Rosa Rubicondior: Refuting Creationism - 242-Million-Year-Old 'Transitional' Lizard Fossil

Agriodontosaurus helsbypetrae fossil (BRSUG 29950-14) in its sandstone matrix.

September: World's oldest lizard | News and features | University of Bristol

Here is yet another fossil that will give creationists a lot to think about. It’s a fossil of the earliest known lepidosaur — the group that includes lizards, snakes, and the tuatara of New Zealand. It is ∼242 million years old and was found in a sandstone deposit in Devon, in southwest Britain. It was picked up on a beach in Devon in 2015, and has been examined by a team from the University of Bristol.

At that age it is very close to the stem of the order Lepidosauria. However, it already displays some “advanced” features, and some of the assumed primitive features are already absent.

One of the primitive features often discussed is the lower temporal bar — a bony rod running between the cheek and the jaw hinge—which is present in the tuatara but absent (“open”) in modern lizards and snakes. This opening gives greater flexibility to the skull, allowing more motion for feeding. Also, many modern lizards have palatal teeth (teeth on the roof of the mouth) which help grip prey.

The fossil skull (from Agriodontosaurus helsbypetrae) has no skull hinge and no palatal teeth, but it does have an open lower temporal bar. In other words, this is a transitional species: it has a mosaic of primitive and derived traits—a pattern Darwin predicted, but which creationists generally dismiss. To creationists, fossils are often denied, mischaracterised, or claimed to be “just as they were created a few thousand years ago.” But this specimen is clear evidence of evolutionary change.

Meanwhile, the evidence of fossil ages—dating back hundreds of millions of years—refutes the idea of a young Earth (~ thousands of years), which cannot be reconciled with the geological, biological, and radiometric data.

None of that undermines the real discovery: an early lepidosaur with a mosaic of features lived in what is now Devon, UK, in the Middle Triassic, about 242 million years ago. As always, in rational enquiry, solid evidence must take priority over magical or mythological claims.

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How the “242 million years” Date Was Derived. This is important, because the age of the fossil depends on the dating of the geological formation it comes from, plus corroborating evidence. Here’s how geologists arrived at the ∼242 Ma estimate:

Geological Formation Age (Helsby Sandstone Formation / Sherwood Sandstone Group).

The fossil is from the Helsby Sandstone Formation (formerly also known in Devon as the Otter Sandstone). This formation is part of the Sherwood Sandstone Group, in England. [1.1]
The Helsby Sandstone is assigned to the Anisian stage of the Middle Triassic. The Anisian spans roughly 247.2 to 242 million years ago. [2.1]

Radiometric Dating of Calcretes in the Formation.

A pilot U-Pb (Uranium-Lead) age dating study of calcrete (calcite cement formed near the surface, often around root systems—pedogenic calcretes) in the Helsby Sandstone in southeast Devon found that the bulk of the calcite in one rhizocretion (a vertical calcrete feature) yields an age of 245 ± ~9 million years (2σ error). [3.1]
Because that calcite appears not to have been significantly altered since it formed, the date is considered reliable for when those sediments (or at least the calcrete horizons) were exposed and forming—thus anchoring the lower bound of that part of the formation to the mid-Anisian. [3.1]

Stratigraphic and Biostratigraphic Correlation.

Other evidence (fossils in associated layers, magnetostratigraphy, ichnofossils / trackways, plant fossils etc.) tie the Helsby Sandstone into the global timescale for the Middle Triassic, especially the Anisian stage. [4.1]
Given that, the fossil is assigned an age close to the top of the Anisian stage, about 242 million years ago, consistent with those lines of evidence. [1.1]

So: the 242 Ma figure is not arbitrary—it is based on geological stratigraphy of the Helsby Formation, radiometric U-Pb dating of calcretes, and global correlation of the Anisian stage.

The real-world evidence is reported in an open access paper in Nature and in a University of Bristol news item.

Digging into the origin of lizards
A new fossil from Devon reveals what the oldest members of the lizard group looked like, and there are some surprises, according to a research team from the University of Bristol. The study is published today [10 September] in Nature.
Today, lizards and their relatives such as snakes together with the unique tuatara from New Zealand, are the most successful group of land vertebrates, with over 12,000 species – more than birds and more than mammals. But what is it about lizards, snakes and the tuatara, called collectively the Lepidosauria, that has made them so successful?

It was always expected that the first lepidosaurs would have had some of the lizard characters such as a partially hinged skull, an open lower temporal bar, and abundant teeth on the roof of the mouth (palate). These are all features of modern lizards and snakes that enable them to manipulate large prey by opening their mouths super-wide (skull hinge) and use teeth on the palate to grasp wriggling small prey animals.

The lower temporal bar is essentially the cheek bone, a bony rod that runs between the cheek and the jaw hinge and is absent in lizards and snakes today. Snakes and many lizards have all these features, as well as some additional flexibility of the skull. Only the tuatara has a complete lower temporal bar, giving it an archaic look reminiscent of some of the earliest and ancestral reptiles; and it also has some large palatal teeth.

The new fossil shows almost none of what we expected. It has no teeth on the palate, and no sign of any hinging. It does though have the open temporal bar, so one out of three. Not only this but it possesses some spectacularly large teeth compared to its closest relatives.

Daniel Marke, co-corresonding author
School of Earth Sciences
University of Bristol
Bristol, UK.

[Daniel Marke] led the project as part of his studies for the MSc in Palaeobiology at Bristol.

In modern palaeontological studies we often X-ray scan the fossils, but the exceptional resolution and quality of scans from synchrotron X-ray sources show us all the fine details and save any risk of damage. An earlier MSc student, Thitiwoot Sethapanichsakul, had worked on the regular scans and found fantastic detail, but it’s so tiny – the skull is only 1.5 cm long, and we could barely see the teeth. So, we were so grateful to be able to make synchrotron CT scans to get even finer resolution, using two powerful beamlines at the European Synchrotron Radiation Facility (France) and the Diamond Light Source (UK).

Dr David I Whiteside, co-author
School of Earth Sciences
University of Bristol
Bristol, UK.

When you look at the fossil, the whole skeleton sits in the palm of your hand. But after the scans and the hard work of our students cleaning up the scan data, we can see the most amazing detail. The new beast has relatively large triangular-shaped teeth and probably used these to pierce and shear the hard cuticles of its insect prey, pretty much as the tuatara does today.

Professor Michael Benton, co-corresponding author
Professor of Vertebrate Paleontology
School of Earth Sciences
University of Bristol
Bristol, UK.

The new animal is unlike anything yet discovered and has made us all think again about the evolution of the lizard, snakes and the tuatara. We had to give it a name to distinguish it from everything else, and we chose Agriodontosaurus helsbypetrae, quite a mouthful, meaning ‘fierce toothed lizard from the Helsby rock” after the Helsby Sandstone Formation in which it was discovered. This specimen not only provides important information about the ancestral skull of all lepidosaurs but also builds on the growing knowledge that the tuatara, while often called a “living fossil”; belongs to a once-diverse order of ancient reptiles with a rich evolutionary history.

Daniel Marke.

The fossil dates back 242 million years, in the Middle Triassic, just before the dinosaurs appeared, and since then the lepidosaurs have diversified in several stages, the early ones flitting in and out of the undergrowth under the feet of the dinosaurs. They owe their success to their amazing ability to capture insects and other prey using a variety of remarkable adaptations, including their highly flexible jaws and, in the case of some snakes and lizards, the use of venom.
When I found the specimen back in 2015 on the beach in Devon, I had no idea what it was because there was so little of it exposed. It’s been great to see such an amazing fossil coming from a site that has been providing fossils for 150 years.

Robert A. Coram, co-author
School of Earth Sciences
University of Bristol
Bristol, UK.

Publication:
Marke, D., Whiteside, D.I., Sethapanichsakul, T. et al.
The oldest known lepidosaur and origins of lepidosaur feeding adaptations.
Nature (2025). https://doi.org/10.1038/s41586-025-09496-9

Abstract
The Lepidosauria is the most species-rich group of land-dwelling vertebrates. The group includes around 12,000 species of lizards and snakes (Squamata) and one species of Rhynchocephalia, the tuatara Spenodon punctatus from New Zealand¹. Squamates owe their success to their generally small size, but also to their highly mobile skull that enables them to manipulate large prey. These key features of lizard and snake skulls are not seen in Spenodon, which makes it important to understand the nature of their common ancestor. Lepidosaurs originated in the Triassic 252–201 million years ago, but confusion has arisen because of incomplete fossils, many of which are generalized lepidosauromorphs, neither squamates nor rhynchocephalians^2,3,4,5. Here we report a reasonably complete skull and skeleton of a definitive rhynchocephalian from the Middle Triassic (Anisian) Helsby Sandstone Formation of Devon, UK that is around 3–7 million years older than the oldest currently known lepidosaur. The new species shows, as predicted, a non-mobile skull but an open lower temporal bar and no large palatine teeth, and it seems to have been a specialized feeder on insects. This specimen helps us understand the initial diversification of Lepidosauria as part of the Triassic Revolution, when modern-style terrestrial ecosystems emerged.

Main
Modern squamates owe their success to extraordinary adaptations in their skulls, which include extensive kinesis (Fig. 1) and the ability to flex the snout up and down (mesokinesis). Their skulls can also move the braincase relative to the cranium (metakinesis) and move the quadrate and jaw articulation (streptostyly). These combined joint movements enable lizards, especially snakes, to manipulate and swallow large prey. Spenodon and fossil rhynchocephalians have largely akinetic skulls that are incapable of any movement except a small degree of metakinesis, which enables powerful bites but limited food manipulation. Modern Spenodon and squamates differ in the presence and absence, respectively, of the lower temporal bar. In squamates, the open temporal bar is a gap between the jugal and the quadrate bones of the skull that is essential for cranial kinesis. Both Spenodon and many squamates have extensive palatal dentition, including substantial teeth on the palatine bone. These palatal teeth function in various ways. The lateral tooth row on the palatine in Spenodon occludes with the lower jaw teeth in shearing food, and the more centrally located palatal teeth, where present in squamates, work the food against horny growths on the tongue or grip prey in the case of snakes.

Fig. 1: Evolution of lepidosaurs among amniotes.

Time-scaled phylogeny illustrating the variation in morphology of the lower temporal bar and modes of cranial kinesis among fossil and extant diapsids. Skulls are not to scale. Ca, Carboniferous; Ng, Neogene.

These differences between the two living clades of lepidosaurs make it hard to reconstruct the probable cranial anatomy and feeding adaptations of the ancestral lepidosaur. Indeed, it is unclear whether these early forms have a kinetic or akinetic skull and what the state of the lower temporal bar and the palatal teeth are. Knowing the ancestors of successful clades is key to dating the timing of origins and the key innovations responsible for their success.

In a review of the modern lepidosaur skull⁶, predictions were made about the nature of the ancestral lepidosaur on the basis of phylogenetic retrodictions from living forms (Fig. 1) and fossils such as Gephyrosaurus bridensis⁷. It was suggested that the skull would have shown some metakinesis but was otherwise akinetic, and probably had an open lower temporal bar and abundant palatal teeth. In this case, rhynchocephalians retained akinesis and closed the lower temporal bar by extending and suturing the posterior process of the jugal to the quadratojugal and squamosal, as seen in modern Spenodon⁸. By contrast, squamates retained the open lower temporal bar and evolved varying degrees of cranial kinesis through bone loss, bone fusion and the formation of new joints. Fossil squamates then might show varying steps along the way to full kinesis, as in many modern lizards and in snakes. All the early forms should show palatal teeth, an inheritance from earlier reptiles.

The fossil record of lepidosaurs is patchy, particularly in its older parts, for which species and specimens are rare^5,9,10. Because of their generally small size and delicate bones, fossil lepidosaur skeletons can also be incomplete and may lack key, diagnostic characteristics. Lepidosauromorpha (or pan-Lepidosauria), the wider clade, originated in the Permian, and Lepidosauria substantially diversified in the Triassic after the end-Permian mass extinction11. The current oldest member of Rhynchocephalia is Wirtembergia from the late Middle Triassic (239–237 million years ago (Ma)), which seems to show an open lower temporal bar; however, the remains are incomplete¹². The oldest known member of crown Squamata is Cryptovaranoides from the Late Triassic (202 Ma), a squamate with anguimorph affinities that has an open lower temporal bar and limited cranial kinesis^13,14.

Here we present a new specimen, the oldest known member of Lepidosauria, that sheds light on the early history of Lepidosauria and of Rhynchocephalia in particular. The specimen confirms that the open lower temporal is the original condition in Lepidosauria. Moreover, mesokinesis and streptostyly were absent and, unexpectedly, palatal teeth were also absent.

Systematic palaeontology

Lepidosauria Haeckel, 1866
Rhynchocephalia Günther, 1867
Spenodonitia Williston, 1925
Agriodontosaurus gen. nov.
Type and only known species. Agriodontosaurus helsbypetrae gen. et sp. nov.

Etymology. Agrio from the ancient Greek epithet of Dionysus, Agrionius, meaning ‘fierce’ and donto for ‘tooth’, which refers to the remarkably large teeth on parts of the dentary and maxilla, and saurus for ‘lizard’. Therefore, ‘fierce-toothed lizard’. The specific term ‘helsbypetrae’ refers to the Helsby Sandstone Formation (locally called the Otter Sandstone), the deposit in which the fossil was found; petrae is the genitive of petra, the latinized form of the ancient Greek word for rock.

Holotype. BRSUG 29950-14 (Fig. 2 and Extended Data Fig. 1), a partial skeleton comprising cranial and postcranial elements. The skull is distorted and lacks the rostrum; the left side is more complete than the right side of the skull. Parts of the palate and braincase are damaged. The skull is estimated to have been about 14 mm in length. Also preserved are postcranial elements, including an articulated sequence of cervical and dorsal vertebrae, articulated pectoral and disarticulated pelvic girdles, several dorsosacral and caudal vertebrae and the proximal limb bones.

Fig. 2: Holotype specimen of A. helsbypetrae holotype BRSUG 29950-14.

a,b, Three-dimensional reconstruction of the skeleton (voxel resolution of 26 μm; Methods) in dorsal (a) and ventral (b) views. c, Lateral reconstruction of A. helsbypetrae based on elements preserved in the holotype. Scale bars, 10 mm. Full details are provided in Extended Data Figs. 4–9. Colours denote individual segmentations of elements, or groups of elements that were segmented together. vert., vertebrae.

Locality and age. The specimen is from the Helsby Sandstone Formation of Sidmouth, Devon, UK. It was excavated as a block by R.A.C. in 2015 from a temporarily exposed foreshore exposure beneath Peak Hill (UK National Grid Reference SY 109865), from the upper half of the formation, perhaps upper Anisian (244–241.5 Ma)¹⁵.

Diagnosis. Small rhynchocephalian with a body length of about 100 mm with a unique combination of the following 13 features: dentary and maxillary anterior teeth are simple and conical but robust; posterior teeth are more triangular with broad bases and set slightly en echelon; anterior maxillary and dentary teeth are acrodont and posterior teeth are pleuracrodont with a residual subdental shelf; maxilla with a pronounced anterior process and high facial process; lateral tooth row on the palatine absent; broad, flat parietal table composed of paired bones; ventral region of orbit bounded mainly by the jugal, which provides about 90% of the boundary and the maxilla the rest; jugal with a prominent, but short, posteroventral process that does not reach halfway in the ventral region of the lower temporal opening; quadrate with conch and large foramen; dentary extends posteriorly to underlie the glenoid of the lower jaw; fused prearticular, articular and surangular in the lower jaw; bicapitate ribs in the cervical and trunk regions; gastralia present; and bulb-shaped expansion of the posteriormost part of interclavicle.

Marke, D., Whiteside, D.I., Sethapanichsakul, T. et al.
The oldest known lepidosaur and origins of lepidosaur feeding adaptations.
Nature (2025). https://doi.org/10.1038/s41586-025-09496-9

Copyright: © 2025 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

Discoveries like this continue to erode the last hiding places of creationist denial. Each new fossil with its patchwork of ancestral and derived traits adds another piece to the evolutionary jigsaw, showing clearly that life’s history is not a series of static, immutable “kinds,” but a dynamic process of change and adaptation across deep time.

This tiny skull from Devon is not just a curiosity—it represents the dawn of one of the most successful groups of land vertebrates. Lepidosaurs would go on to diversify into the vast array of lizards and snakes that dominate reptile diversity today. Even the tuatara, often misleadingly called a “living fossil,” is shown here to be just one branch of a much larger evolutionary story.

To deny that story requires ignoring or rejecting every independent line of evidence: the anatomy of fossils, the geological context in which they are found, the radiometric dating that anchors them in time, and the genetic data that links living species to their ancestors. For those willing to look, the conclusion is unavoidable: evolution is not a theory in crisis but a theory constantly reinforced by new discoveries, from the deserts of South Africa to a beach in Devon.

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