Rosa Rubicondior: Refuting Creationism - Self-Correcting Science Finds Another Transitional Fossil

A reconstruction of Westlothiana based on x-ray scans of the fossil.

Famous "First Reptile" Fossil Wasn’t a Reptile After All | AMNH

One of the supposed earliest reptiles has lost its place in the reptile family tree — and, in doing so, has provided a revealing example of how evolution works and how science improves its understanding of it. For creationists hoping that a revised classification means evolutionary biology is collapsing, the disappointment is twofold: the fossil remains approximately 345 million years old, and its newly revealed anatomy makes the transition towards life on land more interesting, not less evident.

The animal is Westlothiana lizziae, affectionately known as “Lizzie”, a small, superficially lizard-like vertebrate discovered in Scotland in 1984. Its limbs and apparently clawed digits helped establish its reputation as an early representative of the evolutionary transition towards amniotes — the group encompassing mammals and reptiles, including birds. However, interpreting a crushed fossil from its exposed surfaces has limitations. Structures hidden inside the rock can tell a different story, as researchers have now demonstrated using powerful X-ray scans at the European Synchrotron Radiation Facility in Grenoble, France.

The two slabs of NSM G.1990.72.1, the Westlothiana fossil studied by this new research.

Photo by Roger Benson.

The research, published on 30 September in Nature reveals an unexpected combination: a skull retaining ancient anatomical features, bony supports for internal gills, and a mouth bearing thousands of tiny teeth. These are indications of an aquatic or amphibious animal. The researchers place Westlothiana among stem tetrapods, on an evolutionary branch outside the group comprising living amphibians and amniotes and their last common ancestor.

Yet Lizzie also possessed five-digit feet and superficially claw-like finger and toe bones. That combination is the significant point. Features associated with terrestrial vertebrates were already appearing in animals that retained substantial adaptations to life in water. This is an example of mosaic evolution: different parts of the body change at different rates, producing combinations that do not fit the tidy categories we recognise among living animals. It also means that claw-like impressions in ancient trackways cannot, by themselves, establish that the animals making them were early amniotes.

Reconstruction in dorsal, lateral, palatal, and mandibular view of Westlothiana thanks to the experiments at the European Synchrotron.

Evolution has no obligation to produce a fully assembled “reptile package” before an animal can acquire a particular kind of foot. Nor does it work towards a predetermined destination. A feature that later becomes useful on land can originate in an animal whose life still depends heavily on water. Calling such an animal transitional does not mean that it was incomplete or waiting to become something else; it means that its anatomy helps document changes along the branching history of vertebrate evolution.

There is an equally clear lesson here about scientific method. A familiar interpretation has been challenged because improved technology exposed evidence that earlier researchers could not examine. The resulting revision concerns where an animal belongs in evolutionary history and what its anatomy tells us about that history. It supplies no support for a recent creation or for separately created, immutable “kinds”. Lizzie’s place on the family tree has changed because scientists followed the evidence — precisely the willingness to revise an explanation that makes science such an effective way of discovering what actually happened.

Evolution in Instalments^ What Is Mosaic Evolution? Evolution does not transform every part of an animal at the same rate. Limbs, teeth, skulls, respiratory structures and reproductive systems can change at different times, producing combinations of ancestral and newly evolved features. This pattern is known as mosaic evolution.

Westlothiana lizziae provides a striking example. Its five-digit feet and superficially claw-like terminal finger and toe bones once helped support an interpretation of it as an early relative of amniotes. However, scans revealed an internal gill skeleton and other features indicating an aquatic or amphibious lifestyle. Apparently terrestrial features were therefore present in an animal that retained substantial adaptations to life in water.

A Transition Is Not an Unfinished Animal

Calling a fossil “transitional” does not mean that the animal was incomplete, poorly adapted or waiting to evolve into something else. It means that its combination of features helps document an evolutionary transition. Nor must it have been a direct ancestor of a living group: a related side branch can preserve valuable evidence of how particular features evolved.

Other examples illustrate the same principle:

Feathered dinosaurs: feathers existed in dinosaurs before the evolution of bird-like powered flight. Their early functions need not have involved flight; insulation and display are among the proposed roles.

Early whales: fossils document combinations of aquatic adaptations and retained hind limbs, showing that the transition from land to water involved changes to different parts of the body over time.

Early hominins: some combined adaptations for upright walking with anatomical features useful for climbing. Habitual bipedalism did not require every feature associated with climbing to disappear first.

No Foresight Required

A feature can evolve in one context and later acquire another function. Natural selection favours heritable variations according to their effects under existing conditions; it cannot anticipate what descendants might need millions of years later.

Consequently, a terrestrial-looking foot need not have originated in an exclusively terrestrial animal. Westlothiana shows why palaeontologists must assess the whole available anatomy rather than identify an animal from one apparently diagnostic feature.

A Brief Glossary

Mosaic evolution

Evolution in which different features change at different rates or times, producing organisms with a mixture of ancestral and derived characteristics.

Tetrapod

A member of the vertebrate lineage characterised ancestrally by limbs with digits. In broad usage, this includes early limbed vertebrates and their descendants, including animals that later lost their limbs. In stricter classifications, “Tetrapoda” refers specifically to the crown group of living amphibians and amniotes.

Amniote

A member of the group comprising mammals and reptiles, including birds. The group is characterised by embryonic membranes, including the amnion, that enabled reproduction without an aquatic egg or larval stage. Amniotes need not lay eggs: mammals remain amniotes even when their embryos develop inside the mother.

Crown group

The most recent common ancestor of all living members of a group, together with all its descendants, living and extinct.

Stem group

Extinct relatives more closely related to a particular crown group than to its nearest living relatives, but lying outside that crown group. Their anatomy can help reveal the sequence in which characteristic features arose.

Amphibious versus amphibian

“Amphibious” describes a lifestyle involving both water and land. It does not necessarily identify an animal as a member of the group containing modern frogs, salamanders and caecilians.

The research paper in Nature
the European Synchrotron’s explanation of the findings.

The paper in Nature was accompanied by an American Museum of Natural History news release:

Famous “First Reptile” Fossil Wasn’t a Reptile After All
For more than 30 years, a Scottish fossil named “Lizzie” was considered one of the earliest known reptiles. Now, a new look inside the 345-million-year-old fossil is revealing a very different story.
Discovered in Scotland in 1984, Westlothiana lizziae—nicknamed “Lizzie” for its lizard-like appearance—was described in 1990 as the earliest land-adapted amniote, the group that includes reptiles, birds, and mammals. Though the fossil was crushed and difficult to interpret, its claw-like digits and reptile-like leg anatomy made it an important reference point in studies of early amniote evolution.

“Lizzie has been an icon for the early evolution of amniotes for decades,” said Xavier Jenkins, a postdoctoral fellow in the Museum’s Division of Paleontology and co-lead author of the study. “But when we were finally able to see inside the fossil, we found an animal that looked very different from what we expected.”

Using x-ray scans at the European Synchrotron Radiation Facility in Grenoble, France, researchers were able to see through the rock and reconstruct parts of the animal that could not be seen from the surface. What they found changed the picture completely: a primitive skull, internal gills, and a fish-like mouth filled with thousands of tiny teeth.

These features show that Westlothiana was not a reptile at all and likely lived in or around water.

A reconstruction of Westlothiana based on x-ray scans of the fossil.

The surprisingly primitive features of the skull show us that Lizzie was not only not a reptile but belonged to a much more ancient lineage. It turns out looks can be deceiving, and Lizzie lived a completely different lifestyle than we previously thought.

Ben Igielman, co-lead author.
Department of Earth Sciences
University of Oxford
Oxford, UK.

The discovery also reshapes scientists’ understanding of how reptiles and other land-adapted tetrapods evolved. Features such as five-toed feet and claw-like digits—once thought to be hallmarks of early amniotes—were already present in more aquatic members of the tetrapod lineage, the group that includes both amphibians and amniotes.
This is a big surprise. It shows that, although we think of amphibians as being more ‘primitive’ than reptiles today, some of the traits of reptiles were already there in the ancestor of both amphibians and reptiles.

Roger Benson, co-author
Division of Paleontology
American Museum of Natural History
New York, NY, USA.

The findings may even change how scientists interpret ancient fossil trackways. Clawed footprints have sometimes been used as evidence that amniotes originated more than 359 million years ago. But if animals like Westlothiana already had claws, those tracks may have been made by more primitive amphibious relatives instead.
The broader lesson is that terrestrial-looking traits, such as a reptile-like foot, a weight-bearing forelimb, and claw-like phalanges were not unique features of tetrapods, but rather accumulated piecemeal in their close relatives, in animals that were still living in and out of the water.

Dr Xavier Jenkins, co-lead author
Division of Paleontology
American Museum of Natural History
New York, NY, USA.

Publication:
Igielman, B., Jenkins, X., Head, J. et al.
Evolution of terrestrial anatomy revealed by a derived stem tetrapod. Nature (2026). https://doi.org/10.1038/s41586-026-11090-6

Abstract
Tetrapods (limbed vertebrates) include lissamphibians and amniotes, and now comprise half of all vertebrate species, with particular importance on land. Limbs first appeared in stem tetrapods by the Late Devonian, 365 million years ago^1,2,3,4,5. However, many taxa either have limbs with fin-like functional anatomy or have secondarily lost them, raising questions about the ecological context and early evolution of the tetrapod limb⁶. Here we provide considerable new data on the enigmatic Early Carboniferous Westlothiana lizziae, widely cited as the earliest terrestrially adapted stem amniote^7,8. We find unexpected plesiomorphies of the skull roof, palate, braincase and mandible, alongside aquatic adaptations, including an ossified internal gill skeleton and extensive denticles on the palate and mandible. These traits return Westlothiana as a stem tetrapod in our phylogenetic analyses, demonstrating that terrestrial adaptations such as an amniote-like pedal formula, loss of fin-like forelimb function and superficially claw-like terminal phalanges evolved in a mosaic fashion, and that these traits evolved in a transitional, amphibious context before the origin of the tetrapod crown group. Our findings reinforce recent suggestions of a taxonomically inclusive tetrapod-stem lineage, but also illuminate substantial gaps in anatomical knowledge, especially for small-bodied taxa, that obstruct our understanding of early tetrapod evolution.

Igielman, B., Jenkins, X., Head, J. et al.
Evolution of terrestrial anatomy revealed by a derived stem tetrapod.
Nature (2026). https://doi.org/10.1038/s41586-026-11090-6

© 2026 Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.

Westlothiana has lost its claim to be an early reptile, but gained significance as evidence of the mosaic nature of evolution. Its combination of aquatic adaptations and terrestrial-looking features shows why the history of life cannot be divided into neatly separated boxes. Features accumulated at different times, in animals living their own lives under contemporary conditions, with no foresight of the descendants or ecological opportunities that might follow.

For creationists, there is little comfort in this reassessment. Moving a fossil from one branch of the evolutionary tree to another does not make its mixture of anatomical features disappear, still less compress 345 million years into a few thousand. Nor does uncertainty over its precise relationships provide evidence for a supernatural creation event. The questions concern how vertebrate evolution unfolded; invoking a designer supplies neither the missing anatomical information nor a testable explanation of the pattern.

The researchers’ willingness to overturn a familiar interpretation is also instructive. Better technology revealed previously inaccessible evidence, and the classification changed accordingly. Evolutionary theory provided the framework within which those discoveries could be compared and understood. Scientific knowledge advances because explanations remain answerable to evidence, however established or appealing they may be.

Lizzie therefore illustrates two processes at once: the piecemeal evolution of vertebrate anatomy and the progressive refinement of our understanding of it. The animal did not change when scientists examined it more closely. Our knowledge did — and that is precisely how science is supposed to work.

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