You know what they say about dinosaurs with big feet? They left big holes.
Some of the largest footprints known to science were made 70 million to 90 million years ago, when a type of dinosaur believed to be a titanosaur galumphed across the muck in central Asia.
A few of these mud tracks filled with sand and silt, which hardened like plaster. Long after the titanosaur died off, the casts in the sand remained. We know about these big feet because a Mongolian paleontologist discovered a few of them in the Gobi Desert in August.
And what a titanic foot the dinosaur must have had. One of the most detailed tracks was a convex mound 1m in length, with impressions of the animal's massive nails. By US shoe standards, it would stretch its sneakers to a size 104. (The world's largest human feet max out at about 38cm, about a size 23 or 25.) The print was also much wider than any human foot, at 76cm across.
"The footprint is one of the biggest known footprints in the world," said Shinobu Ishigaki, a researcher at the Okayama University of Science in Japan and a member of the joint Mongolian-Japanese expedition to the Gobi. The researchers announced their discovery of the footprint in Japan.
In Morocco and France, paleontologists have also found footprints more than a yard long. "However the Mongolian one is very well preserved," Ishigaki said, "with three clear claw marks." The size of the dinosaur cannot be determined easily from the footprints, but Ishigaki and his colleagues estimate it was 22-33m long.
Paleontologists have been hunting for dino prints in Mongolia since 1957, when a researcher stumbled upon dozens of tracks in the cold, dry desert. As Ishigaki and his colleagues reported in the journal Geological Quarterly in 2009, the Gobi is something of a fossilised footprint mother lode: Between 1995 and 2008, the scientists found more than 20,000 preserved tracks belonging to a variety of dinosaur species.
This titanosaur print was special, as nothing quite of this scale had been found in the area before. Based on the geologic layers of nearby rock, the researchers determined the print to be from the Upper Cretaceous period, about 70 million to 90 million years old. Ishigaki and the other scientists hope that the fossil cast will shed light on the way that these massive creatures walked.
Although paleontologists have found titanosaur fossils on every continent, including Antarctica, the titanosaur remains shrouded in mystery. It is not considered to be a specific dinosaur but a sort of catchall term for a group of four-legged, long-necked herbivores.
All of the titanosaurs lived in the Cretaceous. And they were all, as a rule, giants. Dreadnoughtus, hailed as one of the biggest dinos around when its discovery was announced in 2014, may have tipped the scales at 80 tons. (That weight is debated, however.) Among the other titanosaurs were the 70tonne Argentinosaurus, and a yet unnamed dino whose model skeleton was too big to fit in one room at New York's American Museum of Natural History.
What type of titanosaur left these tracks was not yet determined, but the Mongolian desert is also known for its rich fossil beds - perhaps the sand holds even more clues about these humongous animals.