Dinosaur mechanics: how Allosaurus fed

Computed tomography has clearly proved to be a very valuable aid
to palaeobiological investigations because it has this ability to see
inside objects in an almost magical way. Some technologically
innovative ways of using CT imaging have been developed by Emily
Rayfield and colleagues, at the University of Cambridge. Using CT
images, sophisticated computer software, and a great deal of
biological and palaeobiological information, it has proved possible
to investigate how dinosaurs may have functioned as living
creatures.
As with the case of Tyrannosaurus, we know in very general terms
that Allosaurus (Figure 31) was a predatory creature and probably
fed on a range of prey living in Late Jurassic times. Sometimes
tooth marks or scratches may be found on fossil bones and these
can be quite literally lined up against the teeth in the jaws of an
allosaur as a form of ‘proof’ of the guilty party. But what does such
evidence tell us? The answer is: not as much as we might like. We
cannot be sure if the tooth marks were left by a scavenger feeding
off an already dead animal, or whether the animal that left the
tooth marks was the real killer; equally, we cannot tell what style of
predator an allosaur might have been: did it run down its prey
after a long chase, or did it lurk and pounce? Did it have a
devastating bone-crushing bite, or was it more of a cut and
slasher?

Rayfield was able to obtain CT scan data created from an
exceptionally well-preserved skull of the Late Jurassic theropod
Allosaurus. High-resolution scans of the skull were used to create
a very detailed three-dimensional image of the entire skull.
However, rather than simply creating a beautiful hologram-like
representation of the skull, Rayfield converted the image data into a
three-dimensional ‘mesh’. The mesh consisted of a series of point
coordinates (rather like the coordinates on a topographic map),
each point was linked to its immediate neighbours by short
‘elements’. This created what in engineering terms is known as
a finite element map of the entire skull (Figure 38): nothing quite
as complicated as this had ever been attempted before.

Having mapped the virtual skull of this dinosaur, it was then
necessary to work out how powerful its jaw muscles were in life.
Using clay, Rayfield was able to quite literally model the jaw muscles
of this dinosaur. Once she had done this, she was able to calculate
from their dimensions – their length, girth, and angle of attachment
to the jaw bones – the amount of force that they could generate.
To ensure that these calculations were as realistic as possible,
two sets of force estimates were generated: one based on the
view that dinosaurs like this one had a rather crocodile-like
(ectotherm) physiology, the other assumed an avian/mammalian
(endotherm) physiology.
Using these sets of data, it was then possible to superimpose these
forces on the finite element model of the Allosaurus skull and
quite literally ‘test’ how the skull would respond to maximum bite
forces, and how these would be distributed within the skull. The
experiments were intended to probe the construction and shape of
the skull, and the way it responded to stresses associated with
feeding.
What emerged was fascinating. The skull was extraordinarily strong
(despite all the large holes over its surface that might be thought to
have weakened it significantly). In fact, the holes proved to be an
important part of the strength of the skull. When the virtual skull
was tested until it began to ‘yield’ (that is to say, it was subjected to
forces that were beginning to fracture its bones), it was found to
be capable of withstanding up to 24 times the force that the jaw
muscles could exert when they were biting as hard as ‘allosaurianly’
possible.