When a dinosaur starts coming out of the ground, what species the creature might be isn’t always clear. Paleontologists and field volunteers try to uncover enough to figure out the extent of the bone and trim down the size of the block, leaving the majority of careful, fine-scale preparation for the lab. And even once that skeleton has been painstakingly excavated, glued, and cleaned to the utmost, the dinosaur’s identity still might be mysterious. Such was the case with Nqwebasaurus thwazi, an early “ostrich mimic” dinosaur whose affinities only became clear a decade after first being described.
William De Klerk and coauthors named the dinosaur in 2000. Discovered in the roughly 140 million year old Early Cretaceous rock of South Africa, the body of Nqwebasaurus consisted of a fragmentary skull, the shoulders and arms, complete lower legs, neck vertebrae, and fragmentary parts of the rest of the skeleton. In life, the dinosaur would have only stood about a foot high at the hips, although it wasn’t finished growing yet. The dinosaur’s bone microstructure showed that the animal was about three years old when it died, and had not reached skeletal maturity. This Nqwebasaurus was a subadult when it perished.
Despite the delicate detail and relative completeness of the skeleton, though, De Klerk and coauthors weren’t sure what kind of dinosaur Nqwebasaurus was. They were able to figure out that the dinosaur was a coelurosaur – a major group of feathery theropods that includes tyrannosaurs, ornithomimosaurs, deinonychosaurs, therizinosaurs, birds, and others – but the paleontologists held back from assigning Nqwebasaurus to a particular branch of the family tree.
Last year, Nqwebasaurus finally found its branch. Based upon additional skull bones found in the same block, Jonah Choiniere and colleagues were able to discern that Nqwebasaurus was the earliest, most archaic ornithomimosaur – a dinosaur from the early days of the ostrich-mimic lineage. Among the tell-tale bones was part of the upper jaw bearing small, conical teeth. Even though familiar ornithomimosaurs such as Struthiomimus (in the photo above) and Ornithomimus itself had traded teeth for beaks, these later forms were still the descendants of toothed ancestors.
Nqwebasaurus was closer to that toothed eo-ornithomimosaur. Yet, even though the dinosaur retained simple teeth, Choiniere and coauthors pointed out that Nqwebasaurus also had gastroliths in its stomach – a hint that the small theropod was an herbivore that relied on a “gastric mill” to grind food. Apparently, ornithomimosaurs adopted an omniovorous or herbivorous diet early on in their history, and that shift away from meat shaped the next 75 million years of their evolution.
Previous entries in the Dinosaur Alphabet series:
M is for Montanoceratops
L is for Leaellynasaura
K is for Kileskus
J is for Juravenator
A-I at Dinosaur Tracking.
Choiniere, J., Forster, C., de Klerk, W. 2012. New information on Nqwebasaurus thwazi, a coelurosaurian theropod from the Earl Cretaceous Kirkwood Formation in South Africa. Journal of African Earth Sciences. 71-72: 1-17
De Klerk, W., Forster, C., Sampson, S., Chinsamy, A., Ross, C. 2000. A new coelurosaurian dinosaur from the Early Cretaceous of South Africa. Journal of Vertebrate Paleontology. 20, 2: 324-332