It is characterized by unique teeth that allow it to break even the shell of a turtle. The analysis of its fossils now reveals not only the origin of this species of shark, but also its antiquity.
The fossil history of modern sharks se dates back to 295 million years ago. But it has not always been easy to find complete remains of these animals. Their skeletons, composed almost entirely of cartilage, have only been preserved under very special circumstances during the fossilization process.
Despite this absence in the fossil record, most of the extinct sharks have been know thanks to their teeth well mineralized, which grow and are replaced throughout their lives. It is these fossils that provide a deeper perspective on the evolutionary history of these predators.
A study published in the journal Paleobiologyhas now made it possible to review the fossil record of the 22 extinct species from tiger sharksbelonging to the genus Galeocerdothanks to the analysis of the morphological diversity and disparity of its teeth.
To do this, scientists from the Department of Paleontology at the University of Vienna (Austria) used geometric morphometry, a tool based on reference points to determine the shape and morphological characteristics of the teeth depending on the different extinct species of tiger shark and the current one.
The results show that, although these sharks were more diverse in the past, only five of the 22 known fossil tiger shark species are actually valid taxa, apart from the current one (Galeocerdo cuvier), the only one that has survived to the present day and only representative of the genus.
Tiger shark teeth. / D.Ross Robertson.In addition to its characteristic stripes on its back, more marked in juvenile specimens and that fade in adults, the modern tiger sharks stand out for their teeth unique: large, sharp, very sharp and with serrated edges that allow them to easily break the bones of other animals as well as the shells of turtles.
However, although there were no remains of tiger sharks in the fossil record of the Middle Miocene, the authors have been able to identify 37 teeth, found in Florida in the USA, from 13.8 million years ago, and associate them with this species. This delays its appearance from the early Pliocene to the middle Miocene and shows that it originated earlier than previously believed.
Tiger shark with diver. / © Michael Vogelsang / www.seapicture.de