Article: Campanian Trachyscaphites spiniger ammonite fauna in north-east Texas

A horizon 46 m above the base of the Ozan Formation in the North Sulphur River north-west of Ladonia in Fannin County, Texas, yielded a fauna of Pachydiscus (Pachydiscus) paulsoni (Young, 1963), Eupachydiscus grossouvrei (Kossmat, 1898), Placenticeras sp., Menabites (Delawarella) delawarensis (Morton, 1830), M. (D.) danei (Young, 1963), M. (D.) vanuxemi (Morton, 1830), M. (D.) sp., Glyptoxoceras sp., Baculites sp. group of aquilaensis Reeside, 1927, Scaphites (Scaphites) sp. group of hippocrepis (DeKay, 1828), Trachyscaphites spiniger spiniger (Schliiter, 1872), and T. densicostatus sp. nov., together with the bivalve Inoceramus (Endocostea) balticus Bohm, 1909. The presence of T. spiniger spiniger, previously known only from western Europe and the USSR, dates the assemblage as early but not earliest late Campanian in a north-west European sense, while stratigraphic relationships to other Gulf Coast Campanian faunas suggest it to be younger than the early Campanian zone of Scaphites hippocrepis III and older than the middle Campanian zone of Baculites mclearni of the US Western Interior. The Western Interior lower-middle Campanian boundary and the European lower-upper Campanian boundary are approximately coincident; this level can be dated at 80 Ma approximately on the basis of radiometric dates from Western Interior bentonites.