Sunday 13 December 2015

Capreolus constantini: A Roe Deer from the Early Pliocene of Hidalgo State, Mexico.

Deer, Cervidae, are one of the most abundant and diverse groups of Artiodactyls (even-toed hoofed Mammals) today. They first appear in the fossil record in Eurasia in the Early Miocene, with the oldest specimens found in North America dating from the Early Pliocene on Florida. Today the Americas have a distinct Deer fauna of their own, comprising the genera Hippocamelus, Mazama, Blastocerus, Ozotoceros, Pudu and Odocoileus, with the Arctic Reindeer Rangifer tarandus and Elk Alces alces found in both the Old and New Worlds.

In a paper published in the journal Acta Palaeontologica Polonica on 16 April 2014, Eduardo Jiménez-Hidalgo of the Laboratorio de Paleobiología at the Universidad del Mar and Victor Bravo-Cuevas of the Museo de Paleontología at the Universidad Autónoma del Estado de Hidalgo describe a Roe Deer, Capreolus constantini from the Early Pliocene Atotonilco El Grande Formation of Hidalgo State in Central Mexico.

The specimen comprises a fragment of mandible with fragments several teeth, plus both humeri, part of an ulna, a tibia, a metacarpal, part of a metatarsal, the left patella, the first right phalanx of a forelimb and an isolated tooth. It was found 60 cm above a volcanic ash layer dated to 4.57 million years ago by fission-track dating and 4.2 million years ago by argon/argon isotope dating, implying a slightly younger age.

Mandible and teeth of the Cervid Mammal Capreolus constantini, from the Pliocene of Hidalgo, Mexico. (A) Left mandible fragment in lateral (A1) and occlusal (A2) views; partial p3 and p4 in occlusal view (A3); p4 and m1 in occlusal view (A4). (B) p3 in occlusal view. Jiménez-Hidalgo & Bravo-Cuevas (2015).

To date the earliest, Roe Deer, Capreolus spp., known from the fossil record was a specimen of Capreolus constantini (the same species as the Hidalgo specimen) known from the Late Pliocene of Udunga in the Republic of Buryatia in eastern Siberia. Both of the living members of the genus, Capreolus capreolus and Capreolus pygargus are also native to Eurasia and the group have generally been assumed to be exclusively Eurasian in origin and distribution, while the New World Deer are thought likely to have originated from a single colonisation event and subsequent diversification. The Hidalgo specimen is the oldest known Roe Deer fossil and of approximately the same age as the oldest known American Deer fossils. It also makes the Roe Deer the first known group of non-Arctic Deer to be found in both the Old and New Worlds. This implies that Deer made the transition between northeast Asia and North America at least twice during the Late Miocene/Early Pliocene, with either a population of Roe Deer making the crossing separately of the ancestors of modern American Deer, or Roe Deer being part of the American Deer group that subsequently crossed back into Asia.

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