Pachyceratidae


Pachyceratidae is a family of Perisphinctoidean ammonites from the upper Middle - and lower Upper Jurassic. Genera within the Pachyceratidae have shells that are in general moderately involte but with most of the inner whorls exposed; whorl sections subquadrate to subtrapezoidal, with rounded venter. Ribbing is strong, in some sharp. Primary ribs typically branch above mid flanks into twos, threes, and even fours.
The Pachyceratidae, according to Donovan et al., were derived from the Perisphinctidae in the mid Callovian at about the same time as the longer lived Aspidoceratidae, lasting only into the subsequent Oxfordian. This differs from the perspective of Arkell, et al. in the Treatise wherein the Pachyceridae is included in the Stephanoceratoidea, derived from the Tulitidae and giving rise to the Mayaitidae.
Genera, as described in the Treatise on Invertebrate Paleontology, Part L. :