T39 Sigma Gamma Epsilon Undergraduate Research (Posters)

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

A PHYLOGENETIC DISSECTION OF THE GASTROPOD SUBFAMILY KNIGHTITINAE ACROSS THE PERMIAN-TRIASSIC BOUNDARY

Paper number: T39-36
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Incomplete systematic revisions of genera often remove a small number of species within a clade to genera with very diagnostic morphologies while leaving a large paraphyletic “residue” of species within a small number (or even one) genus. This can mask diversity dynamics by hiding the waxing and waning of subclades within the larger clade. The Carboniferous-Triassic members of the subfamily Knightininae offers a useful model: a small number of species are placed in the highly derived Knightites or Cymatospira, while most of the species are placed in the genus Retispira. The latter group of species includes some of the only known Triassic bellerophonts.

Twenty-nine taxa of three genera, Retispira, Knightites, and Cymatospira, with stratigraphic ranges from the Lower Pennsylvanian to the Lower Triassic were analyzed based on specimens from collections and published literature. Minimum steps parsimony, stratocladistics and Bayesian methods were used to assess possible relationships. The resultant trees corroborate the monophyly of Knightites and Cymatospira, but also show multiple comparably rich subclades of Retispira species. At least two of these Retispira clades survived the P/T event, but 2-4 others did not. Retispira is only one of approximately fifty gastropod genera suspected of surviving the end-Permian, but in this one example, at least as many subclades went extinct as survived.