Dinosaurs in Motion
What evidence do we have concerning the movement of dinosaurs?
There are three main sources of evidence that help us to understand the movement of dinosaurs: homologies, analogies, and footprints.
Homologies are comparisons in the anatomical structures in organisms derived from the same such structures in a common ancestor. Because the vast majority of evidence we have about dinosaurs are their bones, the reconstruction of the skeleton and muscles can be very useful in helping to understand their movement. To make these reconstructions as accurate as possible, scientists use modern homologues. Unfortunately, the closest relations to the dinosaurs, such as the birds and crocodiles, have all evolved highly modified structures, making a direct comparison to the dinosaurs very unreliable.
In addition to homologies, scientists can observe the movement of modern animals with similar structures and probable behaviors (analogies). For example, the probable motion of ornithomimids is based on that of the ostrich because this modern bird has a similar structure; the movement of the large sauropods is modeled on that of modern elephants. But these analogies are only as good as the similar structure the scientist is examining. Unfortunately again, it may not be truly representative of the actual motion or behavior of the dinosaur. In other words, ostriches are not theropod dinosaurs, and elephants are not sauropods.
The third and most direct evidence for dinosaur movement is the trace fossils of footprints. These records give us a wealth of clues about the speed, gait, posture, and sometimes behavior of these long-dead animals. From the inferred motion represented by these footprints, paleontologists can sometimes obtain evidence of the animals’ behavior. For example, the lack of tail drag marks shows a dinosaur with an erect posture; some trackways show that certain dinosaurs exhibited a herding behavior.