An Initial Investigation into the Acquisition and Conservation History of the Fossil Marine Reptile Stenopterygius acutirostris (Owen) from the Upper Liassic near Whitby, Yorkshire, England
Introduction
A fossil marine reptile, Stenopterygius acutirostris, has been the subject of enquiry to confirm the whereabouts of this specimen by Professor Chris McGowan (Royal Ontario Museum, Canada). In 1974 McGowan placed Ichthyosaurus acutirostris, Owen 1840 in the family Stenopterygiidae and indicated that the holotype specimen BM(NH) 14553 was 'probably' lost. The discovery of the specimen with the anterior part of the rostrum missing together with the unusual composition of the 'complete' paddle initiated the investigation. It was decided to review the acquisition and conservation history of the specimen.
Historical Review
1839
This specimen was first observed by Richard Owen on display in the museum of the Natural History Society of Lancaster. Owen referred the Lancaster specimen to I. acutirostris in his Report of British Fossil Reptiles in the same year.
1840
The specimen was purchased by the British Museum from the estate of Messrs Ripley. Richard Ripley was a surgeon of Whitby and the brother and partner of John Ripley. The two brothers were original members of the Society, and among those who signed the Laws and Regulations drawn up at the inaugural meeting in the Town Hall on January 17th, 1823. Richard Ripley was the Hon. Secretary from 1827 until his death in 1857. The Annual Report of the Society for 1837 shows Richard Ripley, Whitby, as Hon. Member, along with Richard Owen. Further purchases from Messrs Ripley were made by the British Museum in 1841 and 1842.
1. Ichthyosaurus acutirostris BM(NH)14553 (Whitby, Yorkshire) original specimen as photographed by Owen in 1880
1851
The specimen was recorded by Gideon Mantell in his book Petrifactions as being on display in the British Museum, Bloomsbury, and labelled I. longipennis. Mantell also notes 'the collection of ichthyosauri on display comprises 8 or 9 recognised species that have been rigorously examined and carefully determined by Professor Owen'.
The British Museum of Natural History opened on the present site in South Kensington in 1881. The specimen was transferred together with all the natural history collections from the British Museum to the British Museum of Natural History prior to 1881. The specimen was recorded as 'probably lost' by Chris McGowan (1974) when he revised the Longipinnate ichthyosaurs of the Lower Jurassic of England.
2. Ichthyosaurus acutirostris BM(NH)14553 (Whitby, Yorkshire) as
photographed at the time of this research 2001
The specimen was re-located in the ichthyosaur collections store, but was found to have lost the anterior part of the rostrum and anterior-most region of the 'basal part of the left paddle'. A photograph found in an Owen folio shows the specimen framed but with the entire skull and a more complete basal part of the left paddle. Subsequent searches revealed that the specimen was repaired and conserved in the Palaeontology Laboratory in 1983. The attached notes indicate that the snout was missing at that time and part of the right paddle was dismounted and re-assembled.
Conservation
Making a cast
3. Making a mould by applying silicone rubber to the specimen
Prior to any preparation it was decided to make a cast of the specimen areas that were due to be investigated for record keeping and for part of the research. Silicone rubber is a preferred medium for mould-making and skin moulds were produced by applying three layers of rubber which were backed with Jesmonite® reinforced with glass fibre tubing. Plaster of Paris was chosen to make the cast due to its cheapness and the need to cut the cast up into individual sections to attempt rearrange the individual elements of the paddle. Moulds and casts were taken of the main paddle, the end of the broken snout and the end of the right paddle.
Conservation history
The Palaeontology Conservation Unit has extensive treatment records for the last 40 years and these revealed that the specimen was subject to previous laboratory work in 1983.
The treatment record states:
- The specimen was cleaned with solvents and consolidated with a synthetic resin - alvar (polyvinyl acetal) which is no longer used today.
- Cracked and loose plaster was mechanically removed and replaced with plaster, scrim and wood.
- Loose plaster and rock fragments were removed from underneath the main body.
- The 'tail section' was dismantled and reassembled with a synthetic filler AJK Dough (Alvar Jute Kaolin Dough - no longer used). Additionally, an annotated pencil diagram was used for component relocation.
- The 'snout' area had a recess for where the former bone rested. This had been levelled with Plaster of Paris.
- Repaired areas were painted out.
Removal of the matrix and surrounding plaster
A decision was made to concentrate on two parts of the specimen that would hopefully help us identify areas of reconstruction. In order to minimise the disturbance to the whole specimen, it was decided to use an electrically driven flexible drive with a rotary diamond-cutting disk to cut through the matrix. Once areas had been cut, large areas of matrix were removed with hammer and chisel. For more delicate work, a pneumatic percussion air-pen (a commonly used preparation tool) was used when close to the specimen surface. This entire procedure required the use of a vacuum cleaner for dust extraction and for the operator, safety spectacles and a dust mask. The removed plaster and matrix was carefully bagged and recorded for further investigation.
4. Filler/Matrix around the paddle was removed to expose the previously hidden specimen edge
Findings
As expected, the supposed 'original' structure shows the original embedding of the block in a sand/wax matrix covered with a thin layer of plaster and several layers of paint. This is consistent with other specimens mounted in wooden cases of the same time and location. In areas where the specimen had been treated, the various specimen blocks were surrounded with Plaster of Paris, which had also been reinforced with scrim, and had been painted with several layers of paint. This confirms the information on the laboratory treatment card.
With regard to the individual elements as described in the pencil drawing from the previous treatment, the joins also appear to correspond. As expected, this suggests that the specimen components were correctly replaced after the treatment. However, there was no evidence to suggest that the specimen had been tampered with.
Further investigations
In an attempt to understand the treatment history further, a polished section was made from both areas under investigation. Preliminary study under an optical microscope shows that the two areas are identical in construction, i.e. the sand/wax filler with several paint layers. Further analysis will be undertaken over the next few months to understand the structuring in the layers. This may enable us to date the conservation work. Plaster casts taken from the mould of the paddle will be cut into the individual bone elements.
6. Ichthyosaurus acutirostris BM(NH) 1500a (Whitby, Yorkshire) skull.
In addition, further 'core' samples will be taken in the areas of the main body and where the snout originally lay to understand the nature of the reconstruction.
Systematic Description
Name: Stenopterygious acutirostris (Owen, 1840).
Stratigraphy: Alum Shale Formation; Upper Liassic; Lower Toarcian; Early Jurassic.
Locality: Saltwick Alum Pit, near Whitby, Yorkshire, England.
5. Ichthyosaurus acutirostris BM(NH)14553 (Whitby, Yorkshire) detail of right anterior paddle.
Type specimen: BM (NH) 14553 skull plus entire right anterior paddle and imperfect left anterior paddle.
This specimen was first ascribed to I. acutirostris by Richard Owen in 1840 in his Report on British Fossil Reptiles (1839). He reports that the specimen gives a profile of the entire head and one of the anterior paddles. Also that the upper and lower jaws converge to the end of the snout which is sharp and spear-shaped. He also states that the length of the head is 11 inches and 10 lines.
In 1851 Mantell in Petrifactions and their Teachings refers to this specimen then labelled I. longipennis. In particular he refers to the long tapering fin suggesting that it may have been wider in proportion to its length and that many ossicles may have been lost. He also comments that he was unaware of any published description of this species. (see panel on Historical Review)
In 1881 Owen described I. acutirostris in the Mon. Pal. Soc., Liassic Reptiles but figured only the skull in plate 28, figure 2. However the description confirms that the skull belongs to BM(NH) 14553 because it describes the 'right entire fin' and mentions the 'preserved basal portion of the left fin' as belonging to the same specimen. The description of the 'entire' fin includes the emargination of the radius, radio-carpal and succeeding ossicle.
Owen describes the three primary digits plus a small part of the fourth but unlike Mantell believes that because of its juxtaposition that fin bones have not been lost. He also suggests that the paddle was bifurcated. However the skull length anterior to the orbit is noted as 18 inches and 7 lines.
Lydekker 1889 refers to the specimen as the type of I. acutirostris in his Catalogue of Fossil Reptiles volume 2 on page 73.
Ichthyosaurus acutirostris was referred by McGowan 1974 to Stenopterygiidae von Huene 1948 as Stenopterygius acutirostris (Owen) when he recorded that the type specimen, BM(NH) 14553, may have been lost. McGowan figured the skull after Owen 1881 in figure 11 D. Suggesting that the decurved appearance of the snout may have been a little exaggerated in this figure since the feature is not apparent in all the S. acutirostris skulls. The fin was not described in this paper beyond observing that it belonged to the longipinnate ichthyosaurs i.e. anterior paddles with three distal carpels and hence three primary digits.
Further investigation
Further investigation will compare the dimensions of the anterior right paddle and the skull with those compiled by McGowan (1974) for the other referred specimens of Stenopterygius acutirostris for example BM(NH) 1500a.
Bibliography
Blake, 1876 In Tate & Blake The Yorkshire Lias. Pub. Van Voost, London.
Ingles , J. M. & Sawyer, F. C., 1979. A catalogue of the Richard Owen collection of Palaeontological and Zoological drawings in the British Museum (Natural History). Bulletin of the BM(NH) Historical Series vol 6; no 5, p., 136, folio 107.
Lydekker, R., Catalogue of the fossil Reptilia and Amphibia in the British Museum (Natural History). Part II Containing the orders Ichthyopterigia and Sauropterygia. London. 307 pp.
Mantell, G.A. 1851 Petrifactions and their teachings; or, a hand book to the gallery of organic remains of the British Museum. London. H.G.Bohn. 496pp
McGowan, C., 1974 A Revision of the Longipinnate Ichthyosaurs of the Lower Jurassic of England, with Descriptions of Two New Species (Reptilia: Ichthyosauria). Life Sciences Contribution, Royal Ontario Museum no. 97.
Owen, R., 1839 Report on the British Fossil reptiles. Part I. Report British Association for the Advancement of Science, vol. 9, pp.43-126. Simpson. M., 1884 The Fossils of the Yorkshire Lias as described from Nature. Wheldon, London. pp.9.
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Acknowledgements
The authors thank Professor Christopher McGowan, Royal Ontario Museum, Canada, for instigating the investigation and Dr. Andrew White, Head of Museums, Lancashire, for providing archive information. The Photographic Unit staff and the Computer Graphic Service of The Natural History Museum, London, for their assistance. Also Mrs Bente Laudon, volunteer in PCU at The Natural History Museum, London, for her help with the casting. Comments to authors: Adrian Doyle at A.Doyle@nhm.ac.uk and Sandra Champan at S.Chapman@nhm.ac.uk.
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