The Black Hills mountain range, which stretches from South Dakota to Wyoming, is known for its lush forests, scenic waterfalls, and dense, intricate cave systems. But 150 million years ago, humongous, long-necked dinosaurs called sauropods roamed there — and scientists just identified one of their colossal, fossilised feet.
The nearly complete foot fossil, made up of 13 bones, was unearthed in 1998 from a body of rock spanning multiple states called the Morrison Formation.
That area has produced a wealth of dinosaur fossils from the Late Jurassic Period, or between 155 million to 148 million years ago. Scientists there have dug up diplodocuses, allosauruses, stegosauruses — the list goes on. The staggering number of fossils there, compared to the available scientists to examine them, is why it took two decades to identify this massive foot.
The foot seems to have belonged to some kind of brachiosaur that stretched 24m long, the researchers wrote in their paper published Tuesday in PeerJ. To figure that out, they used a 3D scanning technique to make computerised images of the foot bones, and compared them to other sauropod foot fossils.
“It very likely is a type of brachiosaur, the kind that got famous in Jurassic Park (and then got horribly murdered in Fallen Kingdom),” Femke Holwerda, a study-author and palaeontologist at the Bavarian State Collection of Paleontology and Geology, told Gizmodo via email.
“The only problem is that feet can rarely be diagnostic down to species level, hence the assignment to brachiosaur and not to any specific species.”
The same dig site where this foot was unearthed in northeastern Wyoming also contained a separate, smaller, nearly complete brachiosaur, and a handful of other long-necked dinosaurs like diplodocuses and camarasaurs. The research team was surprised to see a brachiosaur that far north, because the animals had been thought to occupy much smaller, more southern chunks of land.
“This brachiosaur showing up in Black Hills in Wyoming brings up some questions,” says David Burnham, a palaeontologist at the University of Kansas who worked on the paper.
“Is it a different species than the brachiosaurs down south? Or maybe they were migrating north to south? It’s several hundreds of miles from where we thought these guys were, so we have a lot of new questions. It’s great — I welcome the new questions and opportunities for further research.”
Still, the huge brachiosaur foot is notable for more than just its surprising location. At just under a metre wide, the researchers said it the largest sauropod foot ever discovered. Philip Mannion, a palaeontologist at Imperial College London who wasn’t involved with this discovery, agreed with that assessment.
“The metatarsals do seem to be longer than those of any other known sauropod dinosaur, so in that regard this is probably the largest foot ever discovered,” Mannion told Gizmodo. “There are other species with feet that aren’t much smaller, though.”
Plus, as Mannion and the study authors point out, we’ve never found the feet of the world’s largest sauropods, the titanosaur and argentinosaurus, who would surely surpass this brachiosaur in foot size.
We haven’t seen those dinosaurs’ feet yet because foot fossils are notoriously elusive, according to study author Anthony Maltese, a palaeontologist at the Rocky Mountain Dinosaur Resource Center in Colorado. Throughout history, they’ve had a much higher chance of being lost in waterways or eaten by scavengers because they’re so small compared to the rest of the animal. That makes the most recent discovery an especially exciting one.
“It’s great to finally have a brachiosaurus foot,” Elizabeth Freedman Fowler, a paleontologist at Dickinson State University who wasn’t involved with this work, told Gizmodo.
“Getting a decently complete foot for any dinosaur is a lucky find. As we keep digging and finding more bones, we are getting an idea of just how huge each dinosaur species can truly grow. I think we are going to keep breaking the record for ‘biggest’ over and over for many years to come.”