Tiktaalik roseaeLate Devonian (375 Ma)I’m back again, after a loooong time neglecting this

Tiktaalik roseaeLate Devonian (375 Ma)I’m back again, after a loooong time neglecting this blog. I’ve been planning to come back for a while, and I’m finally here! I thought I’d return with one of my favorite vertebrate fossils, Tiktaalik roseae! The common ancestor of all tetrapods was probably not Tiktaalik, but something very similar. Scientists use it as a model organism for that ancestor, though, and I’ll be doing the same here.The invasion of the land is a fascinating subject for paleontologists, because it’s one of the first major steps toward life as we know it today. Life evolved in the oceans, and for the majority of earth’s history, stayed there. It’s uncertain when exactly life first made landfall. Rocks from deep in the Precambrian show evidence of photosynthetic microbes who lived on land, and simple plants were sprouting along shorelines by 430 million years ago. Before this, water on earth was confined to oceans or isolated lakes, but the advent of those land plants meant the creation of the first soils and mud, in turn leading to the formation of the first river systems. Not long after the first terrestrial plants, arthropods and their relatives arrived and began carving niches for themselves.By the middle Devonian (~385 Ma), terrestrial ecosystems proliferated. The first forests covered the landscape, and invertebrates ran rampant, including the earliest insects. Fish, though, had yet to leave the water. So, what took them so long? Simply put, they waited until they had a good enough reason to go poking around up there. Although the land is my main focus today, the Devonian is more famously known as the Age of Fishes. This was the first time jawed vertebrates rose to the top of their ecosystems, and the first time they got truly big. This was the height of the placoderms, armored fishes like the infamously gigantic Dunkelosteus, and Bothriolepis, which kind of looked like a shield with fins. On the cartilaginous side were the spiny ‘sharks,’ as well as true sharks like Cladoselache and Stethacanthus.At this point I’m just naming prehistoric fish that I like, so let’s get back to tetrapod evolution.Most of the traits we associate with tetrapods evolved in fully aquatic fish. Specifically, in a branch of fish called Sarcopterygians, or lobe-finned fish. Today, lobefins are represented by a handful of lungfish and the coelacanth, but they were all over the place in the Devonian. Early ancestral cousins of tetrapods were animals like Eusthenopteron, which looked like ordinary fish on the surface, but had unique skeletal structures. Particularly, their pectoral fins are built similarly to tetrapod limbs. Later animals would develop larger, sturdier fins they used for walking along the bottom of rivers, rather than land.This is where our star comes in. Tiktaalik was adapted to live in shallow rivers or streams. It had a wider, flatter body than most fish, and it had lost its dorsal and anal fins. The four fins on its underside were built very similarly to tetrapod limbs. Tiktaalik is also one of the first vertebrates with a proper neck, meaning, in the words of Will and David from The Common Descent Podcast, you could strangle it, if you ever wanted to do that sort of thing.Tiktaalik was a predator of small-to-medium-sized invertebrates. Its big, triangular head housed pointy teeth, and had two eyes on top. It looked like a crocodile in many ways, and may be one of the earliest animals to adapt the crocodilian lifestyle, laying at the bottom of a body of water and waiting for prey to come by. The placement of Tiktaalik’s eyes may have been useful for peering out from the water surface while staying mostly hidden.Despite being known as the 'fish with feet,’ Tiktaalik wasn’t exactly graceful on land. Rather than walking primarily with limb muscles like most tetrapods do, Tiktaalik walked by heaving itself forward with its front limbs and powerful shoulder muscles. Basically, it walked by doing push-ups. As you can imagine, Tiktaalik probably didn’t spend much time out of the water. But, this goofy style of terrestrial movement was a precursor to the more efficient methods seen in landlubbers today.Tiktaalik is my favorite prehistoric fish, and definitely a contender for favorite vertebrate. It was one of the first animals to really grab my attention once I started seriously getting into paleontology. While I was still trying to understand evolution I read Your Inner Fish, a book written by Neil Shubin, who was a part of the expedition team who discovered Tiktaalik. It discusses the animal in so much more detail than I did here, and is pretty much required reading for anyone who’s interested in paleontology. In fact, I’m gonna go ahead and say it is required reading. If you haven’t already, get on it. I promise you’ll love it.Oh, and another reason I like Tiktaalik is because it’s so charming. I don’t think we could have asked for a cuter, goofier-looking fishapod. The image of it flopping around on land is both hilarious and really, really interesting to me. One day I want to commission a beautiful oil painting portrait of Tiktaalik like rich people do with their dogs.That’s about it for this post! I hope I’m not too rusty. I can’t promise a daily post anymore, but I want to post at least semi-regularly.SOURCES (this is also something I want to start doing btw):Battistuzzi, Feijao, and Hedges 2004 - A genomic timescale of prokaryote evolutionShubin, Daeschler, and Jenkins Jr. 2014 - Pelvic girdle and fin of TiktaalikThe origin of tetrapods - Understanding EvolutionThe Common Descent Podcast Ep. 77 - Fins to Feet: The Fish-Tetrapod TransitionYour Inner Fish, Neil Shubin ****************************************************************************** Buy me a Ko-fi, if you’d like! -- source link

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