Inner Ear Canal Gives Paleontologists Insights on Mammal Evolution

Endothermy or warm-bloodedness is the mammal's unique ability to regulate their body temperature. Experts believe it is the reason behind the mammal's domination of almost every ecosystem. But finding out when mammals evolved to be warm-blooded has proven challenging.

Inner Ear Evolution of Mammals

(Photo: Chris Carter by Pexels)

Warm-blooded mammals are more active than their cold-blooded counterparts, so they can survive in varying conditions and reproduce faster. However, the soft tissues that would give insight regarding warm-bloodedness often aren't preserved in fossils. Hence, paleontologists aren't sure when mammals developed warm-bloodedness.

Recently a team of paleontologists led by Ricardo Araujo published a study in the journal Nature titled "Inner ear biomechanics reveals a Late Triassic origin for mammalian endothermy," to answer the age-old question. The team proposed that the size and shape of the inner ear structures, and canals, could be used to analyze body temperature.

The movement of fluid in the ear canals helps regulate balance and movement. The fluid in cold-blooded species is cooler and thicker, requiring wider canals, compared to warm-blooded animals with less ear fluid and significantly smaller canals.

The team suggests that as the body temperature increases, the animal becomes more active, and the size and shape of the ear canals change to preserve movement and balance.

By comparing ear canals from 341 animals. The team concludes that warm-bloodedness appeared roughly 233 million years ago,

Araujo says that endothermy is a defining characteristic of mammals, including humans. Additionally, high body temperatures help regulate all our behaviors and actions.

However, the first creatures that were warm-blooded aren't officially considered mammals. These ancient animals, mammaliamorph synapsids, had characteristics linked to mammals. The first true mammals, according to researchers, appeared about 30 million years later, reports VOANews.

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Critical Role of Warm-Bloodedness

Co-leader of the study, Ken Angielczyk from the Field Museum, Chicago, says that given how central endothermy is a vital aspect in the body plan, physiology, and lifestyle of today's mammals, understanding when it evolved in our ancestors has been a vital question that has been left unanswered.

Endothermy evolved during a time when vital elements of the mammalian body plan were beginning to fall into place, including changes to the breathing system, backbone, and hearing system.

Having warm-bloodedness helped mammals at a vital evolutionary period when dinosaurs and flying reptiles appeared on the planet. And mammals took over after the mass extinction of dinosaurs roughly 66 million years ago. Today these animals, alongside birds, are warm-blooded.

Araujo adds that it may be too far-fetched but interesting to theorize that the onset of endothermy in mammalian ancestors ultimately led to the construction of the pyramids and technology developments today. Stating that if our ancestors did not become environmentally independent in terms of temperatures, none of these profound human achievements would have been possible, reports Nature.

Although it isn't sure when and why mammals evolved to be warm-blooded, we are sure that it is a vital evolutionary mechanism that paved the road for many of today's species, including humans.