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Colossal New Dinosaur Ruled North America Before T-Rex

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The Siats meekerorum ('Siats' for a cannibalistic monster from Ute Native American mythology, 'meekerorum' for the Meeker family, longtime Field Museum supporters) roved North America approximately 100 million years ago and dominated the early tyrannosaurus rex, according to a study published Friday in the journal Nature Communications by researchers from the Field Museum, the North Carolina Museum of Natural Sciences (NCMNS), and North Carolina State University (NCSU).

Artist: Jorge Gonzales

The carnivorous predator was over 30 feet long and weighed more than four tons, according to the researchers' calculations. Though T. rex of a later period were larger than 30 feet, T. rex teeth from the Siats period indicate that during Siats's reign as apex predator, T. rex were diminutive in comparison.

Though it resembles the T. rex, the Siats isn't a member of the tyrannosaurs family. It belongs to a branch of the carcharodontosaurian family that was previously unknown in North America, according to the paper.

"This dinosaur was a colossal predator second only to the great T. rex and perhaps Acrocanthosarus in the North American fossil record," Lindsay Zanno, lead author on the paper and Director of Paleontology at NCMNS/NCSU, said in a statement.

The newfound dinosaur is dated to the middle of what was previously a 30-million-year gap in known North American fossils of large predatory dinosaurs, according to a statement.

The scattered fossilized remnants of Siats was originally discovered in 2008 by researcher Lindsay Zanno, the lead author on the paper. The excavation took two summers, followed by careful cleaning at The Field Museum.

About The Author


Zoë Schlanger is Frontpage Editor at TPM. Zoë was a TPM intern in 2011, and prior to returning here she was editor in chief of NYU Local, the alternative independent student news site at NYU. Zoë has interned at places like the Nation, InsideClimate News, The Rachel Maddow Show and Gothamist. She can be reached at