Little Dawn Runner
8:44 pm
Scientists have described a new fossil that has the potential to shed light on the origin and evolution of a major branch on the dinosaur family tree.
Eocursor parvus, the “Little Dawn-runner,” lived 210,000,000 years ago in what is now South Africa. It is known from a partial skeleton that preserves parts of its skull, jaw, spinal column, hips, and limbs. A reconstruction of the complete animal suggests that it would have been about a meter long in life and stood about 30cm high at the hips. Its long, slender legs were well-proportioned for running—probably its main defense from larger predators.
What makes Eocursor particularly important is where (and when) it fits on the dinosaur family tree. Eocursor was an early ornithischian, among the first of the great group of beaked, largely plant-eating dinosaurs that would later include armored stegosaurs and ankylosaurs, duck-billed hadrosaurs, horned ceratopsians, and dome-headed pachycephalosaurs. Other Triassic ornithischians are known, but Eocursor is by far the most well-preserved.
Study of this little dinosaur is already providing insight into how ornithischians evolved. Eocursor is similar in shape and (presumably) habits to Jurassic ornithischians like Lesothosaurus and Scutellosaurus, even though it predates them by roughly 10,000,000 years. To the scientists that described Eocursor, this suggests that the later Jurassic radiation of ornithischian dinosaurs was not due to any evolutionary advancement particular to the Ornithischia. Instead, they feel this lends support to the hypothesis that ornithischians expanded into the niches that opened after several groups of non-dinosaurian herbivores went extinct at the end of the Triassic.
Further reading:
Butler, R. J., Smith, R. M. H., and Norman, D. B. 2007. A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithishia [PDF link]. Proceedings of the Royal Society B Published online: doi:10.1098/rspb.2007.0367
Stegosaurus’ little cousin is found, a news article at the (British) Natural History Museum.
And an article from BBC news.
This basically destroys any concept of a “Heterodontosauriformes” as in the Yinlong description. I’d like to know exactly when the ornithischian quadraradiate pelvis evolved. One would think that the “original” ornithischian had a more tri-radiate pelvis by virtue of its ancestry.