An origin reconstructed, not witnessed
Snakes belong within the squamate radiation that also includes lizards. A 2015 analysis combining fossils, anatomy and molecular evidence reconstructed a land-dwelling, nocturnal ancestor that foraged in warm, vegetated environments. These are estimates of ancestral states, not observations of an actual ancestral animal.
A 2018 study of skull shape instead found evidence for a burrowing ancestor of living snakes, preceded by a surface-dwelling ancestor of snakes and their closest relatives. The apparent disagreement matters: the studies use different anatomical information and methods, and examine ancestral nodes that must be specified carefully. “The first snake” is not a specimen whose complete life history is already known.
Sources: Hsiang et al. (2015) · The origin of snakes · Da Silva et al. (2018) · The ecological origins of snakes as revealed by skull evolution
New fossils complicate the picture
In 2026, Simões and colleagues described Tametara mirim from Cretaceous Brazil. CT-based anatomy and bone structure support a burrowing lifestyle for this early snake, while their comparison supports a non-burrowing ecology for Dinilysia. These contrasting lineages reinforce the need to distinguish an early fossil species from the ancestor of all living snakes.
Sources: Simões et al. (2026) · Exceptional brain and ecological diversity in the earliest snakes
Losing limbs means changing development
Limb reduction is more informative than the simple statement that snakes have no legs. Some living lineages retain reduced pelvic structures, while fossils preserve combinations of characters absent from living species. Evolution did not transform every part of the body in a single step.
Kvon and colleagues tested a regulatory DNA element controlling Sonic hedgehog, a gene involved in limb development. Snake versions of this enhancer had lost much of their ancestral limb-driving activity. This connects changes in gene regulation to a major anatomical transition; it does not imply that one mutation alone explains every feature of a snake.
Sources: Hsiang et al. (2015) · The origin of snakes · Kvon et al. (2016) · Progressive loss of function in a limb enhancer
A world opened by change
The modern distribution of snakes reflects dispersal, extinction and the diversification of surviving lineages. Klein and colleagues found evidence consistent with substantial diversification around the end-Cretaceous extinction, approximately 66 million years ago, and subsequent expansion into new regions and ecological roles.
Their dates depend on how fragmentary fossils are placed and used to calibrate evolutionary trees. An atlas should therefore distinguish a locality documented today from a model of where ancestors lived millions of years ago. Neither a modern border nor a coloured range polygon captures that entire history.
Sources: Klein et al. (2021) · Evolution and dispersal across the K–Pg extinction
Follow the evidence
Sources & scope
These sources support the specific claims identified above. Research models, observations, institutional guidance and curatorial interpretations answer different kinds of questions.
- Hsiang et al. (2015) · The origin of snakes
Ancestral reconstruction using living species, fossils and molecular evidence; model-dependent inferences.
- Da Silva et al. (2018) · The ecological origins of snakes as revealed by skull evolution
Skull shape and developmental evidence for ancestral ecology; a different reconstruction from the 2015 study.
- Simões et al. (2026) · Exceptional brain and ecological diversity in the earliest snakes
CT-based fossil neuroanatomy and bone microstructure; contrasting ecologies among early stem snakes.
- Kvon et al. (2016) · Progressive loss of function in a limb enhancer
Experimental evidence about a regulatory DNA element associated with limb development.
- Klein et al. (2021) · Evolution and dispersal across the K–Pg extinction
Molecular dating, fossils and biogeography; estimated timing depends on calibration choices.
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