An ammonoid fauna from the Glencairn Shale Member of the Lower Cretaceous Purgatoire Formation, Baca County, Colorado

Ammonites found in a thin unit of claystone and shale along Horse Creek in northern Baca County, Colorado include flattened specimens of Goodhallites and Idiohamites, genera previously unrecorded from the Western Interior. An associated ammonite is Engonoceras uddeni (Cragin). A solitary coral, at least a dozen species of bivalves and a small gastropod are associated with the ammonites. A late Albian age is assigned to the assemblage.