In 2010 I was working in Los Angeles when I met a young PhD
student from England working at Caltech named Rob Eagle.
Working with Prof John Eiler, they set up a lab to try and solve
one of the greatest mysteries of palaeontology: determining
the body temperatures of dinosaurs.
Since the revelation that birds had evolved from feathered
theropod dinosaurs, an hypothesis supported by the late 1990s
discoveries of Chinese dinosaurs with feathered bodies and
wing-like arms, the burning question had been about when
birds first acquired their warm-blooded metabolism. Did the
theropod dinosaurs have warm-blooded lifestyles well before
they evolved into birds? The functional biomechanics of their
skeletons indicated that they should have had a high metabo-
lism and were likely to be warm-blooded, as birds and mammals
are today.
To solve this problem, Eagle and Eiler developed an entirely
new approach using clumped isotope thermometry, a tech-
nique to measure the temperature that calcitic bonds form in
making organic frameworks inside bone or teeth. It works
because rare isotopes of carbon-13 and oxygen-18 in apatite, the
mineral that forms bone, bond with each other at certain temper-
atures. Measuring the degree of this “clumping” determines
the exact temperature of the environment in which the bonds
form inside bone or teeth –and thus the body temperature of
the living animal.
The control used for this work was to measure the body
temperatures of several living reptiles and see what the isotopes
predicted for their body temperatures. Calibrating this data,
Eagle applied the technique to a range of fossilised dinosaur
teeth, as enamel is less prone to contamination by other isotopes.
In 2011 they announced inSciencethat the gigantic long-necked
sauropod dinosaursBrachiosaurusandCamarasaurus
had body temperatures of 36–38°C, a range that our
human body temperature falls within (36.9°C).
Giant sauropod dinosaurs could also be warm-
blooded if they lived in a very hot world, or by virtue of
their great body mass, as larger body size retains heat
more efficiently. This kind of regulation is termed “gigan-
tothermy” and explains how large marine turtles living
in cold northern seas can have slightly higher body
temperatures than the seawater they live in, yet strictly
speaking they do not have a warm-blooded metabolism.
But the burning question about dinosaurs was really
to do with small theropod dinosaurs, which were the
precursors to modern birds. The team then turned their
attention to getting suitable specimens and testing the
materials.
They recently completed a detailed study of several
specimens of small theropod dinosaur eggshells, which
they then compared with many kinds of living birds and
their eggs. The results, published inNature Communi-
cations, showed that the theropodOviraptorformed its
eggs inside its body at around 32°C, well above the
ambient temperature of the environment they lived in,
which was found to be about 26°C based on independent
tests on fossil soil samples from the same formation.
This fulfils the prediction of palaeontological studies on
body functional mechanics, implying that the ancestors of the
first birds had quite high body temperatures but not as high as
modern flying birds. The team now aims to determine the body
temperatures of much older dinosaurs to find out how and
when warm-blooded metabolism first evolved in dinosaurs.
The same methods could also be applied to look at when high
metabolic rates first appeared in mammals and their ancestors,
the mammal-like reptiles.JAN/FEB 2016|| 43John Long is Strategic Professor in Palaeontology at Flinders University, and current
President of the Society of Vertebrate Paleontology.THE FOSSIL FILE John Long
New research has determined the precise body temperatures of
dinosaurs from the way rare isotopes clump together when bony
structures are formed.
Delving into Dinosaur Body Temperatures
New research finds that the dinosaur ancestors of birds had quite high body temperatures.