Probable Early Callovian ammonite horizons from northwestern British Columbia, Canada

Abstract

Abstract This report describes and illustrates probably Early Callovian ammonites from the Todagin and Tsatia mountains area, at the northern margin of the Bowser sedimentary basin, northwestern British Columbia, western Canada. They include East Pacific eurycephalatinid species Lilloettia lilloetensis Crickmay, Xenocephalites bearpawensis Imlay, and Iniskinites cepoides (Whiteaves), as well as a new East Pacific pseudoperisphinctinid species, Homoeoplanulites todaginensis n. sp., and Choffatia. These ammonites comprise the next two recognizable faunal associations below a previously reported, probably late Early or early Middle Callovian, fauna on the south flank of nearby Tsatia Mountain containing Cadoceras with Indosphinctes. If their determination as Early Callovian is correct, based on the close similarities of H. todaginensis with European forms, it involves an extension of the range of North American Iniskinites above its currently supposed Late Bathonian upper limit. It remains possible that the pseudoperisphinctids represent an endemic East Pacific group older than their European homeomorphs, and perhaps as old Late Bathonian, which would not be inconsistent with the associated Eurycephalitinae.