SciNews has an article about the ancestor of Mackerel sharks. The article is from earlier this month, but posting it seems appropriate with Shark Week occurring this week. An ancestor of the Great White Shark (Carcharodon carcharias) has been found. Palearocarcharias stromeri was a small benthic shark, which lived about 165 million years ago, during the Jurassic period. The researchers looked at tooth structure to determine ancestry in sharks. The findings were published in the Nature journal Scientific Reports.
“Similar to humans, shark teeth are composed of two mineralized structures: a hard shell of hypermineralized tissue (in humans enamel, in sharks enameloid) and a dentin core,” said Dr. Patrick Jambura from the University of Vienna and colleagues.
“Depending on the structure of the dentin we distinguish between two different types: orthodentin and osteodentin.”
“Orthodentin has a very compact appearance and is similar to the dentin we can find in human teeth.”
“In shark teeth, orthodentin is confined to the tooth crown. In contrast, the other dentin type is spongious in appearance and resembles real bone and therefore is called osteodentin.”
“It can be found in the root, anchoring the tooth to the jaw and in some species also in the tooth crown where it supports the orthodentin.”
Using high resolution micro-CT images, the scientists examined the tooth composition of the great white shark and its relatives.
They found a peculiar condition of the teeth of members of this group: the osteodentin of the roots intrudes into the crown and replaces the orthodentin there completely, making it the only type of dentin being present. This condition is not known from any other shark, which all possess orthodentin to some degree and thus it is confined to members of this group.