#stem-birds

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

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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

(I think i'm about to learn something)

Nope! Based on biomechanical modeling *and* footprint fossils, we know they were quadrupedal! They were also plantigrade, unlike dinosaurs (incl birds)! Yet another way dinosaurs are waaaaaay more birdie than pterosaurs.

Azhdarchid Trace Fossil

A group that is defined as the most living common ancestor of all living members of a group, and all of that ancestor’s descendants, is a crown group. So the most recent common ancestor of all modern birds, plus all of that ancestor’s descendants, is crown birds. This includes extinct things, but they’re closely related to living birds. 

A group defined as a living group (such as birds) and all creatures more closely related to that group than to any other group, is called the total or pan group. So all animals more closely related to birds than to any other animal are pan birds. 

The group of creatures that aren’t in the crown group but are in the pan group are the stem group. So all animals more closely related to birds than to anything else, but aren’t descended from the most recent common ancestor of living birds, are stem birds. 

So, “traditional” dinosaurs are stem birds. You can call them birds, if you want. “Birds” is a more accurate name for them than any other at the end of the day. They aren’t crocodiles, because they aren’t in pan-crocodiles. They aren’t lizards, because they aren’t in pan-lizards. They are reptiles, but birds are reptiles too (the group that includes all things that we call reptiles also includes birds because birds are descended from that most recent common ancestor too). Birds is the most specific name for dinosaurs. 

And we call pan-crocodiles crocodiles. Like, we have a real trend of calling all members of the pan-crocodile group crocodiles. And stem-crocs got really, really freaking weird. So there is a precedent for it. 

So: non-avian dinosaurs are in a group that has birds in the name. Birds is the most specific name we can give them. 

All birds are dinosaurs.  Are all dinosaurs birds? 

note: this is a philosophical discussion. at the end of the day non-avian dinosaurs are stem-birds and pan-birds but they aren’t crown-birds. But most of them if you saw them in the street you probably wouldn’t call them a bird (only the ones really close to birds, like Velociraptor, would probably get called a bird). But traits we ascribe to birdhood - beaks, feathers, warm-bloodedness, flight, etc. - all appear in, or are even universal within, dinosaurs. 

So a paper came out that essentially assigned numerical values (ie, how much of a Bird™ a stem-bird is as opposed to a basal stem-bird/its own unique traits) and I felt it was important to share with you all as it might affect your opinion about where you stand on the Bird Political Spectrum 

The origin of this classic meme can be found here and here 

And yet, they were