelycosaurs" (non-therapsid
-synapsids) in the Permian and then the therapsids in the
-. "Pelycosaurs" were probably cold-blooded. They ranged from large
-herbivores like Some (but probably not all) therapsids were warm-blooded, fur-covered,
-and milk-giving. They varied from the beaked, tusked, and herbivorous
-dicynodonts to the sleek, predatory Tetanurae consists of the advanced ,
-including and their ancestors. Tetanurans are
-characterized by three fingers or less, an opening in the skull between the
-antorbital fenestra and the naris (nostril) called the maxillary fenestra, and
-stiffened tails (Tetanurae means "stiffened tails"). The non-neotetanuran groups listed
-here are sometimes grouped together in a group sometimes called
-Megalosauria or Megalosauroidea, although this is probably a paraphyletic
-group, as shown here. Most "megalosaurs" were large carnivores. Some think
- and Torvosauridae (=Megalosauridae) make a
-group, sharing enlarged, sickle-shaped thumb claws. Neotetanurans, an advanced group of tetanurans, had complex air
-passages in their vertebrae and ribs. The furcula, a bone which is not always
-preserved, has been found in a
-( Among terrestrial vertebrates, belong to
-Amniota, a clade characterized by the ability to procreate on land. Of the
-two main branches of amniotes, dinosaurs belong to
-, which includes other
- as well. The sister clade to Sauropsida,
-, includes . These Asian pose some taxonomic problems. They were
-originally classified as , although they have
-some features very uncharacteristic for theropods. Their hips are
-bird-like, although some theropods such as the and themselves have
-bird-like hips as well. The front of the snout is a toothless beak,
-although , ,
-and several lineages have toothless beaks as well.
-But the feet, which have four functional, forward-facing toes, are utterly
-unlike any other theropod feet. Except for some , all theropods have three functional toes and a
-reduced dewclaw. Another theory was that they were an
-outgroup to the , since ornithischians have
-bird-like hips (although they are only superficially bird-like), beaks, and,
-in the most primitive ornithischians, four toes. It has also been proposed
-that they are late-surviving relatives of
-"", since their teeth and feet are
-similar to those of "prosauropods". (They are similar enough that
-one jawbone from the Early Jurassic of China was published as the earliest
-therizinosaur, although it is more likely a "prosauropod".) The discovery of There is still disagreement over which coelurosaurian group
-therizinosaurs are related to. They have been allied with , , and . Theropoda is an incredibly diverse group of . Most of the Mesozoic theropods were sharp-toothed
-predators, although there have been a few toothless, possibly herbivorous
-groups. During the (or possibly ), some theropods evolved into feathered, flying
-forms. Their descendants are today's . The group Theropoda ("beast feet") was named early on in
-paleontological history, along with ("bird
-feet" - a major group). It almost seems as
-though the names were somehow mixed up and improperly assigned, since
-theropods have bird-like feet and ornithopods have somewhat more -like feet, but the names stuck and it's far too late to
-change them now. The non-neotheropod genera shown above
-are often informally referred
-to as "herrerasaurs". "Herrerasaurs" may be basal theropods, as shown
-here, basal , or even basal . They had many primitive features, such as five
-digits on the hands, although the outer two were very small and had no
-claws. It is possible that Ceratosauria as shown here is a paraphyletic group,
-characterized only by primitive features. Neoceratosaurs may be share more recent
-ancestry with tetanurans than with coelophysoids. Thyreophora includes the "armored ", a
-group of primarily quadrupedal with bony
-plates, scutes, and/or spikes protecting their backs from theropod
-predators. Some
-also exhibited armor like this. The more advanced thyreophorans, like These primarily Cretaceous animals represent the last group of before the great K/T extinction. Bony plates have
-been found with some specimens, indicating that they were armored, like
-. South American forms such as Argentinian egg material has been attributed to titanosaurs. The eggs are
-typically 11-12cm in diameter, some up to 17cm. From relatively
-small eggs like these came creatures which would grow thousands of times
-larger! Eggs have also been attributed to The phylogeny above is somewhat tentative. Troodontids (formerly known as
-saurornithoidids) were remarkable in
-having the largest E.Q. (encephalization quotient) of all non- . Intelligence-wise, they may
-have been on level with some modern-day . The large
-brain, huge eyes, and grasping hands of these
-may indicate a nocturnal, predatory lifestyle. However, their teeth may
-indicate omnivory. The feet were equipped with "switchblade claws", similar to those of
-. They were once placed with the
-dromaeosaurids in , but this grouping
-has been questioned. They share some features with , such as a pinched middle metatarsal
-(possibly a speed adaptation), features of the braincase, and large eyes.
-They have also been placed in basal , basal , and as sister group of the - group. This was the last group of huge predatory
-, including the
-ever-popular For all their size and strength, tyrannosaurids had remarkably small arms
-with only two fingers on the hand, the third digit having degenerated to
-near nothingness. The near lack of forelimbs in tyrannosaurids (and to a lesser extent in
-some other large predatory dinosaurs) poses an interesting problem: How
-did they deal with tripping? A recent study of There have been some proposals that
- Within the group of animals that have backbones,
- belong to the tetrapods, or terrestrial
- vertebrates.
- Two different species names have been used in conjunction with the
-same type material.
The first genus to be named.
There is debate over the taxonomy of these species. Some feel they
-should all be lumped into
There is debate over the taxonomy of these species. Some feel that most of them
+should be lumped into
May be a variant of
A small of some kind.
+Hails from the Bajo Barreal Formation.
The Solnhofen specimen may represent a new genus and species,
The specimen as originally published was touted as a
-- link. However, it appears
-instead to be a chimera, the tail and hindlimbs belonging to a deinonychosaur and the rest
-belonging to a bird. The name
This name has an ugly, if brief, history +behind it. Here is an attempt to sum it up.
+ +The name "Archaeoraptor liaoningensis" was originally published in a +National Geographic article in 1999. Pictures of the type specimen, +supposedly a link between and more primitive, -like animals, were also published, but there +was no formal diagnosis. Furthermore, the article disclaimed itself as a +formal description and announced that the animal would be properly +described later. Thus, at that point in time, according to ICZN rules, the +name "Archaeoraptor" was a nomen nudum, completely unofficial.
+ +Shortly after publication, it became clear that the hindpart (tail, +hindlimbs) of "Archaeoraptor" was from a different animal than the rest of +it. This was discovered because the more complete counterslab to the +hindpart had been found, and indicated that that part belonged to a basal +, possibly a . +The forepart was determined to be . At that point I +decided to use the unofficial name "Archaeoraptor" for the avian forepart, +which was the major part of the supposed specimen.
+ +The hindpart and its counterslab were described in 2000 as
Many consider Olson's publication unwarranted and irresponsible. There
+will be a petition to the ICZN to formally reject the name
The avian section has yet to be formally described and named.
+ A poorly known dinosaur,
Like birds and spinosaurs, it had unserrated teeth.
+classified as a because of its unserrated +teeth, but it may be some kind of , perhaps a +juvenile Poorly known. Could be the same thing as
Probably a juvenile of another genus.
Similar to the larger
The single specimen was buried at the bottom of a shallow lake, in +sediment that became the Anacleto Member of the Rio Colorado Formation. +Part of its skull was broken apart.
+A small biped (about 1 meter tall) with armored cheeks. +
Although originally dated as Early Cretaceous, the sediments this dinosaur +is from appear to be Late Cretaceous instead.
As the name implies,
The original cladistic analysis placed
The original cladistic analysis placed
It is possible that
The oldest known , although not quite the most basal.
Originally published as C. a'naensis, but the ICZN does not permit non-alphabetic characters in any taxon's name.
The specimen assigned to
The type specimen of
Named for some scrappy remains, but the name
Similar to
Extremely similar to
This Transylvanian may be a (possibly even a ) or a
-. The ankles might belong to one or two
-different, but similar, animals (
This may be an early member of +, a precursor to the "tyrants" of later +times. It hails from the Wessex formation of the Isle of Wight. +Unlike the later , it retained three +fingers.
+Although originally classified as a , +there are (as yet unpublished) speculations that this species might be a + instead. If a , it would be the earliest one known, indeed, the +earliest known, and would push back the +hypothesized origin of that group by a great amount of time.
+Originally thought to be a , this animal,
+originally called
A close relationship has been proposed with the Australian
+
Hails from the Sao Khua Formation. May be an .
+The spelling will be changed for the final description.
+Either a huge "" or a primitive -.
-The holotype specimen was previously referred to
This animal has features similar to basal - and basal , placing it near the root of - .
+This animal was originally placed as a basal . +Further work has refined it position to just outside .
May be a juvenile of
These two species may be the same.
May have had two horns on its head. Had a thick braincase.
@@ -8995,7 +9316,7 @@ Both may have been very early .The material referred to this species was previously referred to
+
This animal is tied with
This specimen, the only dinosaur known with a bony plate covering +its abdomen, seems to have both +and features. A cladistic analysis has placed +it in .
+This tiny is the smallest known adult from the , under 2Ā½ inches in length, despite its unusually long pygostyle.
+ +The counterslab of the type specimen was originally published as
+
May have had a hyperextensible second pedal digit, like
+the related
About the size of a .
Hails from the Jiufotang Formation. The bill is rather long.
+ Could be a or a young
-
Could be a small or a young
Hails from the Collano Formation.
+This small predator had strange, forward-pointing teeth, like those of +some . It may be a .
+Hails from the Maevarano Formation.
+Tiny and bipedal. -
-Possibly the smallest non- , assuming (as the authors do) +that is is fully grown.
+ +The counterslab to the hindquarters of this specimen
+was already published as half of the chimerical
Although the authors classified this species as a , it has troodontid features (arctometatarsalian
+pes, "waisted" teeth, maxilla bordering naris, closely packed dentary
+teeth) and avialan features (
Wherever this species belongs, it does not appear to be , and thus dispels notions that dinosaurs were too big to
+be bird ancestors. (This species is smaller than
Feathers or (feather-like integument with a
+rachis, or vane) similar to those of
Some features of this species have been +interpreted as indicating a scansorial lifestyle. These include distally +placed metatarsal and pedal digit I.
+ +
Technically, by ICZN rules, this animal
+should be referred to as
This animal has the shortest genus name of any - non- . +
This animal is tied with
May be a variant of
This species was originally to be named after its discoverer (Whittle), - but instead was named after the young boy who won a contest to have - it named after himself. + but instead was named after a young boy (Justin Hoffman) who won a + contest.
Published in Chinese as "Neimenggulong" ("Inner Mongolian + dragon"). Hails from the Erlian Basin.
The only non- known +
The only non- known to have a pygostyle (a fusion of vertebrae at the end of the tail).
This is the first to be named which is
+not from Asia. Its ischium was originally thought to be the squamosal bone
+of
Once identified as a , this scrappy specimen may instead to belong to some kind of .
- -
One of the largest land animals, and the largest known African land animal.
+All specimens come from "Tony's Bone Bed" in the Cedar Mountain Formation +of eastern Utah.
+Hails from the Sinoiju Series.
+
This starling-sized species had long tail feathers which lack barbs and rami toward the base.
+This medium-sized carnivore hails from the Allen Formation.
+The fossil was found in two parts, the thorax in hindlimbs in one part, +and the sacrum, pelvis, hindlimbs, and tail in the other. This led to some suspicion +that it was a chimera, but given that the halves came out in the same position +from cladistic analyses that tested them separately, coupled with additional +anatomic and taphonomic details, it seems quite likely that both +halves belonged to the same individual.
The type specimen of this genus is the most complete
+known. It shows that at least some titanosaurs had low, "horse-like" skulls like
+ rather than "boxy" skulls like
+
One of the largest of its time.
+ May belong to
This genus is named for the father of its namer.
Hails from the Allen Formation.
The earliest known large .
+(
This gigantic may be a huge, late species of
-
Was once allied with . +
Probably a juvenile .
Originally placed as an extremely early , +then as a toothless . Now it seems +to be a toothless .
+A new subadult specimen with well-preserved integumentary structures + may belong to this genus, or a new one.
As remarkable as its length was, even more interesting was the huge sail along the back, formed by long vertebral spines, up to six feet in height @@ -17133,7 +17826,7 @@ content="carcharodontousaurines"/>.
Once thought to be a , but may be a - .
+ , possibly a .May be a . @@ -17569,7 +18270,7 @@ Small bony ossicles covered at least the the throat and hips.
Formerly known as the "Jordan ".
-Could be the same thing as
This had a two-foot-high sail over its @@ -17739,25 +18431,25 @@ was equipped with horns lining the edge of its frill.
super lizardOne of the hugest land animals of all time. Stood 27 feet (8m) high - at the shoulders and had at 40 foot (12m) long neck.
+ at the shoulders and had a 40 foot (12m) long neck. "Ultrasaurus macintoshi" was to be a name for some giant
bones from the Morrison Formation, but before it was
published the name
- May be the same as
May be the same as
The largest Asian predators known. These species were sometimes
+placed in
It is possible that
Eggs tentatively assigned to
Skin impressions from the thoracic and scapular areas show tubercular + scales with two patterns.
Originally classified as a small @@ -18685,19 +19432,6 @@ page="http://www.dinoheart.org/"/>
Might be a misspelling of
One of the first American to be named. Probably the - same thing as another . -
+ One of the first American to be named.
+Although for decades the name
The most complete
The most complete
Recently an enormous coprolite (fossilized piece of dung) from +
Recently an enormous coprolite (fossilized piece of dung) from
Saskatchewan was referred to
Eggs tentatively assigned to
The various species included here in
Many smaller "species"
+now seem to be young
Certain Asian were once included by some
+in this genus, but are now usually placed in
Possessed a "switchblade" foot claw, like those of - and other basal . -
- The teeth (found in rock of volcanic origin) which this genus was named
after actually came from a predator that may have eaten it.
-
The first known with brow horns, and the -oldest named American ceratopsian.
+oldest named American ceratopsian. Its snout is rather long. +An element thought to be a squamosal of this species is actually the
+ischium of
These were large, often huge predators. Some
+of the carcharodontosaurines are the largest known carnivores ever to walk
+upon the Earth, even larger than
A recent find of a group of differently-aged carcharodontosaurines (the
+genus is yet to be publicly named) in association with each other suggests
+that these enormous carnivores may have hunted in packs. Interestingly,
+the largest known land animals of all time,
+such as
There are some cranial similarities
+between and , another
+group of Gondwanan (Southern Hemisphere) carnivores. This is probably due to
+convergence. It has been noted that
This recently discovered group has
+proven difficult to place. The original member,
The discovery of
Alvarezsaurs were small, terrestrial animals with +long legs. Their niche is far from certain. Since their stubby forearms +were built so powerfully, it has been suggested that they used them for +digging. (In fact, some think that their sterna were keeled as a digging +adaptation, similar to moles, and that they evolved keeled sterna +separately from birds, which evolved it for flying.) The overall body plan +of alvarezsaurs is not that of a burrower, but it has been suggested that +they might have fed on colonial insects, ripping into nests with their +single-clawed hands.
+ Anapsida is a clade of of with no fenestrae
+(openings) in the back of their skulls. It includes large herbivores like
+pareiasaurs as well as modern-day turtles. During the , "The Age of Reptiles", turtles grew to great
+sizes. Some, like
In traditional usage, Anapsida included all +without antorbital fenestrae. It has now been restricted to those sharing +more recent ancestry with chelonians (turtles) than with other extant +amniote groups. Membership is mostly the same, but excludes basalmost + (e.g. ) and +basal romeriids (e.g. ). +
+ +Within Reptilia, anapsids are probably the most distant relatives of +.
+Among Earth's enormously vast array of animals, belong to the clade, +which is characterized by the possession of a backbone.
+ Ankylosaurs include the most heavily armored
+dinosaurs of all, the "tanks" of the . The
+entire back was covered with bony plates, studs, and spikes. So was the
+head, right down to the eyelids! (Bony eyelids have been found in
Some nodosaurids bore very large spikes along their sides, the largest +often sprouting from the shoulders. These may have been used as defense, +weapons in rivalry, or both.
+ +These animals are known from all +continents except South America and Africa. They were most prevalent in +Laurasia (the northern supercontinent).
+ A large club at the end of the tail
+distinguishes ankylosaurines and shamosaurines from the more primitive
+ They probably used this club to give
+crippling blows to potential predators. A similar structure existed in the
+
Polacanthines were once classified as +nodosaurids, but are now recognized as a distinct clade closer to the +Ankylosaurinae. It was recently thought that they had small tail clubs, +but this has been refuted.
+ +Shamosaurines had narrow snouts, especially compared to the very wide +snouts of ankylosaurines. This may reflect different niches.
+ +Many ankylosaurines had complex, looping nasal passages, possibly to +enhance their sense of smell.
+Archosauromorpha includes all with +four-chambered hearts, an evolutionary innovation that permitted them +higher activity levels and terrestrial dominance throughout the .
+ +The forms shown here were once all included in +Archosauria in the "grab-bag" taxon "Thecodontia" -- any archosaur that +wasn't a , a , or +a . This form of classification was abandoned +once knowledge about these animals increased.
+ + The non-archosaur archosauromorphs, or "protoarchosaurs", show fairly
+wide diversity, from small hunters with insanely long necks like
The two major groups of Archosauria proper are rather poorly named.
+Pseudosuchia means "false crocodiles", yet it includes true ones.
+Ornithosuchia was named after the creature
Pseudosuchians became the dominant
+terrestrial animals after the demise of the two previous "dynasties" -- the ""
+and the non- . They
+diversified into many niches: armored herbivores (aetosaurs), big
+carnivores (rauisuchians), tiny sprinters (
But by the end of the they had been +outcompeted by their fellow archosaurs, the ornithosuchian . Dinosaurs and pterosaurs would continue to +dominate terrestrial and aerial niches until the end of the , far longer than any previous or subsequent +terrestrial "dynasty" (and they still dominate aerial niches!). Of +all the pseudosuchians, only the aquatic crocodylomorphs survived beyond +the .
+Birds evolved from small, possibly "sickle-clawed"
+ probably sometime during the (some have suggested the ),
+as did their close relatives the . The
+earliest known definite bird is the European
Pygostylian birds are characterized by a
+pygostyle, a fusion of the vertebrae at the end of the tail. This trait
+seems to have evolved convergently in at least one (
Ornithothoracean birds, a large subset of pygostylians that includes +, have a "modern-style" thorax and an alula, +or "bastard wing" -- a group of feathers associated with the first finger +that aids maneuverability in flight.
+ +Unlike the other two groups of
+flying , and
+, the hindlimbs of birds are not in any way coupled with
+the wings, and remain free for running. Due to this and other pieces of
+evidence, some dinosaur researchers argue that birds did not evolve from a
+tree-dwelling ancestor, as the other groups are thought to have. Recent
+studies suggest that
But many disagree with this idea, arguing that flight in birds evolved as
+it seems to have in bats and pterosaurs -- from the "Trees Down".
+They hold that bird ancestors were scansorial coelurosaurs which leaped from
+tree to tree, then evolved into gliders, and from there to fliers. The
+facts that
As of now, the fossil evidence does not clearly favor either the +"Trees Down" or "Ground Up" hypotheses of the evolution +of flight in birds.
+ +The hypothesis that birds descended from
+dinosaurs has been around for a long time. Thomas Huxley (a.k.a. "Darwin's
+bulldog") proposed such a relationship based on similarities between
+
Heilmann's view was finally dispelled by the discovery that some dinosaur fossils (such as those of
A more recent objection to the dinosaur-bird link is the claim that +embryological evidence shows the digits in the hands of modern birds to be +II-III-IV, not I-II-III as in coelurosaurs and other . In fact, the story may be quite a bit more +complicated. It is not certain that the element that has been interpreted +as a vestigial digit I is in fact digit I. Furthermore, other studies show +that frame shift can cause some birds to have digits aligned differently +than in other birds, even with the same species.
+ +Opponents of the dinosaurian theory of bird origins have yet to +propose an explicit alternate theory, generally stating that birds +evolved from basal of some kind. They +also have yet to explain why such an enormous degree of convergence +would appear between birds and terrestrial +when they represent separate niches.
+ The taxon Carnosauria once included all large , from large to to . More recent
+research shows that most of these are more closely allied to other groups.
+Today, only the allosaurids and their relatives are considered true
+carnosaurs (The precise definition: all animals sharing a more recent
+common ancestor with
Many carnosaurs bore crests atop their heads.
+The primitive forms
Carnosaurs did not survive to the end of the +. They may have been out-competed by and . But in +their heyday they included the largest known land predators of all time. +
+ One of the two main lineages of ceratopsids (a.k.a. horned
+dinosaurs"), most centrosaurines bore large horns on their noses. Unlike
+most members of their sister group, the ,
+their neck frills tended to be relatively short, although often
+accentuated by two large spikes at the top, or spikes all along the rim of
+the frill as in
The advanced pachyrhinosaurins had a large, blunt bony growth in place +of the nasal horn. This may have formed the core of a horny pad in life, +or possibly the core of a gigantic nasal horn.
+This group of herbivores contains the frilled , including the horned dinosaurs. Like many other +groups of dinosaurs, they inhabited only Asia and North +America.
+ +
The creatures on this page were all bipedal. From such as these came
+the quadrupedal . Coronosaurs were generally
+larger, although at least one bipedal ceratopsian (
(See for a discussion on the "s" in +Ceratopsia).
+ Unlike their sister group, the ,
+ceratopsines (a.k.a. chasmosaurines), placed more emphasis on brow horns
+than the nasal horn, to the point that some barely had a nasal horn at
+all, hence names like
Their neck frills were longer than those of centrosaurines, except in
+the lineage leading to
There has been some disagreement over the name of this group and all
+other groups named after the genus
Coelurosauria once included all the small .
+It was the sister group to , which included
+all the big theropods. This system of theropod classification has become
+very much outdated, but the original names are still kept for certain
+actual groups. If the more primitive forms of the old Coelurosauria are
+excluded and a few other forms are added (including ), they do form a monophyletic group. Interestingly,
+this group that once contained only small theropods now includes
Coelurosaurs are an enormously diverse group. They include , , , , , and the incredibly varied birds.
+ + Skin impressions are known from several coelurosaurs.
+A partial impression, possibly from the tail of a
+shows scales like those seen in other dinosaurs. All other
+coelurosaur skin impressions, such as those of
The advanced coelurosaurs make up
+Maniraptoriformes. All
+maniraptoriforms sharing a more recent ancestor with
Arctometatarsalia originally included , +avimimids, tyrannosauroids, troodontids, and ornithomimosaurs. It was +named for the arctometatarsalian foot of these animals, wherein the +middle metatarsal is pinched at the top. This trait, an adaptation for +running, is now thought to have evolved separately in caenagnathids +and possibly in all five of the groups. +have an extreme version of this feature.
+This group includes all of the quadrupedal . Coronosaurs tend to be larger and have larger +neck frills than more primitive ceratopsians. There has been much dispute +as to whether the front limbs of coronosaurs were held fully erect or +sprawling to various degrees. An intermediate posture seems most likely.
+ + The most primitive coronosaurs, like the well-known
The function of the neck frills in these and other ceratopsians is not
+certain. They may have borne colorful displays, protected the neck from
+predators, anchored powerful cheek muscles, amplified low-frequency sounds,
+or performed a combination of these functions. In
Hailing from the very latest stretch of
+the , ceratopsids were the pinnacle of
+ evolution. They included some of the very
+largest , such as the mighty
Skin impressions are known from both centrosaurine ceratopsids (
The genera listed here, plus other +were once grouped in the family Protoceratopsidae (=Protoceratopidae), +since they all had claws instead of hooves. Most now consider this a +paraphyletic (and hence invalid) grouping. There may, however, be a +monophyletic (hence valid) group of basal coronosaurs which would be +termed Protoceratopsidae.
+Crocodylomorphs originated around the same time as the . They were the only +to survive the , and survive to the present day +in the form of crocodylians. Of all living animals, crocodylians are the +closest relatives to dinosaurs (excluding , +which are dinosaurs). Unlike other living (except for birds), crocodylians have a +four-chambered heart and a semi-upright stance.
+ +Some "primitive" crocodylomorphs may have been more active and agile +than today's crocodylians, which have evolved a relatively sluggish +lifestyle.
+
The attack strategy of a dromaeosaurid was possibly to leap at its +prey, feet and arms extended. This posture would be balanced by the long, +stiff tail. The dromaeosaurid would grab onto its prey with cruel, +grasping hands, then tear out the unfortunate creature's throat or guts +with the eviscerating foot-claws.
+ +The energy and quickness needed to carry out such a maneuver is one +piece of evidence used in the debate over whether were cold-blooded or warm-blooded.
+ + These dinosaurs may have hunted in packs, as shown by one find where
+three
Dromaeosaurids were probably very close to
+ ancestry, as shown by their bird-like hip arrangement
+(unusual for non- ),
+extremely stiffened tails, and their similarity to the feathered, flying
+
"'Raptors" were one of the major stars of the blockbuster movie
+Jurassic Park. Although this movie and its sequel, Jurassic Park
+2: The Lost World boasts the most accurate dinosaurs in the history of
+movies, there are a significant number of errors, especially with the
+"'raptors". The most obvious problem is that they were much too big. Real
+
The reason for this is probably as follows. Michael Crichton wanted to
+use a fierce, approximately man-sized predator.
For the movie they decided to bump the size up. They also gave it a
+more
Interestingly, while the movie was being made, a new dromaeosaurid was
+found which was even larger than the movie's "'raptor". The discovery of
+this new dinosaur (
So the "'raptor" in Jurassic Park is probably a decent
+approximation of a real, undescribed dromaeosaurid (not a
There are three major types of dinosaur. +includes all of the carnivorous dinosaurs, as well as their modern-day +descendants, the . consists of long-necked herbivorous dinosaurs, +including , the largest land +animals of all time. The third group, , +contains many diverse forms of beaked, herbivorous dinosaurs.
+ + Although the major groups of
+dinosaurs are clearly recognized, there
+is some debate about their relationships to each other and to the
+ancestors of dinosaurs. About the only thing that can be confidently
+stated about early dinosaurian/ evolution is
+that the following evolutionary lineage occured:
+
are thought to have split off from this
+lineage probably before
The confusion about dinosaur ancestry leads to the question "What is a
+dinosaur?" The original definition of Dinosauria, as stated by Sir Richard
+Owen in 1842, was a group of large (which he
+considered a type of ) consisting of
Dinosauria was traditionally divided into the orders Ornithischia
+("bird hips" -- a misleading term) and Saurischia ("lizard hips"). For
+much of the history of paleontology, the status of Dinosauria as a real
+group has been considered dubious -- Ornithischia and Saurischia were
+separated from each other and sometimes were themselves split up. More
+recently, however, cladistic analysis has reaffirmed Dinosauria as a
+natural group. It is defined as the most recent common ancestor of (which are now considered saurischians) and
+
This definition has lead to some disagreement as to whether certain
+primitive ornithodirans are dinosaurs or not. Some include all of the
+genera shown in the above lineage in Dinosauria, whereas others don't even
+consider to be true dinosaurs. On these
+pages
But a minority claim that early sauropodomorphs show more similarities +to early ornithischians than to theropods. They classify Sauropodomorpha +and Ornithischia in Phytodinosauria ("plant dinosaurs") as a sister taxon +to Theropoda.
+ Diplodocids included some of the hugest creatures to walk upon the
+Earth.
These animals have been the focus of several computer-assisted studies +in biophysics. One study suggests that diplodocids could actually crack +their tails like whips, causing loud sonic booms. Another study, focusing +on the other end of the animals, suggests that they could not hold their +heads very high, and thus may have fed on low-growing vegetation. This +goes against previous thought that evolved their +long necks to reach into the trees.
+ +Recently a diplodocid was found with non-bony dermal spines along its +back. Since non-bony structures are rarely preserved, it is not certain +how widely throughout this feature +existed.
+ Members of this group had long, whip-like tails
+(possibly used for defense), peg-like teeth, and high vertebral spines.
+The extremely long spines of some diplodocimorphs, such as
+
Some of these animals, like the dicraeosaurids, made it into the +Cretaceous, but not to the end of the Mesozoic Era.
+ + There is a possible diplodocimorph named
Enantiornitheans were a large group of which +evolved alongside modern-style birds, or , +during the . Their name ("opposite birds") +refers +to the articulation of the scapula with the coracoid, opposite to that of +modern birds. Like neornitheans, advanced enantiornitheans were toothless. +These two lineages, along with , +, and , +represent the five known lineages of toothless +.
+ +Enantiornitheans achieved a fair degree of +diversity, beginning as +small, perching fliers, with some developing into shorebirds. They +ranged from sparrow- to vulture-size.
+ +Although apparently more plentiful than their neornithean cousins +during the Cretaceous, enantiornitheans, like all non-neornithean +dinosaurs, became extinct at the end of the Cretaceous. Why neornitheans +survived while they did not remains a mystery.
+ These "duck-billed" were mostly non-crested,
+although some, like
Before the discovery of
The old genus
These are commonly known as the "duck-billed" dinosaurs, since their +beaks bore a superficial resemblance to those of ducks. They were the last, +largest, and most numerous of the .
+ + More "primitive" hadrosauroids like
Hadrosaurids are divided into two subfamilies, the generally non-crested
+hadrosaurines and the lambeosaurines, which developed large hollow crests
+on their heads. At least one scientist considers them to be two separate families,
+with
It was once thought that the duck-bills, like their namesakes, were +aquatic. This notion seemed to be supported when a fossilized "mummy" of a +hadrosaurid was discovered, showing what appeared to be webbed fingers on +the hands. The hollow crests of the lambeosaurines were supposed to be for +air storage, since they connected to the nasal passages.
+ +This theory is largely out of favor now. The "webbed" fingers, upon +closer scrutiny, more closely resemble desiccated hoof pads. The crests +could not have functioned as air storage, since they were rigid and +inflexible. Air sucked out of them would have created a vacuum. And the +rugged teeth of the hadrosaurids strongly indicate that they ate rough, woody +plant material, not soft seaweed. The teeth in the jaw were aligned in great +"batteries", so that if one wore out there was another one behind it to +replace it. Some hadrosaurid jaws contained as much as 2,000 teeth!
+ +It seems that duck-bills led a largely terrestrial life. They would walk +primarily on all fours, as shown by the hoof-like nails and supporting pads +on the hands, but were easily capable of switching to bipedal locomotion.
+These are the only known marine of the +! Hesperornithiforms had adapted to life in +the oceans of Laurasia, and are best known from the +North American interior, which was covered by a large sea during much of the +.
+ +Unlike the major modern-day group of marine birds (penguins), +which have flipper-like wings, hesperornithiforms propelled +themselves with large, (presumably) webbed feet, like loons +and grebes. Their wings had atrophied to tiny, useless things, and their +feet were set so far back that walking must have been extremely awkward. +Thus, they probably spent very nearly all of their time in the water.
+ Heterodontosaurids were a group of small, primitive
+
+from the . They
+were all fairly similar to each other. Some species, such as
+
Heterodontosaurids were traditionally considered primitive +, although they bear a number of similarities to + as well.
+Despite their name, ichthyosaurs were neither nor +, but +a group of uncertain origin that evolved into +completely marine forms. Like sharks, they had dorsal fins and a tail +fin that swept side-to-side.
+ +Ichthyosaurs arose during the , but did not +make it to the end of the . They were gone +before the K/T Extinction, which killed off other large marine + and the non- +. +
+ + Unlike all other advanced , ichthyosaurs
+had more than five digits. It was once thought that they might be related
+to very early tetrapods like
The major characteristic of these medium- to large-sized herbivores is
+a spiky thumb, possibly used for defense against predators. When
+
The animals listed here cover the transition from early,
+-like iguanodontians to the medium-sized
+
These "duck-billed" bore large, hollow
+crests on their heads. The crests of
The lambeosaurine crests may have been used as sexual displays. For many +lambeosaurine genera, there are two forms known, one with a smaller +crest, one with a larger crest. These were originally classified as different +species, although in some cases they may just be different genders.
+ +In addition to visual display, the tubular crests, which connected to the +nasal passages, may also have been used as giant trumpets, allowing the +lambeosaurines to let out great, deep, resonant bellows across the +prehistoric landscape. Another idea is that the crests enhanced their sense +of smell, allowing them to detect giant predators.
+ Lepidosauromorphs include all with
+overlapping scales. Two types of lepidosauromorph remain alive today:
+
During the late , there were huge, marine +squamates known as mosasaurs. They went extinct at the end of the +, along with all non- +.
+The name Macronaria ("large nostrils") refers to the enlarged nasal +openings of this group. Like all , their nostrils +were situated atop their head, nearly above the eyes. Macronarians +had crests of varying sizes formed by high nasal bones. In some +specimens, these bones were not completely preserved, leaving the skull +looking rather low, like those of . For this +reason, many were once classified with them.
+ +Basal (non-titanosauriform) macronarians, or +"camarasaurs", were fairly typical sauropods of small to average size. +They had boxy skulls and spatulate teeth. Embryonic "camarasaur" material +indicates that some laid eggs with diameters of 24 cm.
+ + Most of the animals listed above as
+non-titanosaurian titanosauriforms have been included at some time in the
+family Brachiosauridae, but their exact relations to one another are
+poorly understood at this time. Among these animals are some of the
+largest land animals of all time, such as
It was once thought that the large crest of "brachiosaurs" was a
+snorkeling device. Since then it has been shown that if a
+
Mammals originated around the same time as the +, but remained in their shadow throughout the +. After the K/T extinction, they diversified to +fit the niches that the dinosaurs left empty, as well as many other niches. +Go us! Dinosaurs may be cool, but who's on top of the food chain now, eh? +I have to go eat some .
+ These were mostly medium-large predators which displayed some primitive
+characteristics, such as four manual digits, one of which was lost in
+the more "advanced" , the other great branch of
+. Although never quite as diverse (or numerous) as the
+tetanurans, neoceratosaurs had some variety. Most were medium-large
+predators, but there were also tiny ones like
+
Neoceratosaurs were generally robust with "tall" heads. Some had a small +opening in front of the antorbital fenestra, similar but probably +convergent to the maxillary fenestra of tetanurans. Neoceratosaurs had six +or seven fused sacral vertebrae, more than other theropods.
+ +During the , neoceratosaurs inhabited the southern, or Gondwanan, +continents. If, as a few suspect, the mighty +are abelisauroids, they may have even been the dominant Gondwanan predators +(although it seems more likely that they are +). Neoceratosaurs persisted to the end of the +.
+This group contains all modern, toothless . +They are divided into paleognathans (ratites and tinamous) and neognathans +(all other modern birds). Beyond that, classification gets tricky -- +there are about as many schemes as there are scientists studying avian +phylogeny. Neornithean systematics is highly volatile at the moment, so +don't be surprised if you see changes here.
+ +When all the other died +out at the end of the , neornithean +birds made an attempt to fill the empty niches left by the large predatory +. In South America, large, ground-dwelling, +carnivorous phorusrhacids evolved and lasted until fairly recently. But +today, with few exceptions, birds are aerial, not terrestrial.
+ +In the skies, however, these last descendants of the mighty dinosaurs +still reign supreme. They beat out in the + (in the smaller niches) and today they keep + from flying during the day. There are over +twice as many living species of bird as living species of mammal. They are +the last vestige of the dinosaurs' dominion.
+
Apart from certain , ornithischians were the only +beaked dinosaurs. They were all herbivorous (save for a few possible +omnivores, like ), and included a very wide +variety of forms: , +, +, , and +.
+ + The earliest ornithischians were small, bipedal plant eaters, like
+
Ornithodira ("bird necks") is divided into two major sections. +Dinosauromorpha includes and their early +ancestors, the "lagosuchians". These ancestors were very small, about +1.5 to 3.5 feet long. They were probably carnivorous or insectivorous.
+ + The other group, Pterosauromorpha, includes ,
+the so-called "flying " (although
+ are also considered reptiles under the cladistic
+system). There are two possible non-pterosaurian pterosauromorphs:
+
Some do not consider pterosaurs to be close relatives of dinosaurs:
+
All ornithodirans walked +with a fully upright stance, like that of most . +The group is named for the S-shaped neck found in most members.
+ +The only living ornithodirans, birds, are highly endothermic (or +"warm-blooded"), but there is still debate as to the metabolic rate of +extinct ornithodirans. The idea that they were endothermic has gained +much acceptance in recent times, but some still maintain that they were +ectothermic (or "cold-blooded"). Others think that they may have had +intermediate metabolisms, or alternate types of physiology. But everyone +agrees that the upright stance of ornithodirans indicates a high level +of activity, regardless of metabolic rate.
+ +It has been suggested that the fur-like integument seen in some pterosaur +fossils and the feathers seen in some dinosaurs (fossil and living) might be +homologous.
+These are commonly known as the +"ostrich mimics" or "ostrich dinosaurs" (although, technically, + are dinosaurs -- and if you think about +it, isn't it ostriches who are ornithomimosaur mimics?). They were possibly +the fastest of dinosaurs, with conjectured running speeds of 40-50 1. +They all had very large eyes, like their possible relatives the +.
+ + A peculiar feature of the ornithomimoids is the toothless, beaked mouth.
+This may indicate that they were one of the few groups of
+non- to abandon a
+predatory lifestyle, possibly assuming an herbivorous or omnivorous mode of
+life similar to that of modern-day ostriches. Early ornithomimosaurs such as
+
Ornithomimoids were all fairly similar. They had lost the first, inner
+toe, a dewclaw in most theropods. The ornithomimids are especially difficult
+to distinguish from each other, and for this reason some feel that they
+should all be lumped into one genus,
Ornithomimosaurs were fairly similar in size, from the most primitive ones
+at 2 meters long to the advanced ones at 3.5-4m. The exception is the giant
+ornithomimoid
This group has at various times included nearly all bipedal
+. By now many forms once included here have
+been recognized as primitive members of other largely quadrupedal groups
+(
It was once thought that the animals listed on this page formed a clade:
+Hypsilophodontia, sister clade of . But newer
+studies indicate that this group was paraphyletic. The only definite
+hypsilophodont is
The animals on this page were small or tiny bipedal runners which may +have lived lifestyles similar to those of such modern-day + as deer, gazelles, and kangaroos. From creatures +such as these came the larger, semi-quadrupedal iguanodonts.
+Ornithurans include modern birds () and +their relatives. Except for neornitheans, ornithurans retained small +teeth in their jaws, except at the front of the upper jaw (premaxilla).
+This group includes the oviraptorids and the caenagnathids. The latter +are a somewhat poorly known group, known mainly by hands and feet, which +are fairly -like.
+ +Oviraptorids were a very peculiar group of . +Their mouths were entirely toothless, forming beaks. They were sometimes +classified with the , another group of +toothless theropods. However, they lack the arctometatarsalian foot of +the ornithomimids and other +theropods.
+ + One oviraptorid specimen was found huddled atop a nest of its own eggs,
+its wing-like arms spread over them. Apparently it was protecting its brood
+when a sand avalanche buried and killed it. (The head of the
+specimen is missing, so it is not certain which type of oviraptorid it is,
+although it may well be
It is not certain whether oviraptorosaurs made it to the very end of +the . There is no evidence of them from very +late sediments, so they may have died out +right before the K/T Extinction. But some dinosaur groups are only known to +have died out in the K/T Extinction because their teeth have been found from +that time. Since oviraptorosaurs had no teeth, and teeth preserve better than +other remains, they may have made it to the end but not left any evidence +that we have yet found.
+This was an odd group of , characterized by an +extremely thick skull roof, often lined with small bumps and spikes. The +most commonly accepted explanation for these thick "bone-heads" is that +they were used to butt heads in mating displays similar to those of +bighorn sheep.
+ +Pachycephalosaurs were once classified as , +mainly because of their bipedal stance. But they seem to be more closely +related to the , due to similarities such +as a ridge along the back of the skull, which evolved into a frill among +the ceratopsians.
+ +The genera listed here were the "flat-headed" pachycephalosaurs. They +were sometimes grouped into the family Homalocephalidae, although this is +probably paraphyletic.
+ +Pachycephalosaurs, known only from the northern hemisphere +(with few possible exceptions), are fairly +rare, leading some to theorize that they may have inhabited environments +that were not conducive to fossilization, such as mountains.
+ Pachycephalosaurids were the "dome-headed" pachycephalosaurs. Their skull
+roofs were immensely thickened to create a large dome of solid bone on the
+top of their skulls. The dome was adorned by bumps and spikes, which grew
+quite long in
Pterodactyloids included the largest flying animals of all time. Giants
+like
These short-tailed came in a wide
+variety of forms, from the forceps-beaked
Pterodactyloid diversity declined throughout the +. By the end there were only a few giant +forms, the smaller niches having all been taken over by +. This last remnant went extinct at the end of the +, as did all +save for .
+Although they were the only other flying , +pterosaurs were not closely related to . Their +wings had a very different structure. Birds support their wings with their +second finger (or possibly third, if the frame shift hypothesis is true), +while pterosaurs used the fourth. Additionally, pterosaurian +wings were largely made up of skin membranes strengthened by fibers, while +avian wings consist mainly of feathers.
+ +Pterosaurs originated at about the +same time as the +. They began as small, long-tailed forms, +sometimes called "rhamphorhynchoids". From these came larger, +short-tailed forms, which make up the group +.
+ + There is a recent theory that pterosaurs were not archosaurs, but
+derived from some type of basal .
+For more:
+
Pterosaurs were unique among in that at least some
+of them were covered with hair, similar but not homologous to
+ hair. Although in some cases fibers in the wing
+membrane have been mistaken for hair, some fossils such as those of
+
Sauropods were giant, long-necked plant-eaters. +All sauropods were quite large. Even the smallest ones were about as big as +the largest members of other dinosaur groups.
+ + Early sauropods like
The eusauropods shown here were often grouped together in Cetiosauridae, +but it is probably a paraphyletic grouping. Vulcanodontidae, consisting of +the non-eusauropod sauropods, is also probably paraphyletic.
+ + There is a wide variance
+of opinion about this group, if it is a group. Some hold that the
+club-tailed
The position of nemegtosaurids is also debated. Some place them +as , others as . +They are currently only reliably known from cranial material, which +is often lacking in sauropod fossils.
+Sauropodomorphs were the long necked, herbivorous, lizard-hipped +, including the largest land animals of all +time.
+ +The primitive sauropodomorphs listed +here are commonly called +"prosauropods". These were semi-quadrupedal herbivores from the + and with large, +hooked claws on their feet. They were once thought to be omnivorous, since + teeth found with them were often mistakenly +thought to be the teeth of the prosauropods themselves. Instead, they were +the largest herbivores of their day (although primitive ones may have been +omnivorous).
+ +It is not certain whether "prosauropods" gave rise to the larger +, or if they are just the sister group to +Sauropoda. No cladistic analysis has yet been done to test "prosauropod" +monophyly. All to date have simply assumed monophyly based on the +fact that prosauropods lack a digit that sauropods possess, lack of a digit +usually being a derived trait, not a primitive one.
+ ++The taxon Brontosauria was originally designated for a group containing +Sauropoda and Prosauropoda, considered paraphyletic by its author. Here +it has been cladistically translated as the node containing Sauropoda +and Prosauropoda (sensu Wilson & Sereno), although this definition +has not yet been used formally, to my knowledge.
+Sauropsida is one of the two great lineages of + (the other being , +which includes ). All known sauropsids +belong to the clade Reptilia.
+ +Reptilia was once a "grab-bag" taxon for every amniote that was neither +a nor a mammal. It was divided into four sections based +on the number and alignment of certain holes in the back of the skull +(temporal fenestrae): Anapsida (no holes), Synapsida (a low hole), +Euryapsida (a high hole), and Diapsida (two holes -- includes +).
+ + Reptilia has since been re-defined as a clade: all the descendants of the
+most recent common ancestor of the four living groups considered reptiles:
+ (turtles),
The groups Anapsida and Diapsida are still used as clades within Reptilia, +slightly modified from their traditional meanings (Anapsida now excludes +the most primitive sauropsids; Diapsida now includes birds). "Euryapsida", +which included marine reptiles such as and +, is now recognized as an unnatural grouping of +various aberrant diapsid lineages which lost their lower temporal +fenestrae.
+ +The is often called "The Age of Reptiles" +because of the reptilian dominance during most of that era. Dinosaurs ruled +the land, ruled the skies, and a great variety +of marine reptiles , plesiosaurs, ichthyosaurs, +etc.) ruled the oceans. Most of these creatures died out in the K-T +extinction (ichthyosaurs died out earlier; champsosaurs, a freshwater +lineage, later).
+Sauropterygians were a group of marine reptiles of uncertain origin. At times +allied to or , they are probably +, possibly a basal lineage of either + or .
+ +Their limbs had evolved into +flippers, which they used to swim through the + seas. The advanced sauropterygians, plesiosaurs, +came in two main body forms. Pliosaurs had long, large heads, and short necks, +similar to the distantly related . Plesiosauroids +had extremely long necks with tiny heads, looking something like a cross +between a and a . +All sauropterygians were carnivorous.
+ +Placodonts may or may not have been sauropterygians. They were +large, probably sluggish creatures somewhat similar in form to today's + and +(manatees and dugongs). Their broad teeth splayed outward from their mouths. +It has been suggested that they used them to crush +shells.
+ +Sauropterygians died out at the end of the , +along with all non- . +There have been reports of modern-day populations of plesiosauroids, but +these have either turned out to be other animals (rotting basking shark +carcasses) or deliberate hoaxes (the Loch Ness monster).
+ Spinosauria once included all theropods with tall vertebral spines. Some
+of these creatures, such as
Spinosaurs all have -like conical teeth. Their +long snouts have kinks like those of and some +early . It is thought that they used these for +fishing, possibly in conjunction with other carnivorous activities.
+ +Baryonychines have more teeth at the end of their lower jaw than +spinosaurines. Spinosaurines are characterized by straight, unserrated +teeth.
+These primarily herbivores had two rows of +plates and/or spikes going down the back.
+ + Although the spikes, which were usually found on the tail, were certainly
+used for defense, the exact purpose of the plates is unknown. They could
+not have made very effective armor, since they left the sides completely
+exposed. Perhaps they performed a similar function to the sails of
+
Stegosaurs did not last to the end of the ,
+but died out during the , possibly due to
+competition from other herbivores or from a
+change in flora (the transition from gymnosperms to angiosperms) which they
+could not adapt to. One creature which was thought to be a
+ stegosaur (
Once called -like , +the animals shown here are no longer considered reptiles. Instead, they were +the non-mammalian members of a separate lineage. Their skin was +probably not dry and scaly like true reptiles.
+ +Synapsids were the first terrestrial vertebrates to truly dominate the +landscape. There were two main "waves", the "pelycosaurs" (non-therapsid +synapsids) in the Permian and then the early therapsids in the +.
+ + "Pelycosaurs" were probably cold-blooded. They ranged from large
+herbivores like
Some (but probably not all) therapsids were warm-blooded, fur-covered,
+and milk-giving. They varied from the beaked, tusked, and herbivorous
+dicynodonts to the sleek, predatory
Tetanurae consists of the advanced , +including and their ancestors. Tetanurans are +characterized by three fingers or less, an opening in the skull between the +antorbital fenestra and the naris (nostril) called the maxillary fenestra, and +stiffened tails (Tetanurae means "stiffened tails").
+ +The non-neotetanuran groups listed +here are sometimes grouped together in a group sometimes called +Megalosauria or Megalosauroidea, although this is probably a paraphyletic +group, as shown here. Most "megalosaurs" were large carnivores. Some think + and Torvosauridae (=Megalosauridae) make a +group, sharing enlarged, sickle-shaped thumb claws.
+ +
Neotetanurans, an advanced group of tetanurans, had complex air
+passages in their vertebrae and ribs. The furcula, a bone which is not always
+preserved, has been found in a
+(
Among terrestrial vertebrates, belong to +Amniota, a clade characterized by the ability to procreate on land. Of the +two main branches of amniotes, dinosaurs belong to +, which includes other + as well. The sister clade to Sauropsida, +, includes .
+These Asian pose some taxonomic problems. They were +originally classified as , although they have +some features very uncharacteristic for theropods. Their hips are +bird-like, although some theropods such as the and themselves have +bird-like hips as well. The front of the snout is a toothless beak, +although , , +and several lineages have toothless beaks as well. +But the feet, which have four functional, forward-facing toes, are utterly +unlike any other theropod feet. Except for some , all theropods have three functional toes and a +reduced dewclaw.
+ +Another theory was that they were an +outgroup to the , since ornithischians have +bird-like hips (although they are only superficially bird-like), beaks, and, +in the most primitive ornithischians, four toes. It has also been proposed +that they are late-surviving relatives of +"", since their teeth and feet are +similar to those of "prosauropods". (They are similar enough that +one jawbone from the Early Jurassic of China was published as the earliest +therizinosaur, although it is more likely a "prosauropod".)
+ + The discovery of
There is still disagreement over which coelurosaurian group
+therizinosaurs are related to. They have been allied with , , and .
Theropoda is an incredibly diverse group of . Most of the Mesozoic theropods were sharp-toothed +predators, although there have been a few toothless, possibly herbivorous +groups. During the (or possibly ), some theropods evolved into feathered, flying +forms. Their descendants are today's .
+ +The group Theropoda ("beast feet") was named early on in +paleontological history, along with ("bird +feet" - a major group). It almost seems as +though the names were somehow mixed up and improperly assigned, since +theropods have bird-like feet and ornithopods have somewhat more -like feet, but the names stuck and it's far too late to +change them now.
+ +The non-neotheropod genera shown above +are often informally referred +to as "herrerasaurs". "Herrerasaurs" may be basal theropods, as shown +here, basal , or even basal . They had many primitive features, such as five +digits on the hands, although the outer two were very small and had no +claws.
+ +
It is possible that Ceratosauria as shown here is a paraphyletic group, +characterized only by primitive features. Neoceratosaurs may be share more recent +ancestry with tetanurans than with coelophysoids.
+Thyreophora includes the "armored ", a +group of primarily quadrupedal with bony +plates, scutes, and/or spikes protecting their backs from theropod +predators. Some +also exhibited armor like this.
+ +
The more advanced thyreophorans, like
These primarily Cretaceous animals represent the last group of before the great K/T extinction. Bony plates have +been found with some specimens, indicating that they were armored, like +.
+ + South American forms such as
Argentinian egg material has been attributed to titanosaurs. The eggs are
+typically 11-12cm in diameter, some up to 17cm. From relatively
+small eggs like these came creatures which would grow thousands of times
+larger! Eggs have also been attributed to
The phylogeny above is somewhat tentative.
+Troodontids (formerly known as +saurornithoidids) were remarkable in +having the largest E.Q. (encephalization quotient) of all non- . Intelligence-wise, they may +have been on level with some modern-day . The large +brain, huge eyes, and grasping hands of these +may indicate a nocturnal, predatory lifestyle. However, their teeth may +indicate omnivory.
+ +The feet were equipped with "switchblade claws", similar to those of +. They were once placed with the +dromaeosaurids in , but this grouping +has been questioned. They share some features with , such as a pinched middle metatarsal +(possibly a speed adaptation), features of the braincase, and large eyes. +They have also been placed in basal , basal , and as sister group of the - group.
+ This was the last group of huge predatory
+, including the
+ever-popular
For all their size and strength, tyrannosaurids had remarkably small arms +with only two fingers on the hand, the third digit having degenerated to +near nothingness.
+ + The near lack of forelimbs in tyrannosaurids (and to a lesser extent in
+some other large predatory dinosaurs) poses an interesting problem: How
+did they deal with tripping? A recent study of
There have been some proposals that
+ Within the group of animals that have backbones, + belong to the tetrapods, or terrestrial + vertebrates. +
+