Mammals can produce their own body heat and regulate their body temperature. This process is known as endothermia or warm-bloodedness.
Scientists believe this may be why mammals probably rule almost everyone ecosystem. Warm-blooded mammals are more active than cold-blooded animals. They can live in a variety of environments, from the frozen Arctic to the boiling desert. And they reproduce faster.
The soft tissues that would provide information about warm- or cold-bloodedness are rarely well kept in fossils. So paleontologists, or experts in the study of fossils, don’t know exactly when mammals evolved and turned into warm-blooded creatures.
A group of scientists tried to answer that question in a study recently published in Nature.
Ricardo Araújo is a paleontologist at the University of Lisbon. Araújo and a group of researchers proposed using the shape and size of inner ear structures, called canals, to study body temperature.
The movement of fluid through the ear canals helps the body maintain balance and movement. This fluid in cold-blooded animals is cooler and thicker, requiring wider channels. Warm-blooded animals have less ear fluid and smaller canals.
The research team suggested that as body temperature increased and the animals became more active, the shape and size of the ear canals changed to maintain balance and movement.
The researchers compared ear canals in 341 animals. They said the ear canals showed that warm-bloodedness, or endothermy, appeared about 233 million years ago, millions of years later than some earlier estimates.
Araújo said: “Endothermy is a determinant” feature mammals, including us humans. Having a … high body temperature arranges all our actions and behaviors.”
But the first creatures to be warm-blooded are not officially considered mammals. These ancient animals, known as mammalian morphic synapsids, had distinctive features associated with mammals. The first true mammals, the researchers said, appeared about 30 million years later.
The importance of being warm-blooded
Ken Angielczyk of the Field Museum in Chicago is co-leading the study. He said, “Given how central endotherm is like for so many… aspects of the body plan, physiology and lifestyle of modern mammals, when the evolved in our ancient ancestors has been a very important unsolved question…”
Endothermy evolved at a time when important elements of the mammalian body plan were falling into place, including changes in the spine, respiratory system, and auditory system.
Warm-bloodedness also helped mammals at an important evolutionary time when dinosaurs and flying reptiles first appeared on Earth. And mammals took over after the mass extinction of dinosaurs 66 million years ago. Among today’s animals, mammals and birds are warm-blooded.
“Maybe It’s Too” far-fetchedbut interesting, to think that the beginnings of endothermy in our ancestors may have eventually led to the construction of the pyramids of Giza or the development of the smartphone,” said Araújo.
“If our ancestors hadn’t become independent of the environmental temperatures, these human feats probably wouldn’t be possible.”
I’m John Russell.
John Russell adapted this story for VOA Learning English based on news from Nature, Scientific American and Reuters.
Words in this story
ecosystem – n. everything that exists in a particular environment
to protect – v. to keep (something) in its original state or in good condition
fossil – n. something (such as a leaf, skeleton, or footprint) that comes from a plant or animal that lived in ancient times and that you can see in some rocks
feature – n. an interesting or important part, quality, ability, etc.
regulate – v. to set or adjust the amount, degree, or speed of (something)
character trait – n. a quality that makes one person or thing different from another
aspect – n. part of something
evolve – v. change or evolve slowly into a better, more complex, or more advanced state: evolving through a process of evolution
far-fetched – adj. probably not going to happen or be true