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CT reconstructions and relationships of the Early Cretaceous tribosphenidan mammal, Slaughteria eruptens (Trinity Group Texas, USA) ABSTRACTAmong the nine taxa of tribosphenidan (boreosphenidan) mammals named from the Early Cretaceous Trinity Group of Texas and Oklahoma, Slaughteria eruptens provides unique information about the evolution of tooth replacement. High-resolution CT scans and SEM imagery elucidate the jaw anatomy of S. eruptens. Associated upper and lower dentitions from Asian Cretaceous mammals provide the basis for a statistical model to quantify the tooth size relationships of the often cited Trinity Group mammals Pappotherium pattersoni and Holoclemensia texana, which were named based upon upper molar teeth. Two groups of Trinity mammals are evident based on lower molar size. Most large teeth are referable to H. texana. The lower m1 of S. eruptens fits neatly into the size range predicted for lower molars of P. pattersoni, and it shares compatible tooth cusp relationships. Slaughteria eruptens is regarded most parsimoniously as a junior synonym of P. pattersoni. Pappotherium pattersoni thus shares the alternate premolar replacement pattern of more primitive therian mammals and basal eutherians, but lacks any hint of a submolariform last premolar, as typifies Eutheria. Other small therian mammal teeth from the Trinity Group should be evaluated as possible deciduous teeth. KEYWORDS: Mammalia; Tribosphenida; Pappotherium; Cretaceous; eruption sequence
PE Article Number: 14.3.21A PE NOTE ADDED IN PROOF:Davis (2011) has reinterpreted the teeth in Slaughteria eruptans based upon a fresh analysis of the same CT data used by Kobayashi et al. (2002). He posits that the partly calcified portion of an unrecognized replacement premolar (p5) exists below ultimate tooth preserved in the jaw, which he interprets as dp5. He supports this new interpretation with the statement (Davis, 2011; page 380): “The crown of the dp5 is more worn than the dp4 (in accord with observations by Slaughter, 1971, and contra Kobayashi et al., 2002).” We offer these observations: in Slaughteria the crown of the 3rd tooth (our interpreted dp4) is heavily worn through the enamel to expose the dentine on the protoconid, metaconid, and hypoconid. The 4th tooth (our m1) shows wear on the paraconid, (unlike the 3rd tooth) and on the hypoconulid (neither exposes dentine), and has essentially no wear on the metaconid and entoconid cusps. The protoconid of the 4th tooth is broken off and missing. Interpretation of wear on the posterior face of the trigonid is a matter of opinion. The 3rd tooth has a much more open trigonid and is proportionately narrow and low crowned, as fitting a deciduous tooth. The 4th tooth does not share this morphology. A mental foramen is present in the jaw beneath the anterior of the 4th tooth, a position usually associated with m1 in other Early Cretaceous tribosphenidans, not the ultimate premolar. The conjectured structure below the 4th tooth which Kobayashi et al. (2002) interpreted as fragments and Davis (2011) interprets as primordial p5 is posteriorly open and resembles neither the cap nor bell stage of a developing tooth. The “partial calcification” disjoining the cusps of the undisputed replacement tooth (below the 3rd tooth in the jaw) that Davis cites is an artifact of low resolution CT data. Thus, while we recognize that new data could provide a real test, we stand by the interpretation of the dentition postulated in Kobayashi et al. (2002). |
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