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This week, scientists discover something in a fish fossil that might give us a hand in finding our earliest land dwelling ancestors.

Hosted by: Hank Green

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Sources:

https://press.nature.com/elpistostege-and-the-origin-of-the-vertebrate-hand/17791576
https://press.nature.com/late-cretaceous-neornithine-from-europe-illuminates-the-origins-/17791596
Thanks to Brilliant for supporting this episode of SciShow.

Go to Brilliant.org/SciShow to learn more. [ intro ]. Now we all know that there is lot’s of important infectious disease science happening right now and three cheers for the people doing that work.

So do today for Scishow News, there will be breaking news, but it will be very, very old. It was during the Late Devonian Period, over360 million years ago, that one group of fish evolved fins from feet, and moved from water to land. This gave rise to a group called the tetrapods, which today includes all amphibians, reptiles, birds, and mammals -- from herons to hippos to humans.

A new study published in the journal Nature describes how an ancient fish represents a crucial stage in that transition. And for scientists interested in understanding how our tetrapod bodies came to be, this new specimen is proving to be very… handy. It’s called Elpistostege watsoni.

It’s not a new species, but this new fossil, found in Quebec in 2010, is one of the most complete skeletons known of any early tetrapod relative. See, this grand evolutionary transition is mostly understood through a handful of Late Devonian animals that blur the line between fish and tetrapods. Some, like Eusthenopteron, are basically fish with very tetrapod-like features, such as well-developed limb bones.

Others, such as the famous four-legged Acanthostega, are considered true early tetrapods that still have very fishy bodies. But many of these fossils are incomplete, leaving gaps in our understanding of how certain parts of the body changed over this transition. This new Elpistostege specimen is well preserved from its head to its tail, but in this study, the researchers were particularly interested in its front fins.

That’s because one of the most important defining features of true tetrapods is the presence of digits -- that is, finger bones. Elpistostege is still fairly fishy, though. And as you might expect from a fish, its front fins ended in thin bony rays.

Using an x-ray imaging procedure that provided a peek at the internal structure of the fins, they found that the bones inside were arranged very much like the digits in our own hands. It wasn’t quite a hand, but it was basically a fish fin with the bones of a hand hidden inside! In fact, the researchers say this is the most tetrapod-like bone arrangement of any fish fin yet studied.

This means that Elpistostege sits at a very important place in our own family tree, a very close cousin of the earliest true tetrapods. And the fact that it had well-developed hand bones inside a functional fish fin supports the idea that the tetrapod limb developed in the water. It might be that these bones provided extra strength for fish crawling around in shallow water, or maybe even for short forays onto land -- setting up the ability to move to land more permanently in its descendants.

This new fossil gives us a clearer picture of exactly when and where certain changes took place along this fish-to-tetrapod transition, which will hopefully guide future fossil research as well. Meanwhile, another new fossil described in Nature sheds light on the early evolution of a much later group of tetrapods: birds! This ancient bird comes from the Late Cretaceous of Belgium, between 66.7 and 66.8 million years ago, right around the end of the Age of Dinosaurs.

The fossil consists of an extremely well-preserved skull along with some bones of the body, with enough unique features for researchers to identify it as a new species:. Asteriornis maastrichtensis. Based on its anatomy, the paleontologists classify it as an early cousin of a group of birds called the Galloanserae, which today includes landfowl and waterfowl, including turkeys, chickens, ducks, and geese.

In fact, some have dubbed it the Wonderchicken. Its skull has a mixture of landfowl-like and waterfowl-like features. But beyond that, this identification makes Asteriornis the oldest known member of a /living/ group of birds.

See, while there are lots of fossil birds known from the Cretaceous Period, they mostly belong to ancient groups that went extinct along with the rest of the dinosaurs. This means Asteriornis also gives us a very rare glimpse at the early evolution of modern bird diversity -- not only what they looked like, but where they lived. Much of the diversity of modern birds clusters in the southern continents, so some scientists have proposed that the early evolution of modern birds took place in the south.

But Asteriornis, being from Belgium, muddies the picture. One the one hand, this means we might be wrong about where modern birds got their start. But on the other, now we know that Europe might be a good place to look for more fossil clues.

And while scientists are trying to understand where these birds lived, they also want to know how they even survived to the present day. Because we’re not sure why specific lineages did/ make it through the end-Cretaceous extinction. Scientists have suggested that the ancestors of modern birds may have had a few features that helped them along: small body size would mean they didn’t need much food, and a generalized diet would mean they weren’t picky eaters -- both good traits to have in an apocalypse.

Asteriornis is indeed a small bird, with an estimated mass under 400 grams. And it was discovered on an ancient shoreline, which means it /might/ have lived a not-very-picky lifestyle like modern-day shorebirds. Of course, this one fossil doesn’t answer any of these questions for sure, but -- like the new Elpistostege fossil -- it gives us a renewed idea of where to look, and what to look for, to find more pieces of these ancient puzzles.

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So check it out and see if it’s right for you -- and thanks for your support. [ outro ].