Natural Science Forum / Biology / Paleontology / June 2006

Earth and Planetary Science Letters, 246 (1-2): 41-54 (15 June 2006).

Oxygen isotopes from biogenic apatites suggest widespread endothermy in
Cretaceous dinosaurs

Romain Amiot, Christophe Lécuyer, Eric Buffetaut, Gilles Escarguel,
Fédéric Fluteau and François Martineau

Abstract. The much debated question of dinosaur thermophysiology has not
yet been conclusively solved despite numerous attempts. We used the
temperature-dependent oxygen isotope fractionation between vertebrate
body water (d18Obody water) and phosphatic tissues (d18Op) to compare
the thermophysiology of dinosaurs with that of non-dinosaurian
ectothermic reptiles. Present-day d18Op values of vertebrate apatites
show that ectotherms have higher d18Op values than endotherms at high
latitudes due to their lower body temperature, and conversely lower
d18Op values than endotherms at low latitudes. Using a data set of 80
new and 49 published d18Op values, we observed similar and systematic
differences in d18Op values (D18O) between four groups of Cretaceous
dinosaurs (theropods, sauropods, ornithopods and ceratopsians) and
associated fresh water crocodiles and turtles. Expressed in terms of
body temperatures (Tb), these D18O values indicate that dinosaurs
maintained rather constant Tb in the range of endotherms whatever
ambient temperatures were. This implies that high metabolic rates were
widespread among Cretaceous dinosaurs belonging to widely different
taxonomic groups and suggest that endothermy may be a synapomorphy of
dinosaurs, or may have been acquired convergently in the studied taxa.

Comment. The c. 40 studied dinosaurian species are Iguanodontidae,
Hadrosauridae, Ceratopsidae, Titanosauria, Ceratosauria, Spinosauroidea,
Tyrannosauroidea, and Dromaeosauridae. Independtly of their body size,
dietary, and living paleolatitude and continent (studied species come
from North America, Europe, Asia and Africa and are in the range [0-70°]
in paleolatitude), they all return D18O-values corresponding to body
temperatures of 37°c (95% Confidence Interval: +/- 2°c).

Gilles.