EARLY PERMIAN VERTEBRATES FROM TEXAS: ACTINOPTERYGII (SCHAEFFERICHTHYS), CHONDRICHTHYES (INCLUDING PENNSYLVANIAN AND TRIASSIC XENACANTHODII), AND ACANTHODII

Large numbers of microvertebrate fossils were recovered by bulk sampling, principally from middle and upper Wichita-Albany exposures, in Baylor County and adjacent areas. Such fossils have previously received little or no study.; Singly occludent concave and convex crushing tooth plates belonging to the platysomoid, Schaefferichthys, possess a phyllodont tooth-replacement structure, heretofore unknown before the Cretaceous. Differences in tooth histology and plate morphology suggest two species are present. Schaefferichthys sp. occurs in the lower to upper Wichita-Albany Group; Schaefferichthys cf. S. leudersensis occurs in the upper Wichita-Albany and slightly younger formations in Texas, Oklahoma, and Arizona.; The xenacanthodiid teeth, including teeth from the Late Triassic of Texas, Late Pennsylvanian of Nebraska, and Permo-Pennsylvanian of the Dunkard Basin, have several morphologic differences which may be used to distinguish Orthacanthus compressus, O. texensis, O. platypternus, Xenacanthus luedersensis, X. moorei, and a new Pennsylvanian species of ?Xenacanthus. These differences suggest a dichotomy in xenacanthodiid evolution. In the "Thrinacodus"-Orthacanthus lineage, the apical button remains isolated, the principal cusps remain compressed, cristae are lost, serrations may develop, and a secondary increase in intermediate cusp number may occur. In the Thrinacodus-Xenacanthus lineage, the apical button has come into contact with the principal cusps, which become cylindrical and retain cristae, serrations are not developed, and intermediate cusps are reduced in number or lost. A few teeth in the collection show evidence of pathological damage. Cephalic spines are uncommon.; Tooth morphotypes of ?Acrodus and Polyacrodus, typical Mesozoic hybodontoid genera distinguished by histologic differences, are grouped into six new species. One species of Polyacrodus possesses a variable tooth histology parallel to that of Heterodontus. Cephalic clasping spines and dorsal fin spines are common.; Minor chondrichthyan taxa present include ctenacanthoids, a helodontid, petalodontiids, and an iniopterygiid. Their distribution, combined with that of the xenacanthodiids, hybodontoids, acanthodiids, and Gnathorhiza preclude specific conclusions about individual habitat preferences of the studied taxa. An estuarial-littoral environment was dominant.; Acanthodes fin spines are very common in the lower to upper middle Wichita-Albany, where more than one species may have been present, but are absent from the upper Wichita-Albany.