Warm-bloodedness may have developed 20 million years earlier than previously thought

Researchers have long speculated that the ‘body heater’ in land animals evolved some 270 million years ago, according to Daily mail

However, new evidence has suggested that warm-bloodedness may have come about 20 to 30 million years earlier.

After analyzing the ancient bones of a long-extinct land animal that lived 300 million years ago, the team discovered its fossilized remains had the same bone form found in today’s land mammals

The breakthrough research was conducted by a team, who looked at humerus bones and femurs of long-extinct animals – specifically the mammal predecessor Ophiacodon that lived 300 million years ago.

 It is impossible to determine the body temperature of a long-extinct animal using a thermometer, but researchers know warm-bloodedness leaves clues behind in the fossilized remains.

It not only means that the animal is not reliant on the ambient temperature, such as how a lizard sun baths, but also enables faster growth.

‘And this is shown in the structure of the bones,’ explained Professor Martin Sander.

Bones are made up of protein fibers, collagen and a biomaterial called hydroxyapatite.

And the more orderly the arrangement of the collagen fibers, the more stable the bone, but the more slowly it normally grows as well.

But the bones of warm-blooded land animals have a special structure that is not only stable, but allows them to grow faster.

‘We call this bone form fibrolamellar,’ Sander said.

Together with his PhD student Christen D. Shelton, the scientists analyzed the bones of the ancient Ophiacodon and determined they grew as fibrolamellar bones – indicating that the animal could already have been warm-blooded, the team explained.

Bones of warm-blooded land animals have a special structure that is not only stable, but allows them to grow faster. The bone form is called bone form fibrolamellar

Other than being nearly six feet (2m) long, Ohiacodon look very similar to the small lizards we see today.

The researchers explain that this is not a coincidence, but mammals and reptiles are actually related because they share a predecessor.

In the family tree, Ophiacodon is very close to the place where these two branches separate.

However, many know that today’s lizards, turtles and other reptiles are cold-blooded and until now, it has been assumed that this was the original form of the metabolism – that the shared ancestors of both animal groups was cold-blooded.

And experts had believed that warm-bloodedness ‘arose over the course of mammalian evolution’.

However, Ophiacodon appeared a very short time after the division between mammals and reptiles.

‘This raises the question of whether its warm-bloodedness was actually a completely new development or whether even the very first land animals before the separation of both branches were warm-blooded,’ said Sander.

If this theory is correct, we would have to drastically correct our image: the first reptiles would then also have been warm-blooded – and would have only discarded this type of metabolism later. 

N.H.Kh