A recent research study by an international group of scientists, led by palaeobiologist Patrick L. Jambura from the University of Viennas Department of Palaeontology, has revealed that cartilaginous fish have gone through more evolutionary modifications than previously thought. The proof for this conclusion was gotten from brand-new fossils of a shark-like ray called Protospinax annectans, which show that sharks were extremely developed during the Late Jurassic period. Sharks, rays, and ratfish are a group of ancient animals known as cartilaginous fishes, which have actually been present on earth for over 400 million years, predating the dinosaurs. They have actually also withstood all five mass terminations and their fossil stays can be found internationally in fantastic amounts. Protospinax lived some 150 million years earlier and was a 1.5-m-long, dorso-ventrally flattened cartilaginous fish with broadened pectoral fins and a prominent fin spinal column in front of each dorsal fin.
Fossil of the Late Jurassic shark Protospinax annectans from Solnhofen and Eichstätt, Germany. Credit: Sebastian Stumpf
The evolutionary history of rays and sharks has been illuminated by a recently built phylogenetic tree.
A recent study by an international group of scientists, led by palaeobiologist Patrick L. Jambura from the University of Viennas Department of Palaeontology, has actually exposed that cartilaginous fish have gone through more evolutionary modifications than previously believed. The evidence for this conclusion was gotten from new fossils of a shark-like ray called Protospinax annectans, which reveal that sharks were highly progressed throughout the Late Jurassic duration. The findings of the study have actually been published in the journal Diversity.
Sharks, rays, and ratfish are a group of ancient animals known as cartilaginous fishes, which have been present on earth for over 400 million years, preceding the dinosaurs. They have likewise sustained all five mass terminations and their fossil remains can be found internationally in terrific amounts. However, usually only their teeth stay undamaged as the cartilaginous skeleton decays in addition to the remainder of the body and does not fossilize.
A distinct window into the past
In the Solnhofen archipelago, a so-called “Konservat Lagerstätte” in Bavaria, Germany, skeletal remains and even imprints of skin and muscles of Late Jurassic vertebrates (consisting of cartilaginous fishes) have been preserved due to unique conservation conditions. The research study team used this situation to take a more detailed take a look at the previously unclear role of the currently extinct species Protospinax annectans in the evolution of sharks and rays, also with the aid of modern genetic proof.
Paleoreconstruction of the Solnhofen Archipelago 150 million years ago showing Protospinax annectans and the Jurassic ray Asterodermus platypterus. Credit: Manuel Andreas Staggl
” Protospinax brought functions that are found in both sharks and rays today,” describes research study author Patrick L. Jambura. Protospinax lived some 150 million years back and was a 1.5-m-long, dorso-ventrally flattened cartilaginous fish with expanded pectoral fins and a popular fin spinal column in front of each dorsal fin. Known from unspoiled fossils, the phylogenetic position of Protospinax has puzzled scientists ever given that it was first described in 1918.
” Of specific interest,” Jambura continued, “is whether Protospinax represents a shift between sharks and rays as a missing link– a hypothesis that has actually acquired significant appeal amongst specialists over the previous 25 years.” Alternatively, Protospinax might have been a really primitive shark, an ancestor of sharks and rays, or a forefather of a specific group of sharks, the Galeomorphii, which consists of the excellent white shark today– all of which are amazing concepts whose plausibility has actually now been clarified by scientists.
One mystery solved, another one remains
Incorporating the most recent fossil finds, Jambura and his worldwide group reconstructed the ancestral tree of extant sharks and rays utilizing genetic data (mitochondrial DNA) and embedded fossil groups– consisting of Protospinax annectans — using morphological information. The outcomes of the analysis were startling: Protospinax was neither a “missing link” nor a ray nor a primitive shark– however an extremely progressed shark.” We tend to consider evolution like a hierarchical, ladder-like system, in which older groups are at the base, while human beings, as a really young species in Earths history, are at the top. In reality, however, advancement has never stopped even for these primitive agents, however they continue to evolve day by day through modifications in their DNA, simply as we do. This is the only way they have actually been able to adjust to constantly changing environments and survive to this day,” says Jambura.
Although cartilaginous fishes as a group have made it through to this day, most species disappeared throughout their advancement, consisting of Protospinax. Why Protospinax ended up being extinct at the Jurassic-Cretaceous boundary some 145 million years earlier and why there are no comparable shark types today, while the environmentally similarly adjusted rays exist relatively unchanged to this day, stays a mystery at this moment.
Recommendation: “Systematics and Phylogenetic Interrelationships of the Enigmatic Late Jurassic Shark Protospinax annectans Woodward, 1918 with Comments on the Shark– Ray Sister Group Relationship” by Patrick L. Jambura, Eduardo Villalobos-Segura, Julia Türtscher, Arnaud Begat, Manuel Andreas Staggl, Sebastian Stumpf, René Kindlimann, Stefanie Klug, Frederic Lacombat, Burkhard Pohl, John G. Maisey, Gavin J. P. Naylor and Jürgen Kriwet, 21 February 2023, Diversity.DOI: 10.3390/ d15030311.
