Crocodile Ancestors Had Fearsome Mouths Too, But Used Them Differently

A crocodile carries the greatest bite force known in the entire vertebrate animal kingdom. The animal’s gaping mouth represents a sense of fear for most of us, but the apex predator of today was much different hundreds of millions of years ago.

It has long been believed that during the Jurassic-era, crocodilians had smaller, slender bodies and longer legs. Many thought the theory applied to the animal’s mouth too, but looks like that was still very much similar to what the present-day beasts have.

An international team, led by researchers from the University of Witwatersrand in Johannesburg, posited this theory after looking at one of the earliest crocodilians from the Jurassic period, the shartegosuchids, in a bid to delve into a less known member of the family and their mode of attack.

Eight years ago, an expedition to late Jurassic-era exposures in Mongolia’s western Gobi desert uncovered fossilized snout of a shartegosuchid. As the small fossil was analyzed through sophisticated CT-scanning techniques in the ensuing years, the team learned about the animal and its physical traits, particularly the mouth.

The findings took a surprising turn when the team noted that shartegosuchids’ mouth had a closed secondary palate, just like modern-day crocodilians that use it for breathing underwater and reinforcing their skull to generate the enormous bite force they are known for.

Though apart from crocodilians, only a few animals groups are known to have this feature, the finding suggests that shartegosuchids developed the critical feature much earlier than previously thought.

The research team described this as a case of convergent evolution wherein a similar feature develops in two unrelated groups. But, there were some minute differences to tell them apart.

"I was surprised to find that there were many features in the palate and snout that were completely different between shartegosuchids and extant crocodilians," Kathleen Dollman, the lead author of the study, said in a statement.

The group noted that shartegosuchids had a thickened and sculptured palate with a tall and short rostrum, while extant crocodilians have a smooth palate with a long and broad rostrum. These differences, as they said, exist because the ancient animals used their features for a different purpose.

"We would expect to see the same palatal structures and snout shapes in both shartegosuchids and extant crocodiles if they were using it for similar functions and had evolved a closed palate for similar reasons," Dollman concluded. "The observed differences tell us that shartegosuchids likely had predation practices to which there is no modern analog in crocodilians."

Apart from that, not much has been revealed about the exact function of the palatal structures in the ancient crocodilians.

The study, titled “Convergent Evolution of a Eusuchian-Type Secondary Palate within Shartegosuchidae,” was published June 18 in the journal American Museum Novitates.