Small-Headed, Long-Necked Dinosaur That Weighs Same as Humans Discovered

A new species of long-necked dinosaur has been discovered, and researchers say it is among the smallest known members of a family of giants. When scientists analyzed a fossil limb bone found in South Africa, they determined that it represented a mature, previously unknown sauropod that lived around 200 million years ago. The sauropod group of dinosaurs includes the largest land-dwelling animals ever to walk the Earth, with some species estimated to have weighed more than 90 metric tons. But in contrast to these giants, the new sauropod described in the study is thought to have had a body mass of only around 75 kilograms (165 pounds)—about the same as some humans—according to a study published Tuesday in the journal Royal Society Open Science.

This places it among the smallest known sauropodomorphs—the group that contains sauropods and their ancestors—ever to roam our planet. It is also the smallest sauropod ever reported from the Jurassic—the geologic period extending from around 201 million to 145 million years ago. "Up until now, we knew that sauropodomorphs appeared in the Triassic, some 233 million years ago. At that time, they were very small, about 10 kilograms [22 pounds]," Kimberley Chapelle, an author of the study, told Newsweek. "But as soon as we get to the Jurassic, they already weigh several hundred kilograms and keep increasing in size until they reached multiple [metric tons]. "That's what sauropods are known for, being the largest land animals to ever roam the Earth," said Chapelle, who is affiliated with the American Museum of Natural History. "But now we know that there were still some small ones in the Jurassic. This is the first sauropodomorph under 100 kilograms in the entire Jurassic." The latest discovery helps scientists to better understand the ecosystems at the time, as well as the evolution of this group of dinosaurs, according to Chapelle.

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The new dinosaur was a plant eater that walked on two legs. It also had a long neck and a small head. "The most surprising thing about the dinosaur is that it is really small—approximately 75 kilograms [165 pounds], which is about as heavy as an impala," Chapelle said. "We also know for a fact that it is an adult and wouldn't grow much bigger." To place the new dinosaur's size into context, the Jurassic sauropodomorph that is the next step up in size is already 50 percent bigger. And most of the sauropodomorph dinosaurs from the time had a body mass of several hundred pounds. The area in which the dinosaur once lived would have been a warmer environment than today, with fewer plants and braided rivers running through the landscape, according to Chapelle.

The fossil limb bone that the study is based on was originally found by James Kitching in 1978 in the eastern part of South Africa's Free State province. Since then, the fossil has been kept at the Evolutionary Studies Institute at Johannesburg's Wits University. Initially, the fossil was thought to represent Massospondylus—Southern Africa's most abundant dinosaur. But it was never really examined on its own until the latest study, which found that it represented a new species—an early ancestor of well-known giants like Diplodocus. Because the study's authors were able to examine only this one fossil bone for their research, they have not yet named the new species. "There may be a more complete fossil of it in a museum somewhere or in the field that will allow us to learn more about it and name it," Chapelle said. "Now that we know it exists, we can go back and look at collections in museums, and there may be another one hiding in there. We also still excavate dinosaurs every year, so we may find one," she said. Do you have an animal or nature story to share with Newsweek? Do you have a question about dinosaurs? Let us know via science@newsweek.com.