(Photo by Pixabay via Pexels)
By Stephen Beech
Crocodiles' ability to eat almost anything helped their ancestors survive two mass extinctions, suggests new research.
The secret to their longevity could help conservationists better protect species today threatened by extinction, say American scientists.
Crocodylians - crocodiles, alligators and gharials - are thought by some to be "living fossils" that have ruled the world’s swamps for millions of years.
But their evolutionary history tells a different story, according to research led by scientists at the University of Central Oklahoma (UCO) and the University of Utah.
They explained that crocodylians are surviving members of a 230-million-year lineage called crocodylomorphs.
Skulls of Araripesuchus gomesii (left), a Late Cretacious terrestrial predator and Cricosaurus suevicus (right), a Late Jurassic aquatic predator. (University of Central Oklahoma via SWNS)
Crocodylian ancestors persisted through two mass extinction events, a feat requiring evolutionary agility to adapt to a rapidly changed world.
The research team discovered that one secret to crocodylian longevity is their "remarkably flexible" lifestyles, both in what they eat and the habitat in which they get it.
Study lead author Dr. Keegan Melstrom, Assistant Professor at UCO, said: “Lots of groups closely related to crocodylians were more diverse, more abundant, and exhibited different ecologies, yet they all disappeared except these few generalist crocodylians alive today.
“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?”
He explained that Earth has experienced five mass extinctions in its history.
Experts argue that we’re living through a sixth, driven by habitat destruction, invasive species and changing climates.
But identifying traits that boost survivorship during planetary upheaval may help scientists and conservationists better protect vulnerable species today.
Some 215 million years ago in what is now northwestern Argentina, the terrestrial crocodylomorph Hemiprotosuchus leali prepares to devour the early mammal relative Chaliminia musteloides. (Jorge Gonzalez via SWNS)
The new research, published in the journal Palaeontology, is the first to reconstruct the dietary ecology of crocodylomorphs to identify characteristics that helped some groups persist and thrive through mass extinctions - the first about 201.4 million years ago, and the second around 66 million years ago.
Study co-author Professor Randy Irmis, curator of paleontology at Natural History Museum of Utah, said: “There’s a danger of trying to draw conclusions from millions of years ago and directly apply it to conservation. We have to be cautious.
“If people study mammals and reptiles and find the same patterns with respect to extinction survival, then we might predict that species with a generalist diet may do better.
"That information helps us make predictions, but it’s unlikely we’ll ever be able to pick out which individual species will survive.”
He said living crocodylians are famous for being semi-aquatic generalists that thrive in environments such as lakes, rivers or marshes, waiting to ambush unsuspecting prey.
The teeth of this fossil Borealosuchus skull typify the toothy grin of semi-aquatic generalist predators that survived the end-Cretaceous mass extinction. (Jack Rodgers / NHMU via SWNS)
They are not "picky" eaters with young ones snacking on anything from tadpoles, insects or crustaceans to fish, baby deer, or even fellow crocs.
But the researchers say the the uniform lifestyle of today’s crocodylians masks a "massive diversity" of dietary ecologies in which past crocodylomorphs thrived.
They explained that, during the Late Triassic Period, pseudosuchia - a broader evolutionary group that includes early crocodylomorphs and many other extinct lineages - ruled the land.
The earliest crocodylomorphs were small-to-medium-sized creatures that were rare in their ecosystems and were carnivores that mostly ate small animals.
In contrast, other pseudosuchian groups dominated on land, occupied various ecological roles and exhibited a dizzying diversity of body shapes and sizes.
But, despite their dominance, once the end-Triassic extinction hit, no non-crocodylomorph pseudosuchians survived.
Whereas hyper-carnivore crocodylomorphs appeared to also die off, the terrestrial generalists made it through.
The researchers hypothesize that their ability to eat almost anything allowed them to survive, while so many other groups went extinct.
Dr. Melstrom said: “After that, it goes bananas.
“Aquatic hypercarnivores, terrestrial generalists, terrestrial hypercarnivores, terrestrial herbivores - crocodylomorphs evolved a massive number of ecological roles throughout the time of the dinosaurs.”
(Photo by Pixabay via Pexels)
But he said something happened during the Late Cretaceous Period that set crocodylomorphs on a decline.
By the end-Cretaceous mass extinction event - punctuated by the meteor that killed the non-avian dinosaurs - most of the survivors are semiaquatic generalists and a group of aquatic carnivores.
Today’s 26 species of living crocodylians are nearly all semiaquatic generalists.
The research team analyzed the shape of fossilized teeth and skulls to glean the basis of an animal’s diet.
They explained that skull shape dictates how an animal moves its mouth, providing a clue to its eating habits.
Deciphering ancient animal diets reveals where it would have hunted, which the research team calls dietary ecology.
The team visited museum collections across seven countries and four continents to get the fossil specimens they needed.
They examined the skulls of 99 extinct crocodylomorph species and 20 living crocodylian species, creating a fossil dataset spanning 230 million years of evolutionary history.
(Photo by Pixabay via Pexels)
The team had previously built a database of living non-crocodylians to compare with, 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.
As semiaquatic ambush predators, the researchers say today’s crocodylians mostly occupy similar ecological roles in lots of different environments.
They continue to have remarkably flexible diets, perhaps a remnant of their deeply diverse evolutionary past.
For critically endangered crocodylians - such as the Gharial of the Himalaya foothills and the Cuban Crocodile - dietary flexibility may give them a chance to survive even longer.
The biggest challenges facing those species are habitat loss and human hunting, according to the research team.
Irmis said: “When we see living crocodiles and alligators, rather than thinking of ferocious beasts or expensive handbags, I hope people appreciate their amazing 200-plus million years of evolution, and how they’ve survived so many tumultuous events in Earth's history."
He added: “Crocodylians are equipped to survive many future changes - if we’re willing to help preserve their habitats.”
