In 2022, researchers at the University of Bristol described Cryptovaranoides microlanius from the Late Triassic of the United Kingdom as the oldest crown squamate. This discovery had shifted the origin of the whole lizard-snake group, called Squamata, back to at least 205 million years old, making it the oldest modern-type lizard on record.
However, this study was challenged in 2023, and the refurnished thoughts reinterpreted Cryptovaranoides as an archosauromorph.
This decision is of utmost importance in enhancing our understanding of the early stages of squamate evolution. The revised placement removes the species from such a role.
In the original study, researchers named the little critter Cryptovaranoides microlanius, which means a hidden lizard and a small butcher, because of its identification as a lizard and its sharp teeth. The team suspects sharp teeth were used for cutting up prey animals.
The team by David Whiteside urged revisers to make careful observations of the fossils and pointed out several errors of observation and interpretation in their work. The lead author and colleagues corrected these references from both; fossil and computed tomography scans.
Dr Whiteside says, “We knew our paper would be controversial. But we were confident that we had looked at every possible feature and compared it with everything we could.“
“We were therefore surprised, perhaps even shocked, that in 2023 another team of academics suggested that Cryptovaranoides was not a lizard or even a lizard relative, but in fact an archosauromorph, more closely related to crocodilians and dinosaurs,” says Professor Benton.
To correct the questions posed by the rival paper, the Bristol team utilized the fossil data and CT scans to reveal details hidden within the rock. Since the team already had CT scans and access to the fossils, they were able to check all their suggestions and found that most of the concerns raised were wrong.
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Professor Benton added, “All the details of the skull, the jaws, the teeth, and the limb bones confirm that Cryptovaranoides is a lizard, not an archosauromorph.“
“In our new paper, we provide great detail of every criticism made and we provide more photographs of the specimen and 3D images from the scans, so everyone can check the detail.“
This study mentions that the rival paper by Brownstein et al. failed to recognize or describe obvious features in the holotype. Brownstein marked the absence of both foramina as the trait for archosauromorphs.
Challenging their view, the Bristol study depicts a clear description and illustration of the humerus ectepicondylar and entepicondylar foramina.
“The result of all this had to be tested by a phylogenetic analysis. This is where we code hundreds of anatomical features in Cryptovaranoides and other modern and fossil lizards, as well as various archosauromorphs,” says Dr Whiteside.
“We ran the analysis time after time, and it gave our original result, that the little Bristol reptile is indeed the world’s oldest modern-type lizard,” Dr Whiteside concludes.
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Journal Reference
- Whiteside David I., Chambi-Trowell Sofía A. V. and Benton Michael J. 2024Late Triassic †Cryptovaranoides microlanius is a squamate, not an archosauromorph. Royal Society Open Science. DOI: 10.1098/rsos.231874
