W. Wait. Hold On A Second. Are. Sharks Whales????????

w. wait. hold on a second. are. sharks whales????????

Nope! Sharks and whales are VEEERY different. They haven’t shared an ancestor since... well.... since the devonian, I suppose. That was over 450 million years ago!

See, it’s...

Oh, bother. Alright, fine, I’ll do an infographic. It’ll be easier to explain, because there’s a lot of stuff to digest.

Let’s go back in time to.... THE CAMBRIAN!!

Disclaimer: I made this in like an hour while slapping together what I knew about these two animals and decorating it with cute images. It isn’t totally accurate, and I’m simplifying a lot for ease of reading. Please don’t eat me, I’m not a bio major!

Transcript below the cut!

[Transcript start: The image is a simple-looking infographic with a green background and chalk-like white lined drawings of various fish.

The Cambrian Explosion, which took place about 541 million years ago, featured a whole bunch of neat stuff crawling around. This included things like: 

Opabinia - a shrimp-like organism with lots of side-fins and a tuby-like appendage which it used to scoop things into its mouth

Trilobites - the ancestor of arthropods, which we consider ‘bugs’ these days.

Dickinsonia - an organism which looks a lot like a leaf, with a middle section and ray-like parts coming out of it and forming most of its body. 

Andsome of the first fishes - the jawless fish, who were our earliest ancestors. The jawless fish resemble lamprey eels - things which don’t have a moving jaw bone.

During the Devonian period (approximately 490 million years ago), the fish line evolved jaws, which was great for them, because they could now smile winningly. (And eat stuff better.) This was the last common ancestor shared between sharks and whales.

The jawed fish evolved into two groups - one was the cartilaginous fish (or fish which have no bones, only cartilage, except for their teeth) - and the other was bony fish, which had a skeleton. These body fish were technically whale ancestors - because the group eventually evolved the species which first came up on land. These were creatures similar to lungfish, who were able to process oxygen out of water and could move themselves through mud using their flippers.

Meanwhile, the shark ancestors continued their lineage in the oceans and evolved into many more funky shapes, including rays (like stingrays) and skates.

As for the fish on land - they were the ancestors to what we know today as the tetrapods - the things which eventually became the amphibians, lizards, dinosaurs... and mammals! 

One of these mammals was the whale ancestor, which looked quite similar to what we think of as a regular land animal - it had four limbs, and a body plan not dissimilar to dogs, cats, etc. Although it could walk on land, it decided to make an evolutionary U-turn and go back into the water again.

They evolved to be optimized for swimming, and eventually lost their hind limbs. They still needed to breathe air, though, and they are still considered mammals, because they birth and nurse their young! 

This begs the question: If sharks and whales aren’t related to each other that much, why do they look so similar?

That’s a great question! That’s because of something we call Convergent Evolution.

It turns out some shapes just work really well when you’re trying to swim in water. Having fins, flippers, and being fish-shaped just gives you advantage, so many water dwelling creatures end up evolving similar bodyplans - like whales and sharks did.

There’s still a reliable way to tell the two apart, though. Check their tails! See if you can tell the difference.]