A Blue View: Your Inner Fish

With fins, scales and a flattened head, the Tiktaalik looks something like a crocodilian fish. Its fossils were first discovered in the early 2000s within the sediments of former streambeds of the Canadian Arctic.

Published January 05, 2016

tiktaalik-by-wikicommons-user-obsidian-soul

Image via Wikicommons by Obsidian Soul.

So what makes this ancient fish so important? For billions of years, all life on Earth existed in the water. According to fossil records, primitive land-living creatures, or tetrapods, didn’t appear until about 365 million years ago. The two worlds may seem disconnected but they are inextricably linked.

The tiktaalik represents that transition from sea to land. Its name is from the Inuit language Inuktitut and translates roughly to large, freshwater fish. But the seafaring animal’s anatomy bears remarkable similarities to the body structure of animals suited for land.

Like most fish, the tiktaalik had scales and webbed fins, but what distinguished it from other sea creatures at the time was its internal structure. It had primitive lungs and within its fins were bones and joints that resembled those of arms, wrists, shoulders and elbows.

The fins were pseudo-limbs that scientists believe may have allowed the fish to paddle through the water and even “walk” on the floor of a lake. The tiktaalik would have been well adapted to life in shallow water, able to prop itself up. A neck enabled the animal to swivel its head from side to side, a feature that sets it apart from most modern fish.

The tiktaalik was the predecessor of amphibians, reptiles and eventually mammals. Some anatomical features similar to the tiktaalik’s can even be seen in humans. It’s cranial bone, or hyomandibula, for example, is much smaller than that of ancestral fish. In fish, the bone attaches to the upper jaw and braincase to assist with breathing through the gills. In land animals, however, the bone is much smaller and has evolved to function as part of an entirely different system—hearing. In humans, it’s called the stapes and is one of the bones found in the middle ear.

The tiktaalik was an intermediate of aquatic and terrestrial life, a creature beginning the evolutionary journey of adapting to a life on land.

Episode Transcript

If you need a new icebreaker for your next dinner party, try this one: “Did you know your skull and head are organized like an extinct jawless fish?” OK That’s weird, but it is true.

Take your philtrum, for example. That’s the groovy indentation on your top lip beneath your nose.

You've probably never thought much about it, but your philtrum a clue to our shared ancestral past.

It is evidence of your "your inner fish,” as paleobiologist Neil Shubin called it in his book of the same name.

Shubin and colleagues discovered the fossil Tiktaalik, the so-called "fish with hands." The discovery has had implications for understanding human evolution. You see, it turns out, our origins are fishy.

And it's not just your philtrum. It's also your neck and many other structures.

The top lip, along with the jaw and palate, started life as gill-like structures on your neck. Our philtrum is a vestige of our evolutionary past, and of our time in utero.

As the human embryo develops, the parts of our face grow independently and then meet in the middle, at the philtrum, which forms a seam. The parts must line up in synchrony. When they don't, the result is a cleft palate.

Comparative embryology is a field of biology that compares the anatomical similarities and differences of animals in their earliest stages of development. The early human embryo looks very similar to the embryo of every other mammal, bird or amphibian—all of which evolved from fish.

Like all the fish in the sea we morphed. Our fins became hands, our tails disappeared and legs sprouted. Now we walk instead of swim. Well, most of us.

Yet we still have vestiges. If you've ever taken a bad fall backward, you know all about your coccyx, or tail bone.

But did you know the anatomy of the human inner ear with its three delicate bones is structurally related to the jaws of a shark?

Consider, also, your knees. Knee injuries are common among humans. The knees are one of our body plan's weakest joints.

That's probably because the first knee-like structures appeared 300 million years ago in the pelvic fins of fish. The animals that had them were mostly aquatic, so their so-called “knees” didn't bear much weight. It was just a simple hinge. And now this hinge must bear the entire weight of our heavy upright bodies as we run, walk, jump, play soccer and pursue sports unthinkable to a fish.

So, let’s take stock: You have an ear like a shark's jaw, knees like a fish—what else? Well, you hiccup like a tadpole. The hiccup reflex of tadpoles helps them breathe through their gills and prevents water from overwhelming their developing lungs.

If that sounds like something out of a science fiction movie, you’d be right. Minus the whole fiction thing.

To learn more about your inner fish, visit aqua.org/ablueview.

Previous Post

Featured Stories

national-aquarium-staff-holding-rescue-sea-turtle-on-beach Animal Rescue Update: February Sea Turtle Release

Yesterday, National Aquarium Animal Rescue released 34 sea turtles on the Canaveral National Seashore in Florida!

Read the full story

artificial-oyster-reef-in-inner-harbor Harbor Happenings: Artificial Oyster Reef

The National Aquarium is taking another step to revitalize Baltimore’s Inner Harbor and attract native species with a new artificial oyster reef using shells from the Oyster Recovery Partnership!

Read the full story

Related Stories

A Blue View: Shark Navigation is All in the Nose

Published June 28, 2016

A Blue View: Oyster Gardens

Published June 21, 2016