Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), III: a new species of Albanerpeton, with biogeographic and paleoecological implications

ABSTRACT

We describe a new species of the albanerpetontid amphibian Albanerpeton from three localities in the Lower Cretaceous Cloverly Formation of Wyoming, U.S.A. Radiometric dates between ∼111–112 Ma indicate it is slightly younger than A. arthridion from the Antlers Formation. The new species is diagnosed on a pair of fused frontals that possess a unique combination of characters, mixing plesiomorphic features of the internasal process with a more derived overall shape and proportions. Referred material includes premaxillae, maxillae, dentaries, atlantes, ‘axes,’ trunk vertebrae, humeri, and an ilium.

Phylogenetic analyses place the new species near the base of Albanerpeton sensu lato but without fully resolving its position. The inclusion of Shirerpeton and Wesserpeton within this clade opens up the possibility that these genera might be incorporated into Albanerpeton, or that a number of species formerly assigned to Albanerpeton might receive new generic assignments. By including several informal species in our analysis, it becomes clear that character distributions are more homoplastic and that past genus typologies are probably less secure. We assign the new species to Albanerpeton conservatively, pending further phylogenetic study.

The Cloverly Albanerpeton is found in unambiguously aquatic deposits, suggesting that the animal lived near these settings for at least part of its life. This is a common habitat for Mesozoic albanerpetontids, unlike the karst-dominated, often drier, deposits in which Cenozoic species are typically found. Despite the recent discovery of a probable arboreal species, it is likely that albanerpetontids inhabited a range of habitats throughout their evolutionary history.

ACKNOWLEDGMENTS

At the NMNH, we thank: S. Jabo and P. Kroehler for their significant efforts during many field seasons and toward fossil preparation for this work; F. Grady for specimen sorting; A. Millhouse and M. Florence for help with cataloging; S. Whittaker for guidance with SEM imaging; D. DeMar for advice on specimen identifications and relevant literature; and J. Morrison for skillfully rendering the line drawings in Figure 2. Many others helped with field and laboratory work, including: E. Duneman, C. Gruet, M. Gruet, J. Guibord, R. Hill, S. McIntyre, J. Mitchell, S. Moran, C. Peredo, and J. Velez Juarbe (all via NMNH), as well as M. Coffey, P. Lopez, and R. Horace-Middleton under the collaborative supervision of G. Wesley-Hunt (all via Montgomery College). We are grateful to C. Manuel, R. Manuel, and E. Kvale for their generous hospitality during several seasons of fieldwork in the Bighorn Basin. This research was supported through the Evolution of Terrestrial Ecosystems group, a Walcott Grant, and two Smithsonian Small Grants (2009, 2011) to MTC. Fieldwork was performed under Bureau of Land Management permits PA03-WY-102, PA05-WY-133, and PA07-WY-151 to MTC, and we thank the BLM (especially M. Bies) for their cooperation and assistance. The authors thank P. Skutschas and J. Gardner for their careful reviews, which greatly improved the final manuscript, and J. Fröbisch for editorial review and guidance.