Siats meekerorum

Named by Lindsay E. Zanno and Peter J. Makovicky, 2013
Diet: Carnivore (Prey included sauropods, ornithopods such as Eolambia, and primitive indeterminate tyrannosaurs)
Length: Juvenile specimen is estimated to be 30 feet (9 meters), while estimated that the adults would've been up to 40 feet (12 meters)
Weight: Juvenile specimen is estimated to weigh up to 2.5 tons, while estimated that the adults would've weighed up to 4 tons
Region: Utah (Upper Mussentuchit Member of the Cedar Mountain Formation)
Age: 98.5-98 million BC (Early Cenomanian stage of the Late Cretaceous)

Described in 2013, Siats was a large theropod dinosaur that stalked Utah during the Late Cretaceous period and is the third largest theropod of North America after Tyrannosaurus rex and Acrocanthosaurus atokensis. 

It was named after "Siats," a man-eating monster of Ute mythology, while meekerorum honours the late geologist, John Caldwell Meeker who bequethed a fund for the support of paleontological research, his widow Withrow Meeker and his daughter Lis Meeker, one of the volunteer's project. 

Known only from a partial postcranial skeleton housed at the Field Museum of Natural History in Chicago, Illinois, it was first discovered by Lindsay E. Zanno, as part of a 2008 expedition led by Peter J. Makovicky. 

However, the only specimen of this giant predator, estimated to be up to 30 feet (9 meters) in length and weighed over 2 tons, wasn't yet fully-grown, so scientists estimated that the adults would've been up to 40 feet (12 meters) long and weighing up to 4 tons, making it similar in size, but less massive, to Tyrannosaurus rex. 

It was found from the Upper Mussentuchit Member of the Cedar Mountain Formation, in Emery County of Utah, dating to the Early Cenomanian stage of the Late Cretaceous period, about 98.5 million years ago. During that time, the region was a broad coastal plain on the edge of a shallow inland sea (known as the Western Interior Seasway) with abundant rainfall or a high water table. Siats was most likely the region's alpha predator, at the top of the local foodchain. As well as preying on sauropods and ornithopods that it shared with, it would've also preyed on some of the small primitive members of the tyrannosauroid family that it lived with. 

The two holes at the top and bottom of the tail vertebrae and thick bar in it shows that its a member of Megaraptora clade and was a close relative of Megaraptor from Argentina (South America), Australovenator from Australia, and Fuikuiraptor from Japan.

A giant neovenatorid, it was thought that it was North America's youngest member of the allosauroid clade and shows that they did not yield to dominance in North America to the tyrannosauroids until the Late Cretaceous period.

However, in 2014, a skull of a juvenile Megaraptor found in Argentina shows tyrannosaur-like features and it shows that the megaraptoras were primitive members of the tyrannosauroid clade, though most paleontologists believe more studies are required on this particular branch of theropods. So Siats is actually more related to T. rex, than Allosaurus and Neovenator, although Zanno insists that it was not a tyrannosauroid.