DINOSAURS IN MOTION
What are some major questions associated with the movement of dinosaurs?
When paleontologists study the movement of dinosaurs, the most prevalent questions concern the postures that dinosaurs typically adopted, their speed of movement, both normal and maximum, and any hunting or herding behavior.
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.
What is an important factor in determining the probable motion of dinosaurs?
One of the most important factors in determining the probable motion of dinosaurs is their posture. Without an accurate knowledge of the animals postures, their motion whether obtained through the use of homologies, analogies, trackways, or a combination of these can be misleading or downright wrong.
By analyzing anatomy and footprint fossils, and by drawing comparisons with todays animals, scientists have made various hypotheses on how dinosaurs like this Deinonychus antinhopus may have moved (Big Stock Photo).
From the evidence of footprints, dinosaurs had an erect (or upright) posture, with their limbs directly under their bodies. This structure resulted in a motion similar to modern mammals, with the limbs held out to the sides and the upper bones nearly parallel to the ground. Surprisingly, this posture was more similar to modern mammals than lizards, which have a sprawling posture.
But there were also variations within this erect posture, leading to some very unique movements. Some dinosaurs were bipedal, walking only on their hind limbs; others were quadrupeds, walking on all four limbs. Other dinosaurs spent most of their time on all fours, but were capable of standing on their hind limbs. Still others reversed this action, spending most of their time on two hind limbs, but capable of moving on all fours. In the end, each had a distinct motion and behavior based on its respective posture.
