Baffling bones from Lyme Regis

A recent find from Lower Jurassic marine deposits on the Dorset Coast consists of a curious association of bones and bone fragments that have so far eluded identification, despite being inspected by some top palaeontologists. Is it a shark? Not according to some shark specialists. Is it a fish? Probably, but despite the presence of several complete bones, none have been identified and there are no scales present. Is it regurgitate? Possibly, but there is at least one very long thin bone that is unlikely to have been swallowed and upchucked again whole, and the matrix in which the bones are preserved does vary. So, is it simply a mass of completely unassociated bones? Unlikely, as there are several examples of at least two types of bone within the fossil. So, they are not a random accumulation, but they do remain a mystery. Do you recognise any of the bones? Do take a look and tell me what you think.

Fig. 1. Richard Edmonds trying to work out which piece goes where.

Discovery of the material

I found the first piece of this specimen on the beach beneath the Spittles Slip, east of Lyme Regis in Dorset, during the Symposium on Vertebrate Palaeontology and Comparative Anatomy (SVPCA) meeting in the town in September 2011. It was a large block (approximately 40kg) from the Shales-with-Beef Member of the Charmouth Mudstone Formation (Lower Jurassic). Bones were visible in cross section on all four sides, within a layer about a third of the way down into the block. Due to weathering, some aspects of the bones other than simple cross-sections were slightly visible. I took the block from the beach and showed it to colleagues at the conference after the talks. After reporting it to staff at Lyme Regis museum and to Richard Edmonds, the Earth Science Manager of the Jurassic Coast World Heritage Team, more material was found on the beach and in the slip by local palaeontologists, Paddy Howe, Chris Andrew and Mike Harrison.

Fig. 2. The various pieces in their approximate relative positions before preparation and not yet glued together.

The specimen then comprised one large block and 14 smaller pieces, many of which joined to form a second large block. As all the pieces recovered contain bones or bone fragments (spread over 102cm in the longest axis), it is clear that the original complete specimen must have been much bigger.

Fig. 3. The main block during preparation, with some of the overburden removed front and right.

Despite many bone fragments being visible naturally, no-one was able to positively identify any of the elements as found. Therefore, the specimen was regarded as potentially of significant scientific importance and, as a result, it was recorded as a ‘category 1’ specimen in the West Dorset Fossil Collecting Code of Conduct (record number 273); and the specimen was donated to Lyme Regis Museum. Funding was then provided by Dorset County Council to undertake a limited amount of initial preparation to facilitate the identification of the material.

Preparation and conservation

The matrix is hard and the bones are generally very small, fragmentary and brittle, and lie in unpredictable positions. An air abrasive unit, using sodium bicarbonate powder, cleaned the exposed bone fragments nicely, but it could not remove the overlying rock on its own. More aggressive powders could have been used to remove the matrix, but these would have been far too damaging to the bones. Therefore, the top 5cm or so of each block had to be removed down to the level of the bone layer with a pneumatic preparation pen, at which point, the bones could be cleaned with the air abrasive. Bones that were visible in the breaks between adjoining pieces were inevitably in poor condition, as they had been damaged on the beach or during their time in the slip. However, the rock was in good enough condition that the adjoining pieces could successfully be glued back together using Paraloid B72 in acetone as a consolidant, followed by Paraloid B72 adhesive. The pieces that had split while on the slip were not glued back together, as this would have involved losing some useful information. All chips of rock more than 2mm in size (amounting to about 10kg) have been retained in case they are useful for research, that is, looking at microfauna to determine the environment the specimen is from.

Fig. 4. Bone 1 (long axis 53mm). Possibly a fish skull fragment or a ‘shoulder girdle’ of a fish?

Fig. 5. Bone 2 (long axis 48mm). Possibly a fish skull fragment, or a pectoral bone or an operculum (the hard bony flap covering and protecting the gills)?

Attempts at identification

The prepared specimen was shown to several well-known collectors on the Dorset coast and was then taken to the SVPCA meeting in Edinburgh during the autumn of 2013, where many palaeontologists spent some time studying it. The general consensus is that at least some of the material is probably fish, maybe a shark, and that it is possibly a disarticulated skeleton with some stomach contents preserved (where dozens of identical bone fragments are found in pockets of softer sediment). Or, it might be regurgitate, containing some fish or shark remains. However, despite being studied by dozens of palaeontologists, many of them fish or shark specialists, nothing has been positively identified and some material could not even be determined as definitely fish or shark, so neither of the above scenarios is necessarily the case. If it is a fish fossil, it does seem odd that there are no fish scales present.

Fig. 6: Bone 3. Possibly stomach contents, or a cololite or coprolite, containing fragments of processed fin rays? These fragments are found in several pockets of much softer and paler sediment.

The presence of the very long thin bone (Fig 7, bone 4) argues against the whole specimen being regurgitate. Likewise, the areas of much paler and much softer matrix, containing what looks like dozens of evenly broken-up sections of long thin bone similar to the bone in Fig 7 (bone 4), would argue against this – why would there be a difference in the sediment if it was all regurgitate? It is possible these paler, softer areas may instead represent small, individual patches of regurgitate or are coprolites or cololites (fossilised gut contents just before anus); and the other bones in the grey sediment may be associated skeletal material. They are unlikely to be just random bones washed in around them, as there are repeating bone types such as in Figs 10, 11 and 12. The bones (if they are bones) in Figs. 10 and 11 are exactly the same specimens, just photographed from different angles, but there are several more examples of this type of ‘bone’ within the specimen. These actually elicited the greatest amount of consensus and apparently may be fin spines (possibly shark, though at least one shark specialist thinks not), but this was by no means unanimous.

Fig. 7. Bone 4 is possibly a bifurcating fin ray (could be either shark or Pachycormid)? Scale bar equals 1cm.

So, please look at these photos and see if you recognise anything. If you do recognise any of the elements or have thoughts about the specimen as a whole. or think you have picked up more of this specimen on the beach at Lyme Regis, then please do get in touch. Email me at: nrlarkin@easynet.co.uk.

Fig. 8. Bone 5 (long axis 41mm). Could be a fin spine or could be a premaxilla, for example, of Thalattosaurus (yes, this is restricted to the Triassic, but maybe a Liassic form is plausible) or Hypsocormus?

All ideas will be warmly welcomed and, if positive identifications are made, you will be suitably acknowledged in any ensuing publication. Many thanks.

Fig. 9. Bone 6 (long axis 73mm). Could be a tail fin vertebra, for example, a hypural tail vertebra?

Acknowledgements

Thanks are due to: the co-collectors Paddy Howe, Chris Andrew and Mike Harrison for their sharp eyes and tenacity; Lyme Regis Museum staff Paddy Howe and David Tucker for their helpfulness; Richard Edmonds of the Jurassic Coast World Heritage Team for encouragement, advice and organising funding for the initial preparation; Natural England for providing the funding; to various colleagues who have kindly looked at the specimen already; and to Dean Lomax, who suggested that the readership of Deposits might collectively help solve the mystery.

Figs. 10, 11 and 12. Bone type 7. Several strange bones, almost identical to one another, with a distinctive figure of eight shape in cross section. Could be fin spines (shark?), pachycormid proximals (under the dorsal fin) or large teeth? One person suggests they are reminiscent of Gyrosteus mirabilis (an extinct ray-finned fish known from the Jurassic of Whitby). Scale bar equals 1mm.

Fig. 13. Beach beneath the Spittles Slip, east of Lyme Regis in Dorset

About the author: Nigel Larkin is a freelance palaeontologist, palaeontological preparator and conservator at www.natural-history-conservation.com.


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