‘Frankenstein’ dinosaur was a mash-up of meat eater and plant eater

Bizarre theropod that roamed South America 150 million years ago may help answer evolutionary questions

Chilesaurus

MIX AND MATCH  Fossils found in Chile reveal a new dinosaur species with a mishmash of anatomy — a little bit T. rex and a little bit Brontosaurus.

Gabriel Lío

Frankensaurus did exist. But don’t worry — the sharp-clawed creature was a vegetarian.

Bones found in Chile reveal a bizarre new dinosaur that had a hodgepodge of anatomical features. Based on an ancestry that links it to Tyrannosaurus rex, Chilesaurus diegosuarezi should have been a meat eater, but preferred plants instead, researchers report April 27 in Nature. The discovery supports the idea that not all early T. rex relatives were out for blood and suggests that dinosaurs in nascent South America may have evolved differently than those on other continents.

“Chilesaurus is so unexpected, so drastically different than anything else we’ve seen before. It’s an anatomical Frankenstein,” says Lindsay Zanno of the North Carolina Museum of Natural Sciences in Raleigh.

Chilesaurus
STANDING OUT Veggie-loving C. diegosuarezi may have been an oddball among his carnivorous theropod cousins. Gabriel Lío
C. diegosuarezi, which roamed South America 150 million years ago, measured about 3 meters from head to tail. Its sturdy back legs, thin body and short, stout arms made it look a bit like T. rex . But its long neck, small head and mouth full of leaf-shaped teeth also gave it a Brontosaurus -like appearance. C. diegosuarezi ’s bizarre mash-up of features made it hard to know to which dinosaur group it belonged, says study coauthor Fernando Novas, a paleontologist at the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires.

Using several computer analyses, Novas and colleagues compared C. diegosuarezi’s features with many other types of dinosaurs. The results revealed that the new dinosaur was an early theropod. Meat eaters like T. rex have made this class of dinosaurs famous, and, as a result, scientists had thought that all theropods were carnivores. But studies have begun to suggest that some theropods evolved into plant eaters, says paleontologist Peter Makovicky of the Field Museum in Chicago. A lot of the fossil evidence for this switch in diet is based on tooth shape and dates to roughly 125 million years ago.

Chilesaurus made the switch to plant eating much earlier. It may have been one of the first experiments in theropod evolution to try the transition,” Novas says. Another theropod called Limusaurus may have made the switch a few million years earlier (SN: 7/18/09, p. 12). Zanno says if C. diegosuarezi’s place in the theropod family tree is confirmed, there may be up to seven instances of theropods straying from their bloodthirsty ancestry.

VEGGIE TALE Based on the shape of its teeth, C. diegosuarezi was not a carnivore, preferring plants instead. Fernando Novas

“Just a decade ago, no one would have imagined that theropod dinosaurs, Earth’s quintessential predators, would turn out to be one of the best evolutionary case studies for how animals adapt to plant-based diets,” Zanno says. Figuring out how and why certain theropods made the switch will be exciting, she says.

Novas argues that C. diegosuarezi’s mélange of features also add a wrinkle to paleontologists’ idea that dinosaurs were similar across the continents throughout the Jurassic period, which ended roughly 145 million years ago. “South America may have been a cradle for different kinds of dinosaurs that were not found elsewhere in the world,” he says.

Makovicky says the idea that dinosaurs were different in South America could be true. But, he says, scientists need to find more dinosaur fossils from the continent in order to confirm it.

photo of Ashley Yeager

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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