Some 200 million years ago in what's now South Africa, a dinosaur that weighed as much as two adult African elephants loomed over the landscape. This massive herbivore got so big in a peculiar way—and it had a downright bizarre way of standing on all fours.
The new dinosaur, unveiled in Current Biology on Thursday, looks like a sauropod, the group of classic long-necked dinosaurs that includes Brontosaurus, but it's technically not. Instead, Ledumahadi is an earlier, more distant cousin called a sauropodomorph. It is a much bigger animal living much earlier in the age of dinosaurs than researchers normally expect to see, so its discoverers etched their surprise into the dinosaur's name: Ledumahadi mafube, Southern Sotho for “a giant thunderclap [at] dawn.”
Like elephants, true sauropods had column-like limbs that efficiently supported the animals' weight. But Ledumahadi took a decidedly different approach. It seems to have had a more mobile forelimb, but it stood in a less efficient catlike crouch, with knees and elbows partly flexed.
“This was the animal that wanted to have everything,” says lead study author Blair McPhee, a paleontologist at the University of São Paulo. “It wanted to be really big, like a sauropod, and wanted to walk predominantly quadrupedally, like a sauropod. But when it came to relinquishing that primitive mobile forelimb, it didn’t want to do that.”
The find suggests that a four-legged gait evolved several times among sauropods and their kin. And like other recent discoveries, Ledumahadi reinforces the notion that key events in sauropod evolution occurred earlier and with more experimentation than evidence once showed. (Find out more about groundbreaking new sauropod fossils.)
“I'm excited by these new discoveries, which are really helping to diversify our understanding of these truly remarkable creatures!” Macalester College paleontologist Kristi Curry Rogers says in an email.
Though Ledumahadi is named for a thunderclap, its discovery was nowhere near that sudden. It took scientists more than two decades, off and on, to find the creature's remains and understand them.
Ledumahadi's story starts around 1990, with the construction of the Lesotho Highlands Water Project, a huge water infrastructure project that links South Africa and Lesotho, which South Africa surrounds. Knowing construction could turn up fossils, the builders hired James Kitching, a paleontologist at South Africa's University of the Witswatersrand (Wits for short), to collect any bones that popped up.
Right away, Kitching spotted large dinosaur bones eroding out of a cliff near the construction site. He collected them, but he wasn't that interested in dinosaurs, preferring instead to study early mammals. So the bones remained incognito until the mid-2000s, when then-Wits paleontologist Adam Yates realized their importance.
From newspaper clippings, Yates tracked down the original site, and he and his Ph.D. student McPhee trekked back there and found some more bones. Later study confirmed that they belonged to the same animal. In 2012, paleontologist Jonah Choiniere arrived at Wits, and McPhee introduced him to the huge dinosaur bones. From 2012 to 2017, the duo returned to the site, digging out more bones of Kitching's dinosaur.
“[Finding Ledumahadi] just played out over all these years, and had these chance happenings and hand-offs of knowledge,” Choiniere says. “At any point, the ball could have been dropped. Luckily, it wasn't.”
Walk the Dinosaur
Researchers then methodically reconstructed Ledumahadi's life, bone by bone. Coauthor Jennifer Botha-Brink, a paleobiologist at South Africa's National Museum, Bloemfontein, showed that the 14-year-old animal had reached full adulthood when it died. University of Cape Town geologist Emese Bordy confirmed that the bones were between 195 and 200 million years old, based on the sediments that encased them.
To see how Ledumahadi walked, the researchers figured out how to tell whether an animal walks on two or four legs. In animals that just walk on their hind limbs, the forelimb bones are relatively thinner and spindlier. Animals on all fours, however, have beefier forelimb bones—all the better to bear the animal's weight.
The team compared arm and leg bones from Ledumahadi against those from different dinosaurs, as well as hundreds of living mammals with known walking styles. Ledumahadi's forelimbs were so stout, the animal almost certainly walked on all fours. But the forelimbs suggest it adopted an unusual cat-like posture.
Now that the team has described Ledumahadi, researchers say that they are looking elsewhere in South Africa for even older fossils. The team is also going back through the collections shelves of Wits, looking for any other undescribed gems hiding there.
“It's amazing,” Choiniere says. “Sometimes stuff can sit on your shelf, and you pass by it every day, but you don't look at it in detail.”