Extracted from the Geological Conservation Review
You can view an introduction to this volume
at http://www.jncc.gov.uk/page-2731
© JNCC 1980–2009

Volume 10: Fossil Reptiles of Great Britain
Chapter 4: British Triassic Fossil Reptile Sites
Site: EMBOROUGH QUARRY, SOMERSET (GCR ID: 986)
 

EMBOROUGH QUARRY, SOMERSET

OS Grid Reference: ST623505

Highlight

Emborough Quarry is the source of a varied fauna of Late Triassic small reptiles. It is the locality where the best specimens of the extraordinary gliding reptile Kuehneosaurus have been found, as well as Kuehneotherium, perhaps one of the oldest mammals in the world.

Introduction

Emborough is a disused quarry formerly worked for Hotwells Limestone (Carboniferous: Asbian), which dips to the north-east (Savage, 1977). The reptile-bearing cavity filling is exposed in a promontory in the south-east corner of the eastern quarry. The site is important for yielding numerous remains of the unusual gliding reptile Kuehneosaurus and the ?trilophosaur Variodens. The fissure site occupies a relatively small proportion of the quarry area, and further collecting is possible.

Reptiles were discovered in fissure sediments at Emborough by Kühne in 1946, but the first discussion on the geology of the deposit and the reptiles was that of Robinson (1957a, 1957b). Robinson (1957b) described a tricuspid reptile, Variodens inopinatus, from Emborough on the basis of two dentary fragments and referred it to the Tricuspisauridae. A description of the Emborough gliding diapsid Kuehneosaurus, the first known, was made by Robinson (1962). Fraser et al. (1985) reported a therian mammal (Kuehneotherium) from Emborough, regarded by them as the oldest therian mammal in the world, and used this as evidence to invalidate earlier claims by Robinson (1957a, 1971) for the existence of a clear-cut distinction between sauropsid-bearing Late Triassic fissure fills and theropsid-bearing Early Jurassic ones (see above).

Description

The sediments may be divided lithostratigraphically into lower and upper units. The lower sediments are unfossiliferous, well-bedded, dark-red clays with green patches. The upper deposit consists of a conglomerate of Carboniferous Limestone clasts, up to boulder-size, set in a matrix of limestone pebbles, pale shale, and silts. The silt is finely bedded and free of clasts in some places, usually red, but sometimes pale green. The reptile fossils are found in the higher part of the conglomeratic deposit in the silts. Most of the fossils are dissociated, but some Kuehneosaurus material is in articulation.

Diapsida: Archosauromorpha: inc. sed.
Kuehneosaurus latusRobinson, 1962
Type material: BMNH R8172
Diapsida: Archosauromorpha: ?Trilophosauridae
Variodens inopinatus Robinson, 1957
Type material: BMNH
Diapsida: Archosauria
Archosaur incertae sedis
Lepidosauria: Sphenodontida
Planocephalosaurus sp.
Mammalia: ‘Symmetrodonta’: Kuehneotheriidae
Kuehneotherium sp.
Tooth AUGD 11133

Interpretation

Robinson (1957a) interpreted the sediments as the filling of a collapsed cave, the lower beds being deposited by underground streams and the upper deposit formed by a collapse of the cave roof, with fine silt and the reptile remains brought in by land-wash. Robinson (1957a) and Savage (1977) mention solution features such as water-worn faces and boulders; these and the presence of stalactite fragments in the conglomerate confirm the impression that the void was part of a cave system.

It has been possible to date the sediments filling the Emborough fissure as Late Triassic on the basis of direct stratigraphic evidence using the topographical relationship of the cavity to the local, normally bedded stratigraphy (Robinson, 1957a; Fraser et al., 1985). This age assignment is in accord with the date given to Icarosaurus (a close relation of the Emborough diapsid Kuehneosaurus) from the Late Carnian (Lockatong Formation) of the Newark Supergroup in New Jersey.

The reptile fauna from Emborough includes the unusual gliding diapsid Kuehneosaurus latus (Figure 4.24D; Robinson, 1962, 1967), which is the most abundant animal present (Fraser, in press), as well as the ?trilophosaur Variodens inopinatus, for which Emborough is the type locality. Robinson (1957a) mentions two other reptiles, an archosaur and a sphenodontid, and Fraser et al. (1985) reported two teeth of the mammal Kuehneotherium.

Figure 4.24: Typical reptiles from the Late Triassic fissures in South Wales and around Bristol. Skeletal reconstructions of (A) the sphenodontid Clevosaurus; (B) the crocodilomorph Saltoposuchus; (C) the prosauropod dinosaur Thecodontosaurus; and, (D) the gliding diapsid Kuehneosaurus. After various sources; in Fraser (in press).

Kuehneosaurus is represented by dissociated as well as good articulated remains, and the skull including the braincase has been figured by Robinson (1962). The only other kuehneosaurs known are Kuehneosaurus latissimus from Batscombe Quarry and Icarosaurus from the Lockatong Formation of the eastern USA (Colbert, 1970). The kuehneosaurs, because of the absence of a lower temporal bar, the presence of a streptostylic quadrate and a pleurodont dentition, were formerly considered to represent primitive squamates, the true lizards and snakes. This view has been strongly doubted by Evans (1980, 1988a), Benton (1985), and others, who regard the kuehneosaurs as primitive archosauromorphs, on the basis of numerous characters that place them close to rhynchosaurs and prolacertiforms in the cladogram. Kuehneosaurus is a gliding reptile (Figure 4.24D), one of the earliest aerial tetrapods known, which displays a remarkable convergence with the extant gliding lizards of south-east Asia (Draco) and also to Weigeltisaurus, a gliding form from the Late Permian of Durham (q.v.), Germany and Madagascar. Kuehneosaurus latus has also been reported from Slickstones Quarry and the Pant-y-ffynon fissures (Fraser and Walkden, 1983). The numerous Emborough specimens, being mostly dissociated, will allow a complete anatomical study.

The ?trilophosaur Variodons inopinatus is known from two dentaries found at Emborough. The trilophosaurs are a diapsid group, currently placed in the Archosauromorpha (Benton, 1985; Evans, 1988a). Trilophosaurs are known from the Triassic of Russia and North America, but Variodens is the only probable representative of the group described from Western Europe. Halstead and Nicoll (1971) have figured a possible trilophosaur from a fissure at Slickstones Quarry. Fraser (1986) and others have hinted that Variodens may be a procolophonid.

The Kuehneotherium tooth from Emborough was claimed to be the oldest therian mammal fossil in the world, coming as it did from probably pre-Rhaetian sediments (Fraser et al., 1985). The determination of the stratigraphic age of the fissure sediments was disputed, and other equally old mammal remains may be known from France. Lucas and Hunt (1990) reported a supposed mammal skull from the Late Carnian Tecovas Formation of West Texas, USA. Nonetheless, the early record of Kuehneotherium points to the possibility of more substantial finds in Emborough.

The fauna is most similar to that of Slickstones (see above), but the dominance of Kuehneosaurus at Emborough might suggest a different depositional environment, or a different age. However, the different proportions of taxa could equally well be the result of differential sampling of the fauna, either by the nature of the fissure or of collection error.

Conclusion

Emborough is the type locality of the remarkable gliding reptile Kuehneosaurus latus, the only known locality of the trilophosaur/procolophonid Variodens inopinatus, and the site for a Kuehneotherium tooth, possibly the oldest record of a therian mammal in the world.

This great palaeontological importance, combined with some potential for re-excavation give the site substantial conservation value.

Reference list

Benton, M.J. (1985) Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society, 84, 97–164.

Colbert, E.H. (1970) The Triassic gliding reptile Icarosaurus. Bulletin of the American Museum of Natural History, 143, 85–142.

Evans, S.E. (1980) The skull of a new eosuchian reptile from the Lower Jurassic of South Wales. Zoological Journal of the Linnean Society, 70, 203–64.

Evans, S.E. (1988a) The early history and relationships of the Diapsida. In The Phylogeny and Classification of the Tetrapods (ed. M.J. Benton), Systematics Association Special Volume, 35A, Clarendon Press, Oxford, pp. 221–60.

Fraser, N.C. (1986) New Triassic sphenodontids from southwest England and a review of their classification. Palaeontology, 29, 165–86.

Fraser, N.C. (in press) Assemblages of small tetrapods from British Late Triassic fissure deposits. In Early Mesozoic Small Tetrapods (eds N.C. Fraser and H.-D. Sues), Columbia University Press, New York.

Fraser, N.C. and Walkden, G.M. (1983) The ecology of a Late Triassic reptile assemblage from Gloucestershire, England. Palaeogeography, Palaeoclimatology, Palaeoecology, 42, 341–65.

Fraser, N.C., Walkden, G.M. and Stewart, V. (1985) The first pre-Rhaetic therian mammal. Nature, London, 314, 161–3.

Halstead, L.B. and Nicoll, P.G. (1971) Fossilized caves of Mendip. Studies in Speleology, 2, 93–102.

Lucas, S.G. and Hunt, A.P. (1990) The oldest mammal. New Mexico Journal of Science, 30, 41–9.

Robinson, P.L. (1957a) The Mesozoic fissures of the Bristol Channel area and their vertebrate faunas. Zoological Journal of the Linnean Society, 43, 260–82.

Robinson, P.L. (1957b) An unusual sauropsid dentition. Zoological Journal of the Linnean Society, 43, 282–93.

Robinson, P.L. (1962) Gliding lizards from the Upper Keuper of Great Britain. Proceedings of the Geological Society of London, 1601, 137–46.

Robinson, P.L. (1967) The evolution of the Lacertilia. Colloques Internationaux du Centre National des Recherches Scientifiques, 163, 394–407.

Robinson, P.L. (1971) A problem of faunal replacement on Permo–Triassic continents. Palaeontology, 14, 131–53.

Savage, R.J.G. (1977) The Mesozoic strata of the Mendip Hills. In Geological Excursions in the Bristol District (ed. R.J.G. Savage), University of Bristol, Bristol, pp. 85–100.