A new caimanine alligatorid from the Middle Eocene of Southwest Texas and implications for spatial and temporal shifts in Paleogene crocodyliform diversity

Dramatic early Cenozoic climatic shifts resulted in faunal reorganization on a global scale. Among vertebrates, multiple groups of mammals (e.g., adapiform and omomyiform primates, mesonychids, taeniodonts, dichobunid artiodactyls) are well known from the Western Interior North America warm, greenhouse conditions Eocene, but dramatic drop diversity these groups, along with introduction more dry-tolerant taxa, occurred near Eocene–Oligocene boundary. Crocodyliforms underwent striking loss at this time as well. Pre-Uintan crocodyliform assemblages central characterized by whereas Chadronian depauperate only Alligator prenasalis previously known. Crocodyliform through intervening Uintan Duchesnean is not understood. The middle Eocene Devil’s Graveyard Formation (DGF) southwest Texas provides new data southern latitudes during that crucial period. A specimen member DGF (late Uintan–Duchesnean) most complete cranial material an alligatorid Paleogene deposits outside Interior. We identify caimanine based notched descending laminae pterygoids posterior to choanae long processes exoccipitals contact basioccipital tubera. Unlike Eocaiman cavernensis , anterior palatine process rounded rather than quadrangular. relationships age taxon support hypothesis modern distribution caimanines represents contraction expansive distribution. hypothesize range tracked shifting humid contracted latitudinally toward hothouse-icehouse transition later Eocene.