Postcranial morphology of Repenomamus (Eutriconodonta, Mammalia): Implications for the higher-level phylogeny of mammals.
Item
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Title
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Postcranial morphology of Repenomamus (Eutriconodonta, Mammalia): Implications for the higher-level phylogeny of mammals.
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Identifier
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AAI3213248
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identifier
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3213248
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Creator
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Hu, Yaoming.
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Contributor
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Advisers: Jin Meng | Michael J. Novacek | John H. Wahlert
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Date
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2006
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Zoology | Paleontology | Paleozoology
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Abstract
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Repenomamus are eutriconodont mammals living in the Early Cretaceous. The genus has two species, R. robustus and R. giganticus, both from Yixian Formation, western Liaoning, China. The postcranium of Repenomamus is described in detail. The atlas has the neural arch and intercentrum unfused. The axis and postaxial cervical vertebrae have short ribs. There are twenty thoracic vertebrae. The scapula has a huge spine and well developed supra- and infraspinous fossa. The coracoid is reduced as the coracoid process. The humerus is stout, with an ulnar and radial condyle and an incipient trochlea. The ulna and radius are compressed transversely. The olecranon is large. The femoral head is oriented proximally and dorsomedially. The tibia is shorter than the femur. The upper ankle joint is tricontact. The astragalus has an incipient head and no distinct neck. The calcaneus has a medioventral directed tuber and a broad peroneal process. The astragalus partially overlaps the calcaneus. The metatarsal V does not contact the calcaneus. Anatomical comparison of Repenomamus with other Mesozoic mammals is conducted in the format of character analysis. 176 postcranial characters are analyzed across major clades of mammals and selected nonmammalian cynodonts. The phylogeny of Mesozoic mammals is generated with the data matrix of 57 taxa and 435 characters (176 postcranial, 151 cranial and 108 dental). The result is consistent with previous analyses regarding the monophyly of Mammalia, paraphyly of non-therian mammals and polyphyly of triconodonts. The analysis also reveals several relationships among groups of mammals, e.g. the close relationship between monotremes and multituberculates, the monophyly of eutriconodonts, the monophyly of symmetrodonts, and close relationships of "Gondwanan tribosphenic mammals" with northern continental tribosphenic mammals. Estimated body masses are 12-14 kg for R. giganticus and 4-6 kg for R. robustus, which make the genus among the largest of Mesozoic mammals. The stomach content indicates carnivory, suggesting Repenomamus competed with small carnivorous dinosaurs. Repenomamus has a mammalian type of larynx, which minimizes the interruption of respiration during mastication. This is an important adaptation in the evolution of the mammalian endothermy and lactation.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
