Tag Archives: warm blooded

Iguana sun basking.

Warm-bloodedness shown to be millions of years older than we thought — maybe as old as the dinosaurs

The first warm-blooded animals may have evolved millions of years earlier than believed, researchers at the University of Bonn report.

Iguana sun basking.

Those of you who have a pet lizard or snake probably know how much they like to bask in the sun or a heat lamp. They’re especially fond of doing this in the morning after a cold night. It’s all because of the way they regulate their internal temperature — reptiles rely on external heat to limber them up, as they can’t don’t use their energy to generate heat. You, me, a mouse, or other mammals and birds instead generate heat internally, by burning calories.

Because of this, reptiles are often referred to as cold-blooded, and as warm-blooded. Cold-bloodedness made a lot of sense in the Earth’s past, as mean temperatures were a lot higher back when reptiles were still news. Today, being cold-blooded is ‘cheaper’ in a nutritional sense — these animals need to eat a lot less because their bodies don’t burn anything to keep warm. Having warm blood means you’re more resilient in the face of environmental factors and allows animals a higher metabolic rate (what you perceive as being ‘lively’,) since the extra thermal energy makes biochemical reactions underpinning their activity take place faster.

Until now we’ve believed that the transition from cold to warm blood took place in a four-legged land animal somewhere around 270 million years ago.

“However, our results indicate that warm-bloodedness could have been created 20 to 30 million years earlier,” says Prof. Martin Sander from the Steinmann Institute for Geology, Mineralogy and Paleontology at the University of Bonn.

Since you can’t exactly slap a thermometer onto a fossil and see how warm the original animal was, the team had to use other methods of discerning between cold and warm-bloodedness. Thankfully, the trait leaves behind certain characteristics in the fossils that the team was able to draw on.

Bone-afide data

Warm-blooded animals tend to grow faster than their cold-blooded counterparts, which is reflected in the structure of their skeleton. Bones are a mix of protein fibers (such as collagen) and a material known as bone mineral, a form of hydroxyapatite. Collagen fibers in particular need to be well ordered during bone development since collagen makes them flexible and binds everything together. The more well ordered these fibers are, the stronger the bone becomes — but it also takes more time to grow.

Ophiacodon bones.

The fossils used for the study.
Image credits Shelton, C.D., Sander, P.M., Long, C. R. Palevol (2017).

Since mammals grow faster than reptiles, their bones are also based on a special structure (fibrolamellar) which allows for faster growth without sacrificing strength. And that’s what the researchers looked for.

Teaming up with his PhD student Christen D. Shelton, Prof. Sander analyzed the humerus and femur bones of the long extinct, lizard-like mammal predecessor Ophiacodon. They found that its bones relied on a fibrolamellar structure, suggesting that the “animal could already have been warm-blooded.”

The finding is especially exciting since Ophiacodon is closely related to both reptiles and mammals — it’s just beyond the spot in the tree of life where these two branches diverge. Up to now, we’ve simply assumed cold-bloodedness was the first type of metabolism to develop since today’s reptiles have the longest evolutionary heritage and are all cold-blooded. Warm blood, the theory goes, developed later as mammals evolved further.

But the findings, coupled with other known or suspected cases of warm-blooded ancient animals, could throw this theory into question.

“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,” says Sander.

It’s currently just speculation, and the team will need to look at a lot more fossils before they have a clear picture. But if their theory is correct, we would have an interesting couple of questions on our hands: when, and why, did reptiles forgo warm blood?

The paper “Long bone histology of Ophiacodon reveals the geologically earliest occurrence of fibrolamellar bone in the mammalian stem lineage” (original title “L’histologie d’os longs d’Ophiacodon révèle l’occurrence la plus précoce d’os fibro-lamellaire dans la lignée souche mammalienne) has been published in the journal Comptes Rendus Palevol.

Ancient reptiles were warm-blooded beasts, study finds

A surprising study found that a group of ancient lizards called mosasaurs were warm-blooded.

Mosasaur skeleton, photo by MCDinosaurhunter.

The first mosasaur fossils were discovered in a limestone quarry at Maastricht in the Netherlands, and since then they’ve become some of the most popular fossils of marine reptiles. They breathed air (didn’t have gills), were powerful swimmers, and were well-adapted to living in the warm, shallow seas of the Cretaceous. They measured between 1 and 17 meters long and were so well adapted to this environment that they actually gave birth to live young without returning to the shore, as modern sea turtles do. But they may have been even more special, according to a new study.

The study found that the aquatic lizards were in fact warm-blooded, having the ability called “thermoregulation.”

“There was a paper published in Science in 2010 reporting the thermoregulation in marine reptiles at the time of the dinosaurs focusing on the iconic extinct taxa: ichthyosaurs, plesiosaurs and mosasaurs,” said author of the new study Alberto Perez-Huerta, an associate professor of geology at the University of Alabama. “This conclusion bothered me a bit because there was not a warm-blooded member organism used for comparison, and we know that size can matter in terms of thermoregulation.”

The researchers conducted an isotope analysis on mosasaur fossils from the University of Alabama collection, comparing them to similar analysis on modern cold-blooded reptiles, as well as warm-blooded organisms like birds. They found more similarities to warm-blooded creatures, indicating that mosasaurs did practice thermoregulation.

“The findings of the present study support that mosasaurs were able to maintain a higher internal temperature independent of the ambient seawater temperature and were likely endotherms (warm-blooded), with values closer to contemporaneous fossil and modern birds and higher than fish and turtles,” the study said. “Although there are small differences of body temperature among mosasaur genera, these are independent of size, and thus inferred body mass.”


Researchers Nick Wegner holding a opah. Image: National Geographic

Meet the first fully warm-blooded fish: the opah

Though it’s a deep ocean fish, the slender opah is actually fully warm blooded – the first of its kind discovered so far. This remarkable insight was made by accident after researchers at the National Oceanic and Atmospheric Administration dissected the fish and noticed its blue and red blood vessels were located inside the gills, rather than in the fish’s swimming muscles. Tuna or sharks, which both have the same vessels but not arranged in the same way, cool their blood once it reaches the gills for oxygen reloading. The opah’s vessels are interwoven inside the gill like a net, which means the the veins that carry warm blood away from the hot muscles are interwoven with the arteries that carry cold blood in from the gills. This makes all the difference. Running so close to each other, the warm blood from the heart heats the cold blood from the gills. This way the Opah is 5 degrees Celsius warmer than its surroundings waters!

Researchers Nick Wegner holding a opah.  Image: National Geographic

Researchers Nick Wegner holding a opah. Image: NOAA FISHERIES WEST COAST

Nicholas Wegner from the National Oceanic and Atmospheric Administration and colleagues were on research trip when they happened to catch some opah fish. While they were at it, they decided to study the fish closely – why not? They eventually found much more than they bargained for.

“That was when we realised what it was capable of,” Wegner said.

For instance, its frisbee-shape isn’t quite an indicator that this is a fast, ferocious predator. But its appearance is deceiving, as the researchers later learned after they tagged the fish with instruments.

“That’s what’s really blew my mind about this discovery,” says Wegner. “Just from looking at it, I really thought it was a slow, sluggish, deep-water fish that doesn’t do very much. But all indications are that this is a very fast fish and an active predator. We’ve put some tags on them to show that they migrate thousands of kilometres.”

The opah is as close to a full-body warm-blooded fish as science has yet discovered. Image: NOAA FISHERIES WEST COAST

The opah is as close to a full-body warm-blooded fish as science has yet discovered. Image: NOAA FISHERIES WEST COAST

Besides the net-woven blood vessels, the fish also retains heat with the help of an extra layer of fat which insulates the heart from the gills. The same applies to the pectoral muscles , where most of the heat is generated by its fins, from the surrounding water. This way, the opah’s heart, brain and muscles are all warmer than the surrounding waters, the researchers report in Science. Not even the great white shark has a warm heart.

“That’s why opah can stay at depth,” says Wegner. “These guys are specialised for living deeper than those other predators.”