Pachylyroceras Ruzhencev and Bogoslovskaya, 1971

Titus, A. L., Korn, D., Harrell, J. E. & Lambert, L. L., 2015, Late Viséan (late Mississippian) ammonoids from the Barnett Shale, Sierra Diablo Escarpment, Culberson County, Texas, USA, Fossil Record 18 (2), pp. 81-104 : 100

Pachylyroceras Ruzhencev and Bogoslovskaya, 1971

Type species: Lyrogoniatites cloudi Miller and Youngquist, 1948 [original designation].

Genus diagnosis: Representatives of the family Neoglyphioceratidae with subevolute conch, which becomes more evolute in the adult stage. 20–30 coarse spiral lines, growth lines, and shell constrictions concavo-convex with shallow ventral sinus. Suture line with rather narrow external lobe, usually with slightly sinuous flanks.

Included species:

cloudi : Lyrogoniatites cloudi Miller and Youngquist, 1948, p. 660 ; Texas.

utahense : Lyrogoniatites utahensis Miller, Youngquist and Nielsen, 1952, p. 154 ; Utah.

Discussion: When they introduced the genus Pachylyroceras, Ruzhencev and Bogoslovskaya (1971) assumed that certain Uralian specimens and the types for Lyrogoniatites cloudi from the Barnett Shale were conspecific. As a result, they based Pachylyroceras on the types of L. cloudi from Texas, rather than the Uralian material they had in their collections and erected three new species, P. angustum , P. consequens , and P. constrictum . We see significant differences in the course of growth lines in all of the Uralian specimens (ventral salient) versus the Texas types of Pachylyroceras (ventral sulcus), and conclude that the genus, which is closely related to Neoglyphioceras , is currently known only from North America.

This excludes all of the Uralian material from Pachylyroceras , and given that there is no existing genus to accommodate these widely umbilicate Neoglyphioceras -like forms with ventral salient in their growth lines and constrictions, we erect the new genus Uralyroceras for the Uralian species (see below).

According to its conch morphology, suture line, and ornament, Pachylyroceras has an intermediate position between Neoglyphioceras and Lyrogoniatites . It possesses the type of shell constrictions with ventral sinus of Neoglyphioceras but the subevolute conch morphology of Lyrogoniatites . In the suture line, Pachylyroceras shows the sinuous flanks of the external lobe like Neoglyphioceras , but at the same time, the external lobe is rather narrow with weakly diverging flanks like in Lyrogoniatites .