Which Dinosaurs Were Warm Blooded or Cold Blooded?

In summary, the research group found indications that some dinosaurs were warm blooded (endothermic), while others (Stegosauri and Triceratops) were apparently reverted to being cold blooded (ectothermic). Additionally, it seems that the flying non-avian reptiles were also warm blooded.
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In another well directed chemical analysis of fossils, a research group has indications that some but not all dinosaurs were warm blooded (endothermic), although some (Stegosauri and Triceratops) had apparently reverted to being cold blooded (ectothermic). In addition, it seems that the flying non-avian reptiles were also warm blooded.
They did this by testing sections of fossilized femurs in a variety of known and extinct animals (all were amniotes, animals with eggs protected by a shell that could be laid on land (amphibians are not amniotes)) and determined the relative amounts of metabolic lipoxidation signals using in situ Raman and Fourier-transform infrared spectroscopy. The amounts of these chemicals are expected to reflect the warm or cold blooded state of the animals. This was confirmed by examining fossils of extent (still around) animals.
This paper is open access and available here.

Here is their phylogenetic diagram summarizing their findings:

Screen Shot 2022-05-25 at 5.28.13 PM.png

How to read the phylogenetic diagram:
  • Time goes left to right (scale at the bottom).
  • Color of the lines in the phylogeny are colored (temp. scale upper left)
  • Lines that go all the way to the right are still alive. Those ending more to the left are extinct.
  • Changes in the temperature trait are indicated by small circles on the lines of the phylogenetic diagram (yellow: transitioning cold to warm blooded, blue: transitioning warm to cold blooded).
  • Birds are at the top and branch off from the dinosaurs near the raptors (Deinonychous).
  • Hadrosaur = the group of duck billed dinosaurs (more cold blooded than their close relatives).
  • The flying non-avian reptiles (Pterodons (they are in Jurassic world for example) and Phanphorhinchoid) branch off from pre-dinosaurs just before they become dinosaurs. they are warm blooded.
  • Plesioaurs (long necked large aquatic reptiles with paddle-like feet) were somewhat warm blooded. Not sure where mososaurs (large whale-like extreme carnovores, also in Jurassic world) would fit in. Maybe they were not tested.
Its thought that being warm blooded would provide a more sustained higher rate of metabolism, which would have some advantages.
On the other hand, its not entirely clear why some of them would switch back to being cold blooded, but being warm blooded continuously requires a lot of energy (unless hibernating like some mammals can do).
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If you're a carnivore / omnivore, being warm blooded is a big advantage in a world full of cold-blooded stuff: You can simply ... graze on them when they're down at night or in the winter. Ask e.g. the hedgehog...

Re. reverting: Obviously, when you're living in a constantly warm environment, like equatorial rainforest, or subtropical forests (not deserts - those get really cold at night), the "warm-bloodedness" advantage disappears, so keeping the metabolic rate as low as possible becomes advantageous again.

What is the difference between warm-blooded and cold-blooded dinosaurs?

The main difference between warm-blooded and cold-blooded dinosaurs is how they regulate their body temperature. Warm-blooded dinosaurs, also known as endothermic dinosaurs, have the ability to generate their own body heat and maintain a constant internal temperature. Cold-blooded dinosaurs, also known as ectothermic dinosaurs, rely on external sources of heat to regulate their body temperature.

How do scientists determine if a dinosaur was warm-blooded or cold-blooded?

Scientists use various methods to determine whether a dinosaur was warm-blooded or cold-blooded. One way is by studying the structure of their bones. Warm-blooded dinosaurs tend to have thicker bones with well-developed blood vessels, while cold-blooded dinosaurs have thinner bones with less blood flow. Another method is by analyzing the growth rings in their bones, which can indicate their metabolic rate.

Were all dinosaurs either warm-blooded or cold-blooded?

No, there is evidence that some dinosaurs may have had a mix of warm-blooded and cold-blooded characteristics. This is known as mesothermy, where the dinosaur has the ability to regulate its body temperature to some extent, but not as efficiently as a fully warm-blooded animal. This theory is still being studied and debated among scientists.

Did all warm-blooded dinosaurs have feathers?

No, not all warm-blooded dinosaurs had feathers. While many smaller theropod dinosaurs, such as Velociraptor and T. rex, are believed to have had feathers, larger herbivorous dinosaurs like Triceratops and Stegosaurus are thought to have had scales. Feathers may have evolved as a form of insulation for smaller dinosaurs, while larger dinosaurs had other methods of regulating their body temperature.

Do we have evidence of warm-blooded and cold-blooded dinosaurs living in the same environments?

Yes, scientists have found evidence of both warm-blooded and cold-blooded dinosaurs living in the same environments. For example, fossilized remains of warm-blooded raptors and cold-blooded sauropods have been found in the same locations in China. This suggests that different types of dinosaurs may have coexisted in the same habitats, each with their own unique adaptations for regulating body temperature.

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