Illustration by Bob Nicholls (c) 2014.
In the scientific community, art serves as a visual source of influential enlightenment, sparking the curiosity of the general public and researchers alike. The palaeoart entitled “Double Death” by Bob Nicholls depicts an exciting contest between two large theropod dinosaurs, Carcharodontosaurus saharicus, fighting over which one will get to eat a medium-sized sauropod dinosaur.
The concept for this picture originally stemmed in the late 1990s when Nicholls watched two birds jointly holding a piece of food. He then translated this idea into a dramatic piece of fleshed out digital art using dinosaurs. The dynamism in the resulting illustration prompted Dr. Donald Henderson, Curator of Dinosaurs, to ask “Could these two theropod dinosaurs REALLY lift a dinosaur almost as big as themselves and not fall over?”
To answer this question, Dr. Henderson conducted a biomechanical analysis using three-dimensional digital models to assess whether a pair of C. saharicus could successfully lift a medium-sized sauropod and not lose balance.
“I calculated how heavy each of the participants were, the two C. saharicus and the sauropod. I also had to know where their centre of weight was.”
With the body mass and centre of mass determined for the C. saharicus, it turns out that a single animal weighing six tonnes could lift two and a half tonnes and not fall over. This two and a half tonnes represents about 40% of the body weight; however, the limb bones of animals in general can easily experience forces equal to two to three times total body weight when walking or running, so the additional 40% is well within the capacity of the limbs. It would appear that two C. saharicus could, between them, lift a five-tonne dinosaur without difficulty.
This led to two more questions: “Are the neck muscles strong enough to hold up a tonne or two of weight?” and “Are the jaw muscles strong enough to hold up a tonne or two of flesh?”
Estimating the jaw and neck muscle strengths of extinct dinosaurs begins by looking at the sizes of the attachment areas of the various muscles on the fossilized bones. Estimates of the cross-sectional areas of the muscles of interest are then determined. From looking at the muscles in living backboned animals today, we can see that skeletal muscles all have about the same force generating capacity, and the total force is related to the cross-sectional areas of the muscles. Applying these observations and a known muscle tension factor, we can calculate a probable lifting/holding force for the muscles of interest.
The jaws muscles were found to be able to exert sufficient force to hold 512 kg, but the neck muscles would only have been able to support 424 kg. This leads to the neck muscles being the limiting factor, and that two C. saharicus could only lift an animal weighing about 850 kg. The apparent excess capacity of the jaw muscles suggests that a high bite force was important for puncturing and pulling apart large prey items. The large body size of C. saharicus, in comparison to the smaller holding and lifting abilities of the neck and jaws, would have provided a stable, not-easily-toppled platform for manipulating small, struggling prey items.
“The animal ended up being a little bit smaller than the one Bob had done in his illustration, but the basic idea is fine. I just used basic first-year physics to work that out.”
The research conducted by Dr. Henderson was published in the August issue of The Anatomical Record along with the scientific illustration by Bob Nicholls.
“Our ideas have changed, but we still need the artists to bring these things to life, to make them more than just a collection of bones. These were real animals that lived in a real environment.”