The first Middle Jurassic dinosaur from Scotland: a cetiosaurid ...

The first Middle Jurassic dinosaur from Scotland: a cetiosaurid? (Sauropoda) from the Bathonian of the Isle of Skye N. D. L.

CLARK1,

J. D.

BOYD 2 ,

R. J.

DIXON2

and D. A. Ross 3

1

Hunterian Museum, University of Glasgow, Glasgow G12 8QQ - BP Exploration, Farburn Industrial Estate, Dyce, Aberdeen AB2 OPB 3 The Staffin Museum, 6 Ellishadder, Staffin, Isle of Skye IV5I 9JE

Synopsis The limb bone of a dinosaur was discovered from the Valtos Sandstone Formation (Bathonian, Middle Jurassic) near Valtos, Isle of Skye. The bone preserves the eroded proximal and distal ends and is missing the mid-shaft. It represents the first unequivocal Middle Jurassic dinosaur bone from Scotland. The bone is of a sauropod dinosaur and may be the femur of a cetiosaurid.

Introduction For many years palaeontologists have been searching for the Scottish dinosaur. The paucity of localities with lithologies of the correct age, environment and exposure has hindered the search. Several candidates have been proposed with the most likely specimen being the early Norian (Triassic) Saltopus elginensis Huene 1910 from Lossiemouth. Benton and Walker (1985) suggested that Saltopus may be related to Procompsognathus. However, the material is not unequivocally dinosaurian and could represent the remains of an early pterosaur or lagosuchid (Norman 1990). In 1982 the first evidence that dinosaurs inhabited what is now Scotland came to light. A dinosaur footprint was discovered in the vicinity of the present find from near the top of the Lealt Shale Formation (Bathonian, Middle Jurassic). It is thought to have been produced by an ornithopod dinosaur (Delair and Sarjeant 1985) although it was originally described as a possible theropod footprint by Andrews and Hudson (1984). The footprint was collected and is now housed in the Hunterian Museum, University of Glasgow. The Staffin Museum specimen (SM 1977.1994.1), described here, was discovered by one of the authors on a sedimentological field trip (J.D.B.). J.D.B. and R.J.D. reported the discovery to the officer at the Staffin Museum (D.A.R.). Before the specimen was found by J.D.B. it had been severely damaged by an anonymous collector. As a consequence of this, a large and significant proportion of this crucial specimen is not available for study (but see note at end of acknowledgements). At about the same time as the sedimentologists from BP made their discovery, Jan Wolfe of the Oyster Catcher Restaurant, Staffin, discovered another bone fragment only yards away from the original find. It is now known that her fragment is the distal end of the same bone, but does not

complete the bone as there still exists a missing section. On searching the immediate surroundings of the BP find, a fragment was found that belonged to Jan Wolfe's bone. It was possible to position this fragment on a piece of external mold which attached to the BP specimen. As a result it was possible to reconstruct the missing fragment with some precision, thus allowing useful measurements to be taken (Clark 1995). Yet another dinosaur limb bone has been discovered recently on the Isle of Skye (Benton et al. 1995). It is the proximal end and shaft of a theropod tibia from the Hettangian Stage of the Lias. This extends the range of dinosaurs into the lower Jurassic in Scotland and also increases the number of dinosaur groups represented. These groups now include the ornithopods (Andrews and Hudson 1984; Delair and Sarjeant 1985), the theropods (Benton et al. 1995), and the sauropods (described here).

Stratigraphical setting The bone was found on a loose block on the foreshore at Valtos (precise grid reference lodged with Scottish Natural Heritage, Edinburgh). It is held in a conglomeratic and sandy horizon closely associated with the bivalve Neomiodon and plant remains. This is characteristic of the Valtos Sandstone Formation (Bathonian, Middle Jurassic) and is slightly younger than the horizon from which the dinosaur footprint was found. It represents terrestrially derived sediment deposited within a lagoonal delta environment (Bell and Harris 1986; Harris 1992).

Context During the Late Bajocian the Sea of Hebrides Basin was subjected to a marine transgression probably allowing a Scottish Journal of Geology 31, (2), 171-6, 1995

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seaway to develop connecting it with the North Minch Basin (Bradshaw and Cripps in Bradshaw et al. 1992, J6a). Later (in the Mid-Bathonian) sedimentological and palaeontological evidence suggests that the basin was subject to salinity fluctuations, with the Lealt Shale Formation and the Valtos Sandstone Formation being deposited in a lagoonal setting (Hudson and Harris 1979; Harris 1992). The lagoon was shallow and periodically exposed to produce hypersaline mudflats (Bradshaw and Cripps in Bradshaw et al. 1992, J6b). In the Late Bathonian there is a trend to more terrestrial and alluvial sedimentation isolating shallow pools from the sea to the south (Bradshaw and Cripps in Bradshaw et al. 1992, J7a). During the Midto Late Bathonian, northern Skye became connected with

the Scottish Landmass in the east and the Hebrides Platform in the west. Palaeocurrent data indicate a predominant north to north-easterly source for the sediment of the Valtos Sandstone Formation (Harris 1992). The Scottish Landmass was connected to the Welsh, Pennine, and Anglo-Brabant Landmasses as well as the Mid North Sea High during the Late Bajocian, although during the Bathonian the southern landmasses were substantially reduced with the development of a seaway between the Cleveland basin and the Cots wold-Weald Shelf. Hudson (1964) suggested that the heavy mineral assemblage in the sandstones of the Valtos Sandstone Formation may have been derived from stripping of a sedimentary cover (Old Red Sandstone) from a metamorphic basement (Moine). The Torridonian and Cambrian

FIG. 1. (a) Cranial aspect; (b) lateral view showing curvature; (c) caudal aspect of the limb bone (all x 0.2) (SM 1977.1994.1).

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rocks in the northwest of Scotland may also have been a sediment source at this time.

Material Both the proximal section of bone (BP Exploration specimen) and the distal section (Wolfe specimen) are registered with the collections of the Staffin Museum, Isle of Skye (SM 1977.1994.1). Casts of both these specimens and the reconstructed missing fragment are held in the collections of the Hunterian Museum, Glasgow (GLAHM101148). A small fragment of abraded bone that was also found close to the other finds was sectioned for analysis and is in the collections at the Hunterian Museum, Glasgow (GLAHM101147).

Description The bone is flattened towards the proximal end and expands markedly towards the joint articulation (Figs. 1 a, c and 2). Muscle scars are clearly seen near to the articulation on the concave side of the bone. The distal bone section, also expands forming a groove with a distinct, although worn, ridge to the anterior (Fig. 1 a, b, c). The bone tapers towards the missing section from an approximate maximum diameter of 28.0 cm on the distal section to a minimum diameter of 13 cm in the shaft. There is a marked bow to the bone that is anteriorly concave. Both parts have been eroded syndepositionally and lack the full extent of their extremeties. The shaft is sub-circular in section with the transverse diameter exceeding the craniocaudal diameter. The cross sectional structure of the bone has a thick perichondral compact bone layer containing a high concentration of haversian canals (2 cm thick on the caudal side of the bone and 3 cm thick on the cranial side) (Fig. 3b) surrounding the endochondral ossification (Fig. 3a). The endochondral ossification has fractured to allow sediment to penetrate (Fig. 3c). The periosteal lamellum is mostly missing due to syn- and post-depositional abrasion. The nature of the bone suggests that the animal had to carry a heavy weight. Judging by the approximate length, and shape of the complete and reconstructed bone, and the microscopic structures, the bone may be considered to be the tibia or femur (Paul Upchurch pers. comm.) of a sauropod. The prominent longitudinal ridge on the distal section may represent part of a worn tibial condyle on the cranial side of a right femur. If the bone is a tibia then this process may help to lock the astragalus in place. No evidence of a ridge on the medial side of the caudal face can be seen, although this may have been present on the missing shaft section. The recovery of the missing midshaft section would possibly provide a more positive identification. Although the outline shape and length of the bone is similar to that of a tibia (Fig. 4), the expansion towards what would be the articulation with the femur is only slight. The missing section marked 'M > 1' (Fig. 2) is narrow as is found in femora towards the articulation with the hip. The

FIG. 2. Diagramatic reconstruction of the limb bone in caudal view (x 0.2) (d, distal section; g, groove; m >, m > 1, missing bone reconstructed; m~, missing bone probably due to erosion; p, proximal section; r, ridge).

distal ridge that represents a partially worn condyle is unlike the articulation with the astragalus but identical to the form seen in the tibial condyle of a femur (Fig. 5). It appears more likely that this bone represents the femur of a sauropod although it is rather shorter than adult sauropod femora. The dimensions of the femur and tibia, however, do not differ significantly from the juvenile to adult stages (Carpenter and Mcintosh 1994). As the bone did not

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FIG. 3. (a) Transverse view of the shaft as seen on the distal section showing 'tree-ring' perichondral bone and the endochondral ossification of the interior of the bone (x 0.85). (b) Transverse secion through perichondral bone showing bone-rings around haversian canals (x 150) (GLAHM 101147). (c) Transverse section through the endochondral ossification showing abundant heavy minerals and other detrital grains filling the hollows between boney material (xl50) (GLAHM 101147).

identify with any known sauropod, it is possible that it represents a new species. However, the erection of a new species on the basis of one incomplete bone is considered by the authors to be beyond the scope of this paper. Lengths: BP Exploration section1 Missing section Wolfe section2 Reconstructed length Minimum diameter of shaft Maximum at same point Circumference of shaft at minimum diameter Reconstructed maximum width of proximal articulation Reconstructed maximum width of distal articulation proximal section; 2 distal section

38 cm 20 cm 30 cm 90 +cm 13 cm 15.5 cm 41 cm 37 cm (approximately) 30 cm (approximately)

Identification The bone represents the first limb bone of a sauropod dinosaur from Scotland. Other contemporaneous British Middle Jurassic sauropod dinosaurs from England (Norman 1990) include the Bajocian Cetiosaurus medius, and Cetiosauriscus long us, and the Bathonian Cetiosaurus oxoniensis, Bothriospondylus robustus, and Cetiosauriscus glymptonensis. Due to the short and thick shaft of the bone, as well as the broad expansion both proximally and distally, it is thought that this may represent the femur of a cetiosaurid. Bothriospondylus and other brachiosaurids have much narrower and longer shafts with less expansion of the distal end. The diplodocids, such as Cetiosauriscus, have a slightly broader but relatively longer shaft. The differences between the relative sizes of the femora and the degree of erosive damage to this bone prevents us from positively identifying with certainty which sauropod it belonged to. The reconstructed length of 90 cm for the bone from the Isle of Skye does not take into account the amount of erosion prior to burial and it may, therefore be slightly longer to take it closer to length of the smaller 1.25 m long Cetiosaurus femur illustrated by Phillips (1871) (Fig. 5a).

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a

Si

FIG. 4. Caudal view of sauropod tibiae for comparison — outlines not drawn to scale, (a) Cetiosaurus sp. (after Phillips 1871, fig. CIX.2, p.282). (b) Apatosaurus louisae (after Mcintosh 1990, Fig. 16.17.1, p.373). (c) "Bothriospondylus madagascariensis'' (after Mcintosh 1990, Fig. 16.17.g, p.373).

What is preserved of the structure of the proximal and distal articulations suggests an affinity with Cetiosaurus, although more diagnostic material will need to be recovered.

Preservation The bone is preserved in phosphate, black with a brown outer edge and is fractured by thin calcitic veins that also penetrate the surrounding sediment. The haversian canals are infilled with a calcite cement and the interstitial system is preserved in apatite. Within the endochondral ossification detrital grains of quartz, feldspar, zircon, rutile, tourmaline, magnetite and garnet have been observed cemented by calcite (Fig. 3c). There is a large number of heavy minerals

dominated by magnetite and zircons. It is thought that the bone may have travelled some distance from the rest of the corpse and it is thus unlikely that more skeletal remains of this animal will be found in the immediate" vicinity.

Acknowledgements We would like to express our gratitude to Jan Wolfe of the Oyster Catcher Restaurant, Staffin, for allowing us to study the section of bone that she discovered and for generously donating it to the Staffin Museum. Dr. J. K. Ingham helped extensively with the preparation of the bone for casting and also discovered the link between the two bones. Mike Taylor is thanked for useful discussion and information on the other dinosaur discovery in Scotland. Paul Upchurch is thanked for indicating the possible limb bone alternatives. BP Exploration, Aberdeen, funded the

FIG. 5. Caudal view of sauropod femora for comparison — outlines not drawn to scale. (a) Cetiosaurus sp. (after Phillips 1871, fig. CVIII.left, p.281). (b) Apatosaurus louisae (after Mcintosh 1990, Fig. 16.16.1, p.372). (c) 'Bothriospondylus madagascariensis' (after Mcintosh 1990, Fig. 16.16.e, p.372.

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project and provided us with the necessary capital to produce casts of the bone for the Staffin Museum, Isle of Skye, The Hunterian Museum, Glasgow, and the National Museums of Scotland, Edinburgh, as well as a copy for BP Exploration, Aberdeen. The missing middle shaft section of the sauropod bone arrived anonymously be post to the Hunterian Museum after the completion of this manuscript. In the parcel were two bone fragments that together were identical in shape and size to the previous reconstruction of that piece. The pieces lacked the trochanter that is seen in many sauropod femurs towards the proximal end. Following the wishes of the anonymous donor, the shaft section is now reunited with the rest of the bone at the Staff!n Museum.

References ANDREWS, J. E. and HUDSON, J. D., 1984. First Jurassic dinosaur footprint from Scotland. Scottish Journal of Geology 20, 129-134. BELL. B. R. and HARRIS, J. W., 1986. An Excursion Guide to the Geology of the Isle of Skye. Geological Society of Glasgow. BENTON, M. J., MARTILL, D. M. and TAYLOR, M. A. 1995. The first dinosaur from the Lower Jurassic of Scotland: a limb bone of a ceratosaur theropod. Scottish Journal of Geology 31, 171-82. BENTON, M. J. and WALKER, A. D„ 1985. Palaeoecology, taphonomy, and dating of Permo-Triassic reptiles from Elgin, North-East Scotland. Palaeontology 28, 207-34. BRADSHAW, M. J., COPE, J.W.C., CRIPPS, D. W., DONOVAN, D.T., HOWARTH, M. K. RAWSON, P. F, WEST, I. M. and WIMBLEDON, W. A. Jurassic. In Cope, J. W. C , Ingham, J. K. and Rawson, P. F. (eds.), Atlas of Palaeo-

geography and Lithofacies. Geological Society, London, Memoirs,'13, 107-29. CARPENTER, K. and McINTOSH, J. 1994. Upper Jurassic sauropod babies from the Morrison Formation. In Carpenter, K., Hirsch, K. F. and Horner, J. R. (eds.), Dinosaur Eggs and Babies 265-78. Cambridge University Press. CLARK, N. D. L. 1995. Scotland's first dinosaur. Earth Heritage 3, 14. DELAIR, J. B. and SARJEANT, W. A. S. 1985. History and bibliography of the study of fossil vertebrate footprints in the British Isles: Supplement 1973-1983. Palaeogeography Palaeoclimatology Palaeoecology 49, 123-60. HARRIS, J. P. 1992. Mid-Jurassic lagoonal delta systems in the Hebridean basins. Thickness and facies distribution patterns of potential reservoir sandbodies. In Parnell, J. (ed.) Basins on the Atlantic Seaboard: Petroleum Geology, Sedimentology and Basin Evolution. Geological Society, London, Special Publications 62, 111-44. HUDSON, J. D. 1964. The petrology of the sandstones of the Great Estuarine Series, and the Jurassic palaeogeography of Scotland. Proceedings of the Geologists' Association, 75, 499-527. and HARRIS, J. P. 1979. Sedimentology of the Great Estuarine Group (Middle Jurassic) of northwest Scotland. In Symposium Sedimentation Jurasique West European. Paris, 9-10 May 1977. Association des Sediments Erancaise, Publication Speciale 1, 1-13. McINTOSH, J. S. 1990. Sauropoda. In Weishampel, D. B., Dodson, P. and Osmolska, H. (eds.), The Dinosauria 345-401. University of California Press. NORMAN, D. B. 1990. Problematic Theropoda: "Coelurosaurs" In Weishampel, D. B,, Dodson, P. and Osmolska, H. (eds.), The Dinosauria 280-305. University of California Press. PHILLIPS, J. 1871. Geology of Oxford and the Valley of the Thames. Clarendon Press, Oxford.

MS. accepted for publication 24th March 1995