The septomaxilla of fossil and recent synapsids and the problem of the septomaxilla of monotremes and armadillos

1990/03/01 by JOHN R. WIBLE, John R. Wible, DESUI MIAO +3 · 65 citations
Earth and Planetary Sciences · Environmental Science · #Armadillo #Biology #Evolution and Paleontology Studies #Fish biology, ecology, and behavior #Paleontology #Paleontology and Evolutionary Biology #Zoology

paper · doi:10.1111/j.1096-3642.1990.tb01207.x

published in Zoological Journal of the Linnean Society 98(3), 203-228 (Oxford University Press)

openalex publication_date 1990/03/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

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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