• mattbonnan

Why I use X-rays and live animals to understand dinosaurs and other fossil animals

Updated: Jun 5

It is wonderful to be a paleontologist in the 21st century!

I am interested in dinosaur locomotion, and in particular the forelimbs because dinosaurs used them for a whole variety of purposes: support and movement in quadrupeds, and prey capture, grasping, and flight in the bipeds. Dinosaur skeletons are often missing a lot of the soft tissues such as cartilage, ligaments, and muscles that dictate how limbs move. I am also interested in how the ancestors of dinosaurs and mammals changed from a sprawling, lizard-like posture to a more upright posture. So as a paleontologist you often turn to living relatives of the fossil animals you study to make predictions about their movements.

Since the ancestors of dinosaurs and mammals were small animals, it is useful to study the locomotion of small, living model animals. That is why my colleagues and I have published on rat forelimb movements (a model for early placental mammals that you and I descended from) and why my colleagues and I are currently preparing studies on lizards (a model for the early ancestors of the animals that gave rise to the dinosaurs) and birds (a model for the movements of small predatory dinosaurs).

Above is my XROMM lab at Stockton University. On the left is the CT scanner that takes stacks of X-rays of an animal and combines them into 3-D models of the bones. On the right is a trackway and the videofluoroscopes that take the calibrated X-ray movies of the animals (in this case bearded dragon lizards).

In my lab, I am able to non-invasively study how the limb bones of living, small animals work using a technique called XROMM (X-ray Reconstruction of Moving Morphology). Briefly, XROMM creates three-dimensional animations of the skeleton by registering (matching) bone models of living animals against calibrated cineradiographic (X-ray) videos of their movements. Because the resulting animations are reconstructed in real world space, movements of and between bones can be used to illuminate skeletal range of movement in a living animal.

Below, the track and videofluoroscope set up my colleagues, students, and I used at the XROMM lab at Stockton University (left). A closeup of one our lizards on the trackway preparing for his see-through debut (right).

Above, XROMM of domestic rat forelimbs from our 2016 study.

The idea here is that because form follows function, we can begin associated bone shape with range of movement. In other words, fossil mammals and reptiles with bone shapes similar to those of modern mammals and reptiles are likely to have had similar ranges of motion and we can therefore begin to narrow down the likely ways dinosaurs and other fossil animals used their limbs.

If you are a prospective student, have a GPA above 3.0, and are interested in participating in XROMM research, contact me!

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