#evolutionary biology

[t-jfh]

Our fossil is a rare new witness. It comes from roughly 80-million-year-old rock in São Paulo state, Brazil. We named it Tametara mirim, meaning “adorned” and “small” in the local Indigenous language.

(Photo: Agustin Martinelli)

The new fossil of Tametara mirim reframes how we understand snake evolution.

(Photo: Agustin Martinelli)

Life reconstruction of the burrowing stem snake Tametara mirim which lived alongside now-extinct stem-birds and sauropod dinosaurs.

(Illustration: Gabriel Ugueto)

The bones of Tametara show it had the skull of a burrower. CT scan volume-rendered with VGSTUDIO MAX.

(Image: Roy Ebel)

One theory about how snakes evolved suggests lizards went underground, lost their limbs and elongated their bodies.

(Illustration supplied - Roy Ebel)

80‑million‑year‑old snake fossil sheds light on why lizards lost their limbs and started slithering

Snakes are everywhere in our legends and mythology. Yet for most of us, our blood runs cold whenever we encounter these strangely undulating, scaly tubes of muscle slithering through the leaf litter.

The loss of an arm or leg poses a challenge. Yet snakes do perfectly well without all four of them. This makes them suspect. It also leaves us unable to fathom how this radical transition produced one of the most successful vertebrate body plans.

More than 4,000 species of snakes are alive today, on every continent except Antarctica, from thread-thin burrowers to massive pythons, on land and in the sea. We have studied them since antiquity, and still the oldest question about them has no answer: what turned snakes into snakes?

We have long suspected their peculiar, limbless body plan is explained by how the earliest snakes lived. In a new study, published today in Nature, my colleagues and I describe a small, exquisitely preserved fossil that brings us closer to an answer than ever before.

By Roy Ebel

Research Officer Herpetology, Museums Victoria Research Institute, Australia

The Conversation - July 23, 2026

80-million-year-old snake fossil sheds light on why lizards lost their limbs and started slithering

Snakes lost their limbs millions of years ago to become undulating, scaly tubes of muscles. Scientists are finally figuring out why.

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Related article >>

Fig. 1: Holotype (MPM 420) of T. mirim.

a, Photograph of the whole specimen with the articulated skull and postcranium in dorsal view. Ant, anterior; Bl, block number; Ce.V., cervical vertebrae; Do.V., dorsal vertebrae; Post, posterior; Sk, skull. b,c, Photographs of the skull in lateral (b) and dorsal (c) view. CB, compound bone; F, frontal; Oto, otoccipital; P, parietal; PFr, postfrontal; Pro, prootic; Ptg, pterygoid; Q, quadrate; Soc, supraoccipital; St, supratemporal. d–g, 3D renderings of an anterior precloacal (‘cervical’) vertebra in lateral (d) and anterolateral (e) views, and mid-precloacal (‘dorsal’) vertebra in dorsal (f) and left lateral (g) views. h–j, 3D renderings of the skull in the right lateral view (h) and with exposed brain endocasts in the right lateral (i) and dorsal (j) views. Mes., mesencephalon; Rho., rhombencephalon; Tel., telencephalon. Scale bars, 100 mm (a), 5 mm (b,c,h–j) and 1 mm (d–g). Specimen photos were taken by A.S.H.

Exceptional brain and ecological diversity in the earliest snakes

Understanding the ecological origin of snakes has remained a century-old challenge, hindered by an extremely sparse early fossil record and conflicting interpretations of fossil ecologies.

Here we describe an exceptionally preserved Cretaceous fossil snake, Tametara mirim gen. et sp. nov., from Brazil, representing one of the earliest-diverging stem snakes. High-resolution micro-CT scans reveal unprecedented details of cranial nerves, inner ear and brain anatomy, enabling the most integrated reconstruction of stem snake neuroanatomy to date. Quantitative and qualitative endocast analyses demonstrate that Tametara had a brain morphology distinct from both other stem and extant snakes, revealing substantial early neuroanatomical disparity — and probably sensory functions — in snake evolution. Independent evidence from telencephalon shape and bone microstructure converges on a fossorial lifestyle for Tametara and non-fossorial for another stem snake: Dinilysia.

These results indicate that major ecological transitions occurred early in snake evolution, and that known stem species do not represent the ancestral condition of crown snakes. Early snake evolution thus involved complex shifts in habitat use and sensory ecology, revealing greater ecological and neuroanatomical diversity than previously thought.

By Tiago R. Simões, Gabriela Sobral, Simone Macri, Roy Ebel, Thiago S. Fachini, Augustin G. Martinelli, William R. Nava, Giovanna M. X. Paixão, Luis M. Chiappe, Nicolas Di-Poï & Annie S. Hsiou

Nature - 22 July 2026

Exceptional brain and ecological diversity in the earliest snakes - Nature

A well-preserved fossil snake from the Late Cretaceous of Brazil shows early ecological and brain shape disparity in the group.

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[markscherz]

Look at these generic-ass frogs.

This is just a Frog™, right?

Wrong. These four frogs belong to four different families (respectively, Dicroglossidae: Limnonectes paramacrodon, Ranidae: Rana temporaria, Mantellidae: Aglyptodactylus madagascariensis, and Pyxicephalidae: Amietia tenuoplicata) from across the world (respectively, I took these photos in Borneo, Denmark, Madagascar, and Tanzania).

These represent just some of the huge number of genera across more than half a dozen families that have independently produced species that look like this:

In Europe: Ranidae: Rana. In North America: Ranidae: Boreorana/Lithobates. In South America: Leptodactylidae: Leptodactylus. In Africa: Pyxicephalidae: Amietia or Arthroleptidae: Arthroleptis. In Madagascar: Mantellidae: Aglyptodactylus. In mainland Asia: any of a dozen or more genera of the family Ranidae; or Ranixalidae: Indirana. In Australia: Pelodryadidae: Rhyaconastes. and more, besides!

Why? Well… that is kind of a fundamental question in evolutionary biology. Why, with the infinite theoretical possibilities of evolutionary processes, do we see the same kind of anatomies evolving again and again? Does this mean that evolution is in some way predictable?

The answer is complex (there are good books on this topic!), but basically, yes: similar pressures can (but do not always) lead to similar solutions. I think this may apply to frogs to an exceptional degree, in part because their body plans are so simple to start with, that the tools available for tinkering are pretty streamlined and refined. These are just one stark example, but you can do this with whole ecological assemblages of frogs in some cases. Madagascar is especially excellent for this, because the island was only naturally colonised by frogs five times, and yet you have practically every main 'type' of frog there, independently derived from one of these colonising lineages.

Yet, each of these generic brown frogs is also subtly different—and their skeletons reveal pretty fundamental differences unique to their lineages. Not to mention their totally distinct tadpoles!! And that is part of the key, too: although some parts of evolution can be predictable, no organism can separate itself from its own evolutionary past. There is always a degree of contingency involved.

I find these frogs to be a really elegant demonstration of this principle. And also, a nice demonstration of why it is fucking impossible to ID frog pictures you guys send me without a more or less precise location.

Thanks for coming to my TED talk.

[casualcarpetshark]

BOW DOWN TO THE ANCIENT ONE

[shitacademicswrite]

[mindblowingscience]

Embryo fossil found in South Africa is world's oldest proof that mammal ancestors laid eggs

Between 280 and 200 million years ago, a group of animals evolved which would eventually give rise to mammals, including humans: the theraps

Between 280 and 200 million years ago, a group of animals evolved which would eventually give rise to mammals, including humans: the therapsids. They were first described more than 150 years ago, based on fossils from South Africa. Since then, many more fossils have been discovered. James Kitching, one of the most talented South African fossil hunters of the 20th century, excavated many thousands of therapsids from the rocks of the Karoo (a semi-arid region of the country's interior). He also found fossilized dinosaur eggs, but neither he nor any paleontologist after him ever found therapsid eggs.

Continue Reading.

[sanguinarysanguinity]

@blablabla640 asked:

if you’re up for explaining why economists are “mostly wrong” while biologists are “mostly right” about game theory, that would be extremely interesting as well!!

Happily!

Let's begin by about talking a little bit about the difference between theoretical and applied mathematics.

Theoretical mathematics is when you start with some collection of statements that you assume to be true (the "assumptions"), and then see what else you can also say is true, if those first statements are. Theoretical mathematics is bomb-proof rigorous: if the initial statements are true, so are all these others, absolutely, positively, and with no exceptions.

Are those initial statements true, though? Theoretical mathematics doesn't know and doesn't care. It's all about who can build the most elaborate fairy castles in the sky out of a set of random what-ifs. And I cannot stress this enough: it does not matter what those what-ifs are. What-ifs that lead to prettier and fancier castles are preferred, but it really is all about the aesthetic and nothing else. Theoretical mathematics is beautiful and abso-fucking-lutely useless. (G.H. Hardy's A Mathematician's Apology is a classic work on math's beauty and uselessness, if you want to know more.)

And unless you think I'm shitting on theoretical math: I fell in love with those beautiful useless fairy-castles when I was seventeen, and I haven't fallen out of love since.

Applied mathematics is the attempt to make theoretical mathematics get a goddamned job and start contributing to the rent.

To do that, you must first assert that those initial what-ifs describe something in the real world. If they do accurately describe some real-world phenomena, then all the logical statements that follow should also describe the real-world phenomena -- and from there, you should be able to predict stuff that's gonna happen, which will potentially be useful to someone. Maybe you'll even make some money out of it.

Historically, there have some big wins in applied mathematics. Navigation. Astrophysics. Engineering. Casinos. Ballistics. Ciphers. Communication technology. Satellite technology. Radar. I could go on listing things for a very long time.

But everything, and I mean everything, depends on how well that initial set of assumptions matches your real world phenomenon. If your assumptions match up to your real world scenario pretty well, you're golden. If they don't, it's all bullshit. (Which is unfair to literal bullshit, as cow manure has been a pretty valuable substance over the centuries! Whereas mis-applied mathematics is valuable to no one but scammers and con artists.)

(I should point out that "how well an assumption matches a real life phenomenon" is all relative. Some fields are grasping for anything that predicts stuff even a little tiny bit. Other fields demand near-perfect correspondence between the theory and the real world or it isn't even worth having the conversation.)

(Also, just to be clear: not everyone who misapplies the math is a scammer or a con-artist. Many, many, many people just don't understand the math very well, and don't realize how badly the math's assumptions map to the reality they're trying to describe.)

Okay, with that in mind, let's talk about game theory!

Game theory centers around the idea of "players" (agents who are capable of making decisions), in well-defined "games" (scenarios where there are different decisions you can make, and the different decisions have different outcomes). Game theory predicts what decisions players will or should make in these games.

Remember: game theory is absolutely 100% true provided its assumptions are true. So what are those assumptions?

I'm not going to get into all of them, because they can get pretty technical. But a critical one is the notion of a util (pronounced "yoodle"). Utils are usually described as a unit that measures a player's amount of satisfaction. Game outcomes are measured in utils: how much satisfaction you get from the different possible outcomes of a game. How much you want this outcome compared to that outcome.

In game theory, all players are trying to maximize the number of utils they can get. Always. Without exception. They have no other motivation in life: they must maximize utils.

What is a util? Who the fuck knows. Game theory doesn't. Game theory is theoretical mathematics and doesn't give a flying fuck what a util might be. It just knows that all players are trying to maximize utils at all times. That's the game: maximize utils. Assuming that players have certain moves available to them, and assuming that each move will get them a certain number of utils, AND ASSUMING THEY WILL ALWAYS CHOOSE TO MAXIMIZE UTILS, what plays will/should they make?

Which is where we get to economists and biologists!

Please keep in mind: I'm not an economist; I'm not a biologist; I haven't cited any information in this post; these are personal opinions I've accumulated over the years.

So.

Economists, when they try to apply game theory to their field, like to say that utils equal dollars (or the cold hard currency of your choice). Which. Is not entirely without merit. When describing a poker game, dollars are a pretty good approximation of utils!

…although even there it falls apart at the edges a little bit. How about when your friend has had an absolutely shitastic day and you deliberately throw your poker hand, just so you can see them smile as they rake in the pot? Suddenly utils aren't dollars anymore. Suddenly utils are "the amount of pleasure I get from seeing my friend smile". And the instant that happens, the utils = dollars assumption no longer predicts what you're going to do, and all the careful charts and equations that are meant to predict how you're going to play your hand, no longer predict how you're going to play your hand.

Which is fine if it only happens occasionally. In the ordinary run of things, utils = dollars describes poker games pretty well!

But the thing is. People? Are motivated by lots of things that aren't dollars. People give up good paying jobs to spend more time with their family. People switch to lower paying jobs because the new job doesn't make them sick to their stomach. People turn down the opportunity to cheat a friend, even when they could get away with it. People will backstab each other even though it will cost them in the long run. People do things for all kinds of reasons that aren't dollars. Love! Spite! Duty! Honor! Justice! Religion! Morals! Ethics! Fashion! Boredom!

(And that doesn't even get into notion that a lot of times, people aren't even all that sure how many dollars particular choices are going to make/cost them. Forget deceptive advertising, how many people really understand compound interest??)

Again, utils = dollars isn't completely without merit. It probably describes corporations pretty well. (Maybe? That's not my field.) But it is shitastic at explaining what Joe Schmoe Everyman on the Street is going to do. Sadly, I have sat in many classes with econ majors who felt very confident that everyone worships at the Shrine of the Almighty Dollar, and thus confidently believed all kinds of absurd things about their fellow humans that I shall not detail here. There's even a whole little field of research in psychology and social science that just goes around proving that different populations of people don't match the predictions of utils = dollars in various scenarios to various degrees.

(One thing those researchers have shown? While there's a whole continuum of how well or badly different groups of humans conform to the predictions of utils = dollars, econ students tend to fall waaaaaaay over at the utils = dollars end of the scale. So maybe utils = dollars does a pretty good job describing financiers and bankers and such-all? But it's not so great at describing the rest of us.)

Biologists, when they play with game theory, assume that utils = reproductive fitness, and use it to predict what behaviors/strategies/morphologies you'll see in a population of organisms. And by god, it is beautiful to watch them work. Game theory does a great job describing how evolutionary theory will affect a population of organisims and what they "choose" to do. Does game theory predict a mixed strategy of 1/3 vs. 2/3 for a particular kind of fish, based on the probability of how many of their offspring live long enough to reproduce? If so (and assuming that the biologists fed accurate data into the model), when you go to look at the actual fishes, one third will have the one body shape and two thirds the other. (Sorry I don't have links for you; I'm not going to go dig my old biology texts out of the basement for this post.)

Now, does game theory perfectly predict everything in evolutionary biology? No, because there are weirdnesses about what is or isn't possible with how genes replicate, or how genes get translated into proteins into organisms into behaviors. Path dependency is a thing. There's a lot of weird spots where the assumptions break down somewhat. Applied math almost always has some slop in it where the assumptions don't quite perfectly match reality, and biology is no exception. But from what I saw as a student, utils = reproductive fitness is a pretty good predictor of how biological organisms behave.

And that's my screed about economists mostly doing game theory wrong, and biologists mostly doing it right. The former wouldn't bug me nearly so much if game theory isn't always and forever described as an economic theory. Because, as biology demonstrates, some of its very best applications are not economics at all.

Thank you for the ask, and I hope reading this essay increased the number of utils in your day!

[feathershy]

the evolutionary principle of "things get more complex over time" (dating back to Lamarckism or further) is generally frowned upon these days; and yet no one believes that the first life form ever popped into existence with all the complexity of modern life.

I guess the revision is "we hit optimal complexity for life pretty quickly"?

that or "evolution makes life better/stronger/more fit over time" is such a frowned upon idea these days that we avoid saying it, even when it might be a little true? Consider that "A gun is better weapon than a spear" clearly means something true, despite all the "but what about sourcing gunpowder?" "it requires too complex metallurgy to make in ancient Greece" style criticisms people use to explain why it is wrong to think of evolution as making things better over time. ("It is only fit for its niche and the past had different niches") Idk what the solution here is, likely at least some dinosaurs would become invasive species in our modern age given a time portal (i.e. the dinosaurs are more fit despite being more primitive). And yet I am not willing to reject the idea that technology improves over time, and a gun is a better weapon than a spear on some level.

[lichenaday]

Psora crystallifera

Yes, this is a real lichen. And no, I don't believe it either. P. crystallifera is a squamulose lichens that grows on dry soil in arid regions of Australia, New Zealand, and southern Africa. It has small, crumpled lobes that are 1-10 mm in diameter, which grow in extensive colonies intermingled with other biological soil crust forming organisms. The squamules are mostly dull grayish-brown, but can appear more green when hydrated. The upper cortex is textured like a turtle shell, divided into thickened, crystal-like, polyhedrons. Besides the fact that this makes the lichen look bedazzled and super rad, this growth form serves an important purpose: it helps to diffuse direct sunlight, reducing solar radiation damage while still allowing less direct light to reach the photobiont layer for photosynthesis! Isn't that incredible??? Evolution is so fucking brilliant man, I can't even believe it some times. Just one of the many ways lichens have adapted to some of the harshest environments on earth.

images: source

info: source | source