What is Convergent Evolution?
You may have heard of the term “evolution”, which describes the process in which organisms change over many generations, developing new traits and characteristics that help them survive better in their environment. Camouflaging coloration is an example of an evolutionary trait – think of a sandy colored fennec fox living in the desert. Its color helps it blend in and hide from predators.
What then, is “convergent” evolution? It describes when two organisms, which may not be related to each other at all, develop similar evolutionary traits. This often leads people to think that the two creatures must be related, but the truth is that sometimes the same sort of evolutionary adaptations can occur. Sometimes, this can occur in entirely different species of animals, or an entirely different class (ie. reptiles and mammals). It can sometimes even occur millions of years apart!
Let’s take a look at some examples of convergent evolution that can help to illustrate what it means a bit better.
Pangolin and Armadillo
The pangolin and the armadillo have a lot in common – they’re both mammals, and they both are covered in scale-like armor that protects them from predators. They also both have a habit of rolling into a ball to protect their non-armored areas.
However, despite both being mammals, these two animals are not closely related to each other, and their armor-like scales developed completely separately. Armadillos belong to a group of animals called Xenarthra, which includes sloths and anteaters in addition to armadillos. This group is unique to North and South America. Pangolins, meanwhile, belong to a group called Ferae, which includes pangolins as well as felines (cats), canines (dogs), hyenas, bears, and seals. Pangolins are only found in Africa and Asia.
There are also some differences in the armor covering these mammals. Pangolins have large, overlapping plates covering most of their entire body. These scales are made of keratin, the same substance that makes up human hair and fingernails, as well as the horns of rhinoceroses. Armadillos have much smaller scales, called scutes, which cover large areas of their body in a shell-like manner. These scutes are made of bones, not keratin.
While both use their scales for protection, they often go about it in different ways. Though both can curl into a ball if needed to protect their vulnerable areas, pangolins rely more on their large scales for direct protection from predators. Armadillos, meanwhile, usually prefer to run away, using their armor to protect them by fleeing into places where predators can’t follow, like a thorny thicket.
Ichthyosaurus and Dolphin
While Pangolins and Armadillos are not closely related, they are both mammals. Convergent evolution doesn’t always stay within the same class, or even the same time period. One extreme example is the modern day dolphin – a mammal – and the prehistoric Ichthyosaurus – a reptile.
Ichthyosaurs were a group of prehistoric marine reptiles that lived in the sea during the Jurassic and Cretaceous Periods, hundreds of millions of years ago. Though they are reptiles, their bodies have developed to be perfectly adapted to live in the ocean. Instead of arms and legs, they have flippers, and their tail developed “flukes” that made it fish-like. They also developed a triangular, shark-like fin on their backs.
Their noses also evolved into long, slender “beaks”. The flippers, fins, beak and fluked tail are all traits shared by a modern-day sea mammal – the dolphin. Despite these similarities, these animals belonged to completely different animal groups, and lived many millions of years apart. This goes to show how convergent evolution occurs to help adapt completely different animals to similar habitats and environments.
Despite their similarities, dolphins and ichthyosaurs aren’t identical. An ichthyosaur’s tail flukes were vertical, like a fish, while a dolphin’s tail is horizontal. The ichthyosaur’s tail propelled it through the water by swishing it from side to side, while dolphins whip their tail up and down to move forward. Ichthyosaurs also have enormous eyes when compared to dolphins. And finally, dolphins only have one pair of flippers, with their rear pair of legs having disappeared long ago. Ichthyosaurs retailed two full pairs of flippers – front and rear.
Bats, Birds and Pterosaurs
Sometimes, similar evolutionary traits can occur across more than just two animal groups. Take, for example, the ability of flight. Throughout history, many different animals have developed the ability to fly by turning their arms and hands into wings.
Bats and birds, for example, are two animals that independently developed flight. While both of their wings derived from arms, they are constructed very differently. The arm bones of birds have largely fused together and their fingers are mostly gone, relying on structures called feathers to help them fly.
Bats, conversely, have greatly elongated fingers, with skin stretching between each finger to create the wings that power their flight. A group of prehistoric reptiles called pterosaurs also developed flight, and their method is somewhere in between bats and birds. With pterosaurs, only a single finger was elongated to create the edge of the wing, and the flaps of skin stretch between that finger and the rear legs, somewhat similar to a bat, but with far fewer fingers.
Triceratops and Shringasaurus
Let’s take a look at one more example of convergent evolution. This time, both animals are prehistoric, but they still lived hundreds of millions of years apart from one another.
Triceratops is one of the most well-known dinosaurs today. It was a large plant-eating dinosaur that lived right at the end of the Cretaceous Period, 66 million years ago. It was one of the last of the (non-bird) dinosaurs on Earth.
One thing Triceratops is particularly known for is its horns – after all, its name means “Three horned face”. It had a horn on its nose, and two larger horns sticking out just above each eye. It’s believed Triceratops may have used these horns for defense, to help protect against predators like Tyrannosaurus Rex.
While Triceratops was discovered over 130 years ago, a much more recently discovered animal also shows a pair of familiar horns sprouting from above each eye. In 2017, scientists described a prehistoric animal they’d discovered called Shringasaurus. While it was a reptile, like Triceratops, it was not a dinosaur. It also lived 247 million years ago. That’s about 180 million years before Triceratops would ever get the chance to show of its fancy horns.
Shringasaurus was an early member of a group of reptiles called “archosauromorphs”, which include reptiles like crocodiles, pterosaurs, turtles and dinosaurs, but does not include snakes and lizards. Other than its horns, Shringasaurus didn’t really resemble Triceratops much at all. It looked more like a large lizard, with sprawling legs, a long tail, and a short, blunt head. Triceratops meanwhile, had a large body held high off the ground, with a relatively short tail and a huge head that included a sharp beak and a shield-like neck frill.
Still, they shared those pointed brow horns. Since some Shringasaur skeletons discovered had smaller horns or lacked them entirely, it’s believed that only males might have had the horns. This means that, instead of using them for battle or defense like Triceratops, Shringasaurus might have used them more for display, with males hoping to attract mates with their horns. Or, males may have used them to fight amongst themselves over females.
These are just some examples of the fascinating phenomenon known as convergent evolution. There are lots more out there! What examples can you find?