Nature paper sheds light on the origin of warm-bloodedness in mammals
An international team of scientists led by Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico researchers, together with colleagues from the Natural History Museum and the Field Museum of Natural History, USA, have revealed the origins of endothermy in mammals, tracing the characteristic’s origins to the Late Triassic period, around 233 million years ago.
The paper “Inner ear biomechanics reveals Late Triassic origin of mammalian endothermy” was published online in Nature on July 20. This is the first time in the history of Portuguese palaeontology that a Portuguese researcher is the first author in a high-impact journal.
Endothermy (warm-bloodedness) underpins the ecological dominance of mammals in diverse environmental settings, but until now it was not known exactly when this characteristic evolved.
Increased body temperature in mammal ancestors necessitated changes to the morphology of the inner ear, allowing scientists to pinpoint the evolution of endothermy by examining the ear structure of 341 different vertebrates.
The scientists based their method on the observation that body temperature affects the viscosity, or runniness, of the endolymph, a fluid contained in the tiny semicircular canals of the inner ear, which detect head rotation and aid balance.
Animals with sustained high body temperatures, such as mammals, have had to change the shape of their ear canals to maintain proper function, meaning the structure of the ear can be used as an accurate guide to when endothermy evolved.
Until now the general expectation was that endothermy was achieved around 252 million years ago near the origin of Cynodontia, a group of mammalian ancestors. The new results suggest that endothermy appeared much later and that many early cynodonts, often pictured as warm-blooded with fur, were actually quite different from mammals.
The findings show that endothermy evolved later than previously hypothesised, but around the same time as when other observably mammalian traits evolved, such as the different parts of the backbone taking on different functions, and the evolution of whiskers and/or fur.
Dr Ricardo Araújo, Junior Researcher at IPFN and Lead Author on the paper, said:
“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 as part of the PaleoMoz Project in Mozambique. This work has, among others, received funding from the Aga Khan Development Foundation, the Portuguese Foundation for Science and Technology and the National Geographic Society.
