As snakes slither along, friction with the ground quite naturally causes
a charge to build up on their bodies. It is a phenomenon familiar to anyone
who has shuffled across a carpet on a dry day, then felt a static discharge
after touching a filing cabinet or other metal object.

Snakes, however, retain this static electricity to a degree that other
animals do not. This is because they have dry, highly insulating skin and
lack the hairs, feathers, spines and bristles that other creatures possess
and which help them to shed the static build-up.

Vonstille suggests that the rattle of the rattlesnake generates static
for electro-location (Nature, vol 370, p 184). He carried out experiments
with rattles cut from snakes which had been killed in road accidents. He
attached the rattles to a vibrating nylon rod and a coil of wire supported
by a plastic strip. He placed a voltmeter next to the strip.

Vonstille detected no voltage when the set-up was at rest. However,
when he shook the rattles 60 times a second, he created a voltage difference
of 75 to 100 volts between the rattle and the ground.

The usual explanation for the rattler’s rattle is that the sound warns
big animals, such as bison or humans, not to step on the snake. However,
Vonstille believes that such avoidance of injury is merely a spin-off. He
points out that the rattles of juveniles and smaller rattler species do
not make a noise when shaken. However, snake researcher Kurt Schwenk of
the University of Connecticut points out that certain rattleless snakes
quiver their tails to deter intruders.

Vonstille’s hypothesis is that rattlesnakes and other snakes use the
static electricity they generate to locate sources of moist air in the environment.
Plumes of moist air, whether from a sheltered hole or an exhaling prairie
dog, pick up an electric charge from the ground.

When a snake is exploring, it waves its tongue backwards and forwards.
The slender tips of its tongue will be repelled or attracted, depending
on the nature of the environmental charges they encounter. Vonstille suggests
that there may be receptor cells that detect these pushing and pulling movements.

Reece Barrick and William Showers of North Carolina State University
made their estimates by analysing the ratio of oxygen isotopes in the fossilised
bone. They found that the dinosaur had a fairly uniform body temperature,
like a modern bird or mammal, and their result has rekindled the long and
bitter row over whether dinosaurs were warm-blooded or cold-blooded.

The debate began 25 years ago, when John Ostrom of Yale University suggested
that dinosaurs might not be the sluggish, cold-blooded behemoths that everyone
imagined. He claimed that a small predatory dinosaur called Deinonychus,
a relative of the raptors made famous in Jurassic Park, was built for an
active and fast-moving life; in other words, it was more avian or mammalian
than reptilian. Since then, other lines of evidence have been used to argue
that dinosaurs are warm-blooded, but this line of reasoning remains controversial.

Barrick and Showers measured the relative ratios of the isotopes oxygen-16
and oxygen-18 in the phosphate from 54 samples of a near-complete T. rex
skeleton. From these measurements they calculated which parts were warmest.
The technique works on the principle that the cooler the bone when it formed,
the more oxygen-18 there was relative to oxygen-16. Atoms of oxygen-18
are heavier than those of oxygen-16. As phosphate precipitates from the
body’s fluid, the weightier, less energetic oxygen-18 is preferentially
trapped in the solid mineral.

The technique cannot reveal absolute body temperatures because the water
the animal drank also affects the isotope ratios in the bone. Showers says
that their Tyrannosaurus was evenly heated (Science, 8 July, p 222). ‘The
T. rex had less than 4 degreeC overall body temperature variation,’ he
reports. ‘Its feet were a little bit colder than its body core, and the
base of the tail was a little warmer than its end.’

This is the pattern found in large birds and mammals, whose bodies keep
themselves at a constant temperature. Cold-blooded animals such as monitor
lizards rely on heat from their surroundings to regulate their temperature,
so the temperature of their extremities fluctuates much more than their
main body parts.

Some scientists are sceptical of the isotope work. Yehoshua Kolodny
at the Hebrew University in Jerusalem doubts whether the isotopic make-up
of the T. rex skeleton is the same as it was when the animal was alive.
However, Showers says the skeleton is particularly well preserved. Found
in Montana in 1990, it has been de-scribed by its excavator, Jack Horner,
as ‘mummified’. It is the same skeleton from which red blood cells are rumoured
to have been extracted. Showers says that comparisons of isotope signatures
in the bone carbonate with after-burial calcite deposits points to the isotope
ratios that he used to calculate temperature being those from life.

Showers and Barrick’s interpretations of the isotope data are also controversial.
‘If it had a physiology like modern animals we would then say that this
animal was warm-blooded like a bird or mammal,’ says Showers. ‘The problem
is there are no living analogues to compare it with. It’s possible dinoasurs
had evolved physiologies that no living animals have today.’