How did Great White sharks evolve?

Sharks are some of the oldest animals on Earth, and thanks to new advances in biological research, we’re still learning more about how Great White sharks have evolved and diversified over time.

What are Great White sharks? 

The Great White shark is one of the most well-known predators of the Earth’s seas and oceans. Its name is derived from its white underbelly and impressive size – Great Whites can grow over 20 feet long and can weigh as much as a car! These sharks share our five senses (smell, hearing, touch, taste, and sight), but can also detect electric fields, which helps them hunt prey in deep and murky waters.

The scientific name of the Great White shark is Carcharodon carcharias. All organisms, including both animals and plants, have a scientific name that consists of their genus and species. In this way, we can classify organisms based on their most recent common ancestor and use their scientific name to easily communicate this information. To understand more about how the Great White shark evolved, we can start by breaking down its name.

Let’s start with the second word, carcharias. Carcharias is from an Ancient Greek word meaning “shark.” The first word, Carcharodon, is made of two Ancient Greek words: carchar, meaning ‘sharp,’ and odon, meaning ‘tooth.’ If we put it all together, we get “big-toothed shark.”

The Great White shark is the last living species of the genus Carcharodon. The genus Carcharodon is part of a larger subclass called the Elasmobranchii, a group of cartilaginous fish that includes sharks and sting-rays. Species in this subclass are defined by their unique skeleton, which is made of cartilage instead of bone. Cartilage is a flexible substance that makes up our noses and ears.

How did Great White sharks evolve?

The Elasmobranchii subclass is very old, older than the dinosaurs! Scales from the earliest known shark, Elegestolepis, are 420 million years old, approximately 200 million years before the rise of dinosaurs. Dinosaurs and sharks co-existed for roughly 200 million years (from 230 to 66 million years ago), until the extinction of the dinosaurs 65 million years ago. 

Scientists originally thought that the Great White shark was descended from the megalodon (Otodus megalodon), a massive ancient shark that lived 23 to 3.6 million years ago. Both the megalodon and the Great White have serrated teeth (like a saw), which suggested a possible ancestral link between the two species. However, recent evidence has pointed to a more likely ancestor for the Great White. 

In 2012, a new species of ancient white shark, Carcharodon hubbelli, was discovered from a fossil in Peru. Based on the serration and shape of its teeth, this shark is now the most likely ancestor of the modern Great White shark. C. hubbelli, also known as Hubbell’s white shark, arose 5 to 8 million years ago. This species was a stepping stone between the Great White shark and the broad-toothed mako shark (Carcharadon hastalis) which existed roughly 15 million years ago.

Although the Great White Shark evolved millions of years ago, it’s not the oldest shark species living today. That would likely be the cow and frilled sharks, which are part of the order Hexanchiformes. The Hexanchiformes evolved approximately 200 million years ago during the Jurassic Period!

Ancient DNA: How have sharks gained or lost traits over time?

The Great White is part of an old family of sharks called the Lamnidae. Some species in this family, including the Great White, have a unique trait: they are warm-blooded, or endothermic. Like us, their bodies are warmer than their environment. Most sharks are cold-blooded, but the Great White’s warm blood helps it hunt comfortably in colder waters. 

Many younger shark species in other families lack this trait, but they have gained different traits through evolution that have made them fitter in other ways. One of the youngest modern species of shark is the walking shark, which evolved around 9 million years ago. These sharks can both swim in the ocean and ‘walk’ along coral reefs by pushing themselves on their sturdy fins.

Implications of Great White Shark DNA: New Discoveries and Ongoing Mysteries

Even though Great White sharks are a very old species, we’re still learning more about them today. New technologies have helped scientists make progress in understanding their biology and history, and in some cases, have revealed new mysteries. For example, with new sequencing technology, scientists analyzed the nuclear and mitochondrial DNA of Great White sharks to learn more about their ancestry and migration patterns, and they got a puzzling result: the two sets of DNA disagreed with each other! 

Before diving deeper into this mystery, let’s take a brief pause to explore the differences between nuclear and mitochondrial DNA, and how they can help us piece together ancestry.

All animals have two sets of DNA: one from the nucleus and one from the mitochondria of the cell. Nuclear DNA is inherited from both parents, while mitochondrial DNA is inherited only from the mother. By analyzing these sets of DNA, we can better understand the migration and breeding patterns of different animals.

When researchers looked at nuclear DNA from Great White sharks located in different parts of the world, it suggested one geographical breeding pattern. However, when they looked at mitochondrial DNA, it suggested a completely different breeding pattern. If mitochondrial DNA is passed on by female shark parents while nuclear DNA is passed on by both shark parents, then how can there be such a huge genetic mismatch?

Previous theories about the genetic diversity of Great White sharks assumed that female Great Whites migrated during the year but returned to the same breeding grounds where they were born, leading to a distinctive pattern in mitochondrial DNA that did not match that of nuclear DNA. However, a recent study of Great White sharks’ mitochondrial DNA discovered that this assumption does not actually account for the discrepancy between the mitochondrial and nuclear DNA. Basically, we’re back to the drawing board and the mystery continues!

So, where do we go from here? 

The technology we use to study genetics is advancing every day. By continuing to ask questions, revisit old studies, and challenge our assumptions, we can make exciting new discoveries about animal biology and evolution.