Crocodiles have not always been cold blooded, scientists say
Some prehistoric crocodiles were HOT BLOOD, which allowed them to survive the cold wave of the Jurassic 150 million years ago, according to a study of fossilized teeth.
- The ancient ancestors of today’s crocodiles were warm blooded to survive the cold.
- British researchers analyzed oxygen isotope compositions in fossilized teeth
- At least one crocodile from the extinct metriorhynchid family was warm blooded.
- Warm blood was key to developing a dolphin body and living in open oceans.
- The metriorhynchids prospered during a period of global cooling 150 million years ago
According to a new study, some ancient ancestors of today’s crocodiles were warm blooded.
Paleontologists at the University of Edinburgh analyzed the mineral composition of the crocodile fossil teeth of the extinct metriorhynchid family.
They discovered at least one ancient crocodile ancestor of the metriorhynchid family that was not cold-blooded.
The results indicate that they could raise your body temperature to keep warm as temperatures fall, in the same way as modern birds and mammals.
And it could have helped them prosper during a period of global cooling about 150 million years ago at the end of the Jurassic period.
Skeleton of a metriorhynchid, an extinct family of aquatic crocodiliformes – ancestors of crocodiles
WHAT ARE THE THREE GEOLOGICAL ERAS?
The Mesozoic Era is the name given to the period from 250 million to 65 million years ago.
The era is divided into three main periods: Triassic, Jurassic and Cretaceous.
The metriorhynchids lived during the Jurassic periods (201.3 million to 145 million years ago) and Cretaceous (145 million to 66 million years ago).
Mesozoic was the age of dinosaurs and lasted almost 180 million years.
The Mesozoic Era followed the Paleozoic Era, during which arthropods, molluscs, fish and amphibians evolved.
Mesozoic was followed by the Cenozoic Era, during which the continents assumed the configuration we know today.
Being warm-blooded was key for metriorhynchids to develop a dolphin-like body, including fins and a caudal fin, and venture into the open oceans.
Today’s crocodiles are cold-blooded and cannot generate their own heat, which means they hibernate or become inactive during the colder months.
“This discovery helps us better understand these strange crocodiles,” said Dr. Mark Young of the University of Edinburgh.
‘They quickly changed from animals that resembled modern crocodiles with a long snout, some with fins, a caudal fin and huge, forward-facing eyes.
“Their transition from terrestrial inhabitants to seafarers increasingly reflects the most well-known transformation that dolphins and whales underwent millions of years ago.”
Oxygen levels in the enamel of fossil teeth were affected by the animals’ body temperature and measuring them allowed researchers to find out if they were cold-blooded or hot-blooded.
Artistic impression of the metriorhynchid lover of the sea. The ancestors of hot-blooded crocodiles were able to maintain a higher body temperature than their surroundings: the sea
The analysis showed that metriorinophids could raise their body temperature above their environment by using their metabolism to generate heat.
While they were less efficient for warming than most other warm-blooded animals, their adaptability probably helped them survive when temperatures fell at the end of the Jurassic Period, about 150 million years ago.
On the contrary, the teleosaurs, the cold-blooded cousins, struggled to adapt but eventually survived.
The teleosaurs were cold-blooded and kept warm when sitting in the sun, in the same way as modern crocodiles.
They may have had trouble keeping warm when the sea temperature dropped, which could partly explain why so many died at the end of the Jurassic Period.
The study has been published in Philosophical Transactions of the Royal Society B.
WHAT DO WE KNOW ABOUT THE EVOLUTION OF THE COCODRILS?
Of all the reptiles alive today, crocodiles may be the least changed of their prehistoric ancestors from the late Cretaceous period, more than 65 million years ago.
However, even earlier crocodiles of the Triassic and Jurassic periods wore some characteristics clearly not similar to those of crocodiles, such as bipedal postures and vegetarian diets.
Together with the pterosaurs, the family of flying reptiles, and their terrestrial relatives, dinosaurs, crocodiles were a branch of archosaurs, the “ ruling lizards ” of the early to middle Triassic period.
The first dinosaurs and the first crocodiles looked much more like the first pterosaurs, which also evolved from the arcosaurios.
What distinguished the first crocodiles from the first dinosaurs was the shape and musculature of their jaws, which tended to be much more deadly, as well as their relatively extended limbs, unlike the straight, “locked” legs of the theropod dinosaurs .
It was only in the Mesozoic Era that crocodiles developed the three main features with which they are associated today: stubby legs; elegant and armored bodies and marine lifestyles.