© C. Lécuyer, R. Amiot, lab. Paléoenvironnements et paléobiosphère Scanning electronic microscopy (x400) of AgPO4 crystals obtained from a tooth of the dinosaur Spinosaurus.
© C. Lécuyer, R. Amiot, lab. Paléoenvironnements et paléobiosphère
Scanning electronic microscopy (x400) of AgPO4 crystals obtained from a tooth of the dinosaur Spinosaurus.
Were dinosaurs cold-blooded (ectothermic) reptiles or warm-blooded (endothermic), like birds and mammals? A study1 by CNRS researchers answers the much debated question of the thermophysiology of these animals who disappeared 65 million years ago. Teams of geophysicists,2 paleontologists, and geochemists,3 pooled their skills. “This approach allowed us to focus on the question without forgetting the geochemical or biological issues,” explains paleontologist Eric Buffetaut.
To investigate the matter they used a natural thermometer: oxygen isotope fractionation. The oxygen present in the hard tissues of the organism exists in various isotopic forms and is mainly derived from water that the animal either drinks or takes in by eating. It is then incorporated into the organism's hard tissues (bones and teeth) in a phosphate form. The composition of the different oxygen forms (isotopes) depends on the animal's temperature at the time of this incorporation. The best place to look for this oxygen signature is in tooth enamel. Present-day studies of vertebrate teeth demonstrate that ectotherms and endotherms have different isotope compositions even if they live in the same location and drink from the same water source. Therefore, researchers looked at fossil teeth of dinosaurs, including very small theropods, small ornithopods, and large theropods and sauropods, all living during the Late Cretaceous (-100 to -65 million years) period. They compared the isotope contents with those of turtles and crocodiles from the same fossil sites.
“The quantitative results show that endothermy was widespread among dinosaurs, at least in the Late Cretaceous,” concludes Buffetaut. A finding that's significant for theorizing dinosaurs' demise. “The global cooling hypothesis as the reason for their extinction cannot be correct,” argues the paleontologist. “Being warm-blooded, they should have survived.” The hypothesis of a meteoritic impact that darkened the sky, causing the decline of plants, is more realistic. “The herbivorous dinosaurs needed plants in great quantity to live and carnivorous dinosaurs needed lots of herbivores!” This finding also explains why dinosaurs had such evolutionary success. Thanks to their more advanced physiology (endothermy) they could sustain a higher level of activity. It turns out that a dinosaur is something more than a “terrible lizard” (in Greek deinos: terrible and sauros: lizard).
This work was supported by the ECLIPSE and ECLIPSE 2 programs of CNRS and by the Jurassic foundation.
1. R. Amiot, et. al., “Oxygen isotopes from biogenic apatites suggest widespread endothermy in Cretaceous dinosaurs,” Earth Planet. Sci. Lett. 246: 41-54. 2006.
2. Laboratoire de Paléomagnétisme (CNRS/ Institut de Physique du Globe joint lab)
3. Laboratoire Paléoenvironnements et paléobiosphère (CNRS / Université Claude Bernard Lyon-1 joint lab).
Paléoenvironnements et paléobiosphère, Lyon.