How trace fossils revealed T. Rex's surprisingly sluggish top speed
All we have are fossils and footprints, so how do we know how dinosaurs moved?
Tyrannosaurus rex lived 66 million years ago and no human has ever seen one alive. How do we know how it – or any other long-extinct dinosaur – moved? This is part of a larger question in palaeontology: how do we understand the behaviours of extinct species? In general, we rely on information from fossils, tests using computer modelling, and comparisons to modern-day animals, especially birds (the descendants of dinosaurs) and crocodiles (the closest living cousins to dinosaurs).
Fossils can tell us certain things about dinosaur movement. Simply by looking at a skeleton, we can grasp the basics of whether the dinosaur walked on all fours, or only on its hind legs. Skeletons can also give us an indication of whether a dinosaur was likely to be slow or plodding, based on how robust the bones are and how the limbs are held.
Even more accurate information comes from a different type of fossil: trace fossils. These are the records dinosaurs left behind, like footprints and handprints. The spacing between successive footprints can tell us how fast a dinosaur was walking or running, using a basic mathematical formula developed by studying modern animals.
The gist of it is this: if you’re walking slowly on a beach there’ll be small spaces in between your footprints in the sand, but if you’re running then the tracks you leave behind will be spread much farther apart.
More recently, palaeontologists have turned to computer modelling to understand dinosaur locomotion. We can use computer-assisted tomography (CAT) or laser scans to build an accurate model of a dinosaur skeleton, digitally add the flesh, muscle and other soft tissues based on comparisons to modern animals, and then use animation software to test whether certain speeds, body postures and running styles were possible. This type of work, for example, reveals that T. rex was far too large and bulky to run faster than about 10mph (16km/h).
- Did T. Rex actually have feathers?
- How do we know what dinosaurs looked like?
- What was the first dinosaur?
- When did dinosaurs become birds?
Asked by: Gary, via email
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Steve is a professor and palaeontologist at the University of Edinburgh and the author of the book The Rise And Reign Of The Mammals (£20, Picador), a 325-million-year odyssey of mammalian evolution and the people who study mammal fossils.
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