Palaeontologists have uncovered the world’s oldest known cerapodan dinosaur at a fossil site in Morocco, identified by a distinctive femur. We know this dinosaur group would eventually spread across the globe, but the early stages of cerapodan evolution have remained a mystery due to the scarcity of Middle Jurassic rocks worldwide. That makes this latest find an exciting breakthrough and highlights Morocco as a key location for uncovering the missing chapters in these dinosaurs’ history.
Cerapodans were small, plant-eating dinosaurs that scampered around on two legs. Come the Cretaceous, the fossil record tells us they were all across the planet, but their movements during the Middle Jurassic are much more mysterious because, put simply, we haven’t been able to find the fossils.
Before this, we had evidence that ornithopod dinosaurs had probably already evolved based on a few fossilized trackways, but this is the oldest body fossil that there is.
Dr Susannah Maidment
You can understand the team’s excitement, then, when they realized they had found part of an upper limb bone from the Middle Jurassic while excavating in Morocco’s Middle Atlas Mountains. It was a femur belonging to a cerapodan dinosaur, marking the oldest record of these animals in Earth’s history.
A femur might not sound like much to work from, but palaeontologists are masterful detectives capable of recognizing and identifying features from isolated bone fragments. As Dr Susannah Maidment of the Natural History Museum, London, and lead author on the study told IFLScience, leg anatomy can be a dead giveaway for the cerapodans.
The left femur of the world’s oldest cerapodan dinosaur.
“It had a groove on the back of the head of the femur (the bit that fits in the hip socket) for a ligament, and we only see that in cerapodans,” she said. “Also, the head of the femur is really distinct and separated from the shaft on a neck, which we don’t see in earlier-diverging ornithischians.”
The previous title holder for world’s oldest cerapodan ornithischian fossil went to an iguanodontian femur that was retrieved in Leeds, England. This newest specimen was retrieved from Bathonian rock in the El Mers III Formation in Morocco, meaning it dates back around 168 million and therefore beats the previous record holder by 2 million years.
“Before this, we had evidence that ornithopod dinosaurs had probably already evolved based on a few fossilized trackways, but this is the oldest body fossil that there is,” said Maidment. “So, it essentially confirms that these dinosaurs had diversified by the Middle Jurassic.”
Given the modest collection of Middle Jurassic fossils we’ve found so far, this discovery marks a significant finding for our understanding of their evolution in filling a gap we still have much to learn about. It also tells us that if we want to find out more, the Middle Jurassic rocks in Morocco are a great place to carry on looking.
In fact, the El Mers III Formation has also yielded the world’s oldest ankylosaur (which was also the first ever found in Africa), and one of the world’s oldest stegosaurs. It seems if we want to get to know the ornithischian a little better, we best get digging.
The study is published in the journal Royal Society Open Science.
