. Breviora. 26 BREVIORA No. 485 project anteriad as is the case primitively in pelycosaurs. The angular shares with those of members of the Ophiacodon-Dimetro- don clade the presence of an extended ventral plate in the region of the articular. Thus these character-states indicate that Stereophallo- don is a member of the Ophiacodon-Dimetrodon clade. Within the Ophiacodon-Dimetrodon clade, Stereophallodon is most parsimoniously placed as the closest sister-taxon of Ophiaco- don (Fig. 18) and forms with Ophiacodon a monophyletic taxon defined by five characters. Two of these, the ventral orienta
. Breviora. 26 BREVIORA No. 485 project anteriad as is the case primitively in pelycosaurs. The angular shares with those of members of the Ophiacodon-Dimetro- don clade the presence of an extended ventral plate in the region of the articular. Thus these character-states indicate that Stereophallo- don is a member of the Ophiacodon-Dimetrodon clade. Within the Ophiacodon-Dimetrodon clade, Stereophallodon is most parsimoniously placed as the closest sister-taxon of Ophiaco- don (Fig. 18) and forms with Ophiacodon a monophyletic taxon defined by five characters. Two of these, the ventral orientation of the basipterygoid processes and the antero-posteriorly oriented articular surfaces have been discussed above and are present elsewhere in pelycosaurs only in Ophiacodon. Three additional features not discussed by Brinkman and Eberth (1983) can be interpreted as derived and shared by only Ophiacodon and Stereophallodon. In interpreting the polarity of these charac- ters, the methodology used in Brinkman and Eberth (1983) was employed. The outgroups used are, 1) members of the Casea- Varanops clade, which is the closest sister-taxon of the Ophiacodon- Dimetrodon clade and, 2) the taxa that were used as outgroups in interpreting the polarities of character-states within pelycosaurs. The polarity of character-states was interpreted according to the distributions shown in Brinkman and Eberth (1983: Fig. 2). Casea Varanops Aerosaurus Ophiacodon Edaphosaurus Dimetrodon Sphenacodon. Figure 18. Cladogram showing the interrelationships of seven genera of pelyco- saurs. From Brinkman and Eberth (1983).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. , Museum of Comparative Zoology, Harvard University
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