Fossilized remains of a 290-million year old shark with petal-shaped teeth have been found in China for the first time. They were discovered at Qianshi limestone mines near Yangquan City, north central Shanxi Province and their study has provided insight into how this ancient species lived through its evolutionary history as well as what environmental conditions may have shaped it over time.
The study, led by Gai Zhikun, an associate researcher at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, was published in the most recent publication of Acta Geologica Sinica.
Petalodus is a genus of small, enigmatic chondrichthyan. There are two species that have been assigned to this group; One with seven teeth found in Yangquan City and another located off the coast of PEI (a Canadian province). These differences can be seen through subtle features like their cingulum (the ring around each tooth) which has an unusually narrow shape for its length as well as being vertically longer than it horizontally expansive – almost resembling a root more so than rest-or growing edge near its tip.
In terms of size, the Petalodus tooth fossil is close to the tooth of the great white shark (Carcharodon carcharias). It can be estimated that it is a prehistoric giant shark with a body length of three to five meters.
The study showed that these teeth are very sharp, have a spade-like crown and long tongue-shaped root. These features may be useful when biting soft tissues because it makes them perfect for slicing open flesh in order to catch prey or defend themselves against predators with irritant chemicals on their skin
The vertical fine grooves running along the edge of each blade help keep food trapped between rows while horizontal imbricated ridges embrace its base which would prevent escape by increasing friction once pierce through a soft tissue.
In modern sharks, some teeth have been significantly modified from the typical ‘spade’ shaped tooth. In tiger sharks for example, their anterior teeth are very slender and laterally compressed with a sharp cutting edge as seen on meat-slicing machines. These teeth start to appear as curved triangular forms with serrations on both edges in the anterior section of the jaw which is used for grabbing on prey then twist into ‘fishhook’ form with serrations only on one edge before becoming relatively smaller but more deeply rooted teeth which are shaped like a typical spade-shaped teeth.
The fossil site of Yangquan was part of a shallow, warm and light-permeable sea close to the equator that existed more than 200 million years ago. The isolated position on an ancient craton would undoubtedly act as a barrier for Petalodus’ dispersal into other areas during this period when all landmasses were connected via waves or currents instead.
“The successful dispersal of Petalodus from Laurusia to the North China Block along the Paleo-Tethys Ocean indicated that Petalodus might already have the ability to migrate across the ocean, and it may be a top predator with strong swimming ability, rather than a benthic shell cruncher,” said Dr. Gai.