ABSTRACT

The dentition in the only known specimen of Adalatherium hui, a gondwanatherian mammal from the Late Cretaceous of Madagascar, is markedly different from that of any previously known mammaliaform, extinct or extant. The two preserved upper incisors and single lower incisor of Adalatherium are each very large, open-rooted, and bear a restricted band of enamel. A shallow-rooted, rudimentary upper canine is present. The upper postcanine dentition is composed of a small, simple, two-rooted tooth mesially and four large, multiple-rooted (five roots or more) teeth distally. The latter are quadrangular in outline, each with four major cusps and three perimetric ridges bordering a central valley that opens buccally. There are four lower postcanines, also with four major cusps each. The first postcanine has two roots, but the following ones each have (or likely had) at least four. The two distal lower postcanines bear a prominent mesiobuccal basin. The cusps and other topographic features of the postcanines cannot be unambiguously homologized with those of other known mammaliaforms. Diastemata are present in the upper dentition between the incisors and canines and between the canines and postcanines, and in the lower dentition between the incisors and postcanines. Adalatherium, like several gondwanatherians from the Late Cretaceous and Paleogene of Argentina, retains relatively plesiomorphic, ‘normal’ radial enamel (i.e., single-layered schmelzmuster, non-decussating small prisms, interprismatic matrix anastomosing around prisms). This stands in contrast to the modified radial enamel found in other gondwanatherians from the Late Cretaceous of India and Madagascar, which exhibit prominent interrow sheets of interprismatic matrix.

摘要

来自马达加斯加晚白垩世的独角兽哺乳动物Adalatherium hui的唯一牙齿样本中的牙列与任何已知的灭绝或现存的哺乳动物形式都有明显的区别。两个保留上门牙和单个下门牙Adalatherium都非常大，无根，并带有有限的珐琅带。存在一个浅根的，基本的上犬。犬后齿列由近端的小而简单的两根牙齿和远端的四大而多根（五个或更多根）牙齿组成。后者的轮廓为四边形，每个都有四个主要的尖尖和三个周边的山脊，与一个中央开口的颊谷相接。有四个较低的犬科犬，每个犬都有四个主要尖端。第一个后犬有两个根，但随后的每个都有（或可能有）至少四个。下犬齿的两个远端带有一个明显的近颊颊盆。后犬的牙尖和其他地形特征不能与其他已知哺乳动物的那些明确地同源。Adalatherium，像来自阿根廷的晚白垩和第三纪几个gondwanatherians，保持相对祖征，“正常”径向搪瓷（即，单层schmelzmuster，非小decussating棱镜，interprismatic矩阵周围棱镜吻合）。这与印度晚白垩世和马达加斯加的其他冈瓦纳特人发现的改性放射状搪瓷形成对照，后者表现出明显的晶格矩阵。