SALT LAKE CITY — Earth has experienced at least five “mass extinction” events throughout its existence, but some species have been able to survive these major shifts.
Utah researchers say they believe they now know how existing crocodile, alligator and gharial species were able to survive the last two extinctions — each tens of millions of years ago — which could help understand how certain species can survive future events. It all has to do with being able to adapt to sudden shifts in surroundings, says Randy Irmis, curator of paleontology at the Natural History Museum of Utah and a professor at the University of Utah’s Department of Geology and Geophysics.
“These animals that lived on land and were fairly generalist in what they ate — they mostly ate animal matter, but they might eat bugs and small crustaceans, as well as small lizard-sized animals as well — those sort of species that had flexible diets and lived on land tended to be the ones that survived these mass extinction events,” Irmis told KSL.com. “Whereas, things that were very specialized in what they ate or where they lived were more at risk (of) extinction.”
Irmis was part of a research team whose findings were published Wednesday in the journal Palaeontology. The study is the culmination of almost a decade of work.
Keegan Melstrom, an assistant professor at the University of Central Oklahoma, started working on the study when he was a doctoral student at the University of Utah under Irmis’s tutelage. Melstrom had previously researched the relationship between reptile diet and the complexity of their teeth, applying it to fossils millions of years old.
While previous studies have focused on how invertebrates have evolved, the team wrote that research is “not evenly distributed phylogenetically” when it comes to vertebrates and mass extinction events. The little research available indicated that dietary ecology played some type of role.
This time, the research focused on skull shape and diets.
The team examined the skulls of nearly 100 extinct crocodylomorphs and 20 more extinct crocodylians collected from six continents, all of which spanned more than the last 200 million years, according to the paper. This allowed time to review species that would have lived around the time of the end-Triassic extinction, about 201 million years ago, and the end-Cretaceous extinction, 66 million years ago.
They were compared with over 100 combined mammal and lepidosaur species, along with a few other species, including living alligators, crocodiles and gharials.
It wasn’t easy work, which is why the study took so long to compile. Melstrom traveled to museums across the world to review many of the fossils and compile all the data. However, the research yielded interesting results.
“Extinction and survivorship are two sides of the same coin,” he said in a statement. “Through all mass extinctions, some groups manage to persist and diversify. What can we learn by studying the deeper evolutionary patterns imparted by these events?”
The finding that flexibility seemed to matter when it came to crocodile, alligator and gharial species was somewhat surprising. Previous research leaned toward that being a factor for mammals that also survived catastrophic events, but the new study found more similarities in the species that survived, despite different responses over the last two major extinction events, Irmis adds.
Future studies may focus on other fossil parts or even other reptile species during this time.
In the meantime, this study might offer a window into the future of crocodile-like species, especially how they handle current or future threats like habitat loss. Irmis points out that many of the current species are still fairly flexible in their diet, but that might not be enough if they now deal with new challenges, including certain human pressures.
“Crocodiles are really flexible and adaptable if we give them a chance,” he said. “In terms of making sure they persist for a long time, it’s really a matter of preserving their habitat and not hunting them to extinction.”
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