T131 Species and Speciation in the Fossil Record II

Monday, 10 October 2011
1:30 PM - 5:30 PM
Room 205CD

PHYLOGENETIC REVISION OF THE ORDOVICIAN BRACHIOPOD GENUS GLYPTORTHIS

Paper number: T131-9
Program: Technical Sessions
Time: 3:30 PM – 3:45 PM

Authors

Abstract

The genus Glyptorthis, Foerste 1914, comprises a diverse, cosmopolitan clade of orthid brachiopods characterized by the presence of strongly lamellose concentric ornamentation patterns on the exterior of their shells. Glyptorthids are common constituents of Middle Ordovician to Lower Silurian benthic marine faunas of North America. A phylogenetically informed revision of Glyptorthis is presented here as part of a larger project which aims to assess phylogenetic biogeographic patterns among Ordovician orthides. Glyptorthis insculpta (Hall 1847) participated in the Upper Ordovician Richmondian Invasion into the Cincinnati region. A species-level phylogenetic analysis of Glyptorthis may, therefore, yield insight for testing hypotheses regarding the evolutionary and biogeographic origin of the Richmondian invaders.

Type specimens from museum collections were examined to determine character states for phylogenetic analysis of all North American species of Glyptorthis. Non-type and specimens figured in the literature were also examined when possible to assess the range of morphologic variation within each species. A phylogenetic analysis was performed on both internal and external morphological characters using parsimony-based PAUP software and analyzed with MacClade. Both discrete and continuous characters were used. Continuous characters states were differentiated through morphometric analysis and coded as qualitative states.

A set of well supported trees were recovered from parsimony analysis. The strict consensus of these is highly resolved and delineates four monophyletic clades within the genus. Each clade is supported by multiple synapomorphies. These relate primarily to characters of shell ornamentation, valve convexity, shape of the ventral muscle field, and angular relationships within the ventral cardinal area. Preliminary biogeographic analysis suggests that G. insculpta invaded the Cincinnati region from basins in either the central or southeast USA.