Wear facet morphology and evolution of occlusal function in Proboscidea

在扫描电镜下对象科颊齿进行了定性检查，试图识别象科颊齿的基本磨损模式。在菲奥米亚，磨牙的磨损面可以分为三类；齿与齿接触形成明显边缘的磨蚀面和齿与食物接触形成模糊边缘的内外磨蚀面。沟坡和外磨蚀面发育舌颊方向平行纹，内磨蚀面、中脉和后牙锥尖发育凹坑。在菲奥米亚看到的磨损模式一定是在咀嚼食物时，磨牙的山谷和山脊之间的深度连锁形成的。一些非四齿兽的齿形动物，如中国乳齿象和猛犸象颧齿象，保留了在齿形动物中所见的磨损模式。Gomphotherium、Cuvieronius、Anancus、Stegodontidae和Elephantidea的磨损特征与Phiomia不同，它们的内磨损表面也有条纹。后一种磨损模式一定是由于咀嚼时磨牙谷脊之间的咬合较浅或没有咬合而形成的。重建了日本中新世剑龙畸形颅骨。重建结果表明，一些日本剑龙可能是侏儒兽，这是最古老的长鼻侏儒兽的例子。

Cheek teeth of Phiomia were examined qualitatively under SEM in an attempt to recognize basic wear pattern of cheek teeth in Elephantoidea. In Phiomia, wear facets of molars can be classified into three categories; facet with distinct margin formed by tooth to tooth contact, and inner and outer abrasion facets with vague margin formed by tooth to food contact. Parallel striae with ligualobuccal orientation are developed on valley slopes and the outer abrasion facet, while pits dominate on inner abrasion facet, central conule and apex of posttrite cones. Wear pattern seen in Phiomia must have been formed by deep interlocking between valley and ridges of molars during trituration of food.Some of non-tetralophodont gomphotheres, such as Sinomastodon and the mammutid Zygolophodon, retain wear pattern seen in Phiomia. However, wear feature in Gomphotherium, Cuvieronius, Anancus, Stegodontidae and Elephantidea differs from that of Phiomia in that striae are found also on inner abrasion surface. The latter wear pattern must be formed by shallow or no interlocking between valley and ridges of molars during mastication.A deformed skull of stegolophodon from Japanese Miocene was reconstructed. The reconstruction suggested that some Japanese stegolophodons could be dwarf form, which is the oldest example proboscidean dwaft.