Comparison of Thrinaxodon, Kryptobataar and Monodelphis turbinate structures (3D recon)

Comparison of cross sections through the snout of the Triassic cynodont Thrinaxodon, the Cretaceous multituberculate Kryptobataar and the extant marsupial Monodelphis. The evolution of mammalian endothermy (warm-bloodedness) has been debated for decades. One of the most recent clues to its origin lies in the nose and internal structure of the nasal capsule, where, several recent researchers have argued, the presence of turbinate bones is a possible indication of endothermy. In warm blooded birds and mammals the turbinate bones lie concealed within the housing of facial bones that surround the nasal capsule. The problem in understanding turbinate evolution has been detecting turbinate structures in fossils without breaking the rare, precious specimens. High-resolution CT provides a means of inspecting the internal structures, and the image above shows several different stages in the development of the mammalian turbinate complex. Thrinaxodon (top) lacks bony respiratory turbinates altogether. The Cretaceous mammal Kryptobataar (middle) probably possessed turbinates, most likely broken away from the skull during fossilization. The extant mammal Monodelphis (bottom) shows the complexity of the nasal structures in modern mammals. (Thrinaxodon and Monodelphis courtesy of Dr. Tim Rowe, University of Texas at Austin, Kryptobataar courtesy of Dr. Guillermo Rougier, American Museum of Natural History).

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