Saurischian Dinosaurs

saurischian philogeny
The saurischian dinosaurs may be divided into several main groups:
the bipedal predators Theropoda, aberrant herbivorous Segnosauria,
and herbivorous quadrupedal Sauropodomorpha.
Both the theropods and sauropodomorphs existed from the Late Triassic until the end of the Late Cretaceous and the segnosaurs are known only from the Late Cretaceous.
The theropods greatly diversified in size, structure and style of life.
Two of their groups, the carnosaurs and maniraptorans, are represented at the exhibition.
The carnosaurian theropods include the largest terrestrial predators ever to have
inhabit the Earth. They began to evolve as early as the Early Jurassic or even
Late Triassic but they flourished in the Late Cretaceous.
In that time the largest carnosaurs of the genus Tyrannosaurus
lived in both what is now Central Asia and North America.
The Asian species, Tyrannosaurus bataar
(which is frequently assigned to its own genus Tarbosaurus),
is smaller than its North American relative Tyrannosaurus rex.
As the former is some more ancient than the latter, it suggests the genus could initially
have appeared in Asia and then entered North America through the wide land
bridge connecting these continents in the Cretaceous.
The tyrannosaurs possessed a huge head with very large cutting serrated teeth, stout and rather long hindlimbs, and forelimbs greatly reduced as typical of all carnosaurs.
The brain in this tremendous animal was unbelievably tiny in comparison with body size.
The maniraptoran theropods are represented at the exhibit by dromaeosaurs,
oviraptorids, and avimimids.
These dinosaurs have never reached such huge size, like the carnosaurs.
All maniraptorans are distinguished from the latter by well-developed,
long and powerful forelimbs, although they were definitely bipedal like the carnosaurs,
and did not use the forelimbs for support when walking.
The dromaeosaurs were medium-sized predators with an extremely large sickle-like talon on the inner toe. The earliest dromaeosaur Deinonychus comes from the Early Cretaceous of North America.
In the Late Cretaceous several genera of dromaeosaurs are known from North America and Central Asia (Velociraptor).
The oviraptors come exclusively from the Late Cretaceous of Mongolia.
They differ from other maniraptorans by toothless jaws with frontal parts probably covered by a horny bill. Such an unusual structure provoked a suggestion that oviraptors ("egg burglars") might feed on eggs of other reptiles, but it is more likely they fed on mollusks using powerful toothless jaws to crash their shells.
A single known species of avimimids come from the Late Cretaceous of Mongolia.
This very unusual dinosaur shares with birds some characters in the
structure of the forelimb and shoulder girdle.
The evolutionary history of sauropodomorphs was very successful and they had global
distribution beginning from the Late Triassic untill the end of the Late Cretaceous.
Their advanced members, the sauropods, embody the largest
terrestrial tetrapods ever to have inhabited the Earth.
Some of them were more than 40 meters long and up to 60-70 tons in weight.
Besides the skeletal remains the record of this abundant and diverse group
of dinosaurs includes well-preserved egg clutches, like one from the
Late Cretaceous of Mongolia displayed at the "Russian Dinosaur Exposition".
The segnosaurs come only from the Late Cretaceous of Mongolia and China
and are not well studied because of the insufficient fossil record.
They were large or medium-sized bipedal planteaters with relatively small head, massive body and stout hindlimbs. The relatively very long and powerful forelimbs in segnosaurs possessed giant claws, that might be up to 80 centimeters (2,6 feet) in length, like in Therizinosaurus from Mongolia.
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