Delepinoceratidae Ruzhencev, 1957

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 : 93-94

Family Delepinoceratidae Ruzhencev, 1957

Family diagnosis: Representatives of the superfamily Goniatitaceae with advanced suture lines possessing a Y-shaped external lobe and a tectiform ventrolateral saddle. The adventive lobe and also the prongs of the external lobe show the tendency to become tridentate.

Discussion: There exist three diverging concepts about the classification of the advanced goniatitid species and genera. Ruzhencev and Bogoslovskaya (1971, 1978) separated the families Delepinoceratidae (including Platygoniatites and Delepinoceras ) and Agathiceratidae (including Dombarites , Pericleites , Proshumardites , and Agathiceras ) on the basis of the subdivision mode of the external lobe, thus delineating two independent evolutionary lineages. Leonova (2002, 2011) doubted the assignment of Agathiceras in the order Goniatitida and transferred it into the order Tornoceratida (which has usually only been accepted as a suborder within the Goniatitida ). Finally, Kullmann et al. (2007) and Kullmann (2009a, b) separated Agathiceras and closely related forms in the independent superfamily Agathiceratoidea within the suborder Goniatitina . In Kullmann’s concept, the genera Dombarites and Proshumardites are grouped in the subfamily Dombaritinae within the family Delepinoceratidae .

If Agathiceras is excluded from the discussion of the phylogeny of the family Goniatitidae and its descendants (for instance, if the central or sub-central position of the siphuncle in the juvenile stage is been taken as a reason for separation on higher taxonomic levels), then the phylogenetic analysis (see below) speaks for the extension of the family Delepinoceratidae to also include the subfamily Dombaritinae ( Kullmann, 2009a) . This subfamily, however, also requires re-definition to include the genera Revilloceras , Lusitanoceras , and Choctawites .

For resolving the phylogenetic relationships of the goniatitid ammonoid genera, we performed a cladistic analysis based on the character matrix of Korn (1997a). In contrast to that analysis, we used Progoniatites uncus Korn, Bockwinkel and Ebbighausen, 2010 as the outgroup species and included three more ammonoid species in the new analysis, Choctawites choctawensis , Revilloceras granofalcatum , and Dombarites falcatoides . We included a new character, the presence of shell constrictions, in the matrix.

The heuristic cladistics analysis performed with PAST ( Hammer et al., 2009) led to 35 most parsimonious trees of 35 steps length, of which a majority consensus tree was formed ( Fig. 10 ). This tree shows some unresolved branches but demonstrates that a crown group is well established with the genera Choctawites , Lusitanoceras , Revilloceras , Dombarites , Proshumardites , Platygoniatites , and Delepinoceras , which are all characterized by the apomorphies of a Y-shaped external lobe and a tendency towards a tectiform ventrolateral saddle. This clearly defined clade can best be described as the family Delepinoceratidae . One has, however, to take into account that a similar tendency of sutural development also occurs in the more conservative lineage leading to Neogoniatites .

The cladogram also shows that Choctawites is more plesiomorphic than the other of the genera, which are all defined by the presence of outer shell constrictions in the juvenile stage. The crown group is subdivided into two independent clades, one represented by the advanced Dombarites species D . tectus and Proshumardites and the other represented by the genera Platygoniatites and Delepinoceras .

Figures

Figure 10. Cladogram of selected genera, represented by well-known species, of the superfamily Goniatitaceae.