Abstract
New material of Agriotherium from the late Hemphillian (~6 Ma) Quiburis Formation in Arizona, North America is reported. These specimens represent a new species, Agriotherium hendeyi, sp. nov., of small size and with a bucco-lingually narrow lower dentition distinguishing it from North American “Agriotherium” schneideri as well as the genotype and other Old World species of Agriotherium. Strikingly, the m1 metaconid-entoconid complex of the new species exhibits a morphologically transitional state between the pattern observed in Indarctos (three cusps) and the typical Agriotherium pattern (two cusps). Together with a review of the variation in A. africanum, a geometric morphometric analysis permits identification and discussion of a proposed transformation pathway from the Indarctos pattern to the Agriotherium pattern. It is shown that the two cusps in the metaconid-entoconid complex in Agriotherium correspond to the two entoconids in Indarctos, whereas the ancestral metaconid is reduced or lost in Agriotherium. From a developmental perspective, the metaconid fused to the anterior entoconid as a result of the shortening of the talonid, rather than via replacement of the metaconid by a posterior shift of the entoconid, presumably under selective pressure towards a more typically hypercarnivorous tooth morphology and carnivorous diet.
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Abbreviations
- AMNH:
-
American Museum of Natural History, New York, USA
- AMNH F:
-
AM Frick collection (Fossil Mammals), Division of Paleontology, AMNH, USA
- AMNH M:
-
Mammalogy (Vertebrate Zoology) collections, AMNH, USA
- IVPP:
-
Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China
- L:
-
Specimens housed in Iziko South African Museum, Cape Town, South Africa
- P/p:
-
upper/lower premolar
- M/m:
-
upper/lower molar
- Hh3:
-
Hemphillian3, late Hemphillian North American Land Mammal Age (NALMA)
- Hh4:
-
Hemphillian4, latest Hemphillian NALMA
- MN:
-
Neogene land Mammal Zones of Europe
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Acknowledgements
We thank A. Valenciano from the Iziko South African Museum, Cape Town, South Africa for providing photos of A. africanum; and M. Hopkins, W. Harcourt-Smith, and A. Watanabe for guiding the geometric morphometric analysis. We also thank J. Meng, R. O’Leary, and J. Galkin for their help in accessing the AMNH fossil mammal collections; M. Surovy, E. Hoeger, and S. Ketelsen for their help in accessing the AMNH modern mammal collections; and Z. Qiu and J. Chen for help in accessing fossil collections of the IVPP. We are also thankful to the two reviews’ suggestion, which greatly imporved the quality of the manuscript. The current work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB26000000 and XDA20070203), Key Frontier Science Research Program of the Chinese Academy of Sciences (Grant Nos. QYZDY-SSW-DQC-22 and GJHZ1885), the National Natural Science Foundation of China (Grant Nos. 41430102, 41872001, 41872005 and 41772018), and China Scholarship Council in award to the senior author (QJ).
Author Contributions Statement
Q.Jiangzuo and J.J.Flynn wrote the main manuscript text and Q.Jiangzuo prepared the geometric morphometric and statistical analyses. All authors reviewed the manuscript.
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Jiangzuo, Q., Flynn, J.J. A New Species of Agriotherium from North America, and Implications for Understanding Transformations in the Metaconid-Entoconid Complex of Bears. J Mammal Evol 27, 775–787 (2020). https://doi.org/10.1007/s10914-019-09480-x
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DOI: https://doi.org/10.1007/s10914-019-09480-x