An article in the journal “Nature Communications” describes a study of fossilized eggs of various species of dinosaurs which allowed to infer their body temperature. A team of scientists from UCLA obtained different results and concluded that some dinosaurs were warm-blooded while others had a limited ability to control their temperature, halfway between reptiles and birds.

The problem of the dinosaurs’ body temperature has been debated for a long time. Until a few decades ago, dinosaurs were generally considered to be similar to reptiles and therefore cold blooded (ectotherms) but in the ’70 research started that, based on new findings and analyzes, radically changed this vision.

This new research by a team led by Robert Eagle is based on the analysis of eggs of various dinosaurs including 3 from Argentina and 3 from Mongolia. It’s based on the chemical composition of their shell, from which it’s possible to determine the temperature at which it formed and therefore the temperature of the females that laid them.

The eggs from Argentina belong to a species of sauropod titanosaurs, huge long-necked animals that lived around 80 million years ago. Those coming from the Gobi Desert in Mongolia belong instead to oviraptorid theropods such as the Citipati osmolskae (photo ©Eduard Solà) that lived between 71 and 75 million years ago, dinosaurs much smaller that were relatives of the T. rex but also of birds.

Spectroscopic analysis of the isotopic composition of the egg shell focused in particular on the relationship between the isotopes of oxygen and carbon. The result is that different species of dinosaurs showed they had a different body temperature.

The sauropods titanosaur had a temperature between 37.6° C (99.6° F) and 39.6° C (103.3° F), therefore similar to that of mammals. However, this doesn’t necessarily mean that they were warm-blooded (endothermic) because it’s possible that their large size allowed them to accumulate heat as it happens in some large turtles living today.

The oviraptorids had a lower body temperature, around 32° C (almost 90° F) with differences among the various species. Those are temperatures too low for them to be endotherms were too for them to be ectotherms. It’s possible that they produced a certain amount of internal heat but not as much as birds. Being at least partially endotherms mean that the oviraptorids had an ability to move around to search for food superior to that of modern animals such as alligators.

Robert Eagle and his colleagues had already published the results of an analysis of fossilized dinosaur teeth 2011. The chemical study of the teeth of sauropods titanosaurs indicated that their body temperature was between 35° C (95° F) and 37.7° C (100.5° F). Those are results similar to those of the new research, which also provides idication on oviraptorids’ body temperature.