Our Ancient Relative That Said 'No Thanks' To Land

next Wednesday October 12th is National fossil day and we'll be doing a live stream to celebrate and encourage folks to support us on patreon see you then for four hours of games q and A's and special guests in 2004 a team of paleontologists was on an expedition in the remote Canadian Arctic their mission to scour the late devonian rocks for clues about one of the most important events in Natural History the transition of vertebrate life from water to land they were looking for fossils that could bridge the gap between the lopefin fish that lived around 380 million years ago and four limbed tetrapods that appeared 365 million years ago and after years of searching with little success one day they finally found what they were looking for several partially complete skeletons from around 375 million years ago that belonged to a large species halfway between a fish and a Tetra bun a Fisher pun it had scales gills and fins like a fish but like early tetrapods it had primitive lungs and a flat head with a neck and it's stubby pectoral fins contain bones that match the arm and wrist bones of tetrapods it was named tiktolic and overnight it became an icon of natural history for its place at the cusp of transition from water to land but evolution rarely happens in a simple straight line and nothing about it is inevitable see there was another fossil collected earlier on that same trip that would lie forgotten for years while tiktolik got all the attention one that would show just that because around the time that some of our fishopod relatives were crawling out of the water others were turning around and Diving right back in tiktolic and the other Fisher pods are members of a group called The alpistos de galleons that lived in the mid to late devonium period they were flat crocodile shaped predators that lived and hunted in Shallow Waters and in some cases may have even ventured on to land at times you may remember these guys from our old episode when fish first breathed air and they were part of a larger group of fishes called The sarcopterygians Who differ from other bony fish and having pairs of fleshy lobe fins connected to their bodies with a single bone today this ancient group of fish is represented only by coelacans lungfish and technically us tetrapods yes from a certain point of view we are a type of sarcopterygian landfish because this is the group of fishes that we can trace our ancestry to Via Vel pistosugalians but exactly which ones we have to think or blame for the transition to land is still unclear for example we don't know whether tiktolic is a direct ancestor of modern tetrapods or just a close relative we might actually Trace our lineage to a different fischopod lineage that we haven't found fossils of yet when you're trying to trace a family tree back nearly 400 million years exact relationships become pretty hard to pin down but tektalik was exactly the kind of transitional animal that we expected to find and almost 50 50 split of fish and tetrapod so even if it's not our direct ancestor and it's more like a cousin instead it still lets us Glimpse what our fishapod ancestors were probably like in morphology and lifestyle tiktolic was found in sediment from a river Delta and while it was clearly a swimmer its fins were also made for walking or at least for propping itself up and pulling its body around when the situation required it probably did this mostly in the shallows underwater but it may have even occasionally ventured onto land for periods of time now tiktolic got pretty big at up to 2.7 meters long so propping itself up was an impressive feat that it only achieved thanks to its impressive feet well technically it's pectoral fins these had the beginnings of the tetrapod limb structure with bones corresponding to the upper arm bone a lower arm bone and even parts of a wrist this was an important moment in the transition from paddle-like fins to weight-bearing Limbs and it was thought for a while that tiktolic operated in front wheel drive mode mostly using its new stubby front fins to get around but more recently describe fossils of its back half suggest that its pelvis also had some tetrapod like features many parts seem to have become bigger more robust and more mobile including the pelvic girdle the ball and socket hip joint and the pelvic fin so it's hind fins had become pretty powerful which may have given it more of a four-wheel drive mode while paddling propping itself up and occasionally scooting around now it's not every day that you find an extinct species that fills an evolutionary Gap so perfectly so it makes sense that it was instantly recognized as a very big deal but it's easy to look at an animal like tiktolic and Come Away with an idea of evolution that's too simple the development of Limbs from fins and the transition to land from water can seem like a sign of inevitable evolutionary progress but the Fisher pods weren't leveling up into four limb tetrapods because that was simply their evolutionary Destiny the inexorable next advance from life is fish because Evolution doesn't work like that at all it it would just take another Fisher pod to show how messy this transition really was see during that 2004 Expedition just a few days before finding tiktolic the researchers had collected some other fossils from a site 1.5 kilometers away they'd noticed a few small jaw fragments teeth and scales embedded in some rocks which they collected to study later but when tiktolic was discovered and captured everyone's attention those other fossils were all but forgotten about in fact it wasn't until 2020 that the researchers actually got around to scanning the material and found that to their surprise embedded in one of the Rocks was a complete pectoral fin from a new species a Fisher pod they named it kikatania way guy and while it was both smaller and older than tiktolic it was clearly a close relative but it did have one other major difference while tectonic had fins that seemed to be evolving into limbs kikatania had fins that seemed to be evolved from limbs it had an upper arm bone like tiktolics but it was Boomerang shaped and smooth without the attachment sites for muscles that tiktolic had so it wasn't capable of propping itself up or taking steps this was a full-time swimmer but its fin structure was also unlike any other swimming fish in fact it was so unusual that the researchers concluded that it was the result of this fishopod doing an evolutionary 180. like tectonic its ancestors had fins built solely for swimming that were then remodeled into stubby weight-bearing fins but at that point right when kikatania's ancestors were on the cuspo transitioning to land they just didn't they returned to the water instead their weight-bearing fins were then remodeled back into slender fins this gave them different morphology from the fins of their ancestors a legacy of having gone through the stubby limb like stage after all once a fin has become more like a limb natural selection has to work with what's there and in this case that meant the development of a fin that was good enough for swimming but not exactly like the fins of its ancestors they once again became open water fish but their fins still had structures from a time when they lived at the water's edge as something tetrapod like now exactly what it was about life on land that didn't Vibe with kikatania's ancestors is still a mystery but its discovery shows us how Evolution really works not in simple March of progress style linear Journeys towards a single end goal instead it's more like a messy branching tree of species heading off in any number of evolutionary directions propelled by all kinds of different pressures some species undergo major Transitions and never look back While others return to ways of life from their past but that doesn't mean that some are more evolved or more advanced than others it just means that species even closely related ones can settle on wildly different ways of making a living and one Fisher pod's exciting ecological future is another's disappointing past foreign [Music] I'd like to officially thank this month's eontologists Annie and Eric Higgins Chase archambeau Colton Jake Hart John Davidson Ing and Melanie lamb Carnival become an ionite at patreon.com eons and you can get fun perks like submitting a joke for us to read here's one from Catherine G which dinosaur has the best manners the Plesiosaurus and as always thanks for joining me in the Adam Lowe Studio subscribe at youtube.com eons for more primordial ordeals [Music] we are a type of sarcopterygian landfish this fish crawled out of the ocean now I have to pay rent and taxes okay [Music]

Channel: PBS Eons

Views: 629,863

Keywords: fishapod, qikiqtania, devonian, vertebrates, tetrapods, lobe-finned fish, tiktaalik, evolution, Elpistostegalians, sarcopterygians, limbs, fin, natural history, paleontology

Id: Ke0BjyO41Qg

Length: 9min 56sec (596 seconds)

Published: Tue Oct 04 2022