New Scottish fossil sheds light on lizard origins

A fossil discovery from Scotland has provided new information about the early evolution of lizards, during the age of the dinosaurs.

The tiny skeleton discovered on the Isle of Skye, called Bellairsia gracilis, is just 6cm long and dates from the Middle Jurassic, 166 million years ago. The extraordinary new fossil includes a nearly complete life-like articulated skeleton, missing only the snout and tail. This makes it the most complete fossil lizard from this era anywhere in the world.

Bellairsia has a mix of ancestral and modern features in its skeleton, providing clues to what the ancestor of today’s lizards (which belong to the larger group of animals known as “squamates”) might have looked like.

The research, a joint project between researchers at the universities of Warsaw, Oxford and UCL, is reported in the journal Nature. First author Dr. Mateusz Tałanda (University of Warsaw and UCL) said: “This small fossil allows us to see evolution in action. In palaeontology you rarely have the opportunity to work with such complete, well-preserved fossils from a time when we know so little.”

The fossil was found in 2016 by a team led by the University of Oxford and National Museums Scotland. It is one of several new discoveries of fossils from the island, including early amphibians and mammals, that reveal the evolution of important animal groups that persist to this day.

Dr. Tałanda commented, “Belairsia has some modern lizard features, such as features related to cranial movement – that is the movement of the skull bones in relation to each other. This is an important functional feature of many living lizards.”

Co-author Dr. Elsa Panciroli (Oxford University Museum of Natural History and National Museums Scotland) who discovered the fossil, said: “It was one of the first fossils I found when I started working on Skye. The small black skull poked out of the pale limestone, but it was so small I was lucky to spot it. Looking closer I saw the tiny teeth and realized I had found something important, but we had no idea until later that almost the entire skeleton was in there.”

Squamates are the living group that includes lizards and snakes, and include more than 10,000 species today, making them one of the most species-rich groups of living vertebrates. They include animals as diverse as snakes, chameleons and geckos, found all over the world. The group is characterized by numerous specialized features of the skull and the rest of the skeleton.

Although we know that the earliest origin of squamates is 240 million years ago in the Triassic, the lack of fossils from the Triassic and Jurassic has made their early evolution and anatomy difficult to trace.

Analysis of the new fossil alongside living and extinct fossils confirms that Bellairsia belongs to the “stem” of the placid family tree. This means that it split from other lizards shortly before the origin of modern groups. The research also supports the finding that geckos are a very early branching lineage and that the enigmatic Oculudentavis fossil, previously suggested to be a dinosaur, is also a gazelle.

To study the sample, the team used X-ray computed tomography (CT) which, like medical CT, allows for non-invasive 3D imaging. This allowed the researchers to image the entire fossil, even though most of the specimen is still hidden by surrounding rocks. While medical scanners operate on the millimeter scale, Oxford University’s CT scanner revealed details down to a few tens of micrometres.

Subsequently, parts of the skeleton were imaged in even greater detail, including the skull, hindlimbs and pelvis, at the European Synchrotron (ESRF, Grenoble, France). The intensity of the synchrotron beam allows resolution of 4 micrometers, revealing details of the smallest bones in the skeleton.

Co-author Professor Roger Benson (Department of Earth Sciences, University of Oxford), said: “Fossils such as this Bellairsia specimen are of enormous value in filling the gaps in our understanding of the evolution and history of life on Earth. It was once almost impossible to study such tiny fossils as this, but this study shows the power of new techniques, including computed tomography, to image them non-destructively and in great detail.”

Co-author Professor Susan Evans (UCL), who first described and named Bellairsia from some jaw and skull bones from Oxfordshire 25 years ago, added: “It’s great to have a complete specimen of this enticing little lizard and see where it fits in the evolutionary tree. Through fossils like Bellairsia we gain a better understanding of early lizard anatomy. Angus Bellairs, the lizard embryologist after whom Bellairsia was originally named, would be very pleased.”

The study was conducted by Dr. Mateusz Tałanda (University of Warsaw) and involved researchers from the Department of Earth Sciences, Oxford University, Oxford University Museum of Natural History, UCL (University College London), European Synchrotron Radiation Facility, Natural History Museum London and in the National Museums of Scotland.

The study will be published in Nature.