MEANING: Siats
PERIOD: Late Cretaceous
CONTINENT: North America
Siats is a controversial large theropod from the Late Cretaceous of North America, named after a man-eating monster of Ute mythology. Thanks to the uncertain nature of its fossil remains, it has been classified as a megaraptoran, allosauroid, and tyrannosaurid at various stages of research. Siats as an allosauroid would show that this group survived all the way to the Late Cretaceous before ceding to tyrannosaurs as the apex predators of North America. At 12 m in length and 4 t in body mass, it would certainly be the top predator in its habitat. But until further fossil evidence is discovered, the debate goes on regarding its phylogenetic affinities.
Siats is from the Cretaceous. The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct flora and fauna, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
Siats is a theropod. Theropods are dinosaurs that are characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally carnivorous, although a number of theropod groups evolved to become herbivores and omnivores. Theropods first appeared during the Carnian age of the late Triassic period and included all the large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous. In the Jurassic, birds evolved from small specialized theropods, and are today represented by about 10,500 living species.
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