Tyrannosaurus rex, the king of the dinosaurs, is commonly shortened to T. rex. It was one of the best known of the dinosaurs, a meat eater approaching the mass of an elephant with the killing instinct of a tiger.
Perhaps the best description of what this dinosaur might have been like comes from
one of the world’s leading palaeontologists, Professor Robert Bakker, who is widely
credited with the dinosaur renaissance of fast active dinosaurs. In his book, The
Dinosaur Heresies, he described why he believes that T. rex was a fast and agile
hunter. The legs were built for speed with massive muscles capable of propelling
T. rex forward at great speed. The lung and heart cavities were large to enable him
to pump the blood and oxygen required by his massive leg muscles.
Unfortunately, in complete contrast to this renaissance of a fast T. rex, various
studies of the leg muscles and bones of T. rex show it would struggle to run at all
in our present gravity.
The paradox of an animal that looks like it could run but can’t in our present gravity
is resolved once we realise that it evolved to run in a reduced palaeogravity, the
ancient surface gravity on the earth. This would have enabled this elephant sized
animal to be a fast hunter.
One fundamental technique to quantify palaeogravity is to compute weight against
mass estimates of ancient animals. This technique has been applied to four specimens
of T. rex, representing some of the most complete theropod dinosaur skeletons known.
The results using T. rex and a range of other life indicate that they lived in a
reduced palaeogravity of about 0.63g at 67 million years ago.