. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Figure 24. A, occiput of the Triassic turtle, Progonoche/ys, sketch based on photographs in Parsons and Williams (1961] B, occiput of Proco/ophon. C, occiput of Protocaptorhinus pricei. this genus might be slightly closer to archosaurs than are other known romeriids, the similarities are not even close enough to differentiate between romeriids and pelycosaurs as potential archosanr ances- tors. At present it does not seem appro- priate to specif)" romeriids as any more than the ultimate ancestors of archosaurs. C
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Figure 24. A, occiput of the Triassic turtle, Progonoche/ys, sketch based on photographs in Parsons and Williams (1961] B, occiput of Proco/ophon. C, occiput of Protocaptorhinus pricei. this genus might be slightly closer to archosaurs than are other known romeriids, the similarities are not even close enough to differentiate between romeriids and pelycosaurs as potential archosanr ances- tors. At present it does not seem appro- priate to specif)" romeriids as any more than the ultimate ancestors of archosaurs. Chelonian ancestry. The ancestry of turtles remains one of the greatest un- sohed problems in reptilian phylogeny. Since they lack lateral or dorsal temporal openings, it can be safely assumed that the\- did not evolve from any of the advanced reptilian groups with synapsid, diapsid or parapsid skull configurations. If phyletically reptilian, they could ha\e evohed onh' from primitive anapsid forms. Although no real intermediate forms are known, rela- tionship with various "cotylosaurs" has been suggested: pareiasaurs (Gregory, 1946); diadectids (Olson, 1947); and procolo- phonoids (Romer, 1964 and 1966). The interrelationship of these groups and their phylogenetic position relative to other primiti\e reptiles is subject to continuing dispute. None seem to have evolved from romeriids as such. If turtles had evolved from any of these groups, they would be only distantly related to the remaining rep- tilian subclasses, all of which may be rea- sonably traced to the romeriids. In working with Protocaptorhinus and Captorhinus, one is struck by the similari- ties in the occiput to the primitive chelonian Proiianochelys (Fig. 24). In both the captorhinomorphs and the turtle there are large posttemporal fossae, separated by a narrow supraoccipital. The paroccipital processes extend laterally toward the squa- mosal and are braced against this bone in Captorhinus. The tabular i
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