TURBINATES IN THERAPSIDS: EVIDENCE FOR LATE PERMIAN ORIGINS OF MAMMALIAN ENDOTHERMY

Area of Science:

• Paleontology and Evolutionary Biology
• Comparative Anatomy
• Vertebrate Physiology

Background:

• Nasal conchae (turbinates) in reptiles, birds, and mammals vary in complexity and function.
• Mammalian turbinates, particularly the maxilloturbinal, are crucial for reducing respiratory desiccation and are linked to endothermy.
• Fossil evidence of turbinates relies on attachment ridges within the nasal cavity.

Purpose of the Study:

• To review the structure and function of nasal conchae across extant reptiles, birds, and mammals.
• To examine the relationship between mammalian turbinates and endothermy.
• To identify fossil evidence of respiratory turbinates in mammallike reptiles to infer the evolution of endothermy.

Main Methods:

• Comparative anatomical review of nasal conchae in extant groups.
• Analysis of fossilized nasal cavities for turbinate attachment ridges.
• Correlation of ridge location (olfactory vs. respiratory) with airflow patterns and function.

Main Results:

• Reptilian conchae are simple and primarily olfactory; bird and mammal conchae are complex with respiratory epithelium.
• The respiratory maxilloturbinal in mammals reduces desiccation during ventilation, a key adaptation for endothermy.
• Anterolateral ridges, indicative of respiratory turbinates, were identified in the therocephalian Glanosuchus and cynodonts, previously unrecognized in these groups.

Conclusions:

• The presence of respiratory turbinates in advanced mammallike reptiles suggests the evolution of mammalian oxygen consumption rates began in the Late Permian.
• Endothermy likely evolved in parallel in therocephalians and cynodonts.
• Full mammalian endothermy may have taken 40-50 million years to develop.