When Did We Become Warm-Blooded?
A New Technique Explores the Question
We humans and other mammals can regulate our body temperature because we’re endothermic (warm-blooded). is has enabled us to move into all sorts of environmental extremes. No sitting around on a sunbaked rock for us!
Paleontologists have long debated the rise of endothermy. How can you tell cold- or warm-bloodedness from fossilized remains in rocks hundreds of millions of years old? Some look to oxygen isotopes in ancient bones.
Others look at bone structure and estimated growth rates. In the journal Nature, an international team led by Ricardo Araújo (University of Lisbon, Portugal) and Romain David (Natural History Museum, London, UK) suggests inner ear canals.
e researchers examined the bony inner ear structures of 50 living vertebrate species from sh to mammals, then developed an index to accurately predict body temperature when examining a new inner-ear canal. With that index in hand, they proceeded to analyze fossilized ear structures of 56 extinct synapsids or reptile-like critters that led to mammals. eir conclusion? Endothermy arose in mammals 230 to 200 million years ago, during the Late Triassic Period, a time of turbulent climate change. And it wasn’t a gradual process. ey believe it happened abruptly, geologically speaking, within a span of just a million years.
Case closed? Well, never really in science. e technique is earning a lot of respect, but some paleontologists still cling to old methods and beliefs and ask for more evidence.