Were dinosaurs hot blooded or cold blooded?

2014-06-13 10:35


Multimedia   ·   User Galleries   ·   News in Pictures Send us your pictures  ·  Send us your stories

Washington - The hot question of whether dinosaurs were warm-blooded, like birds and mammals or cold blooded like reptiles, fish and amphibians finally has a good answer.

Dinosaurs, for eons Earth's dominant land animals until being wiped out by an asteroid 65 million years ago, were in fact somewhere in between.

Scientists said on Thursday they evaluated the metabolism of numerous dinosaurs using a formula based on their body mass as revealed by the bulk of their thigh bones and their growth rates as shown by growth rings in fossil bones akin to those in trees.

The study, published in the journal Science, assessed 21 species of dinosaurs including super predators Tyrannosaurus and Allosaurus, long-necked Apatosaurus, duckbilled Tenontosaurus and bird-like Troodon as well as a range of mammals, birds, bony fish, sharks, lizards, snakes and crocodiles.

A debate

"Our results showed that dinosaurs had growth and metabolic rates that were actually not characteristic of warm-blooded or even cold-blooded organisms. They did not act like mammals or birds nor did they act like reptiles or fish”, said University of Arizona evolutionary biologist and ecologist Brian Enquist.

"Instead, they had growth rates and metabolisms intermediate to warm-blooded and cold-blooded organisms of today. In short, they had physiologies that are not common in today's world."

There has been a long-standing debate about whether dinosaurs were slow, lumbering cold-blooded animals, as scientists first proposed in the 19th century or had a uniquely advanced, more warm-blooded physiology.

As scientists unearthed remains of more and more fast-looking dinosaurs like Velociraptor, some championed the idea dinosaurs were as active and warm–blooded as mammals and birds. The realisation that birds arose from small feathered dinosaurs seemed to support that view.

University of New Mexico biologist John Grady said the idea that creatures must be either warm-blooded or cold-blooded is too simplistic when looking over the vast expanse of time.

Like dinosaurs, some animals alive today like the great white shark, leatherback sea turtle and tuna do not fit easily into either category, Grady added.

"A better answer would be 'in the middle'. By examining animal growth and rates of energy use, we were able to reconstruct a metabolic continuum, and place dinosaurs along that continuum. Somewhat surprisingly, dinosaurs fell right in the middle", Grady said.

The researchers called creatures with this medium-powered metabolism mesotherms, as contrasted to ectotherms (cold–blooded animals with low metabolic rates that do not produce much heat and bask in the sun to warm up) and endotherms (warm–blooded animals that use heat from metabolic reactions to maintain a high, stable body temperature).

Grady said an intermediate metabolism may have allowed dinosaurs to get much bigger than any mammal ever could. Warm–blooded animals need to eat a lot so they are frequently hunting or munching on plants. "It is doubtful that a lion the size of T rex could eat enough to survive", Grady said.
Read more on:    us  |  animals  |  research  |  paleontology

Join the conversation!

24.com encourages commentary submitted via MyNews24. Contributions of 200 words or more will be considered for publication.

We reserve editorial discretion to decide what will be published.
Read our comments policy for guidelines on contributions.

24.com publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.

Comment on this story
1 comment
Comments have been closed for this article.

Inside News24


Book flights

Compare, Book, Fly

Traffic Alerts
There are new stories on the homepage. Click here to see them.


Create Profile

Creating your profile will enable you to submit photos and stories to get published on News24.

Please provide a username for your profile page:

This username must be unique, cannot be edited and will be used in the URL to your profile page across the entire 24.com network.


Location Settings

News24 allows you to edit the display of certain components based on a location. If you wish to personalise the page based on your preferences, please select a location for each component and click "Submit" in order for the changes to take affect.

Facebook Sign-In

Hi News addict,

Join the News24 Community to be involved in breaking the news.

Log in with Facebook to comment and personalise news, weather and listings.