The septomaxilla of fossil and recent synapsids and the problem of the septomaxilla of monotremes and armadillos |
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Authors: | JOHN R WIBLE DESUI MIAO JAMES A HOPSON |
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Institution: | Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois60637, U.S.A. |
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Abstract: | The septomaxilla is a paired intramembranous ossification in the external nares that occurs in Lepidosauria among Recent Sauropsida and is purported to be present in Monotremata and Dasypodidae (armadillos) among Recent Mammalia. A review of neontological and palaeontological evidence regarding this element in mammals supports the following conclusions: (1) monotremes have a true septomaxilla resembling that known for non-mammalian therapsids and some Mesozoic mammals; (2) the element in dasypodids is a neomorph; it neither resembles the septomaxilla of other synapsids nor does it exhibit the same relationship to the developing nasal-floor cartilage as the septomaxilla of lepidosaurs and monotremes; (3) a septomaxilla is lacking in all Recent therians, and there is no evidence that this bone is fused to the premaxilla in Recent therians, as has been suggested by previous authors. |
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Keywords: | Septomaxilla mammals monotremes dasypodids Mesozoic mammals synapsids premaxilla external naris |
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