The narial morphology of Metarhinus and Sphenocoelus (Mammalia, Perissodactyla, Brontotheriidae)

[摘要] The brontothere genera Metarhinus and Sphenocoelus (=Dolichorhinus) are both characterized by an unusual redirection of the air passageway in which the internal nares are effectively closed off and new openings that serve as the functional internal nares have appeared posteriorly. Rather than passing lateral to the vomer, the airstream appears to pass over or through the bone (thus bypassing the anatomical internal nares) and exits through an enlarged vomerine notch. If correctly interpreted, this morphology is unique among mammals. In the past it has been suggested that the posterior displacement of the internal nares is either an amphibious adaptation or an adaptation to enhance olfaction. The current paper favors the latter interpretation. Among other reasons is that the change in morphology channels the airstream directly toward the olfactory epithelium in the area of the ethmoid. In order for the vomer to channel air, the septal cartilage would require significant modification. It is speculated here that the respiratory septum (vomer, crest of the maxilla, and crest of the palatine) might have been wholly or partially isolated from the olfactory septum (perpendicular plate of the ethmoid and septal cartilage), allowing air to be channeled through (or over) the vomer.

[学科分类] 地质学

[关键词] Bryn J. Mader;titanothere;Dolichorhinus;vomer;nasal breather;nasal cycle;evo-devo