Sharks haven't changed in millions of years, right? Wrong!

If evolutionary success is measured in terms of longevity, then the Chondrichthyan fishes are one of the most successful vertebrate groups. Their lineage has persisted for more than 400 million years and has survived several mass extinction events, including that which famously killed the dinosaurs. People often misunderstand this to mean that extant species of sharks, rays and chimaeras are ancient animals that haven't changed in millions of years. This couldn't be further from the truth. Mass extinction events leave various ecological niches unoccupied. These events are often followed by periods of rapid adaptive radiation as organisms evolve and adapt to fill them again. This means that the Chondrichthyan fishes have had tremendous opportunity to evolve and diversify over the course of their long history. The result is a group of modern and supremely adapted shark, ray and chimaera species that exhibit a diversity of morphological and ecological forms. 

Here you can see the chondrocrania (brain case) of just 15 different species, showing the extent of variation that exists across the Chondrichthyan Tree of Life.

 

We can map variation like this for any trait of interest onto our phylogenetic tree and use it as a road map to study how the trait has evolved. 

On our website, you can compare anatomical structures across species using our interactive platform for exploring CT scans.

 

 

Here's an example, comparing the meckel's cartilage of sharks from the Orders Orectolobiformes (Orectolobus maculatus, spotted wobbegong), Lamniformes (Isurus oxyrinchus, shortfin mako) and Carcharhiniformes (Carcharhinus plumbeus, sandbar shark).