Sharks are arguably the ultimate predators. They’ve been around since before trees evolved 400 million years ago, and they’ve survived multiple mass extinction events, including the Great Dying, which killed off around 96 percent of all life on Earth. Their gloriously sharp teeth are a key part of their hunting apparatus, and a new study published in the journal Developmental Biology reveals how they’re able to keep a continual supply of them.
It has long been known by researchers that animals with skeletons comprised of cartilage, including sharks and rays, have the remarkable ability to continuously regenerate their teeth, which are often arranged in deadly, backwards-facing rows.
Researchers from the University of Sheffield, led by Dr. Gareth Fraser, decided to investigate the method behind this continual production of teeth in sharks. As these animals represent an incredibly ancient evolutionary lineage, any insight into how their dentition evolved is essentially a look into the evolution of teeth in all jawed vertebrates.
The team decided to look at the genomes of species within the catshark genus, Scyliorhinus. These sharks are found in temperate and tropical seas all cross the world, and first evolved back in the Cretaceous period, 145 to 66 million years ago.
A catshark not looking particularly pleased. Susana_Martins/Shutterstock
In various catshark species, they identified a set of genes associated with early dental strength, the beginning of tooth growth, and the regeneration of teeth. In addition, these genes were connected to a group of specialized cells called the dental lamina. These cells are found in both humans and sharks, and are responsible for growing teeth.
The difference, of course, is that sharks have a theoretically endless supply of teeth, and that at some point during our evolution, we’ve lost this trait. Unlike humans – who lose their dental lamina early on in life – sharks have a permanent dental lamina within their jaw, which initiates the growth of a new tooth each time one is lost.
The growth of teeth in catshark embryos was also observed by the team. The catshark’s first set of teeth are somewhat irregular and poorly developed, and are fairly superficial – they appear to be rather like the baby teeth found in humans, in that they are designed to be replaced by a stronger, more regular second generation of teeth. As time goes on, multiple generations of teeth may be present in the shark’s jaw at any one time.
The associated tooth-growing genes were also considered by the researchers to be incredibly ancient; in fact, they were likely responsible for growing the very first set of vertebrate teeth. If so, that means that these genes are the very same ones that control teeth growth in all vertebrates.
Although it may seem like a good idea to try and incorporate these regenerative abilities into human teeth, it's not quite clear how this might be done. In fact, it may actually be a good thing that humans don’t have constantly regenerating teeth. “We have a dentition that is designed to ‘fit’ together,” Fraser told IFLScience. “If humans had continuously regenerative dentitions or at least multiple rounds of replacement, then there would be a good chance of developing misaligned and non-functional teeth.”