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Brasilitherium (Triassic cynodont) nasal anatomy

Ben Creisler

A new paper:

Irina Ruf, Wolfgang Maier, Pablo G. Rodrigues and Cesar L. Schultz (2014)
Nasal Anatomy of the Non-mammaliaform Cynodont Brasilitherium
riograndensis (Eucynodontia, Therapsida) Reveals New Insight into
Mammalian Evolution.
The Anatomical Record 297(11): 2018–2030
Special Issue: Special Issue The Vertebrate Nose: Evolution,
Structure, and Function
DOI: 10.1002/ar.23022

The mammalian nasal cavity is characterized by a unique anatomy with
complex internal features. The evolution of turbinals was correlated
with endothermic and macrosmatic adaptations in therapsids and in
early mammals, which is still apparent in their twofold function
(warming and moistening of air, olfaction). Fossil evidence for the
transformation from the nonmammalian to the mammalian nasal cavity
pattern has been poor and inadequate. Ossification of the
cartilaginous nasal capsule and turbinals seems to be a feature that
occurred only very late in synapsid evolution but delicate ethmoidal
bones are rarely preserved. Here we provide the first µCT
investigation of the nasal cavity of the advanced non-mammaliaform
cynodont Brasilitherium riograndensis from the Late Triassic of
Southern Brazil, a member of the sister-group of mammaliaforms, in
order to elucidate a critical anatomical transition in early mammalian
evolution. Brasilitherium riograndensis already had at least partially
ossified turbinals as remnants of the nasoturbinal and the first
ethmoturbinal are preserved. The posterior nasal septum is partly
ossified and contributes to a mesethmoid. The nasal cavity is
posteriorly expanded and forms a distinctive pars posterior (ethmoidal
recess) that is ventrally separated from the nasopharyngeal duct by a
distinct lamina terminalis. Thus, our observations clearly demonstrate
that principal features of the mammalian nasal cavity were already
present in the sister-group of mammaliaforms.