云南地区中新世晚期的玛姆象和嵌齿象类化石的归类一直存在较多的争议, 尤其是涉及中华乳齿象 (Sinomastodon)的起源问题。本文对此前发表及最近发现的产自元谋盆地中新世晚期小河组(8.2?7.2 Ma)的玛姆象类化石进行了深入研究, 从中辨认出了两个颊齿形态截然不同的类群。一类颊齿轭形化程度高, 将其鉴定为曾经在禄丰、昭通等地报道的禄丰玛姆象(Mammut lufengense), 代表了高轭型化的玛姆象类在中国南方中新世晚期的一个分支。另一类鉴定为竹棚上新乳齿象(Pliomastodon? zhupengensis comb. nov.), 如同期的其他玛姆象类, 比如马修上新乳齿象(Pliomastodon matthewi)和斜脊玛姆象(Mammut obliquelophus), 竹棚上新乳齿象具有直而略向上弯的上门齿, 下颌联合部中等伸长, 具有短棒状的下门齿, 但它的颊齿轭形化程度低, 具有如下特征: 齿嵴和新月嵴粗钝, 保存主齿柱中心小尖, 侧视主齿柱达到齿谷的一半高度, 副齿柱分裂程度低, 以上特征与禄丰玛姆象等高轭形化的类群相区别。竹棚上新乳齿象颊齿形态特征继承了中国北方中新世中期的戈壁中新乳齿象 (Miomastodon gobiensis), 又与其后昭通盆地(6.5?6.0 Ma)的先中间中华乳齿象(Sinomastodon praeintermedius)有被继承的关系, 很可能是后者的祖先。中华乳齿象不大可能是比它晚的美洲的南方乳齿象(Notiomastodon) (2.5?0.01 Ma)演化而来, 也可能如早期所认为的归为玛姆象类, 而非嵌齿象类。

This paper reports fossil mammutid proboscideans from the late Miocene of the Xiaohe Formation, Yuanmou Basin, Yunnan Province. They were recovered from three localities: Zhupeng, Huiwoqing, and Leilao, and belong to two taxa: Pliomastodon? zhupengensis comb. nov. and Mammut lufengense. SYSTEMATIC PALEONTOLOGYOrder Proboscidea Illiger, 1811 Family Mammutidae Hay, 1922 Genus Pliomastodon Osborn, 1926 Pliomastodon? zhupengensis (Zhang et al., 1991 in Ji and Zhang, 1997, comb. nov.) Type specimen YICRA YV0787, left M3, see Ji and Zhang (pl. 28, fig. 1). Type locality Zhupeng. Diagnosis Pliomastodon? with moderately elongated symphysis and lower tusks, lacking the posterior mental foramen. Upper tusks straight, dorsally bent and enamel-less. A low degree of cheek teeth zygodonty: relative to Mammut, subdivision of lophs/lophids not pronounced, thick pretrite crescentoids with the possibility of presence of pretrite central conules, interlophs/interlophids half stuffed by pretrite crescentoids and/or central conules. Referred material MCY C1134ZA94, mandible, with associated palate and right upper tusk, from Huwoqing; YMM 297, incomplete mandible, from Leilao; YICRA YV768 and YV784, two left M3s, as well as YMM 3121X081, right m3, from Zhupeng (Figs. 3, 4). Age: Late Miocene, ~8.2?7.2 Ma (Dong and Qi, 2013). Description and comparison The mandibular possesses a straight ventral border. The mandibular symphysis is narrow and moderately elongated with a deep trough. It tips slightly downward. The corpus is strong and the ramus is low. The upper tusk is straight and long. It is slightly dorsally bent without an enamel-band. The lower tusks are short rod-like. They are closely apposed with a nearly round cross-section. The above features are very similar to those of Mammut obliquelophus(Tobien, 1976). The M3 is tetralophodont. The lophs are blunter than those of Mammut. The interlophs are narrow. The pretrite half lophs possess thicker anterior and posterior crescentoids than those of Mammut. Occasionally the pretrite central conules are present. In lateral view from the pretrite side, the crescentoids and/or central conules reach at least half of the interlophs. The posttrite half lophs are less subdivided than those of Mammut. The posttrite main cusp and mesoconelets are generally well-separated. The zygodont crests are blunt. The m2 is trilophodont, and the m3 is tetra- or pentalophodont. The interlophids are wider than the M3, and the posterior pretrite central conules are usually present. Lophids are obliquely arranged with a somewhat chevron in the distal lophids. In some cases, the second pretrite and posttrite half lophids are alternatively positioned. The other features are similar to those of the M3, and differs from the m3 of Mammut in the same way as those of its M3. Pliomastodon? zhupengensis succeeded the low degree of zygodonty from Miomastodon gobiensis of the Middle Miocene of northern China (Wang et al., 2020). Like the other Late Miocene mammutids with high zygodonty, i.e., Mammut and Pliomatodon (Tobien, 1976, Osborn, 1936), Pliomastodon? zhupengensis curved the upper tusks upward and lost the enamel band. The molar morphology of Pliomastodon? zhupengensis displays few differences from Sinamstodon praeintermedius (Figs. 6-A–6-D), except the lower tooth crown and fewer lophids of the m3. It is the potential direct ancestor of the latter, which was recovered from the Shuitangba locality, Zhaotong Basin in the vicinity, ~6.5?6.0 Ma (Wang et al., 2016). Tobien et al. (1986) believed that Sinomastodon is morphologically and phylogenetically close to the American brevirostrinegomphotheres, especially the Notiomastodon, and migrated back from American. This opinion is questioned here: 1, the earliest Notiomastodon occurred at ~2.5 Ma in South America (Mothé et al., 2016), which is far later than the occurrence of Sinomastodon; 2, Sinomastodon sensu Tobien et al. actually comprises two morphological types, a more zygodont-like type (Mastodon intermedius, originally attributed to Mammutidae) from the Pliocene, and a more bunodont-like type from the Pleistocene (originally attributed to Gomphotherium); 3, collagen sequence of Notiomastodon are closer to that of Mammut than of the true elephantids (derived from the gomphotheres) (Buckley et al., 2019), which reveals that the evolution of Gomphotheriidae and Mammutidae was deeply involved rather than simply detached. Sinomastodon is more likely a mammutid. Genus Mammut Blumenbach, 1799 Mammut lufengense (Zhang, 1982) Type specimen YICRA YV0131, left m3, see Zhang (pl. 1, fig. 1). Type locality Shihuiba, Lufeng, Yunnan Province. Referred material YICRA XDYV001, right M2, YICRA XDYV002, anterior two lophs of right M3, YICRA XDYV003, left m2, YICRA XDYV004, left m3, unearthed at the same time from Leilao, Yuanmou, Yunnan Province (Fig. 5). Age: Late Miocene, 6.9?6.2 Ma (Dong and Qi, 2013). Description and comparison The deeply worn M2 and m2 are trilophodont. The M3 (keeping the anterior two lophs) possesses sharp lophs. The posttrite half lophs are subdivided into small conelets with an obscure separation between the main and mesoconelets. The pretrite mesoconelets are short crest-like, and the pretrite crescentoids are thin and sharp, reaching the bottom of the interlophs in side views. The zygodont crest are thin and clear. The m3 is tetralophodont. The lophids are highly mesiodistally compressed with wide interlophids. The posttrite half lophids are moderately to highly subdivided, and the separation between the main and mesoconelets is clearer than that of the M3. The pretrite crescentoids are somewhat thicker than those of the M3, and reach the 1/3 of the interlophid height. Chevron is developed on the posterior two lophids. Generally, the tooth morphology of Mammut lufenense shows little difference from the contemporary Eurasian species, Mammut obliquelophus (= M. preatypicum). Unfortunately, the condition of the upper and lower tusks, and mandibular symphysis is unknown. Here we temporarily keep the species name, ‘lufengensis’, and transferred it to Mammut, as a highly zygodont mammutid representative of southern China during this age. Besides from Yuanmou, Mammut lufenense was also recovered from the adjacent Lufeng (6.9?6.2 Ma) (Dong and Qi, 2013) and Zhaotong (6.5?6.0 Ma) (Ji et al., 2013), Yunnan Province (Figs. 6-E?6-H). It can be inferred that two types of Mammutidae, the less zygodont Pliomastodon?, and the high zygodont Mammut, coexisted in a long period during the late Miocene of southern China.

中国科学院战略性先导科技专项(XDB26000000, XDA20070203)和中国科学院前沿科学重点研究计划(QYZDY-SSW- DQC022, GJHZ1885)联合资助