Credit: John Grady
Reading aloud Adapting to the ambient temperature or generating body heat itself - these two concepts divide today's animal world into cold and warm blooded animals: fish, amphibians and reptiles represent the so-called ectothermic creatures, mammals and birds the endotherms. But what were the dinosaurs? This question has now been answered by a team of US researchers with a "neither - nor". The researchers around John Grady from the University of New Mexico at Albuquerque assign the dinos to a new category: mesothermal creatures. That is, they were able to increase their temperature through metabolic activity but did not maintain it at a constant level like warm-blooded animals. Even a handful of extant living beings still use this concept, they report: for example, tuna or the anteater.

Like crocodile and co, dinosaurs were long regarded as clearly cold-blooded creatures. Ectothermia is definitely a tried and tested concept: Cold-blooded energy saves a lot of energy because the body heat is not generated by the body itself, but comes "free" from the outside. Of course, this system also has drawbacks: Cool conditions literally make ectothermic animals cold, and even when warm, they are not as agile as the warm-blooded. But the endothermic animals also pay a high price: they have to absorb a lot of food in order to afford their "expensive" metabolism.

In the 1960s, for the first time, "heretical" voices were heard calling into question the cold-bloodedness of the dinosaurs. Since then, the evidence in this direction increased: Studies have shown, for example, that dinosaurs grew comparatively quickly, which requires high metabolic rates, which can hardly be reconciled with cold-bloodedness. But warm-bloodedness also seemed questionable, emphasizes John Grady. According to him, enormous amounts of food would have been needed to supply the sometimes gigantic bodies of the dinosaurs. "A warm-blooded Tyrannosaurus rex should have starved to death, " said the paleontologist.

Mesothermia - a compromise

He and his colleagues have now systematically evaluated data from 381 living and extinct species - including 21 dino species. In today's living things, they recorded the growth rates and metabolic data. In the extinct species they could close the growth rate by layers in the fossil bones. They developed mathematical equations that reflect the relationship between metabolism, growth and body size.

It became clear: warm-blooded animals grow fast and have an intensive metabolism, while cold-blooded animals have significantly lower values ​​for both parameters. But there are still a handful of beings in our wildlife today that are in between: some shark species, tunas, large sea turtles and a few curious mammals like the anteater. They increase their body temperature through metabolism, but do not defend a specific body temperature, as in the case of humans 37 degrees Celsius. The researchers now call them mesothermic animals for the first time. According to her models, this category also fits the characteristics of the dinosaurs. display

According to Grady and his colleagues, mesothermia could have given the dinosaurs enormous height and agility - despite their relatively low energy consumption. So they could occupy other ecological niches than the cold-blooded reptiles, dominating the earth for millions of years. Only the prominent asteroid impact at the end of the Cretaceous period then remixed the maps of evolution and apparently played the aces to the warmbloods.

Original work of the researchers:

  • Science, doi: 10.1126 / science.1253143
© science.de - Martin Vieweg
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