Dinosaurs were the dominant group of animals on Earth for more than 150 million years. Long-necked sauropods that eat plants like Brontosaurus, Diplodocus and Brachiosaurus They are probably among the most famous dinosaurs, thanks in part to their enormous size and strange body shape (consisting of a long neck, long tail, round body, and columnar limbs). Some of the largest sauropods are up to 37 meters long.
But less well known is that they descended from much smaller, two-legged, omnivorous creatures or that feed on plants called sauropodomorphs. My colleagues and I recently identified a new species of dinosaur that represents the oldest known evolutionary step among the earliest sauropodomorphs and sauropods, about 225 million years ago.
Sauropodomorphs were among the first dinosaurs to have existed during the late Triassic period, from around 230 million years ago. During this time, dinosaurs were not yet the dominant group of animals on Earth and had to share the world with, among others, crocodile-like reptiles called phytosaurs and mammal-like reptiles, such as Morganucodon.
Towards the end of the Triassic and earlier Jurassic, environmental changes led to the evolution of larger and more immediate predecessors of sauropods. These dinosaurs were larger, had longer necks, ate only plants, and, most importantly, walked on all fours due to their size. These transition species include Pulanesaura from approximately 190 million years ago in what is now South Africa, and Leonerasaurus from a similar time in what is now South America.
Our new dinosaur, which we have called Schleitheimia, falls into this category. Some of its bones were first found in Switzerland as early as 1915. Others were found in Hallau, near Zurich, in the 1940s, and others of the same geological layer were discovered in Schleitheim, also near Zurich, in the 1950s. But for years, these fossils were thought to belong to an earlier species of sauropodomorphs.
In 1986, paleontologist Peter Galton identified this set of fossilized dinosaur remains, kept at the University of Zurich in Switzerland, as belonging to a common sauropodomorph known as Plateosaurus. Plateosaurus He had a fairly long neck, but he didn’t walk on all fours all the time.
However, when Munich paleontologist Oliver Rauhut examined the bones more recently, he noticed strange features in them, making it impossible for them to belong to them. Plateosaurus. So in 2015 he and I visited the Zurich Paleontological Museum and thoroughly examined the bones. We discovered several sauropod-like adaptations in the dorsal vertebrae (spinal column), the femur (leg bone), and the pelvic or hip area.
Utrecht University., Author provided
All these adaptations suggest that the dinosaur was heavier and walked primarily on all fours, so it could not be a Plateosaurus. It had to be something else, and in fact it turned out to be something new.
We carry out a phylogenetic analysis, which compares the anatomical features between different animals and calculates how many evolutionary steps are necessary to relate them to each other. This suggested our new dinosaur, Schleitheimiawas actually an intermediate type between sauropodomorphs like Plateosaurus and true sauropods like Brontosaurus.
Older transition species
This does Schleitheimia special in two ways. First, it is much older than the other known types of transition dinosaurs between sauropodomorphs and sauropods. And second, it is the first known form of transition from Europe.
What’s even more interesting is that some of the Schleitheimia fossils were found in the same quarry as a real one Plateosaurus. This means that both ancestral sauropodomorphs and transitional forms shared the same habitat for a time. Eventually, however, the true sauropods took over the environment.
Perhaps their size and longer necks helped them forage, we are not sure. But what we do know is that in the early Jurassic period, about 170 million years ago, sauropods already lived around the world, from China to Argentina. Schleitheimia provides one more piece of the puzzle about what happened in the very early history of sauropods on Earth.
The next steps here will be to look at other material of about the same age from Switzerland. The original and historical hole where Schleitheimia was found, has been reopened to see if there is more material.
We want to know if there were more intermediate sauropodiforms around, like Schleitheimiaor just more sauropodomorphs? And how did the first sauropods diversify and spread in the early Jurassic? The fact that we can still find new species of dinosaurs, even in historical museum collections, gives us hope of answering these questions.
