Dinosaurs Were Not Cold-Blooded After All, Study Claims

The findings may change what we know about avian evolution. metha1819/Shutterstock

Dinosaurs may not have been the cold-blooded killers we once thought they were, at least in part. New research suggests that the prehistoric giants may have had the ability to regulate their body temperatures, not unlike birds of today, which could change what we know about avian evolution.

Scientists at Yale University employed a new technique known as clumped isotope paleothermometry to analyze the chemistry of dinosaur eggshells, looking specifically at the makeup of carbon and oxygen atoms in fossil eggshells. When the order of these atoms is known, researchers say they can calculate the mother’s internal temperature at the time she laid her eggs.

Fossil eggshells from between 69 and 75-million-years-old were tested, each representing three major dinosaur groups – Ornithischia, Sauropodomorpha, and Theropoda – some of which are more closely related to birds and others that are only distant cousins. Eggs from the Troodon species, a meat-eating bipedal theropod, were calculated at 38ºC, 27ºC, and 28ºC (100.4ºF, 80.6ºF, and 82.4ºF), while the duck-billed dinosaur Maiasaura clocked in at 44ºC (111ºF). Both species were from Canada. A third species from Romania, Megaloolithus, was calculated at 36ºC (nearly 97ºF).

Petrographic microscope images of dinosaur eggshell from this study. Science Advances

Modern eggshells from cold-blooded invertebrates and warm-blooded bird species were collected from the same areas in Alberta, Canada, and Romania in order to determine a baseline temperature for egg-layers in their local environments. Troodon specimens were 10ºC degrees (18ºF) warmer than their environment, the Maiasaura (not as well preserved as the other two samples) were 15ºC degrees warmer (27ºF), and the Megaloolithus samples were 3ºC and 6ºC degrees (roughly 5ºF and 11ºF) warmer.

“What we found indicates that the ability to metabolically raise their temperatures above the environment was an early, evolved trait for dinosaurs,” lead author Robin Dawson, who conducted the research as a doctoral student at Yale and is now a postdoctoral research associate at the University of Massachusetts-Amherst, said in a statement. Dawson added that the three major clades of dinosaurs were characterized by warm body temperatures, or were able to metabolically control their thermoregulation.

Preservation of the fossil carbonates may skew the results, so researchers first examined the eggshells using scanning electron microscopy to ensure that the eggshells were in roughly the same shape. The results suggest that dinosaur body size and growth rate do not necessarily indicate body temperature, as was previously believed. Furthermore, their work adds to an ongoing discussion about the evolution of birds from dinosaurs, particularly about the biological use of feathers. Previous research in 2014 suggested dinosaurs were possibly somewhere between cold- and warm-blooded creatures.

“It’s possible that dense feathers were primarily selected for insulation, as body size decreased in theropod dinosaurs on the evolutionary pathway to modern birds,” said Dawson. “Feathers could have then later been co-opted for sexual display or flying.”

A dinosaur eggshell fossil in cross-section under a microscope using cross-polarizing light. Notice the clusters of biomineralized calcite crystals radiating out from central nodes, along the interior margin of the shell at the bottom of the image. This and the bumpy surface of the exterior margin (top of image) is usually indicative of titanosaur, sauropod dinosaurs. Image credit: Robin Dawson/Science Advances

 

  

 

 

Simplified archosaur phylogeny illustrating the taxa investigated in this and previous clumped isotope studies. Science Advances

 

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