An Ancient Jurassic Shark Fossil Reveals Surprising Evolutionary Truths

An Ancient Jurassic Shark Fossil Reveals Surprising Evolutionary Truths ...

Protospinax annectans from Solnhofen and Eichstätt, Germany, is a fossil. Credit: Sebastian Stumpf

A recent research led by palaeobiologist Patrick L. Jambura from the University of Vienna's Department of Palaeontology reveals that cartilaginous fish have undergone far greater evolutionary evolution than previously assumed. The evidence for this conclusion was obtained from new fossils of a shark-like ray called Protospinax annectans, which demonstrate that sharks were highly evolved during the Late Jurassic period.

Sharks, rays, and ratfish are all members of the ancient cartilaginous fishes, which have been on earth for over 400 million years, predating the dinosaurs. Their fossil remains are still present throughout the world in large quantities because of their decay.

Due to special preservation conditions, skeletal remains and even imprints of skin and muscles of Late Jurassic vertebrates (including cartilaginous fishes) have been preserved in the Solnhofen archipelago, also with modern genetic evidence.

The Solnhofen Archipelago's paleolithic features include Protospinax annectans and the Jurassic ray Asterodermus platypterus. Credit: Manuel Andreas Staggl

According to study author Patrick L. Jambura, Protospinax exhibited features that are still found in both sharks and rays today.

Protospinax may have been a very primitive shark, an ancestor of rays and sharks, or a member of a certain group of sharks, the Galeomorphii, which includes the great white shark today. All of these concepts have their place in science.

Jambura and his international team reconstructed the family tree of extant sharks and rays using genetic data and embedded fossil groups — including Protospinax annectans — using morphological data. “Evolution has never stopped for these primitive animals, but they continue to evolve day by day, just as we do,” says Jambura.

The majority of cartilaginous fishes as a group evolved during their evolution, including Protospinax. The reason why Protospinax became extinct at the Jurassic-Cretaceous boundary some 145 million years ago and why there are no comparable shark species today, while the ecologically similar rays exist relatively unchanged to this day, is unresolved.

Patrick L. Jambura, Eduardo Villalobos-Segura, Julia Türtscher, René Kindlimann, Stefanie Klug, Frederic Lacombat, John G. Maisey, Gavin J. P. Naylor, and Jürgen Kriwet, 20 February 2023, Diversity. DOI: 10.3390/d15030311.

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