About 252 million years ago, 96 percent of species on Earth were wiped out during the massive die-off event called "The Great Dying" or the Permian mass extinction.
It was one of the Big Five events that altered the course of history, and all life on Earth today — including animals and humans — is descended from the 4 percent of the species that survived.
How did the remaining species build their lives from scratch? Although there is no single conclusive answer yet, the discovery of marine reptile fossils may offer insight about life after the Permian mass extinction.
What The Hammerhead Marine Reptile Discovery Says About Evolution
Discovered in Yunnan Province in China were the fossils of the Atopodentatus unicus, a strange marine reptile with a peculiar horizontal hammerhead.
Findings such as this one are quite important as they offer a glimpse on the resilience of life on Earth while bouncing back from the devastation of mass extinction, says study co-author Olivier Rieppel.
These animals that survived the years surrounding the Permian mass extinction help scientists see how life reacted.
Rieppel, who is an evolutionary biologist and curator at The Field Museum, says the existence of animals such as A. unicus shows us that life on Earth recovered and diversified faster than what was previously believed.
"It's definitely a reptile that no one would have thought to exist," says Rieppel.
In the study featured in the journal Science Advances, researchers described the anterior edges of the reptile's lower and upper jaws as lined with "batteries of chiseled teeth." Despite the ferocious description, the A. unicus actually preferred a plant-based diet.
The reptile's chisel-shaped teeth could have been used to scrape algae from the seafloor. Its needle-like teeth could have also filtered out the seawater, the same way a baleen whale sifts plankton from the water.
Study authors say the findings mark a distinct deviation from past hypotheses about skulls with downward snouts, now suggesting that these animals did not eat invertebrates.
If this is true, the A. unicus is the second prehistoric marine reptile ever to have developed herbivory aside from the turtle-like creature called Henodus.
Rieppel says the jaw structure of A. unicus is clearly that of a plant-eater, as it has similarities to herbivorous marine animals with filter-feeding system. The marine reptile is also unique for possessing a "hammerhead adaptation" for subsurface grazing, he adds.