Evolution and dispersal of Mammutidae (Proboscidea, Mammalia)
Final Report Abstract
Mammutidae are one family within the order Proboscidea. The earliest mammutids are found in Africa, then they expanded into Eurasia and North-America. Their fossil record is fragmentary, with the exception of Mammut americanum, the youngest member of this family in North America. The goal of this project was to survey poorly known aspects of the mammutid record to refine our understanding of their biogeography and evolution. Undescribed and poorly known materials in Thuringia (Museum Schleusingen) and Oregon (OMSI, Portland and OR-University in Eugene) were the impetus for this project. In the traditional view, the African immigrant Zygolophodon gave rise to the genus Mammut. Mammut borsoni from the Plio-Pleistocene is the youngest mammutid in Eurasia, and in the late Miocene Mammut immigrated to North America. About 14 000 years ago the well-known Mammut americanum, the youngest North American species went extinct. The presence of Zygolophodon in North America during the middle Miocene at about 16 Ma introduces an additional possibility, that Mammut derived endemically from Zygolophodon in North America. Prior to this study, the available fossil record did not provide clarity on this issue. The new Miocene material examined as part of this study strengthens the hypothesis of an endemic evolution. This record shows relatively continuous morphological change in North American mammutids, not a sudden appearance of new characters which would be expected if Mammut represented a separate immigration into the continent. Thus, the new materials plausibly indicate continuous endemic evolution from Zygolophodon to Mammut in North America. This conclusion causes nomenclatural problems. The genus Mammut cannot have originated twice, in Europe as well as in North America. The genus name Mammut is attached to North American Mammut americanum. Therefore, the Eurasian lineage should have a separate genus name. We are reluctant to create a new genus name at this time, therefore we use the name ‘Mammut’ with quotation marks for the Eurasian form to highlight this problem. The ‘Mammut’ skeleton from Kaltensundheim provided the opportunity for detailed descriptions of postcranial elements. For the first time, we have prepared a solid base for further anatomical comparisons in mammutids. The cranium from Unity (Oregon) of Zygolophodon proavus, the main object of our investigation, is preserved with its mandible. For the first time, this allowed the correlation of measurements between the upper and lower molars. This is very important because most mammutid records consist of isolated dentitions. The mandibles from Unity and Kaltensundheim both have lower tusks, but mammutid mandibles without tusks occur at the same stratigraphic levels in Eurasia and North America. In our study morphological differences between co-eval mandibles from Black Butte (OR) and Unity (OR) were discussed as a possible sex-linked difference. The presence and absence of lower tusks may be variable in space and time, therefor, and is not strictly a sexually dimorphic character. Even if not all problems could be solved because of the limited fossil record, this study contributed many new morphological details to the Mammutidae and clarified basic aspects of their geographic history.
Publications
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A partial skeleton of “Mammut” borsoni (Proboscidea, Mammalia) from the Pliocene of Kaltensundheim (Germany). Palaeontologia Electronica.
Koenigswald, Wighart; Březina, Jakub; Werneburg, Ralf & Göhlich, Ursula
