Siats

Name: Siats ‭(‬after a creature from Ute Native American Mythology‭)‬.
Phonetic: Se-ats.
Named By: L.‭ ‬E.‭ ‬Zanno‭ & ‬P.‭ ‬J.‭ ‬Makovicky‭ ‬-‭ ‬2013.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Saurischia,‭ ‬Theropoda,‭ ‬Carcharodontosauria,‭ ‬Neovenatoridae,‭ ‬Megaraptora.
Species: S.‭ ‬meekerorum‭ (‬type‭)‬.
Diet: Carnivore.
Size: Holotype individual estimated to be about‭ ‬9‭ ‬meters long.‭ ‬Fully grown adult are estimated to have approached‭ ‬12‭ ‬meters long.
Known locations: USA,‭ ‬Utah‭ ‬-‭ ‬Cedar Mountain Formation.
Time period: Cenomanian of the Cretaceous.
Fossil representation: Holotype fossil remains consist of a partial post cranial skeleton including remains of the pelvis,‭ ‬lower legs and vertebrae,‭ ‬from a juvenile/subadult.

       Although only known from the incomplete remains of a juvenile,‭ ‬the dinosaur Siats seems to have been one of the larger theropod dinosaurs from North America.‭ ‬The partial remains of the holotype individual which mostly include elements of the hind quarters are estimated to have come from an individual dinosaur that was about nine meters long.‭ ‬However,‭ ‬the neural arches of the vertebrae of this individual are unfused,‭ ‬which is clear evidence that this individual was not fully grown.‭ ‬Although only speculation,‭ ‬the adult size of Siats is currently thought to have approached twelve meters,‭ ‬though the only way we can be certain about the true adult size is if a second and fully grown specimen is found.
       With an estimated adult size around the twelve meters mark,‭ ‬Siats may well be one of the largest theropod dinosaurs to have lived in North America.‭ ‬However,‭ ‬just as the name Siats is based upon a mythical creature in Ute legend,‭ ‬an almost mythical air about the size of Siats has already become established,‭ ‬with a common claim made about Siats is that it was the largest theropod dinosaur after the earlier Acrocanthosaurus and the later Tyrannosaurus.‭ ‬This would be true for the Cretaceous as we currently understand it,‭ ‬but if you want to go back further into the Jurassic,‭ ‬then Saurophaganax,‭ ‬a theropod estimated between ten and a half and thirteen metres long may have also have been larger than Siats.

       Siats has been identified as a member of the Megaraptora,‭ ‬a sub group of the Neovenatoridae.‭ ‬This is sister group to the Carcharodontosauridae,‭ ‬and both these groups sit under the Carcharodontosauria,‭ ‬which is why Siats is commonly referred to as a carcharodontosaur instead of a neoventaorid,‭ ‬though both terms are correct.‭ ‬Siats has been interpreted as being a megaraptoran neovenatorid,‭ ‬meaning that it is more closely related to genera such as Australovenator from Australia,‭ ‬Fukuiraptor from Japan and Aerosteon and Megaraptor from South America.‭ ‬When preserved,‭ ‬these genera are noted for having large claws on the ends of their fingers,‭ ‬and although corresponding fossils in Siats have not yet been found,‭ ‬it’s quite possible that Siats would have had enlarged claws on the fingers,‭ ‬going by familial association.

       As a predator,‭ ‬Siats lived at a time in North America when the dominant herbivorous dinosaurs would have been hadrosauroids and nodosaurs.‭ ‬However not long after Siats is known to have lived,‭ ‬there was a population explosion in horned ceratopsian dinosaurs and ankylosaurs,‭ ‬dinosaurs that were far tougher and bonier than what even a large theropod like Siats was adapted to handle.‭ ‬The emergence of these new types of herbivores alongside the hadrosaurs may have been what allowed the tyrannosaurs,‭ ‬theropods ideally suited to tackling tougher prey animals,‭ ‬the opportunity to rise up and challenge older theropod forms like Siats for dominance.‭ ‬While it may have been possible for a few older forms like and similar to Siats to exist as niche predators of less armoured prey like hadrosaurs,‭ ‬eventual competition with the big tyrannosaurs such as Bistahieversor,‭ ‬Albertosaurus and of course Tyrannosaurus may have eventually driven the older theropods to extinction in North America.‭ ‬Only additional older form theropod remains from deposits later in the Cretaceous would prove that they managed to exist alongside the big tyrannosaurs.

Further reading
-‭ ‬Neovenatorid theropods are apex predators in the Late Cretaceous of North America.‭ ‬-‭ ‬Nature Communications‭ ‬4.‭ ‬-‭ ‬L.‭ ‬E.‭ ‬Zanno‭ & ‬P.‭ ‬J.‭ ‬Makovicky‭ ‬-‭ ‬2013.



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