In Depth
Not a lot is known about Eshanosaurus, yet it has still managed to be a controversial dinosaur. Thought to be one hundred and ninety-six million years old, the partial dentary of Eshanosaurus (currently the only part known) goes as far back as the Hettangian stage of the Jurassic. The describers of the dentary proposed two things, one, the dentary may be from the first coelurosaur. Two, aside from being the first coelurosaur, it may be the first therizinosaur, speculation based upon traits that match those of the therizinosaurs.
Not all palaeontologists agree with these ideas however mainly because this would create a massive gap of tens of millions of years between Eshanosaurus and the first confirmed therizinosaur remains that to date are known from the Early Cretaceous. One notable case is the description of the first known North American therizinosaur by Kirkland and Wolfe, where the teeth of Eshanosaurus were described as having ridges similar to prosauropods. The describers of Eshanosaurus however tested for this and found the dentary and teeth to still be those of a therizinosaur. Support for the original theory also comes from a 2009 study by Paul Barrett that yielded the same conclusion that the Eshanosaurus holotype has known therizinosaur features that are absent in known prosauropods.
For the time being Eshanosaurus remains a problematic genus. But if other factors to explain the similarity to therizinosaurs such as convergent evolution can be ruled out, and ideally the discovery of further remains found that can bridge the gap and complete our understanding of the coelurosaurs and therizinosaurs, then Eshanosaurus may yet help to re-write palaeontology books across the board.
Further Reading
– A new therizinosaur from the Lower Jurassic Lower Lufeng Formation of Yunnan, China. – Journal of Vertebrate Paleontology 21(3):477-483. – X. Xu, X. Zhao & J. M. Clark – 2001. – The affinities of the enigmatic dinosaur Eshanosaurus deguchiianus from the Early Jurassic of Yunnan Province, People’s Republic of China. – Palaeontology. 52 (4): 681−688. – P. M. Barrett – 2009.
