Paleoecology of the Quarry 9 vertebrate assemblage from Como Bluff, Wyoming (Morrison Formation, Late Jurassic)

Abstract

Quarry 9 is among the richest microvertebrate localities in the Morrison Formation, having thus far produced the remains of dozens of Late Jurassic taxa. Because this lenticular claystone deposit records such a high diversity of contemporaneous species, it provides an exceptionally detailed view of their paleoecology and local paleoenvironment. In this study, we reexamined the entire Quarry 9 collection, totaling more than 3700 specimens, and developed a revised faunal list that was used to determine taxonomic and ecological diversities. Comprehensive abundance data were collected as well, revealing significant discrepancies between the most diverse and most abundant groups. Amphibious taxa (crocodilians and turtles) were very abundant, and seemed to fill an important ecological role as “connectors” between the terrestrial and aquatic food webs. In contrast, small terrestrial taxa (small theropods, mammals, and small reptiles) were very diverse, highlighting their central placement within the terrestrial food web. Lithologically and sedimentologically, the deposition of Quarry 9 occurred in a low-energy pond or swamp, an interpretation supported by the available taphonomic data.