Aerugoamnis Paulus, New Genus and New Species (Anura: Anomocoela): First Reported Anuran from the Early Eocene (Wasatchian) Fossil Butte Member of the Green River Formation, Wyoming

Abstract

Five anurans have been previously reported from the Eocene Green River Formation, of which only two, a nearly complete skeleton and a tadpole,have been described. The skeleton has been identified as either Eopelobates Parker, 1929, or a pelobatid close to Eopelobates and PelobatesWagler, 1830, but the tadpole is indeterminate. Another specimen has been figured but not described, another is a skin impression that is probablyindeterminate, and the other is presumably lost. A sixth specimen is reported here. It represents a new genus and species,Aerugoamnis paulus,which is the first anuran to be reported from the Wasatchian (early Eocene) Fossil Butte Member of the Green River Formation. It consists of asingle specimen that is dorsoventrally flattened and exposed primarily in dorsal view on one slab of rock, with a poor impression of the skull anda few bone fragments representing the counterpart. The specimen is nearly complete and the bones are preserved in articulation or in close association.The presence of a spiral groove of the iliac shaft suggests affinity with Anomocoela, a hypothesis that was tested through a phylogeneticanalysis including representatives of the major clades of Costata, Xenoanura, Neobatrachia, and Anomocoela. The analyzed data set consists of 66osteological characters scored for six fossil and 20 extant taxa. Results of the analysis place Aerugoamnis as a member of the stem of Pelodytidae.This placement is based on possession of two synapomorphies: presence of a distinct otic ramus of the squamosal and the crista parotica is poorlydeveloped. Unlike extant pelodytids, Aerugoamnis has nasals that are separated by a narrow gap, a ventral flange on the pterygoid, and unfusedtibiale and fibulare. Prior to the discovery of Aerugoamnis, fragmentary remains from the middle Eocene of Europe, the earliest of which areLutetian (MP 13), have been questionably referred to the family. Aerugoamnis now is the earliest known occurrence of the anomocoelan lineagerepresented today by Pelodytidae.