Sunday 13 October 2013

A new species of Abelisauroid Dinosaur from the Late Cretaceous of Madagascar.

The Albelisauroids were a group of Theropod Dinosaurs that appeared in the Middle Cretaceous, and underwent a major diversification in the Cretaceous. They were restricted to the southern continent of Gondwana, which by the Cretaceous had separated from the supercontinent of Pangea and started to break up into the continents of today's Southern Hemisphere; Albelisauroids are known from Africa, Madagascar, India and South America. Albelisauroids were noted for having short, but tall and often ornamented skulls, as well as often having greatly reduced forelimbs.

In a paper published in the journal PLoS One on 18 April 2013, Andrew Farke of the Raymond M. Alf Museum of Paleontology in Claremont, California and Joseph Sertich of the Department of Earth Sciences at the Denver Museum of Nature and Science, describe a new species of Abelisauroid Dinosaur from the Late Cretaceous of Madagascar.

The new species is named Dahalokely tokana, where 'Dahalokely' means 'small bandit' and 'tokana' means lonely, both in Malagasy; references to the species' small size for an Albesauroid and location on the isolated landmass of Madagascar. The species is described from six complete vertebrae and one partial vertebra, plus one complete and three partial ribs. This material is enough to confidently place Dahalokely tokana within the Abelisauroidea, but not to make any good estimation of its place within the group. It is calculated that the specimen was about 3.5 m long when living.

Dahalokely tokana. (A) Reconstructed silhouette with preserved elements indicated in white. Cervical vertebra (C?5) in (B) cranial; (C) left lateral; and (D) dorsal views. Dorsal vertebra (D 2) in (E) cranial; (F) left lateral, and (G) dorsal views. Dorsal vertebra (D?6) in (H) cranial; (I) left lateral; and (J) dorsal views. Abbreviations: cprl, centroprezygapophyseal lamina; didfs, dorsal infradiapophyseal fossa; diprfs, dorsal infraprezygapophyseal fossa; dp, diapophysis; ep, epipophysis; ha, hypantrum; ho, hyposphene; idfs, infradiapophyseal fossa; ipofs, infrapostzygapophyseal fossa; iprfr, infraprezygapophyseal foramen; iprfs, infraprezygapophyseal fossa; lpfr, laminopeduncular foramen; ns, neural spine; pfr, pneumatic foramen; posf, postspinal fossa; poz, postzygapophysis; pp, parapophysis; prel, prezygoepipophyseal lamina; prsf, prespinal fossa; prz, prezygapophysis; sprl, spinoprezygapophyseal lamina; vidfs, ventral infradiapophyseal fossa; viprfs, ventral infraprezygapophyseal fossa. Farke & Sertich (2013).

Madagascar and India are thought to have separated from the rest of Gondwana around 100 million years ago, and from one-another around 88 million years ago. The deposits from which Dahalokely tokana was recovered are thought to be around 90 million years old, thus potentially shedding light into this period of time, when little fossil material is known from Madagascar. Most Cretaceous material from Madagascar, including all previously described Abelisauroids from the island, is around 70 million years old, making Dahalokely tokana the oldest known member of the group from Madagascar by around 20 million years.

The approximate location of the site where Dahalokely tokana was discovered. Farke & Sertich (2013).

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