In the dinosaur age (Jurassic) about 150 million years ago, where the Bavarians live today, sharks lived in lagoons on coral islands alongside Archeopteryx protozoa, explains Patrick Jambura of the Department of Paleontology at the University of Vienna. Contrary to previous assumptions, these five-foot-long, flat Jurassic sharks were not the primitive ancestors of today’s cartilaginous fish, but highly evolved sharks, he reports.
“From an evolutionary point of view, cartilaginous fish such as sharks and rays are a very old group of animals that lived on Earth more than 400 million years ago, before the dinosaurs,” the researcher said in a broadcast from the University of Vienna. There are over 500 species of sharks and over 600 species of rays. These fish have survived all five of Earth’s previous mass extinctions. Numerous fossils of them have been found all over the world. Usually, however, only their teeth remain, while the cartilaginous skeleton has decomposed like the rest of the body.
Impressions of skin and muscles obtained
In a deposit in Bavaria, the “Solnhofer Archipelago”, the conditions are very special: not only skeletal remains, but even imprints of the skin and muscles of the cartilaginous fish from the Jurassic era have been preserved. 150 million years ago there was an archipelago in the Tethys Sea (primeval Mediterranean) on this site with coral islands where there were insects and the ancient bird Archeopteryx, as their remains testify.
Relationship was previously unclear
In turn, the lagoons were home to “Protospinax annectans”, cartilaginous fish. This species was first described in 1918 as “1.5 meters long, flattened cartilaginous fish with extended dorsal fins and two prominent spines for each dorsal fin,” according to the release. Until now it was unclear where to classify them. Among other things, it was discussed: as the “missing link” between sharks and rays, as a primeval shark or as the ancestor of a subgroup that produced the great white shark that lives today.
Jambura’s team first created a family tree of sharks and rays living today based on their genetic codes (mitochondrial DNA). Next, the researchers compared 224 shape features (morphological features) in Protospinax annectans, extant sharks and rays, and other fossil sharks and rays. This enabled them to determine the relationships and position of Protospinax annectans in the evolutionary tree of sharks and rays. Their study was published in the journal Diversity.
“Our analysis revealed that Protospinax’s closest relatives are the living angelsharks and sawsharks,” Jambura reported. However, the differences between the two are so great that he probably belonged to his own, very well-developed group. “That was unexpected, because with such an old species you would actually expect an original shark or an ancestor of a group,” said the paleontologist.
“Even if cartilaginous fish have survived to this day as a group of animals, most species have disappeared in the course of evolution,” the researchers write: this also happened with Protospinax annectans on the boundary between the Jurassic, for unknown reasons. and the Cretaceous (about 145 million years ago). So before the demise of all dinosaurs, which marks the end of the Cretaceous Period (66 million years ago).
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