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| Tametara mirim Simões, Sobral, Macrì, Ebel, Fachini, Martinelli, Nava, Paixão, Chiappe, Di-Poï & Hsiou, 2026 |
Abstract
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.
Systematic palaeontology
Squamata Oppel, 1811
Serpentes Linnaeus, 1758
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| Holotype (MPM 420) of Tametara 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. |
Tametara mirim gen. et sp. nov.
Diagnosis. Tametara mirim can be distinguished from all other snakes based on the following combination of characters: postfrontal present but parietal (posterior) process absent*; parietal with posteromedial process present*; supraoccipital with sagittal crest, posterolaterally projecting nuchal crests*, well-developed anterolateral processes* and strongly overlapped by the parietal dorsally; otoccipitals not contacting each other medially (separated by posterior process of supraoccipital); quadrates with quadrate conch, suprastapedial process and pterygoid lappet; posterior surangular foramen present; precloacal vertebrae with well-developed and ventrolaterally oriented ...
Etymology. Tametara, meaning ‘adorned’ (referring to the pronounced sagittal crest of the holotype); mirim, meaning small-sized, in the native Brazilian, Tupí-Guaraní language.
Holotype. MPM 420 (Museu de Paleontologia de Marília, Marília, State of São Paulo, Brazil). Posterior half of a 3D-preserved skull and mandibles articulated with the anterior portion of the postcranium, including 103 presacral vertebrae.
Locality and age. The fossil was discovered by W.R.N. and G.M.X.P. in 2020, in William’s Quarry 2 at Sítio Paleontológico ‘José Martin Suárez’ (Presidente Prudente municipality, State of São Paulo, Brazil); Adamantina Formation, Bauru Group, Bauru Basin, late Santonian to early Campanian age (approximately 85–75 million years ago (Ma))22.
Tiago R. Simões, Gabriela Sobral, Simone Macrì, Roy Ebel, Thiago S. Fachini, Agustín G. Martinelli, William R. Nava, Giovanna M. X. Paixão, Luis M. Chiappe, Nicolas Di-Poï and Annie S. Hsiou. 2026. Exceptional Brain and Ecological Diversity in the earliest Snakes. Nature. DOI: doi.org/10.1038/s41586-026-10809-9 [22 July 2026]
