All inside the head? Scans of skulls question theories on the evolution of mammalian „warm-bloodedness“

Science News
CT-scans of several mammal skulls
Copyright: Q. Martinez

The emergence of "warm-bloodedness" (endothermy) was a milestone in the evolution of mammals: The ability to maintain a high and constant body temperature enables the colonisation of new habitats even in harsh environments.

Although "warm-bloodedness" (endothermy) is one of the most important and successful adaptations of mammals, studying its evolution is often challenging. Fossil remains usually have few features that allow assumptions about the animals' body temperature or heat production (metabolic rate). One of those features is the construction of the nasal cavity and the bony structures it contains, such as the so-called maxilloturbinal. Since the latter contributes to thermoregulation, it has been proposed that the maxilloturbinal plays an important role in the development of endothermy. In theory: The larger the relative surface area of the maxillotrubinal the more developed the endothermy.

An international team led by Dr Quentin Martinez of the State Museum of Natural History Stuttgart has now shown that there is no direct relationship between the structure of the maxilloturbinal and the body temperature or metabolic rate of mammals.

For their study Dr Martinez and his team scanned skulls from over 300 different mammal species using micro-computed tomography. Even a human skull was included: Dr Martinez scanned his own head. For science!

The results: for many mammals the relative surface area of their maxilloturbinals does not always reflect the expected body temperature or matabolic rate. E.g. Mammal species with similar body temperatures can have differently sized maxilloturbinals.

Original publication