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[dinosaur] Bony labyrinth of late Permian Biarmosuchia (Therapsida) (free pdf)

Ben Creisler

A new paper in open access:

Benoit, Julien; Manger, Paul R; Fernandez, Vincent; Rubidge, Bruce S (2017)
The bony labyrinth of late Permian Biarmosuchia: palaeobiology and diversity in non-mammalian Therapsida.
Palaeontologia Africana 52: 58-77
URI: http://hdl.handle.net/10539/23023

Biarmosuchia, as the basalmost group of Therapsida (the stem group of mammals), are important for understanding mammalian  origins and evolution. Unlike other therapsid groups, the bony labyrinth of biarmosuchians has not yet been studied, despite insightful  clues that bony labyrinth morphology can provide to address palaeobiology and phylogeny of extinct animals. Here, using CT  scanning, surface reconstruction and a 3D geometric-morphometric protocol of 60 semi-landmarks on the bony labyrinth of  30 therapsids (including three Mammaliaformes), it is demonstrated that bony labyrinth morphology of biarmosuchians is very  distinctive compared to that of other therapsids. Despite the primitive nature of their cranial morphology, biarmosuchians display  highly derived traits in the structure of the bony labyrinth. The most noticeable are the presence of a long and slender canal linking the  vestibule to the fenestra vestibuli, an enlarged and dorsally expanded anterior canal, and the absence of a secondary common crus  (except for one specimen), which sets them apart from other non-mammalian therapsids. These characters provide additional support  for the monophyly of Biarmosuchia, the most recently recognized major therapsid subclade. Although implications of the derived  morphology of the biarmosuchian bony labyrinth are discussed, definitive interpretations are dependent on the discovery of  well-preserved postcranial material. It nevertheless sheds light on a previously overlooked diversity of bony labyrinth morphology in non-mammalian therapsids.

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