Obscure Dinosaur of the Week: Eoabelisaurus mefi

Lateness due to confirmation preparation. Awesomeness due to the origin of abelisaurid short arms!

Name: Eoabelisaurus mefi
Etymology: From the greek "eos" (dawn), and Abelisaurus, type genus of the Abelisauridae; and the popular abbreviation of the Museo Paleontologico Egidio Feruglio (MEF)
Distribution:  Middle Jurassic (Aalenian-Bajocian) of Patagonia
Type Specimen:  Near complete skeleton, missing only some neck and tail vertebrae (cervical and caudal), and the lower jaw (mandible)
Estimated size:  6 - 6.5 m in length

Interesting fact: Evidence of tiny arms pushed back 40 million years
Ever wondered where those preposterously short arms of Tyrannosaurs and other large theropods came from?

Meet Eoabelisaurus mefi, a recently discovered abelisaurid (theropod dinosaur) from Patagonia. The skull is in the top left corner of the frame, with the tail stretching to the right. Just look at those shoulder blades in the top left, compared with the upper arm, and even smaller lower arm! Interestingly, this species pushes back the appearance of short arms by 40 million years, from the early Cretaceous back to the mid Jurassic. And as the authors so cleverly state, "The apparent rarity of ceratosaurs in the Jurassic does most probably not reflect true low taxonomic diversity, but is owed to the poor fossil record of Jurassic theropods in the Southern Hemisphere" (Pol et al., 2012); i.e. either fossils haven't been found yet, good rock outcrop doesn't exist, or the carcasses weren't fossilised in the first place. Taphonomic bias strikes again!

Simplified cladogram of all dinosaurs. E. mafi was an abelisaurid, within theropoda.

---

References
Pol, D., Rauhut, O. (2012). A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs. Proceedings of the Royal Society B, 1-6: 10.1098/rspb.2012.0660