The Western Interior Seaway, which existed roughly 80 million years ago, split North America into North and South. It was a warm, shallow sea teeming with life from the Arctic Ocean to the Gulf of Mexico. Fish, squid, and marine reptiles—the lizards that hunted them—inhabited this bountiful marine desert.
Some of these predators included large-bodied, or sometimes giant-sized, mosasaurs. These semi-aquatic reptiles re-evolved to live in the ocean, along with long-necked polycotylids. To date, how did so many large predators exist and thrive in the same aquatic space without exhausting their food supply?
This has been the focus of an international research collaboration, yet only now is there a comprehensive biomechanical answer based on recent 3D scanning, engineering simulation, and experimentation. The results provide clear evidence of the biomechanical differences between mosasaurs and polycotylids. These distinct physiological configurations represent distinct ecologies and prey types rather than direct competitors.
This biomechanical analysis utilized several different methods from finite element analysis, an established numerical method within structural engineering. In finite element analysis, when an engineer needs to determine how a component, such as a bridge or aircraft part, reacts to various stresses, the engineer produces a digital model of the object. Simulated loading conditions are then applied in order to observe where deformations occur in the product.
The same methodology applies to how bone responds to loading, stressing, and deformation. A digital jaw was subjected to a realistic bite force simulation. This enabled researchers to see where stress points developed, how quickly and efficiently the jaw delivers force to prey, and how much energy is absorbed by the jawbone before any risk of breaking occurs.
Previous research on marine reptiles’ feeding ecology was primarily based on tooth shape. This indicates what and how much the animal was physically capable of eating. Stable isotope ratios and bite marks then provide evidence related to the animal’s diet. Through finite element analysis, researchers were able to obtain another type of evidence. This evidence indicates how well the skeletons of marine reptiles mechanically performed.
Francesco Della Giustina, lead author of this study and a paleontologist at the EDDy Lab at the University of Liège, stated: “The mechanical performance of the skull is an excellent way to better understand the ecological roles of these animals. The ability to perform analysis and tests in a virtual setting are now possible, which would have otherwise not been available from the fossil record.”
The researchers surface scanned the skulls and jaws of 16 taxa that lived in North America during the Late Cretaceous. They generated models with a maximum of 10 million individual elements across 13 species of mosasaurs and 3 species of polycotylid plesiosaurs.
The muscles that would have attached to the jaw were reconstructed using both attachment scars found on the fossils and evidence collected through comparisons with living relatives. Biomechanical formulas were then used to estimate the forces generated by those muscles. The same process of creating digital jaws and recording mechanical responses took place using two positions along the tooth row of each animal. It also included two different gape angles.
The findings provided a clear distinction between the two groups of reptiles. Polycotylid plesiosaurs have longer, thinner snouts. They also have needle-like teeth, which are designed to effectively pierce prey. The mechanical analysis of their jaw structure indicates that most of the energy produced by the jaw muscles is not transferred to the prey. Additionally, their jaws absorbed more energy during the bite than those of other reptiles. This suggests that these jaws possess greater flexibility but are weaker under stress.
The area of the joint between the two halves of the lower jaw, called the mandibular symphysis, was relatively strong and able to withstand stress. However, it was also the area where the plesiosaur was most vulnerable. The mechanics of the jaws are supported by fossils, which suggest that the needle-like teeth were used primarily for catching soft-bodied creatures.
Fish remains are known from at least one specimen of Dolichorhynchops. The long, narrow snouts of these creatures allowed them to catch quick, small prey. However, this design imposed trade-offs. A jaw that is designed to snap quickly will be less effective at restraining large, hard, or struggling prey.
Mosasaurs represent the other end of the spectrum. Their jaws create significantly greater amounts of force at the point of bite than is produced by the jaw muscle input. Additionally, mosasaur jaws show less internal energy absorption during bites. This indicates that their jawbones had greater resistance to deformation than those of polycotylid plesiosaurs.
One of the key structural differences involves the coronoid process. This is a tall bony projection located posterior to the alveolar ridge and serves as the primary point of muscle attachment for the jaw. The lengthening of the coronoid process enables a much greater lever arm for the muscle. This increases the mechanical advantage of muscle contractions. The robust skeletal geometry of mosasaur skulls and large attachment areas for jaw muscles created a greater distribution of stress throughout the jaw. This reduced the likelihood of concentrated stress points.
“All ecosystems, including underwater systems, have limited food resources for their apex predators,” said Francesco Della Giustina. “The fact that we see multiple large predators co-existing in the same region in North America from the Cretaceous period indicates that these predators filled different niches. Rather than having direct competition, they would have different prey items that they travelled to forage for.”
The amount of diversity within mosasaurs is also noteworthy. The data showed a wide range of bite performance across the 13 species included in the study. This supports the hypothesis that there were large differences in skull morphology, body size, and tooth shape.
Two examples of this relationship are Mosasaurus hoffmanni and Tylosaurus proriger. Both species are over 10 meters long and had the highest simulated bite force in the dataset. They also showed the best ratio of mechanical efficiency to mechanical stress. Data from preserved stomach contents of both species demonstrate that they were primarily apex predators. Their diet included fish, sharks, turtles, other plesiosaurs, and smaller mosasaurs. The data supports a feeding pattern with minimal limitations related to prey type.
Mosasaurs with slender snouts, such as Clidastes and Plotosaurus, had biting capabilities similar to those of the polycotylid family rather than larger mosasaurs. Because of their relatively small size, it is likely that they were adapted to feed on small prey. For instance, the Plioplatecarpinae mosasaurs had jaw shapes that were more compactly arranged than the modern animals they resemble. Their jaw structure provided better mechanical leverage for greater bite force than their snout shapes would suggest. However, it also increased the likelihood of stress failure.
Globidens, a durophagous mosasaur, had teeth adapted for crushing hard-shelled prey. The analysis demonstrated that these teeth remained within stress tolerance limits even when crushing softer prey. Therefore, the unusual tooth structure likely helped distribute stress across multiple contact points. This explains why Globidens exhibited high stress levels in simulations.
The researchers studied how mosasaurs’ biting performance changed over time. They compared communities from the Coniacian and Santonian periods, approximately 86 to 84 million years ago, with those from the Campanian and Maastrichtian periods just before the mass extinction event 66 million years ago.
They observed an evolutionary trend during the mid-Campanian period. Evidence appeared during a known faunal turnover in the Western Interior Seaway. Early mosasaurs, from the Niobrara assemblages, exhibited a stress point near the junction of the dentary and posterior lower jaw. This indicates that early forms had some structural weakness in jaw design.
Later mosasaurs from the Navesink assemblage were much sturdier overall, particularly mosasaurines. It became clear that this group underwent significant changes that optimized jaw design. Whether these improvements resulted from natural selection or from the replacement of one fauna by another remains unclear.
Researchers believe that these findings can be applied beyond the Western Interior Seaway. They provide insight into how large predators interact while sharing the same energy resources. Finite element analysis of mosasaur jaw design offers an additional way to understand how ancient predators divided ecological roles.
The team argues that no single method is sufficient to study these systems. Dental microwear analysis examines the surface of teeth to identify wear patterns caused by food. Researchers have now published such analyses for many species from the Western Interior Seaway. Stable isotope analysis of fossils helps determine where animals fed within their environments.
When combined with biomechanical simulations, these methods allow researchers to build a timeline. This timeline shows how these animals used their mechanical capabilities and how specialized they were based on jaw structure. “By integrating fossils with the use of modern technologies,” Della Giustina stated, “we’re drawing closer and closer to creating an image of how these animals lived and interacted in the oceans of long ago.”
In contrast to common perceptions of prehistoric marine ecosystems as being dominated by monsters, a more nuanced understanding is emerging. The research illustrates how differences in size, jaw configuration, tooth shape, and feeding style created ecological niches. These niches allowed multiple species to coexist for millions of years.
Research findings are available online in the journal Palaeontology.
The original story “Bite mechanics of ancient marine predators yields surprising results” is published in The Brighter Side of News.
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