Pachyceratidae
Encyclopedia
Pachyceratidae is a family of Perisphinctacean
ammonite
s 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 (1981), 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 (1957) in the Treatise
wherein the Pachyceridae is included in the Stephanocerataceae
, derived from the Tulitidae and giving rise to the Mayaitidae.
Genera, as described in the Treatise on Invertebrate Paleontology, Part L. (1957)
:
Perisphinctaceae
Perisphinctoidea, formerly Perisphinctaceae, is a superfamily of Middle Jurassic to Lower Cretaceous ammonites, commonly with evolute shells with strong ribbing that typically divides about mid flank before crossing the venter....
ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
s 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 (1981), were derived from the Perisphinctidae
Perisphinctidae
Perisphinctidae is a family of Middle and Upper Jurassic discoidal ammonites in the order Ammonitida. They have a shell morphology that is mostly evolute, typically with biplicate, simple, or triplicate ribbing...
in the mid Callovian
Callovian
In the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 164.7 ± 4.0 Ma and 161.2 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian....
at about the same time as the longer lived Aspidoceratidae
Aspidoceratidae
The Aspidoceratidae comprise a family of middle and upper Jurassic ammonites that make up part of the superfamily Perisphinctaceae, characterized by evolute shells, commonly stocky, that tend to develop tubercles....
, lasting only into the subsequent Oxfordian. This differs from the perspective of Arkell, et al (1957) in the Treatise
Treatise on Invertebrate Paleontology
The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...
wherein the Pachyceridae is included in the Stephanocerataceae
Stephanocerataceae
Stephanocerataceae is a superfamily of middle Jurassic ammonoid cephalopods within the order Ammonitida containing diverse forms, generally with sharp ribbing and complex suture lines...
, derived from the Tulitidae and giving rise to the Mayaitidae.
Genera, as described in the Treatise on Invertebrate Paleontology, Part L. (1957)
Treatise on Invertebrate Paleontology
The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...
:
- Erymnoceras: moderately involute; primary ribs branch into mulitiple secondaries. (M CallovCallovianIn the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 164.7 ± 4.0 Ma and 161.2 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian....
). - Erymnocerites, subgen of Erymoceras with more numerous secondary ribs. (M Callov).
- Pachyerymnoceras: involute, last whorl becoming compressed and Pachyceras-like; subgen of Erymnoceras. (U Callov)
- Rollierites: evolute, more or less planulate; ribs coarse, branching from tubercles at umbilical edge. (M Callov).
- Pachyceras: basically involute; umbilical edge rounded, non tuberculate; ribs fade on inner half of whorl sides; last whorl commonly smooth or with ventral folds only. (U Callov - L OxfOxfordianOxfordian may refer to:* Oxfordian theory of Shakespeare authorship, view that Edward de Vere wrote under Shakespeare's name* Oxfordian , a geological time interval...
). - Tornquistes: differs from Pachyceras s.s. by coarsening ribs on last whorl and developing eccentric coils; subgenus(?) of Pachyceras. (L- U Oxf).