An international team of scientists led by researchers from the Institute for Plasmas and Nuclear Fusion, at Instituto Superior Técnico, the Natural History Museum, London, UK and the Field Museum of Natural History, Chicago, USA, has identified the origin of mammalian endothermy, tracing their origins to the Upper Triassic, about 233 million years ago – about 20 million years later than presumed so far. The article “Inner ear biomechanics reveals a Late Triassic origin of mammalian endothermy” was published online, on July 20, in Nature journal, and it is the first scientific article in the history of Portuguese paleontology in which a Portuguese is the first author, in a high-impact scientific journal.
The method used by the team is based on the observation that body temperature affects the viscosity, or fluidity, of endolymph, a fluid within the tiny semicircular canals of the inner ear, which monitor head rotations and are essential for motor coordination.
Animals capable of maintaining warm body temperatures, such as mammals, had to undergo a transition in the shape and size of their ear canals to maintain optimal functionality. This means that the structure of the ear can be used as an accurate indicator to determine when the evolution of the endothermy occurred.
Until now, there was a strong consensus that endothermy first appeared 252 million years ago, at the same of Cynodontia (mammal ancestors). These new results reveal that endothermy appeared much later, and that many of the earliest cynodonts – often portrayed as fur and warm-blooded animals – were actually very different from mammals.
This discovery shows that the endothermy evolved at the same time as other characteristics of mammals, such as changes in backbone or the appearance of whiskers and/or fur.
According to Ricardo Araújo, researcher at Institute for Plasmas and Nuclear Fusion, Instituto Superior Técnico, and co-author of the article: “Contrary to current scientific thinking, our paper surprisingly demonstrates that the acquisition of endothermy seems to have occurred very quickly in geological terms, in less than a million years. It was not a gradual, slow process over tens of millions of years as previously thought, but maybe was attained quickly when triggered by novel mammal-like metabolic pathways and origin of fur”.
Some of the fossils studied were discovered under the PaleoMoz Project, in Mozambique. Funding for this project was provided by the Aga Khan Development Network, Fundação para a Ciência e a Tecnologia, and the National Geographic Society, among others.