An Oklahoma State University Center for Health Sciences researcher has shed light on how alligators and crocodiles developed the ability to bite with several-thousand-pounds of force and successfully ambush prey near the water’s edge.
Paul M. Gignac, Ph.D., assistant professor of anatomy and vertebrate paleontology, at OSU-CHS, has published two studies examining the evolution of crocodile jaw bones and jaw muscles.
Gignac and Gregory M. Erickson, Ph.D., professor of anatomy and vertebrate paleontology at Florida State University, found that crocodilians’ largest jaw-closing muscle – the ventral pterygoideus muscle – has evolved to be so massive that it spills out behind the head, giving alligators and crocodiles the appearance of a fat neck.
This study, “Ontogenetic bite-force modeling of Alligator mississippiensis: implications for dietary transitions in a large-bodied vertebrate and the evolution of crocodylian feeding,” shows that the large muscle is responsible for up to 70 percent of the nearly 4,000 pounds of bite force that has propelled crocodilians to the top of the food chain.
“Large, apex predators don’t start out life at the top of the food chain,” Gignac said. “Figuring out how they climb their way to the top is important for understanding the complexities of modern faunas, how natural selection operates during development, and why today’s crocodiles and alligators are capable of crushing bites with recording-setting forces.”
Growing their largest jaw muscle to lie alongside the neck turns out to be effective for both camouflage and forceful biting simultaneously. For their size, big alligators and crocodiles have low-profile heads and bodies. They are surprisingly stealthy, “like animal submarines. In hunting mode only, the sensory devices are at the surface—the engine and weapons lay below” said Erickson.
The research was published online on June 15 in the Journal of Zoology.
In a separate open access study published in Integrative and Comparative Biology on June 6, “Suchian Feeding Success at the Interface of Ontogeny and Macroevolution,” Gignac and Haley D. O'Brien, Ph.D., OSU-CHS research associate in vertebrate paleontology, traced the evolution of crocodile jaw bones that transmit these remarkable forces during biting. Their findings revealed that the evolution of stronger bite forces correlate with the success of young reptiles in competing for prey.
Pressure for juveniles to grow up quickly yielded steady increases that, after millions of years, resulted in modern adults with exceptional bites known to reach 4,000 pounds of force. “A forceful bite early in life is critical for small crocodilians, but these animals continue to grow throughout their lives,” Gignac said. “This seems to carry adult bite forces far beyond what’s needed to capture prey, puncture bones or shatter turtle shells.”
The research also explains why nearly all living species of alligators and crocodiles are able to generate such extraordinary bite forces. “Although our mathematical modeling traces bite-force evolution back to the Jurassic period, we see a more rapid increase in bite forces beginning with the ancestors living crocodilians. The speed of juvenile growth carries a sort of evolutionary-developmental inertia that also amplified adult bite forces beginning about 150 million years ago,” said O’Brien.
Both studies were funded by the National Science Foundation.
To read the studies, visit Oxford Journals at http://icb.oxfordjournals.org/content/early/2016/04/28/icb.icw041 and Wiley Journals at http://onlinelibrary.wiley.com/doi/10.1111/jzo.2016.299.issue-4/issuetoc.
To read more about Gignac’s work, visit https://statemagazine.okstate.edu/Discoveries_in_the_Dirt. To watch a video of Gignac discussing his OSU-CHS research, visit the university’s Research Spotlight website at http://www.healthsciences.okstate.edu/researchspotlight/.