NEW CRANIAL MATERIAL OF THE RARE DIADECTID DESMATODON-HESPERIS (DIADECTOMORPHA) FROM THE LATE PENNSYLVANIAN OF CENTRAL COLORADO

Additional skull and lower jaw material of the rare diadectid Desmatod on hesperis is described from the Late Pennsylvanian Badger Creek loca lity in the Sangre de Cristo Formation of central Colorado. A new part ial maxilla suggests that the more primitive degree of molarization of the cheek teeth-one of the features used to distinguish D. hesperis f rom D. hollandi-may actually reflect a difference in maturity rather t han a taxonomic character. Other characters used to distinguish these species remain unchallenged. The new material further demonstrates tha t the cranial morphologies of D. hesperis and Diadectes are nearly ali ke, with only the marginal and palatal dentitions providing a substant ial means for distinguishing between them. Previously described differ ences between the maxillary dentitions in juvenile and adult stages of growth are further documented. Among the D. hesperis elements describ ed for the first time here are adult specimens of the dentary and near ly complete lower jaw; the cheek teeth exhibit the same primitive degr ee of molarization as the maxillary cheek teeth when compared with tho se of comparably sized adult specimens of Diadectes. The presence of t eeth on the transverse flange and twice as many teeth of smaller and v ariable sizes in the medial tooth TOW Of the palatal ramus of the pter ygoid also separates D. hesperis from Diadectes. The lower jaw of D. h esperis can also be contrasted with those of comparably sized Diadecte s specimens by its much shallower depth, reflected also in the shape o f the adductor fossa and medial fenestra, and its much lower labial pa rapet of the dentary. A previously reported occurrence of Desmatodon a ff. D. hollandi from the Late Pennsylvanian Cutler Formation of El Cob re Canyon, New Mexico, may represent only the second occurrence for th e species and the third for the genus.