(CN) — Birds and mammals have undergone numerous changes to better adapt to their environments over millions of years. Beaks curved over time to better pluck insects from tree bark and pelts grew thicker for animals to weather a colder climate.
Yet the humble crocodile has ambled along over the last 200 million years, relatively unchanged from its Jurassic period ancestors.
A study published Thursday in the journal Nature Communications Biology explains why crocodiles have followed an apparently slow evolutionary pattern.
As far as reptiles go, crocodiles are closely related to dinosaurs. But they’re incredibly complex biological organisms that survived the meteor impact that ended the Cretaceous period roughly 66 million years ago — and did in their dinosaur relatives.
So in a completely different era, why do crocodiles still look like mini dinosaurs that roam the earth?
According to researchers, the crocodile found the most suitable body type for its survival. They found crocodiles achieved a punctuated equilibrium, or a sort of stasis in their evolutionary journey.
This theory contrasts with the idea that evolution happens over a long period of time with gradual changes, which scientists can see in the fossil record.
Crocodiles, the study authors argue, are an example of a species that changed in response to their environment over short bursts.
The study authors used machine learning to measure the rate of evolution.
“Evolutionary rate is the amount of change that has taken place over a given amount of time, which we can work out by comparing measurements from fossils and taking into account how old they are,” said lead author Max Stockdale from the University of Bristol in a statement accompanying the study. “For our study we measured body size, which is important because it interacts with how fast animals grow, how much food they need, how big their populations are and how likely they are to become extinct.”
Long before the giant meteor set off the cataclysmic extinction event that killed all their cousins, crocodiles came in different types and sizes.
There were giant and iguana-sized crocodile relatives. Others were plant eaters, some ran quickly and others still were sea serpents able to thrive in the warmer climate of the Jurassic period.
Crocodiles, dinosaurs and winged pterosaurs all descended from the archosaur. But only the crocodile survived a post-meteor world, and its survival could be due to a complex system of senses and other traits that allowed it to become an apex predator.
Modern crocodiles can tolerate saltwater thanks to special salt glands that filter out minerals. They replace their teeth up to 50 times throughout their life and they also have a cerebral cortex, which is vital for perception, memory and consciousness. They can hunt prey by following movement patterns, like when an animal goes to a body of water for a drink. Some crocs have been observed using sticks to lure birds in for the kill.
In other words, crocodiles are flexible creatures.
The researchers next hope to uncover why some prehistoric crocodile species died, while others survived and thrived.
“It is fascinating to see how intricate a relationship exists between the Earth and the living things we share it with,” said Stockdale. “The crocodiles landed upon a lifestyle that was versatile enough to adapt to the enormous environmental changes that have taken place since the dinosaurs were around."
The study authors did not respond to questions about their research.
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