A new baenid, Edowa zuniensis gen. et sp. nov., and other fossil turtles from the Upper Cretaceous Moreno Hill Formation (Turonian), New Mexico, USA

Abstract

We describe the first Turonian baenid turtle, Edowa zuniensis gen. et sp. nov., from the Moreno Hill Formation in New Mexico, which is located within a baenid temporal hiatus of approximately 12 million years. It was retrieved in a phylogenetic analysis as sister to the well understood basal baenodd (derived baenid) Plesiobaena antiqua from the Campanian of Montana and Alberta, with which it is morphologically similar. The two are sister taxa, forming a “Plesiobaena-grade” clade that is in a basal position within the derived clade Baenodda, outside of the two main clades of derived baenids, Palatobaeninae and Eubaeninae. Its occurrence in the middle Turonian Moreno Hill Formation suggests a southern Laramidian origin for Baenodda. The new site is (along with the Menefee Formation) younger and stratigraphically continuous with the Fruitland and Kirtland Formations, which are among the most productive Upper Cretaceous fossil sites in North America. New material of the endemic helochelydrid stem turtle Naomichelys is also described, as are several ichnotaxa on the type specimen of E. zuniensis gen. et sp. nov. The Moreno Hill Formation fossil turtle assemblage contains relict, derived, and immigrant components and is transitional between typical Early and Late Cretaceous faunas. Preliminary comparisons are made between the Moreno Hill Formation turtle assemblage and those of later San Juan Basin fossil sites, showing significantly greater baenid diversity in younger strata, the presence of trionychids throughout, and Naomichelys, which is also known from the younger Menefee Formation.