Fossils point to earliest dinosaurs that lived in herds

A jumble of eggs, young and adults suggest Mussaurus stayed together through their lives

illustration of nine dinosaurs of differing ages

A herd of Mussaurus patagonicus — including hatchlings in nests, a group of juveniles and fully grown adults — appear together in this artist’s representation.

Jorge Gonzalez

A newfound trove of fossils in South America offers a peek into dinosaur family life. All of them belonged to a species known as Mussaurus patagonicus (Muh-suh-SAW-us Pat-uh-GON-ih-kah). It was an early, smallish ancestor of huge, long-necked sauropods (SAHR-oh-pahdz). (Think Apatosaurus and the behemoth Dreadnoughtus schrani.) The jumble of fossilized eggs, nests and bones now suggest these creatures traveled in herds.

Clutches of eggs were found alongside the skeletons of dozens of newborn, juvenile and adult dinos. This mix suggests the creatures stayed together throughout their lives. Their herds would have roamed some 193 million years ago. Other types of dinos showed signs of herd-living. But the new fossils are at least 40 million years older than the previously oldest evidence of dinosaur herds. Researchers described the new find October 21 in Scientific Reports.

a hand holding a fossilized egg, with a dry landscape in the background
This fossilized egg dates to about 193 million years ago. It was found in dry southern Argentina. The site held bones from individuals of many ages as well as egg clutches. Together, they suggest these dinos traveled in herds.Roger Smith

Diego Pol is a paleontologist with the Museum of Paleontology Egidio Feruglio. That’s in Trelew, Argentina. He was part of a team that unearthed the new fossils in southern Argentina. They found 80 dinosaurs and more than 100 eggs.

Each nest held eight to 30 eggs. Pol’s group closely examined five of the nests. In each, the eggs lay in two or three layers within shallow trenches. The age of the herding animals ranged widely. A close review showed some skeletons turned up at least two adults and nine juveniles. At least 11 others were under a year old.

Fossils of the first known dinosaurs date to around 245 million years ago. By about 201 million years ago, the Triassic Period was coming to an end. Sauropod ancestors, including Mussaurus, were among the most abundant plant eaters on land. Mussaurus roamed in what’s now Patagonia’s deserts. During their era, this area was semi-dry. Nearby was a lake that may have flooded and sometimes evaporated. A sudden flood might explain this herd’s demise.

Mind-bogglingly massive sauropods didn’t arise until the Jurassic Period. That came just after the Triassic. But fossils of Triassic relatives like Mussaurus were already showing evidence of a growth spurt. Bigger bodies would have needed more food. Those needs may have encouraged these creatures to work together. Forming herds would have helped them forage across long distances, the researchers suggest.

Carolyn Gramling is the earth & climate writer at Science News. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.

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