Morphology of the Viper Prefrontal Bone and a New Pliocene Agkistrodon

Mead, Jim I. Swift, Sandra L.

The Mammoth Site

Hot Springs, SD USA

The earliest record of the family Viperidae arose perhaps in Eurasia during the late Oligocene. The rugged structure of a snake vertebra and their abundance per animal permits these skeletal remains to be commonly preserved in the fossil record. Lab technicians have come to easily distinguish these remains as belonging to snakes when sorting fossils, thus fossils are selected for identification. Consequently, vertebrae are the predominant skeletal element when identifying fossil snakes. The ability to identify genera and species of snakes based solely on vertebral characters has varying levels of success and acceptance within the research community. North American researchers have concentrated on vertebral remains when analyzing fossil snake faunas. European researchers also target vertebral remains but often include cranial remains. Cranial remains have proven diagnostic to genus and to species with varying success. A hindrance to using the various cranial elements for identification of fossil remains includes lab personnel do not always recognize a number of the cranial elements, therefore specimens are not consistently made available for identification. The recovery of fossil snake cranial bones (earliest Pliocene) leads us to study the prefrontal of viperine snakes from Western Hemisphere and Eurasia. Here we assess the morphological attributes and variation of the prefrontal from extant Eurasian Viperinae (5 genera) and Azemiopinae (1 g.), along with members of Crotalinae from Asia (7 g.) and the Americas (11 g.) for a total of 184 specimens. Results indicate that isolated and complete prefrontal bones typically can be identified to genus (e.g., Agkistrodon) and occasionally to species. At this time the prefrontal within specious genera (Crotalus) cannot be identified to species. We have identified a new, Pliocene-age species of Agkistrodon within the Copperhead group, yet distinct from the clade containing the other species.

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