In a complete redefinition of the ‘cute’ concept, an international team of paleontologists has identified the smallest known footprint of stegosaurs.
Preserved in the stone in China’s Xinjiang Province for 100 million years, the imprint measures only 5.7 centimeters (2.24 inches) long, and was likely created by a baby stegosaur (ichnogenus Delta mode) around the size of a cat, the research team said.
Fascinatingly, while we don’t know the exact species of the small animal, the print has allowed scientists to conclude that baby stegosaurs may have walked differently than the adults.
“This footprint was created by a herbivorous, armored dinosaur commonly known as a stegosaur – the family of dinosaurs that includes the famous stegosaurus,” said paleontologist Anthony Romilio of the University of Queensland in Australia.
“Like the stegosaurus, this tiny dinosaur probably had spines on its tail and bony plates along its back as an adult. With a footprint of less than six inches, this is the smallest stegosaur footprint in the world.”
The stegosaur’s footprint. (Xing et al., Palaios, 2021)
We know that stegosaurs lived in the region. Dozens of tracks up to 12 inches long have been found, as well as skeletal remains. Elsewhere in the world, stegosaur tracks rarely exceed 50 centimeters.
The footprints of very young stegosaurs and other armored dinosaurs are incredibly rare compared to other species, and it’s not entirely clear why.
It’s possible that while living in a herd, many of their prints were overrun by larger, heavier adults, but that doesn’t quite explain how the baby prints of other herd dinosaurs survived. Other explanations include the rapid growth – the animals may not have been small long enough to leave many tracks; or that breeding habitats were generally not conducive to footprint conservation.
Whatever the reason for the scarcity, somehow this one track survived. The baby’s three-toed foot was pressed into the mud; time turned the mud into mudstone, creating a mold that was filled with debris that turned to sandstone over time, creating a cast of the little step that survived when the mudstone weathered.
While not much detail has been preserved, the shape of the print was intriguing – it wasn’t elongated like the tracks of older stegosaurs, the researchers said.
The prints of older stegosaurs found at the site. (Xing et al., Palaios, 2021)
“Stegosaurs usually walked with their heels on the ground, just like humans, but on all fours, leaving long footprints,” Romilio said.
“The small track shows that this dinosaur moved with its heel off the ground, just like a bird or cat does today. We didn’t see these kind of shortened tracks before when dinosaurs walked on two legs.”
This tantalizing discovery suggests that baby stegosaurs could have moved lighter and more agile than the adults, walking on their toes and turning to their heels as they grew. However, with just a single footprint, it’s impossible to tell.
The particular individual stegosaur who made it could have had a strange gait; or maybe he put his foot down in a strange way, just for that one step.
“A complete set of traces of these tiny footprints would give us the answer to this question,” said paleontologist Lida Xing of the China University of Geosciences, who found the print, “but unfortunately we only have a single footprint.”
The area in which the print was found has yielded nine different dinosaur track locations; and the particular assembly containing the baby print also had 16 other prints from older stegosaurs. Now that one baby print has been found, the team plans to search the formation for clues that can help us answer these fascinating questions.
The research is published in Palaios