Subjects: Biology >> Zoology submitted time 2023-03-14 Cooperative journals: 《古脊椎动物学报》
Abstract： The zygodont proboscideans from the Miocene strata of China are widely distributed. However, the materials are scarce, and their classification has experienced a longtime controversy, from the chaotic state of multiple Zygolophodon species to the only one species, Zygolophodon gobiensis. The combined species Z. gobiensis comprises both the gracile type with a high degree of zygodonty and the robust type that is between the typical bunodont and zygodont morphology. Recently, as the robust type has been re-allocated to another genus Miomastodon and new fossil remains were discovered, it is necessary to further evaluate and classify the zygodont proboscideans from the Miocene of China. In the present paper, we restudied the previously published zygodont specimens of the gracile type, as well as several unpublished Mammutidae specimens. The former including Z. nemonguensis, Z. gromovae, Z. jiningensis, Z. chinjiensis and two specimens of Gomphotherium xiaolongtanensis, represents Zygolophodon in the original sense in China. In these specimens, the tip of the loph(ids) are sharp. The anterior and posterior pretrite central conules are absent or very weak, and the anterior and posterior crescentoids are sharp and slender. The posttrite mesoconelets are well subdivided and the zygodont crests are developed. In buccal view, the loph(id)s are “Ʌ-shaped” and the interloph(id) s are “V-shaped”. Their molar morphology resembles that of Z. turicensis, and hereby, they were identified as Zygolophodon cf. Z. turicensis. Several unpublished specimens from Hezheng, Gansu, Tunggur, Nei Mongol, Tongxin, Ningxia and Junggar, Xinjiang exhibit a lower degree of zygodonty, corresponding to the “robust type of Zygolophodon” in which the molar morphology is between the typical bunodonts and zygodonts. The pretrite crescentoids are thicker than Zygolophodon cf. Z. turicensis, and the pretrite central conules usually present on the first and second interloph(id)s. According to the stratigraphic age and characteristics, two species, Miomastodon gobiensis and Mio. tongxinensis were identified. The anterior and posterior pretrite crescentoids of Mio. tongxinensis are weaker and the pretrite central conules are larger than Mio.gobiensis. Geographical distribution indicates that Miomastodon is the predominant member of zygolophodonts in the Early and Middle Miocene in northern China. The discovery of new materials and the reclassification of zygolophodonts provide further evidence for dispersal of Mammutidae from Eurasia to North America and the evolutionary relationships among the species of the family Mammutidae in China.
Subjects: Biology >> Zoology submitted time 2021-08-11 Cooperative journals: 《古脊椎动物学报》
Abstract： A cuboid specimen collected from the Late Miocene stratum at Qingyang, Gansu, China is described here. The size of the Qingyang specimen is comparatively huge, even larger than the average size of Elasmotherium caucasicum collected from Nihewan, Hebei, China. The morphology of the Qingyang specimen is identical to that of other specimens of Elasmotheriini; thus, the Qingyang specimen belongs to a huge elasmothere, most probably Sinotherium. By comparison with extant rhino species, the complex of the main body and the apophysis exhibit functional significance. The angle between the frontal plate of the cuboid and the main axis of the apophysis can suggest the ecological conditions occupied by an elasmothere. From analysis of the morphology of the cuboid, Sinotherium and the more derived elasmotheres probably lived in forested or wooded environments, differing from the previous hypothesis of their paleoenvironment.
Subjects: Biology >> Zoology submitted time 2021-07-30 Cooperative journals: 《古脊椎动物学报》
Abstract： The mastodont-grade proboscideans represent an important stage in the evolution of the group, establishing the basic pattern of the evolution of the crown groups of proboscideans. The research on mastodons has a history of more than 400 years. The classification and nomenclature have been revised and changed many times, and the problems in their evolution were fully reflected in the history of mastodon nomenclature. In this paper, we undertook a bibliographical research into the nomenclature and etymology of various mastodont groups, reviewing 175 translated Chinese names of mastodont-grade proboscideans, including 12 taxon names higher than the genus level, 46 genera, and 117 species, covering almost all the species of the mastodont radiation. On this basis, we review the principal phylogenetic hypotheses of mastodont interrelationships, and highlight problems in the classification and nomenclature of mastodonts. The evolution of the skull and mandible of mastodons is continuous in all clades, reflecting the same parallel evolution trend; while, although the morphological characteristics of cheek teeth across all lineages are not obvious, they are relatively stable in each lineage. Choerolophodontidae is the most robust monophyletic group within the mastodonts, of which Synconolophus may be a distinct, valid genus. Miomastodon and Pliomastodon of Mammutidae may both be valid, but they are not necessarily the direct ancestor of Mammut americanum. The phylogenetic relationship between Platybelodon danovi, P. grangeri and Aphanobelodon zhaoi within the Amebelodontidae is questionable, depending on whether the lower incisor section of P. danovi is the dentine rod structure or not, while Konobelodon britti in America may be a synonym of Torynobelodon loomisi. The species assigned to Konobelodon in Asia is possibly not amebelodontids, but probably attributable to Paratetralophodon, instead; Serridentinus of Gomphotheriidae may be a valid taxon, representing a trend towards somewhat zygodonty in Gomphotheriidae that terminated with the Cuvieroniinae. The Cuvieroniinae may only include Cuvieronius and Rhynchotherium, while other brevirostrine gomphotheres in America, such as Stegomastodon may have been evolved from a lineage of amebelodonts. Notiomastodon may be related to Sinomastodon, which itself may have originated from Pliomastodon (?) zhupengensis in southern China. The name Mastodon intermedius Teilhard de Chardin & Trassaert, 1937 (now Sinomastoodon intermedius) has the senior primary homonym Mastodon intermedius Eichwald, 1831. We suggest that Sinomastodon intermedius should be replaced with its senior synonym– Sinomastodon sendaicus (Matsumoto, 1924).
Subjects: Biology >> Zoology submitted time 2020-03-31 Cooperative journals: 《古脊椎动物学报》
Abstract： The elephantimorph proboscideans, Serridentinus gobiensis Osborn & Granger, 1932, and Miomastodon tongxinensis Chen, 1978, from the Middle Miocene of northern China, were revised as Zygolophodon gobiensis (Osborn & Granger, 1932). However, their phylogenetic positions are still being debated because of their intermediate morphology between the typical bunodont (Gomphotheriidae) and zygodont (Mammutidae) elephantimorphs. In the present paper, we compare their dental and mandibular morphology with that of the Eurasian Z. turicensis, Gomphotherium subtapiroideum, and G. tassyi, as well as the North American Mio. merriami and G. productum. It appears that S. gobiensis and Mio. tongxinensis share with Mio. merriami the slightly more bunodont molar morphology than that of Z. turicensis, e.g., the thicker enamel, thicker pretrite crescentoids, higher interlophid enamel pillars in buccal view, and the narrower contour majorly caused by the narrower posttrite half loph(id)s. S. gobiensis and Mio. merriami also possess an “erected oval cross-sectioned mandibular tusk”, in which the cross-section is mediolaterally compressed (dorsoventral diameter being larger than the mediolateral one). Whereas, in Z. turicensis and G. productum, the mandibular tusk is “laid oval cross-sectioned”, in which the cross-section is dorsoventrally compressed (dorsoventral diameter is smaller than the mediolateral one). Therefore, it is reasonable to revive the genus Miomastodon Osborn, 1922, which contains the species that were previously attributed to Zygolophodon, but they have relatively bunodont molar morphology (i.e., the robust type of the Z. turicensis group). The mandibular tusk with erected oval cross-section seems to be a synapomorphy of Miomastodon species. Furthermore, the molar morphology of G. subtapiroideum and G. tassyi also exhibits intermediate status between the typical bunodonts and zygodonts. However, the mandibular symphysis of G. subtapiroideum and G. tassyi is stronger than that of Miomastodon, and the mandibular tusk is pyriform cross-sectioned. The validity of Miomastodon and G. subtapiroideum/tassyi obscures the boundary between the Gomphotheriidae and Mammutidae, and suggests that the evolutions of the Gomphotheriidae and Mammutidae are deeply involved in with each other, rather than straightforwardly detached. This phenomenon has been revealed by a collagen sequence analysis among Notiomastodon, Mammut, and extant elephants, which should be further studied.
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