Newly discovered reptiles mimicked the iconic shapes of distant dinosaur relatives.
228 million years ago — long before the emergence of a group of dome-headed dinosaurs called pachycephalosaurs — a suspiciously pachycephalosaur-looking reptile appeared on the scene.
Called Triopticus primus, meaning the "First of Three Eyes", this reptile — discovered in the Otis Chalk site in Texas — sported a large groove at the top of its head, leading to the appearance of a third eye. But the sheer thickness of Triopticus’ skull is what gave this reptile such a strong resemblance to the pachycephalosaur dinosaurs that lived more than 100 million years later.
It’s a clear case of convergent evolution, researchers write in the journal Current Biology, whereby distantly related organisms that inhabit similar environments independently evolve similar traits.
“Triopticus is an extraordinary example of evolutionary convergence between the relatives of dinosaurs and crocodylians and later dinosaurs that is much more common than anyone ever expected," said study lead author Michelle Stocker, from Virginia Tech College of Science, in a press release.
"What we thought were unique body shapes in many dinosaurs actually evolved millions of years before in the Triassic Period, about 225 million years ago."
Amazingly, many of the other reptile buried in the same layers as Triopicus, also bear features that were common in later dinosaurs, including the long snouts of Spinosaurus, the toothless beaks of ornithomimids, and the armor plates of ankylosaurs.
"After the enormous mass extinction 250 million years ago, reptiles exploded onto the scene and almost immediately diversified into many different sizes and shapes,” said study c-author Sterling Nesbitt, from Virginia Tech. “These early body shapes were later mimicked by dinosaurs.”
And the mimicry was not limited to external shape. Through CT scanning, the researchers discovered strong similarities between internal parts of Triopticus’ skull with the later dome-headed pachycephalosaur dinosaurs — the structures of the bones, and even the brains, were alike.
"With a combination of CT scans and fossil comparisons we were able to give this old fossil new life," said Katharine Criswell, a co-author and doctoral student at the University of Chicago.
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