Sciences. - The column was formed in a tetrapod as it was 300 million years ago

Madrid, 30 years (Europe Press)

Antoine Ferrier and colleagues were able to reconstruct patterns of vertebral bone formation in the ancestors of all terrestrial vertebrates based on a large data set of modern and fossil vertebrates, including rare new data from the reptile Mesosaurus tenuidens. , 300 million years ago. The results are published in Scientific Reports.

The spine is the identifying and naming feature of all vertebrates, and its evolution is generally well understood. However, some crucial aspects of its evolutionary history remain obscure. A new study by a team from Humboldt-Universität zu Berlin and the Museum für Naturkunde in Berlin (Germany) reveals new aspects to this story.

Paleontologist Antoine Ferrier, first author of the study conducted as part of his doctoral research, says the project began with exceptionally well-preserved fossils of the reptile Mesosaurus tenuidens. Mesosaurus was the first reptile adapted to life in water. With a long snout and a powerful swimming tail, it inhabited an inland sea in the southern parts of the supercontinent Pangea.

In some rare events, we’ve noticed that the neural arches, the spines that sit on the main part of the vertebrae, closed from head to tail as the animals grew, like a zipper. We wanted to know how this pattern fit into the evolutionary history of terrestrial vertebrates, but we quickly We realized that very little information was available, so we decided to investigate it ourselves,” he explained in a statement.

The team looked at four of the main patterns of spine development from the amnion:

– ossification of the center (the main body of the vertebra) – ossification of the paired neural arches – fusion of the elements of the neural arch initially formed in the spine – fusion of the neural arches with the center, also called neural fusion.

They used statistical models to track the evolution of these patterns through the roughly 300 million years of terrestrial vertebrate history, thus reconstructing the patterns of the common ancestor of all terrestrial vertebrates.

“What surprised us most was that these patterns appeared to be relatively stable over the past 300 million years,” says Professor Jörg Froebsch. “Modern and extinct vertebrates are highly diverse in terms of their body shapes and lifestyles, and the elements of their spines are organized into complex units that vary greatly between species. However, the ossification patterns were more conservative than might be expected because of the great morphological diversity.”

Although the studied patterns remained relatively stable throughout evolution, due to the huge time lag considered, some deviations occurred. In particular, birds, mammals, and squamous reptiles have evolved their own patterns of vertebral ossification, which differ from the ancestral state of the amniotes. However, within these groups, the patterns were surprisingly stable.

“Ostriches and gulls, for example, have very different anatomy and lifestyles, but their spines ossify in a similar way. This shows that some changes can be observed between the major lineages of terrestrial vertebrates, but within each of the major lineages, and backbone growth has again remained stable.” says Professor Nadia Frobisch.

“Our study is another great example of how fossil and modern animal data can be brought together to gain a much deeper picture of the evolution and evolution of major body structures,” says Antoine Ferrier.