A two-centimeter skull just rewrote 166 million years of furniture
Marmoretta oxoniensis, a stem lepidosaur (an early branch of the lineage that leads to today’s lizards, snakes, and the tuatara, a lizard-like reptile found only in New Zealand) that lived around 166 million years ago, spent part of its life climbing trees, not paddling through lagoons as researchers assumed for decades. The reversal comes from a 2025 study led by Dr. David Ford, with Roger Benson, Elizabeth Griffiths, and Susan Evans, published in Proceedings of the Royal Society B, which put the animal’s fossil skeleton under a micro-CT scanner and then under a synchrotron, an X-ray source strong enough to resolve the internal structure of bone smaller than a grain of rice.
The fossils come from Oxfordshire and the Isle of Skye, dated to the Middle Jurassic. The skull at the center of the new analysis measures about 0.8 inches (2 cm) end to end, and its individual finger bones run only a few millimeters, about the width of a matchstick. That a reptile known from pieces this small can have its entire ecological identity rewritten is the real headline: the fossil did not change. The way it was read did.
Curled fingers, stiff spine: how bone shape confesses a lifestyle
The study reports that Marmoretta’s finger bones, specifically the unguals (the clawed tip bones) and the penultimate phalanges, are long and curve downward along their length, with enlarged tubercles (small bony bumps that anchor tendons) on their underside, a hand built to grip bark rather than push water. Aquatic reptiles from the same period show flattened or webbed digits instead. The study also found that the steep angle of Marmoretta’s thoracic zygapophyses (the small joints linking one vertebra to the next) made its spine stiffer than that of known swimmers, useful for holding still on a branch and a liability in water, where a flexible spine helps propulsion.
None of that would mean much on its own. The team ran a linear discriminant analysis, a statistical method that sorts measurements into predefined groups, on Marmoretta’s partial hand, scored against a training dataset built from the hand skeletons of living squamates (lizards and snakes) whose habits are already known: arboreal, scansorial (climbing on rough surfaces like bark), ground-dwelling, or aquatic. Marmoretta’s numbers landed inside the cluster occupied by scansorial and arboreal iguanians, lizards alive today that climb for a living. The method essentially asks a living animal’s skeleton whether a fossil hand matches its own, and lets the measurements answer instead of the eye.
Going vertical: the oldest escape plan in the lizard family
The researchers propose that Marmoretta lived in trees fringing a subtropical lagoon, something close to a modern mangrove edge, and that climbing was less about fruit or shade and more about staying out of reach of whatever was hunting on the ground. That part is their interpretation, not a measurement: the fossils supply the hand and spine shape, the team supplies the reason behind it.
What carries the finding past one animal is the timing. The researchers connect it to the broader run of lepidosaurs, a lineage that has persisted for more than 160 million years since, and note that small Triassic mammals reportedly used a similar trick, going vertical to dodge ground predators. If climbing was already a survival move this early in the lepidosaur story, height was not scenery for Marmoretta. It was the exit.
It was buried near the sea, so everyone assumed it swam
For years Marmoretta was filed as semi-aquatic, and the reasoning was simple: its fossils turned up in lagoon deposits alongside marine species. That is guilt by association, not anatomy. Nobody had actually measured whether its bones matched a swimmer’s. The 2025 analysis checked, and the bones say the opposite: the finger curvature and the stiffened spine point to branches, not water, the same evidence laid out above. The myth did not survive contact with a CT scanner.
What nobody has yet is enough skeletons
Lepidosaurs and archosaurs (the lineage leading to crocodilians and birds) split from a shared ancestor an estimated 260 million years ago, and what either group was doing with its body in the tens of millions of years that followed is still mostly a blank, because well-preserved fossils from that window are rare. An earlier 2021 study by much of the same team, Griffiths, Ford, Benson, and Evans, had already used micro-CT to recover previously unknown skull bones in Marmoretta: the squamosal, the postorbital, a more complete parietal, the pterygoids, and the mandible (lower jaw), confirming its place as a stem lepidosaur before anyone had looked closely enough at its hands to ask how it actually moved.
The Middle Jurassic reptile picture is still being filled in one specimen at a time, and the researchers are plain about how much is missing: there is still a lot to learn. A two-centimeter skull just moved one small, climbing reptile from one shelf to another. The shelf itself is still mostly empty.