Before the Reign of Tyrants

Christmas came early this year, with the discovery of a giant carnivorous dinosaur from the Cretaceous Period. Dubbed Siats meekerorum, the beast was a large allosaurid dinosaur. The Allosauroidea dominated the large predator niche for much of the Jurassic period and the early Cretaceous period. Siats is specifically a Neovenatorid allosaur. The Neovenatorids are currently considered a sister group with the Carcharodontosaurids, a allosauroid group which achieved staggering size in the southern hemisphere.

While much of the news coverage implies that Siats bullied or terrorized the early tyrannosaurs, I have to note that the tyrannosaurs eventually supplanted the allosauroids in North America in striking fashion. The tyrannosaurs belong to the coelurosaur clade, the coelurosaurs are best defined as theropod dinosaurs more closely related to birds than they are to carnosaurs such as the allosaurs (including Siats). Before the tyrannosaurids were recognized as coelurosaurs, most small carnivorous dinosaurs were lumped in with the coelurosaurs much as most large carnivores were lumped in with the carnosaurs, they were considered to have evolved from allosaurid ancestry. The tyrannosaur lineage started out as small, gracile carnivores such as Dilong paradoxis, a primitive, feathered tyrannosaur from the early Cretaceous.

Siats represents a late survival of the allosaurs, its discovery sheds a little light on a transitional period before the tyrannosaurs basically locked up the large predator niche in the late Cretaceous northern hemisphere. For a dinosaur nut like myself, this is most exciting news.