Crocodiles are persistent — not just in their deadly pursuit of prey, but in terms of their existence. The contemporary species hails from a 230-million-year lineage that has survived two mass extinction events.
A study in the journal Palaeontology identifies flexibility as a key to their longevity. Crocodylians that survived over millions of years can eat a variety of foods and live in multiple habitats. Understanding this level of adaptability could help threatened species survive.
“Extinction and survivorship are two sides of the same coin. 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?” said Keegan Melstrom, professor at the University of Central Oklahoma and an author of the study, which she began as a graduate student there, in a press release.
Crocodiles as Living Fossils
Crocodylians are often referred to as “living fossils.” But that may be a bit of a misnomer, because that label suggests lack of change. The study of how they survived so long runs counter to that. The creatures have prevailed for so long because they’ve managed to change where they live and what they eat, even as the world around them shifts.
That happened during two mass extinction events. The first was during the end-Triassic, about 201.4 million years ago. The second was at the end-Cretaceous, about 66 million years ago.
Read More: The 5 Mass Extinctions That Have Swept Our Planet
Evolution After Mass Extinction Events
During the Late Triassic Period (237 million years to 201.4 million years) Pseudosuchia, a broad group that includes early crocodylomorphs and many other extinct lineages dominated. The crocodylomorphs then were small-to-medium-sized creatures, relatively rare, and mostly ate small animals, likely in the water.
Other pseudosuchian groups dominated the land, and came in a wide range of body shapes and sizes. But this level of specialization probably did them in during the end-Triassic extinction, leaving crocodylomorphs as one of the most dominant and adaptable species remaining.
“After that, it goes bananas,” Melstrom said in the release. “Aquatic hypercarnivores, terrestrial generalists, terrestrial hypercarnivores, terrestrial herbivores — crocodylomorphs evolved a massive number of ecological roles throughout the time of the dinosaurs.”
Crocodylomorph species began a slow decline during the Late Cretaceous Period, with the more specialized species fading out. After a meteor contributed to a mass extinction event that killed of all the dinosaurs, only the aquatic and semi-aquatic crocodylomorphs remained.
Crocodile Diets Over Time
The scientists determined crocodylian diets over millions of years by analyzing skull and teeth shape of different species over time. Jaws lined with sharp dagger-like teeth were most likely associated with carnivores, while others set with the dental equivalent of mortar and pestles likely ground plant matter into digestible food.
To glean an idea of the animal’s diet over time, the researchers examined the skulls of 99 extinct crocodylomorph species and 20 living crocodylian species. They visited zoological and paleontological museum collections across seven countries and four continents, ultimately examining the skulls of 99 extinct crocodylomorph species and 20 living crocodilian species.
They then created a fossil database covering 230 million years. Next, they compared it to a previous dataset that of living non-crocodylians including 89 mammals and 47 lizard species. The specimens represented a range of dietary ecologies, from strict carnivores to obligate herbivores, and a wide variety of skull shapes.
Today’s 26 species of living crocodylians are nearly all semiaquatic generalists. This lends some credence — at least in evolutionary terms — to the saying that it is better to be a jack of all trades and rather than a master of none.
Read More: These Extinct Giant Crocs May Have Hunted Our Ancient Ancestors
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
