Thousands of teeth tell the long history of sharks
10 March 2020
Sharks have roamed the earth’s oceans for around 450 million years. Although they survived the catastrophic extinction event that wiped out the dinosaurs, that event did alter the balance between two important shark groups. In his degree project, Mohamad Bazzi investigates which types of shark have been most successful during different periods.
Sharks have skeletons of cartilage. This is a light, flexible material but it is rarely preserved, meaning that there are very few fossils of shark bodies. Something that we do have in significantly larger quantities is shark teeth, which are the raw material for Mohamad Bazzi’s research; teeth that he has collected himself, teeth in natural history collections and photographed teeth in scientific literature. In total, this amounts to approximately 20,000 teeth, compiled in various datasets and arranged by shape and size.
It is from this abundant material that Mohamad Bazzi studies the evolution of sharks and their biological variation over time. It is only now that the tools are available to conduct this type of study and the hope is that the new results can fill in the gaps in knowledge regarding the evolutionary journey of sharks.
The extinction event that wiped out the dinosaurs occurred 66 million years ago. One central question in Mohamad Bazzi’s study is how it came about that ground sharks (Carcharhiniformes) increasingly began to dominate after this catastrophe, while mackerel sharks (Lamniformes), which had previously ruled the roost, went into decline. Today, this group numbers only 15 species compared to over 290 species of ground shark.
“This is the reverse of the situation 66 million years ago, something that is absolutely crying out for an explanation,” says Mohamed Bazzi.
Sharks – facts:
The tooth belongs to a group of lamniform sharks known as orthodontics. This is the same group that Otodus megalodon belonged to, a species that lived some 56 million years ago and is generally considered to be the largest shark ever to exist.
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