Pachylyroceras is a large, generally subglobular, Upper Mississippian gonitite and included in the cephalopod subclass Ammonoidea.

Recognition

Pachylyroceras produced a large shell that is moderately evolute to moderately involute and thickly discoidal to subglobular, with a rather wide umbilicus. Surface sculpture consists of coarse, widely spaced longitudinal lirae. Constrictions where present are wide and deep. Its suture has a narrow bifurcated ventral lobe with slightly divergent to subparallel sides and a median saddle less than half the height.

Taxonomic position

Pachylyroceras, named by Ruzhentsev & Bogoslovskaia (1971), is included in the Neoglyphiocerataceae

Neoglyphiocerataceae

Neoglyphiocerataceae is one of seventeen superfamilies of the Goniatitina suborder. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopodes, and cuttlefish, and more distantly to the nautiloids....

, (sometimes written Neoglyphioceratoidea), but its position within the superfamily varies according to whose classification.

The revised version of the Treatise, Part L (W. M. Furnish et al. 2009 ) includes Pachylyroceras as well as Alaoceras

Alaoceras

Alaoceras is an ammonoid cephalopod from the upper Paleozoic included in the goniatitid family Cravenoceratidae, named by Ruzhentsev & Bogoslovskaya in 1971....

, Caenolyroceras, Dombarigloria

Dombarigloria

Dombarigloria is a genus belonging to the goniatitid family Cravenoceratidae; extinct ammonoids which are shelled cephalopods more closely related to squid , octopus and other coleoids than to the superficially similar Nautilus...

, and Lyrogoniatites

Lyrogoniatites

Lyrogoniatitites is a neoglyphiocercean ammonite, in the order Goniatitida, related to genera like Alaoceras, Cravenoceras, Dumbarigloria and Pachylyroceras.-Description:...

in the Neoglyphioceratidae

Neoglyphioceratidae

Neoglyphioceratidae is one of six families of the Neoglyphiocerataceae superfamily. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids....

 and subfamily Lyrogoniatitinae

Lyrogoniatitinae

Lyrogoniatitinae is one of two subfamilies of the Cravenoceratidae family. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids.-References:...

. Dieter Korn (2006) also included Pachyhlyroceras in the Lyrogoniatitinae, but in the family Cravenoceratidae

Cravenoceratidae

The Cravenoceratidae is one of six families included in the ammonoid superfamily Neoglyphiocerataceae, which lived during the latter part of the Paleozoic era....

. Saunder, Work, and Nickoleava (1999) also included Pachyhlroceras in the Cravenoceratidae, but without regarding subfamilies. Others (GONIAT) include Pachylyroceras in the Gravenoceratid subfamily Cravenoceratinae

Cravenoceratinae

Cravenoceratinae is one of two subfamilies of the Cravenoceratidae family. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids.-References:...

 instead.

The Treatise (Miller, Furnish, and Schindewolf 1957) includes Lyrogoniatites, from which Pachylroceras is probably derived, in the subfamily Neoglyphioceratinae along with Neoglyphioceras, but in the superfamily Goniatitaceae

Goniatitaceae

Goniatitaceae is one of seventeen superfamilies of the Goniatitina suborder. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopodes, and cuttlefish, and more distantly to the nautiloids.-References:...

. The might suggest where Pachylyroceras might have been put, if it had been named and described at that time.

References

• GONIAT online
• W. M. Furnish et al. 2009 Revised 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...
  
  Part L Vol 2 http://paleodb.org/cgi-bin/bridge.pl?action=basicTaxonInfo&taxon_no=13803
• D. Korn, 2006. Paleozoic ammonoid classification. http://paleodb.org/cgi-bin/bridge.pl?a=displayReference&reference_no=18963
• Saunders et al 1999. Evolution of Complexity in Paleozoic Ammonoid Sutures, Supplementary Material. http://www.sciencemag.org/site/feature/data/1043099.xhtml