Footprints found in one of Africa's largest diamond mines show a mixed group of animals including a dinosaur, a crocodile-like creature and a mammal the size of a raccoon wandered across the landscape -- 118 million years ago.
In the Catoca mine in Angola almost 70 clear and distinct tracks were found in a small sedimentary basin in the crater of one of the mine's kimberlite pipes, researchers reported.
The mammal's tracks are the most surprising, they said, suggesting a creature "exceptionally large for its time," bigger than other warm-blooded creatures previously known from the time, most no bigger than rats, said Marco Marzola of the PaleoAngola Project, an international effort studying vertebrate paleontology in Angola.
"Mammals evolved from very small-sized individuals," he said. "The first mammals were the size of a squirrel or even smaller, like a mouse. They evolved to become bigger in size, but only after the time of the dinosaurs."
Fossil evidence of mammals from the time of the dinosaurs is rare, the researchers said, so fossilized footprints offer a chance to learn about the elusive creatures, he said.
Ripple marks preserved in the sediments around where the tracks were found suggest an ancient shallow lake that may have enticed the animals as a source of water, the researchers say.
The various creatures may have visited the lake at different times, they note, but all left their tracks in the same area.
In addition to the mammal footprints, 18 tracks were found that likely belonged to sauropods, long-necked dinosaurs that were the largest animals that ever trod on the Earth.
Those footprints were up to 20 inches wide and showed no evidence of toes or digits, which was no surprise, Marzola said.
"We don't know any other possible animal in the Cretaceous that could have left such a big track, other than a sauropod dinosaur," he said.
A final find was the preserved tracks of a crocodilomorph, from a group that includes both extinct and modern crocodiles.
A unique feature of those footprints was evidence of the feet being rotated to the side by almost 150 degrees -- something that's been seen before, Marzola said.
"This might look like a bizarre characteristic, but it's not so uncommon," he said. "This characteristic was also found in other track ways that are associated with crocodilomorph of the early Jurassic in North America and France, and the early Cretaceous in Spain."
The researchers presented their work at the at the Society of Vertebrate Paleontology's annual meeting in Berlin.