Palaeontologists from the Universitat de València reconstruct the appearance of one of the first vertebrates of more than 350 million years ago

The work of this team of the Faculty of Biological Sciences and Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBE) has focused on establishing the relationship between the current sharks’ body morphology and its locomotion, in order to make comparisons and understand the body shape of extinct fish species. The essential discovery of the work has been the fact that within the sharks group that swim continuously and actively, the larger species need proportionally larger tails (or caudal fins.)

This phenomenon is due to the need to compensate a loss of buoyancy which is in bigger individuals, since the frequency which they beat their tails diminish with the size, explains Humberto Ferrón, researcher of the Department of Geology of the Faculty of Biological Sciences.

Moreover, he assures that this fact explains that the largest species of sharks, like the well-known white shark (Carcharodon carcharias,) have very wide and sickle tails. In fact, he adds, this phenomenon has been already documented previously in other groups unrelated to sharks, such as dolphins or tunas, or even in extinct marine reptiles groups such as the ichthyosaurus.

The research concludes that Dunkleosteus terrelli might had a much wider caudal fin than previously speculated, more consistent with physics principles that govern the locomotion of marine animals. “This idea agrees with the recent discovery of a structure of the sharks called ceratotrichia in placoderms fossils, that constitute the tissue responsible for expanding and shaping the fins beyond the skeletal elements” explains the expert.

The reconstruction of this vertebrate has count on the participation of the paleoillustrator Hugo Salais.

About placoderms

According to Humberto Ferrón, placoderms were the first vertebrates in acquire jaw and they lived in our seas and rivers around the work during Silurian and Devonian periods (between 440 and 360 million years ago.) They were fish with a bone shell that covered the most anterior part of the body (head and thorax), while the rest of the trunk and tail were usually covered with small scales and their skeleton was cartilaginous in nature. As a consequence, in many cases, the only placoderms remains that have been preserved in the fossil record are the bony plates of the head, which is why the body shape is unknown in most of species discovered so far.

Dunkleosteus terrelli, the largest carnivorous placoderm described so far, is not an exception. Most of the classical reconstructions of this species have been purely speculative. Nevertheless, a few have been based on the appearance of smaller placoderms where some remains of the tail and other body parts are known.