Jaws of predatory dinosaurs grew stronger as they evolved

Go to any natural history museum, watch any dinosaur movie, and undoubtedly the big bad will be a theropod. This terrifying, exceptionally toothy group includes Tyrannosaurus, Velociraptor, Allosaurus, and many others. Paleontologists are finally unraveling how the murderous jaws of these predatory dinosaurs evolved.

A new study, published in the journal Current Biology looked at the lower jaws of over 40 theropod dinosaur species. While the most well-known theropods are big and toothy, they also came in many shapes and sizes. Some were small, and some were, in fact, toothless. 

By running the different jaws through computer modeling to test their strength, the researchers found that over the course of their evolution, theropod jaws grew progressively stronger. The predatory dinosaurs expanded the rear, or posterior, portion of their jaws (sideways or laterally), and the mechanical strength increased over the course of their over 100-million year history. 

“Although theropod dinosaurs are always depicted as fearsome predators in popular culture, they are in fact very diverse in terms of diets. It is interesting to observe the jaws becoming structurally stronger over time, in both carnivores and herbivores. This gives them the capacity to exploit a wider range of food items,” explained study lead author Dr. Fion Waisum Ma of the University of Birmingham.

“Theropod dinosaurs underwent extreme dietary changes during their evolutionary history of 165 million years. They started off as carnivores, later on evolved into more specialized carnivores, omnivores and herbivores. Studying how their feeding mechanics changed is key to understanding the dietary transitions in other vertebrate animals too.”

While it makes sense that the hypercarnivorous meat-eaters would increase their lower-jaw strength, the herbivorous lineages also developed stronger jaws. 

“It is fascinating to see how theropod dinosaurs had evolved different strategies to increase jaw stability depending on their diet,” said study co-author Dr. Stephan Lautenschlager. “This was achieved through bone remodeling – a mechanism where bone is deposited in regions of the jaw that experience high stresses during feeding.” 

This evolutionary pattern is reflected in the ontogeny, or growth, of the individual animals. For example, juvenile tyrannosaurs possessed proportionally slimmer and downturned jaws compared to adult individuals. 

“The similarity between jaw strengthening through growth and through time suggests that developmental patterns in juvenile dinosaurs ultimately affected the evolution of the whole group,” concluded Dr. Lautenschlager  “This likely facilitated the jaw evolution of theropod dinosaurs and their overall success for over 150 million years.”

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By Alex Ruger, Earth.com Staff Writer