Westlothiana ("animal from West Lothian") is an extinct genus of tetrapods from the Mississippian (early Carboniferous) of Scotland. It is known from a single species, Westlothiana lizziae. Westlothiana is one of the most noted fossils of the East Kirkton Quarry fossil site, living about 341 million years ago during the latest part of the Viséan age. It was a small tetrapod with a long body, short limbs (with five toes on the hindlimb), and a blunt-nosed skull with small fangs on the roof of the mouth.
The relations of Westlothiana have gone through much revision. It was initially regarded as the oldest known reptile (or, more specifically, the oldest known member of Amniota, the group containing reptiles, mammals, and birds). Further study argued that it was not quite an amniote, but rather a non-amniote tetrapod (amphibian, in the broad sense) more closely related to amniotes than to modern amphibians. This would still qualify it as one of oldest known crown group tetrapods. A comprehensive 2026 redescription using synchrotron X-ray tomography instead found Westlothiana to be a stem-group tetrapod, diverging prior to the common ancestor of modern amphibians and amniotes. In this analysis, it is regarded as an amphibious or aquatic animal closely related to the limbless aistopods.
Discovery and naming
The type specimen of Westlothiana was discovered in 1988 by Scottish fossil hunter Stan Wood. He found it in unit 82 of the East Kirkton Limestone, a fossil-rich layer exclusive to the East Kirkton Quarry near Bathgate in West Lothian, Scotland. A 2025 study estimated that unit 82 is around 341 ± 3 million years old. The type specimen is a compression fossil split into part and counterpart slabs, both catalogued as NMS G.1990.72.1. It represents a mostly-complete skeleton, only missing part of the tail and hands.
Stan Wood nicknamed his find "Lizzie the lizard", and this name was quickly adopted by other paleontologists and the press. University of Cambridge paleontologist Timothy R. Smithson briefly described the fossil in a 1989 issue of Nature. By that time, it had already been featured in the first episode of Lost Worlds, Vanished Lives, a David Attenborough miniseries on new fossil discoveries.
Around January 1990, Stan Wood auctioned the fossil, which was purchased by the State Museum of Natural History Stuttgart for £180,000 (£ adjusted for inflation), which the museum said was to avoid the specimen falling into a private collection. The fossil subsequently was kept in the UK and purchased by the National Museums Scotland around August 1990 following a public appeal, which raised £195,500 (£ adjusted for inflation) to purchase the specimen.
Timothy R. Smithson and National Museums Scotland paleontologist W.D. Ian Rolfe formally provided a scientific name in 1990, combining the generic name Westlothiana (referencing West Lothian) with the specific name "lizziae", an homage to its nickname. Despite its similar body shape, Westlothiana is not a lizard, as true lizards would not appear until more than 100 million years later. The anatomy of Westlothiana contained a mixture of both "labyrinthodont" and reptilian features, and was originally regarded as the oldest known reptile or amniote (tetrapods laying hard-shelled eggs, including synapsids, reptiles, and their descendants).
Further studies have shown that this original identification is not entirely accurate. Instead of being one of the first amniotes, Westlothiana was quickly reevaluated as an amphibian closely related to Amniota. This revised conclusion was published in 1993 by Smithson and his colleagues, as part of a more comprehensive description of the fossil. Most paleontologists since the original description place the genus within the group Reptiliomorpha (or Stem-Amniota), among other amniote relatives such as diadectomorphs and seymouriamorphs. Some analyses place the genus as the earliest diverging member of Lepospondyli,Marjanović, D. & Laurin, M. (2019) Phylogeny of Paleozoic limbed vertebrates reassessed through revision and expansion of the largest published relevant data matrix. PeerJ:6:e5565. doi: 10.7717/peerj.5565. eCollection 2019. a collection of unusual tetrapods which may be close to amniotes or lissamphibians (modern amphibians like frogs and salamanders), or potentially both at the same time. A redescription by Igielman et al. (2026) regards Westlothiana as a stem-group tetrapod, not closely related to either modern amphibians nor amniotes. This redescription was made possible thanks to synchrotron X-ray tomography, a technique to scan and reconstruct hidden parts of the skull and skeleton.
Smithson et al. (1993) referred a second East Kirkton tetrapod skeleton to Westlothiana lizzae. This second specimen, catalogued as NMS G.1991.47.1, is from unit 76, which is a slightly younger layer at the quarry. Igielman et al. (2026) disagreed that this skeleton is a fossil of Westlothiana, noting its differing number of vertebrae and foot bones.
Description
Westlothiana probably lived in or around freshwater lakes, hunting for other small creatures that lived in the same habitat. It was a slender animal, with rather small limbs and a presumably long tail. Together with Casineria, another transitional fossil found in Scotland, it is one of the smallest reptile-like amphibians known, estimated to be less than in adult length. The small size has made it a key fossil in the search for the earliest amniote, as amniote eggs are thought to have evolved in very small animals.Carroll R.L. (1991): The origin of reptiles. In: Schultze H.-P., Trueb L., (ed) Origins of the higher groups of tetrapods — controversy and consensus. Ithaca: Cornell University Press, pp 331-353.Laurin, M. (2004): The Evolution of Body Size, Cope's Rule and the Origin of Amniotes. Systematic Biology no 53 (4): pp 594-622. articlePaton R.L., Smithson, T.R. & Clack, J.A. (1999): An amniote-like skeleton from the Early Carboniferous of Scotland. Nature no 398: pp 508–513
Ruta et al. (2003) interpreted the long body and small legs as a possible adaption to burrowing, similar to modern skinks.Ruta, M.; Coates, M.I. & Quicke, D.L.J. (2003): Early tetrapod relationships revisited. Biological Reviews no 78: pp 251-345.PDF On the other hand, Igielman et al. (2023) noted many features consistent with an aquatic or amphibious lifestyle, such as gill arches, a wide notochord, and hindlimbs longer than forelimbs. Westlothiana were heavily scaled, with thin dermal (bony) scales on the belly and many rows of thick, overlapping scales on the back, similar to early tetrapods but in contrast to amniotes, in which the scales are epidermal, or formed in the skin.
Skull
The skull is small compared to the overall body length, and although flattened in the holotype, many components are visible. When reconstructed digitally, the skull measures in length. Components which were initially hidden by the crushing, such as the palate (roof of the mouth), were later revealed by further preparation and X-ray scans. The skull is coated with tiny pits. The orbits (eye sockets) are quite large, each filled with a scleral ring. The skull is fairly broad, but not as shallow as in some early tetrapods.
The teeth are all the same size, unlike many early amniotes which have larger fang-like teeth in the middle of the mouth. There are 9 teeth in the premaxilla and 34 teeth in the maxilla. Westlothiana has often been considered to lack "labyrinthodont" folding, a type of maze-like internal tooth structure most common in large prehistoric amphibians. This trait appears to be correlated with size, rather than evolutionary relations, and the teeth of Westlothiana do have some internal folding at the base. There is a small hole in the skull (an internarial fenestra) between the premaxillae, unlike amniotes and their close relatives. Like other early tetrapods, the quadrate bone (which holds the upper half of the jaw joint) slants back towards the jaw joint. The postfrontal bones, which typically occupy the upper rear corner of the orbits, are very elongated in Westlothiana. They stretch forward to form most of the upper rim of the eye sockets, and contact the prefrontal bones at the front edge of each socket, unlike amniotes. The prefrontals are also prolonged forward, far enough to contact the nostrils.
Skull roof The bones of the skull roof (the upper part of the skull, behind the eyes) have several distinctive features. The largest components are the parietal bones, which are wide enough to reach the sides of the skull. The skull roof is loosely attached to bones of the cheek region (such as the straight-edged squamosals), similar to amniotes and various amphibians. The rear edge of the skull roof is formed by three pairs of bones, the postparietals, tabulars, and supratemporals (listed from inwards to outwards). The postparietals are wide, the tabulars are blunt overhangs, and the supratemporals are narrow. This inward-to-outward series is similar to protorothyridids but very different from the condition in microsaurs. Many larger Paleozoic amphibians have a wide otic notch for a spiracle between the squamosal and tabular. In Westlothiana, the otic notch is reduced to a narrow slit. Broad parietals and a narrow otic notch are also seen in aistopods and embolomeres. The rear edge of the skull roof does not bend down to meet the braincase, unlike amniotes or many microsaurs.
Supratemporals are rare among lepospondyls, but they are similarly present and narrow in urocordylids and a few early aistopods. Each supratemporal contacts the elongated postorbital bone behind the orbit, cutting off the parietals from the squamosals. This contrasts with sauropsids (reptiles), but is similar to the condition in diadectomorphs and early synapsids. Microsaurs do not have supratemporals, though their typically large tabular bones also prevent parietal-squamosal contact. In more basal tetrapods, an additional bone known as an intertemporal was positioned at the intersection of the four bones. Most reptiliomorphs which lost the intertemporal filled the space using a 'lappet' of the parietal bones. In Westlothiana, Limnoscelis, and lepospondyls, this space is instead filled by an expansion of the rear branch of the postorbital bone, behind the eye.
Palate Although the skull generally shows a combination of amniote and non-amniote features, the palate (bony roof of the mouth) notably lacks amniote adaptations. The entire palate is covered with small tooth-like prickles known as denticles. This is not unusual among early amphibians (palatal dentition is widespread among early tetrapods), but early amniotes usually concentrate their denticles into isolated patches or rows. The denticles of Westlothiana even extend onto the parasphenoid bone, which forms part of the underside of the braincase.
The largest and most centralized bones of the palate are the pterygoids, which have simple tapering extensions towards the jaw joint. This is a notable contrast to all early amniotes, in which each pterygoid bends outwards with a tooth-covered prong known as a transverse flange. Other typical basal tetrapod traits include large ectopterygoid bones and prominent fangs on the palate: one fang pair on each elongated vomer, and one pair on each palatine bone. These fangs were only recognized once synchrotron scans revealed the palate as a whole in the 2026 redescription.
Braincase and gills