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A newly described skull of the Permian reptile Eunotosaurus africanus has overturned a long-standing idea about turtle origins. A 2026 Current Biology study places Eunotosaurus with millerettid stem reptiles, outside the turtle lineage. Its broad ribs therefore resemble turtle ribs through convergent evolution rather than shared ancestry. The same analysis supports turtles as close relatives of archosaurs, the reptile group that includes crocodilians and birds.
What the 2026 fossil study discovered
The “discovery” is skull evidence from a newly described Eunotosaurus specimen found in 2016, not a newly living reptile or a wholesale reclassification of reptiles. High-resolution X-ray micro-CT scans revealed internal and previously unseen skull anatomy. Researchers combined those observations with anatomical data from candidate stem turtles and a broad phylogenetic analysis—the statistical comparison of traits across a family tree.
The paper, “The phylogenetic origin of turtles,” was published online on 28 May 2026 and appeared in the 8 June 2026 issue of Current Biology (journal record and abstract). The Natural History Museum’s account of the work was published 4 June 2026 (museum report).
The new placement of Eunotosaurus
The analysis recovers Eunotosaurus africanus as a millerettid stem reptile. In practical terms, it is an early branch of the reptile family tree that is not an ancestor or stem relative of turtles. Its turtle-like body profile reflects a similar adaptation that evolved separately.
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Why the skull changed the interpretation
Fossil bodies can look deceptively alike when unrelated animals face similar environmental pressures. Eunotosaurus has broad, flattened ribs, a feature long treated as an important clue to turtle ancestry. The new skull characters, examined together with the rest of the skeleton, fit millerettids better than turtles.
CT scanning lets researchers inspect bone surfaces and internal structures that may be hidden by rock or inaccessible on a fragile fossil. It was not the scan alone that settled the question: the study used the new anatomical observations in a comprehensive phylogenetic analysis. As lead author Xavier Jenkins told the Natural History Museum, “By peering inside the skull of Eunotosaurus and undisputed fossil turtles with this cutting-edge technology, we could see never-before-seen aspects of their anatomy.”
Ribs are evidence, not a family label
The study and museum report interpret the expanded ribs of Eunotosaurus and turtles as independently evolved. A plausible shared pressure was fossorial life—digging or burrowing, which can favor a reinforced, flattened trunk. Similarity in one striking feature cannot outweigh a wider set of skull and skeletal characters.
How the 2015 and 2026 studies differ
The conclusion has changed as new material and analyses became available. The 2015 interpretation was a legitimate result based on the evidence then published; it did not include the later-described skull evidence.
| Question | 2015 Nature study | 2026 Current Biology study |
|---|---|---|
| Key evidence | CT examination and phylogenetic analysis of the material available at the time | Additional anatomical observations, including newly described skull information, plus a comprehensive phylogenetic analysis |
| Interpretation of the skull | Supported a diapsid skull undergoing secondary closure of temporal openings and a transitional role in turtle evolution | Skull and other characters place Eunotosaurus among millerettid stem reptiles |
| Relationship to turtles | “Critical transitional form” in turtle evolution | Outside the turtle lineage; turtle-like ribs evolved independently |
| Published source | G. S. Bever and colleagues, Nature, 2 September 2015 (paper) | Xavier A. Jenkins and colleagues, Current Biology, 2026 (paper record) |
What the study says about turtle relationships
The 2026 phylogeny supports turtles as close relatives of archosaurs, consistent with molecular studies of living reptiles. In the museum’s account, coauthor Serjoscha Evers said: “Our results show that turtles do indeed belong to the group of archosaurs and occupy a very basal position in the family tree.” Here, “basal” means near the base of that branch—not primitive or inferior, and not a statement that modern turtles are unchanged.
The study places turtle origins toward the end of the Permian, around 255 million years ago. That estimate is distinct from the approximate 260-million-year age assigned to Eunotosaurus, described by the Natural History Museum as Middle Permian. Those dates should not be read as proof that Eunotosaurus gave rise to turtles; the new analysis specifically rejects that ancestry.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What remains uncertain
Turtle origins are not a completely closed question. Fossil relationships can shift when new skulls, better-preserved specimens or different character samplings are added. The Natural History Museum notes that more work remains. The present result is best understood as a strongly argued revision of Eunotosaurus’s position and a reinforced turtle–archosaur hypothesis, not a final ban on every alternative turtle family tree.
What this means for reading fossil evidence
- A dramatic resemblance, such as broad ribs, may be convergent evolution rather than inherited similarity.
- Skull anatomy can provide characters that are more informative for deep relationships than overall body shape.
- CT data are most powerful when combined with explicit comparisons across many fossils and a reproducible phylogenetic analysis.
- Scientific classifications can change without making the earlier study careless; new evidence can change which explanation best fits all observations.
Key takeaway
Eunotosaurus africanus was once considered an important early turtle relative because of its turtle-like ribs. The 2026 study’s newly described skull evidence and broader analysis instead identify it as a millerettid stem reptile. The resemblance to turtles was probably an independent adaptation associated with burrowing, while turtles themselves are placed near the base of the archosaur branch and likely originated about 255 million years ago, toward the end of the Permian.
