Today’s animal (fossil?) started as a request from my partner. A guitarist from a band he likes just released a Tiktaalik-inspired solo album, and he wanted to know more.
And then, just a few days later, we saw a Tiktaalik exhibit at the Harvard Museum of Natural History! So I obviously HAD to tell you about it after seeing it on two separate occasions in the span of a week.
I should be clear up front: Tiktaalik (Tiktaalik roseae) is extinct. They lived during the Late Devonian Period, which occurred about 375 million years ago. Also called the Age of Fishes, the Devonian Period is when life began transitioning to living on land. It started with an immense variety of fishes. While they were all doing their fish thing, primitive shrubs and trees began populating the land. Eventually, there were probably too many fishes, and the water of inland lakes became depleted of oxygen. But remember! There are plants and trees now, creating oxygen outside of the water! So, certain fish began to evolve lungs in order to take advantage of this oxygen.
Which brings us to the Late Devonian Period and the Tiktaalik. With forests taking shape on land, animals began to move out of the water. One of those animals: the Tiktaalik.
Discovery
But of course, in order to know anything about Tiktaalik, we had to first find their fossils.
Tiktaalik is actually a pretty recent discovery: the first three fossilized Tiktaalik were found in 2004. A group of researchers found them on Ellesmere Island, Nunavut, up in northern Canada. This might seem like a cold place to be finding fish, but remember: Tiktaalik lived millions of years ago. At this point in time, Ellesmere Island was actually centered on the equator and had a nice, pleasantly warm climate.
After it’s discovery, the researchers asked around for potential names. They got the suggestion Tiktaalik from Inuit elders of the Nunavut Territory. Tiktaalik is an Inuktitut word that means “large freshwater fish.” The second half of the name, roseae, comes from an anonymous donor.
Armed with fossils and a name, researchers began to study Tiktaalik in depth.
The best (?) of both worlds
What they found was fascinating: Tiktaalik is a transitional fossil. It has characteristics of both ancestral life forms (i.e., fish) and descendants (i.e., land-living animals). Tiktaalik represents the transition from living in water to living on land.
What exactly are these traits? Let’s start with the fish ones. Tiktaalik have fish gills, fish scales, and fish fins. They lived primarily in water and swam around. You know, classic fish things.
But Tiktaalik also has tetrapod characteristics (tetrapods are any 4-limbed animals. We’re tetrapods). Tiktaalik had tetrapod rib bones and lungs. These large ribs are a key tetrapod feature, as fish don’t need strong ribs because their body is supported by the surrounding water. Tiktaalik also had forelimbs that could support their weight and eyes on the top of their head. They are even the first known fish to have a neck – unlike most fishes, Tiktaalik has a pectoral girdle that is separate from their skull.
Tiktaalik also has intermediary, or “fishapod,” traits. Their limbs and joints look like a mix of fish and tetrapods, with a functional wrist joint like a tetrapod and fish-like fins instead of toes. Their ear also seems to be an intermediary – they had a spiracle, or small gill slit, that would become an ear further down the evolutionary line.
Likely behavior
Obviously, humans weren’t around 375 million years ago, so we don’t have any first-hand accounts of Tiktaalik behavior. However, we can make some assumptions based on Tiktaalik skeletal structure and commonalities with present-day animals.
We’re pretty sure Tiktaalik was a predator: it’s skull has sharp teeth and well-developed jaws that could catch prey. The fact that they had a neck means that Tiktaalik could more easily hunt on land or in the shallow water. They also probably hunted much like crocodiles do today and likely had a line of receptors in the upper layer of their skin that sensed nearby prey.
We also think that Tiktaalik lived in shallow streams or a swampy habitat. Researchers discovered the Tiktaalik fossils in the Fram Formation, an area that in the Devonian Period was a system of meandering streams. During this time period, there was also a reliable amount of deciduous plants shedding their leaves into the water. This attracted smaller prey to the shallows where it was difficult for larger fish to swim. But not for Tiktaalik! The Tiktaalik pelvic girdle is pretty solid, and researchers say they could support the body of a Tiktaalik moving across shallow water or land. So, Tiktaalik very likely was able to hunt the smaller prey hiding in the shallows of the streams. They probably moved across mudflats like mudskippers, a present day amphibious fish that moves overland by propping themselves on their fins.
Evolutionary importance
Tiktaalik is a key piece of our evolutionary history. Its fossils catch the transitional moment when life started to move from the water onto the land. Perhaps even more importantly, it confirms that there was an intermediary step. It’s one thing for scientists to say that “obviously life started in the ocean and eventually evolved to live on land.” Tiktaalik provides evidence that this transition did indeed occur.
So there’s Tiktaalik. A key part of our evolutionary history that I also find strangely cute.
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