title: A burrowing frog from the late Paleocene of Mongolia uncovers a deep history of spadefoot toads (Pelobatoidea) in East Asia.
abstract: Fossils are indispensible in understanding the evolutionary origins of the modern fauna. Crown-group spadefoot toads (Anura: Pelobatoidea) are the best-known fossorial frog clade to inhabit arid environments, with species utilizing a characteristic bony spade on their foot for burrowing. Endemic to the Northern Hemisphere, they are distributed across the Holarctic except East Asia. Here we report a rare fossil of a crown-group spadefoot toad from the late Paleocene of Mongolia. The phylogenetic analysis using both morphological and molecular information recovered this Asian fossil inside the modern North American pelobatoid clade Scaphiopodidae. The presence of a spade and the phylogenetic position of the new fossil frog strongly support its burrowing behavior. The late Paleocene age and other information suggestive of a mild climate cast doubt on the conventional assertion that burrowing evolved as an adaptation to aridity in spadefoot toads. Temporally and geographically, the new fossil provides the earliest record of Scaphiopodidae worldwide, and the only member of the group in Asia. Quantitative biogeographic analysis suggests that Scaphiopodidae, despite originating in North America, dispersed into East Asia via Beringia in the Early Cenozoic. The absence of spadefoot toads in East Asia today is a result of extinction.
authors.affiliation: Department of Earth and Environmental Sciences, Columbia University, New York 10025.|Division of Paleontology, American Museum of Natural History, New York 10024.
authors.forename: Jianye
authors.initials: J
authors.lastname: Chen
authors.affiliation: Division of Paleontology, American Museum of Natural History, New York 10024.|Department of Anatomy, New York Institute of Technology, College of Osteopathic Medicine, New York 11568.
authors.forename: Gaberiel S
authors.initials: GS
authors.lastname: Bever
authors.affiliation: School of Geosciences, University of Edinburgh, Edinburgh EH9 3JW.
authors.forename: Hong-Yu
authors.initials: HY
authors.lastname: Yi
authors.affiliation: Department of Earth and Environmental Sciences, Columbia University, New York 10025.|Division of Paleontology, American Museum of Natural History, New York 10024.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Norell
mesh_terms: D000818:Animals; D001001:Anura / Q000145:classification; D001208:Asia; D005075:Biological Evolution; D005580:Fossils; D008986:Mongolia; D010163:Paleontology; D010802:Phylogeny