In the Callovian mudstones associated with the Christian Malford Lagerstätte (Wilby et al., 2008), exceptionally large numbers of statoliths have been found in normally prepared (White Spirit method of Brasier, 1980) micropalaeontology residues. Statoliths, like the otoliths in teleost fishes, are aragonitic ‘stones’ found in the stato-acoustic organs (statocysts) of squid. While statoliths are relatively well known in the biological literature (Lipiński, 1986, 1997; Hanlon & Messenger, 1996) they remain almost undescribed in the field of micropalaeontology.
Otoliths are the stato-acoustic organs of bony (teleost) fish and can be well preserved as fossils (Frost, 1924, 1926; Rundle, 1967; Stinton & Torrens, 1968; Lowenstein, 1971; Patterson et al., 1993; Patterson, 1998, 1999; Hart et al., 2006, 2009). In some of these accounts of Jurassic otoliths there are a number of illustrations of what are, more correctly, regarded as statoliths (e.g. Frost, 1926, figs 13, 14; Martin & Weiler, 1954, pl. 3, fig. 116; Rundle, 1967, text-fig. 4).
Statoliths
Statoliths are the small, aragonitic ‘stones’ which lie in fluid-filled cavities or statocysts within the cartilaginous skulls of all living and (probably) all fossil members of the Coleoidea (Clarke & Fitch, 1975, 1979; Clarke, 1978, 2003; Clarke & Maddock, 1988a, b; Clarke et al., 1980a, b). Often co-occurring with otoliths, and being of similar appearance, size, colour, etc., has caused the confusion in the past, although it is probably the case that the various authors were completely unaware of the existence of statoliths at the time of writing. While a number of authors have noted the occurrence of statoliths in Jurassic sediments (Clarke, 1996, 2003), there is no taxonomic nomenclature available. Indeed, the only specific description and illustration of Jurassic statoliths (Jurassic sp. A and Jurassic sp. B; Clarke, 2003, figs 14, 15) leaves the two taxa in open nomenclature. Recently Hart et al. (2009, fig. 3(F)) have illustrated a statolith from the Wattonensis Beds (Upper Bathonian) of South Dorset and this is very close to the form, or forms, identified as Jurassic sp. A of Clarke (2003, fig. 15).
In the case of the Christian Malford Lagerstätte, Wilby et al. (2008) illustrate and describe a number of coleoids that were collected over 170 years ago during construction of the Great Western Railway. During a re-investigation of the site in 2007, the British Geological Survey drilled a number of short boreholes and one of these (Core 10) has been investigated at Plymouth University. Processed samples from this core have yielded exceptionally large numbers of statoliths (c. 400 g–1 of sediment in some cases). Almost all of the individuals found, along with abundant squid hooks, otoliths and foraminifera, appear to be the same species (Fig. 1) and a full description of the assemblage is in preparation. The ‘squid’ represented by the statoliths is not yet identified, although Belemnoteuthis, as a hook-bearing belemnite without a solid rostrum – and which is well known from Callovian sediments in the British isles – may be the favoured taxon. Malcolm Clarke (pers. comm., 2010), though retired from the Marine Biological Association in Plymouth, is currently working on the taxonomy of the Jurassic statoliths while our work continues on the assemblages from Christian Malford.
Anterior view of a large left statolith from 70–80 cm in Core 10, Christian Malford. Scale bar is 200 µm. This specimen is almost identical to ‘Jurassic sp. A’ of Clarke (2003).
Summary
Statoliths are, following the work of Clarke, now known to exist in the fossil record from the Lower Jurassic to Recent, though few micropalaeontologists know of their existence. Despite working on many thousands of Cretaceous residues, MBH has no record of statolith-like microfossils from the Cretaceous, though squid hooks have been recorded. Within the chalk facies this may be a result of dissolution of the aragonitic statoliths as other aragonitic microfossils (e.g. epistominid foraminifera) are also rare or non-existent. It is important that such microfossils are noted (and described) by those working on microfossil residues in order that their full potential as palaeoenvironmental indicators is attained.
The authors wish to thank the British Geological Survey, and Dr P. Wilby in particular, for access to the material from Christian Malford. Professors D. Fuchs and D.T. Donovan are thanked for their helpful comments, all of which have improved this Notebook.
ReferencesBrasierM.D.1980. . George Allen & Unwin, London, 193pp.ClarkeM.R.1978. The cephalopod statolith – An introduction to its form. , 58: 701–712.ClarkeM.R.1996. The role of cephalopods in the world’s oceans: An introduction. , ser. B, 35: 979–983.ClarkeM.R.2003. Potential of statoliths for interpreting coleoid evolution: A brief review. , 3: 37–47.ClarkeM.R.FitchJ.E.1975. First fossil records of cephalopod statoliths. , 257: 380–381.ClarkeM.R.FitchJ.E.1979. Statoliths of Cenozoic teuthid cephalopods from North America. , 22: 479–511.ClarkeM.R.MaddockL.1988a. Statoliths from living species of cephalopods and evolution. InClarkeM.R.TrumanE.R. (Eds), . The Mollusca, 12, WilburK.M. (Ed.) Academic Press Inc., London, 169–184.ClarkeM.R.MaddockL.1988b. Statoliths of fossil coleoid cephalopods. InClarkeM.R.TrumanE.R. (Eds), . The Mollusca, 12, WilburK.M. (Ed.). Academic Press Inc., London, 153–168.ClarkeM.R.FitchJ.E.KristensenT.MaddockL.1980a. Statoliths of one fossil and four living squids (Gonatidae: Cephalopoda). , 60: 329–347.ClarkeM.R.MaddockL.SteurbautE.1980b. The first fossil cephalopod statoliths to be described from Europe. , 287: 628–630.FrostG.A.1924. Otoliths of fishes from the Upper Kimmeridgian of Buckinghamshire and Wiltshire. , 14: 139–143.FrostG.A.1926. Otoliths from fishes from the Jurassic of Buckinghamshire and Dorset. , 18: 81–85.HanlonR.T.MessengerJ.B.1996. . Cambridge, Cambridge University Press, 232pp.HartM.B.HendersonA.S.FraylingT.AdairT.2006. Microfossils from the Wootton Bassett Mud Springs (Wiltshire, UK). , 11: 199–204.HartM.B.De JongheA.GrimesS.T.MetcalfeB.PriceG.D.TeeceC.2009. Microfaunal analysis of the Wattonensis Beds (Upper Bathonian) of South Dorset. , 12: 134–139.LipińskiM.R.1986. Methods for the validation of squid age from statoliths. , 66: 505–526.LipińskiM.R.1997. Morphology of giant squid Architeuthis statoliths. , 18: 299–303.LowensteinO.1971. The Labyrinth. InHoarW.S.RandallD.J. (Eds), , 5, Sensory Systems and Electric Organs. Academic Press Inc., London, 207–240.MartinG.P.R.WeilerW.1954. Fisch-Otolithen aus dem deutschen Mesozoikum (Dogger bis Wealden). , 35: 119–192.PattersonW.P.1998. North American continental seasonality during the last millennium: High resolution analysis of sagittal otoliths. , 138: 271–303.PattersonW.P.1999. Oldest isotopically characterized fish otoliths provide insight to Jurassic continental climate of Europe. , 27: 199–2002.PattersonW.P.SmithG.R.LohmannK.C.1993. Continental paleothermometry and seasonality using the isotopic composition of aragonitic otoliths of freshwater fishes. InSwartP.K.LohmannK.C.McKenzieJ.SavinS. (Eds), . American Geophysical Union Monograph, 78, 191–202.RundleA.J.1967. The occurrence of Upper Liassic otoliths at Holwell, Leicestershire. , 2: 63–72.StintonF.C.TorrensH.S.1968. Fish otoliths from the Bathonian of southern England. , 11: 246–258.WilbyP.R.DuffK.PageK.MartinS.2008. Preserving the unpreservable: A lost world rediscovered at Christian Malford, UK. , 24: 95–98.