Kelmayisaurus Gets a Family

What was Kelmayisaurus? Discovered in 1973, the lower jaw and partial upper jaw of this large, predatory dinosaur from the Early Cretaceous of China have been frustratingly difficult to interpret. Maybe Kelmayisaurus belonged to some obscure lineage of archaic theropod dinosaurs, or perhaps the fossils were simply parts of some other, already-known dinosaur. In a forthcoming Acta Palaeontologica Polonica paper, researchers Stephen Brusatte, Roger Benson and Xing Xu finally solve the mystery.

Complete, articulated dinosaur skeletons are exceptionally rare finds. Most often, paleontologists find scraps—many dinosaurs are known from only a few parts of their skeleton. Determining the identity and relationships of a partial skeleton is dependent upon knowledge of other species. Tell-tale skeletal landmarks that are peculiar to some groups, but not others, allow paleontologists to narrow down the list of possibilities for what a particular fragment or bone might represent. Thanks to a recently improved understanding of a group of large, meat-eating dinosaurs known as carcharodontosaurids, the enigmatic Kelmayisaurus could be properly placed among its extinct relatives.

Unraveling the identity of Kelmayisaurus required two steps. First, Brusatte and co-authors had to determine whether the dinosaur could be distinguished as a unique species. Contrary to the idea that the remains were too scrappy to make such a determination, Kelmayisaurus had a distinctive groove on the front portion of the outside of the lower jaw. Kelmayisaurus is a valid dinosaur name, after all.

With the first question resolved, the paleontologists set about determining what sort of dinosaur Kelmayisaurus was. The best-supported hypothesis was that Kelmayisaurus was a carcharodontosaurid, related to Giganotosaurus, Acrocanthosaurus and others. Aspects of the Kelmayisaurus toothrow, such as the depth of some of the bone around the teeth, and the absence of features often seen in other groups of predatory dinosaurs placed the dinosaur among the "shark-toothed" predators. Though not as large as some of the largest dinosaurs in this group, Kelmayisaurus was still pretty big—about the size of its distant cousin Allosaurus.

But Kelmayisaurus was not the first dinosaur of its kind to be found in China. In 2009, Brusatte, Benson, Xu and several co-authors described another carcharodontosaurid from another long-neglected partial skull they called Shaochilong. This means that there are now two of these large predators known from a "dark period" spanning 140 to 90 million years ago in the history of Asia's dinosaurs. The two known species were separated by at least 8 million years, further supporting the identification of Kelmayisaurus as a distinct species, but the recognition of these large predators in China hints that there are likely other carcharodontosaurids waiting to be found. Perhaps they already have been, and are waiting in museum collections to be redescribed like their relatives have been.

References:

Brusatte, S., Benson, R., Xu, X. (2011). A reassessment of Kelmayisaurus petrolicus, a large theropod dinosaur from the Early Cretaceous of China Acta Palaeontologica Polonica DOI: 10.4202/app.2010.0125

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.