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The English Chalk and London Clay: Two Remarkable British Bony Fish

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The English Chalk and London Clay: Two Remarkable British Bony Fish Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 The English Chalk and London Clay: two remarkable British bony fish Lagersta¨tten MATT FRIEDMAN1*, HERMIONE T. BECKETT1, ROGER A. CLOSE1 & ZERINA JOHANSON2 1Department of Earth Sciences, University of Oxford, South Park Road, Oxford OX1 3AN, UK 2Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK *Corresponding author (e-mail: [email protected]) Abstract: The Late Cretaceous (Cenomanian–Maastrichtian) Chalk Group and Eocene (Ypre- sian) London Clay Formation are two British marine deposits that yield globally significant assem- blages of fossil actinopterygian (ray-finned) fishes. Materials from these units, especially the Chalk, featured prominently in the work of Arthur Smith Woodward. Here we summarize the history of study of actinopterygian fossils from the Chalk and London Clay, review their geological and palaeoenvironmental context and provide updated faunal lists. The Chalk and London Clay are remarkable for preserving fossil fishes in three dimensions rather than as the flattened individ- uals familiar from many other famous Lagersta¨tten, as well as capturing detailed ‘snapshots’ of marine fish faunas that bracket the major taxonomic shift that took place near the Cretaceous– Palaeogene boundary. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. The Late Cretaceous (Cenomanian–Maastrichtian) symposium volume. Responsible for the world’s English Chalk and Eocene (Ypresian) London Clay finest collection of fossil fishes from these locali- are two fossiliferous British marine deposits that ties at what is now the Natural History Museum, are significant in the history of palaeontology gener- London, Smith Woodward produced numerous ac- ally, and palaeoichthyology specifically. Fossils counts of Chalk and London Clay specimens (e.g. from both units featured prominently in early contri- Woodward 1887a, b, 1888a–d, 1889a–e, 1891a, b, butions that played a major part in the develop- 1893a, b, 1894a, b, 1895a–c, 1898, 1899a–c, ment of modern geology and palaeontology (Luidii 1900a, b, 1901, 1902, 1903, 1905, 1906a, b, 1907a, (¼Lhuyd) 1699; Woodward 1729; Jacobs 1777a, b; b, 1908, 1909, 1911, 1912a, b, 1913, 1917, 1923, Mantell 1822; Agassiz 1833–44; Fig. 1; Owen & 1926, 1936; Woodward & Sherborn 1890, 1891), Bell 1849). Fossil fishes from the English Chalk naming numerous species in the process (see Smith served as touchstones in early debates on the succes- 2015). A handful of major contributions added to sion of assemblages through time (Agassiz 1833–44, understanding of fishes from these deposits in the 1859) and the rates of evolutionary change (Huxley decades following Smith Woodward’s death (body 1862, 1870; Woodward 1912a: 252; summarized fossils: Patterson 1964; Casier 1966; Goody 1969; in Patterson 1981) and, more recently, provided Forey 1973, 1977; otoliths: Stinton in Casier 1966; key ancient comparators in the discovery and inter- Stinton 1975–84). However, more recent contribu- pretation of the living coelacanth Latimeria (Smith tions have been more limited in their scope, focus- 1939; Woodward 1940). The popularity of fossil- ing on specific taxa or specimens (e.g. Forey 2004). hunting in the London Clay during the mid-1800s The actinopterygians (ray-finned fishes) of the led to James Bowerbank’s foundation of the Lon- Chalk and London Clay are notable not only for don Clay Club (1836–47), which would eventually their diversity, but also for their remarkable pre- give rise to the modern Palaeontographical Society servation. Unlike most fish faunas of comparable (Elliott 1970). age, in which specimens are preserved as greatly The English Chalk and London Clay provided flattened compression fossils, these British deposits ample material for study and description by Arthur yield three-dimensionally preserved specimens of Smith Woodward, the principal subject of this either whole individuals (Chalk) or heads (London From:Johanson, Z., Barrett, P. M., Richter,M.&Smith, M. (eds) Arthur Smith Woodward: His Life and Influence on Modern Vertebrate Palaeontology. Geological Society, London, Special Publications, 430, http://doi.org/10.1144/SP430.18 # 2015 The Author(s). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 M. FRIEDMAN ET AL. Fig. 1. Historical representations of English Chalk and London Clay fossil fish specimens: (a) the Chalk taxon Halec, from Horsfield & Mantell (1824), The History and Antiquities of Lewes and Its Vicinity, Volume 1; (b)‘Beryx Lewesiensis from the Chalk, Lewes’ from Mantell (1851), Petrifactions and their Teachings; (c, d) the Chalk taxa Homonotichthys and Osmeroides, from Dixon (1850), The Geology and Fossils of the Tertiary and Cretaceous Formations of Sussex;(e) the Chalk taxon Ctenothrissa, from Smith Woodward (1901), Catalogue of Fossil Fishes in the British Museum (Natural History). Part IV;(f) ‘Head of a Pike’ from the London Clay (probably Aulopopsis), from Douglas (1785), A Dissertation on the Antiquity of the Earth;(g) the London Clay taxon Teratichthys, from Ko¨nig (1825), Icones Fossilium Sectiles;(h) the head of the London Clay taxon Albula, from Smith Woodward (1901), Catalogue of Fossil Fishes in the British Museum (Natural History). Part IV. Clay). Following in Smith Woodward’s footsteps, can only be applied to some specimens from the subsequent workers have realized the significance London Clay and, in these cases, must be completed of these fossils, applying acid preparation tech- with great care. Non-destructive computed tomog- niques to extract considerable detail on the skulls raphy (CT; Sutton et al. 2014) offers an approach of fishes from the Chalk (Patterson 1964; Goody to studying the remarkable fish fossils of the Chalk 1969; Forey 1973, 2004; Forey & Patterson 2006). and London Clay without any of the drawbacks Although powerful, this approach is not without associated with traditional preparation techniques its limitations. First-generation acid preparation (Fig. 2; Beckett & Friedman 2015). We are currently yielded detailed anatomical information, but the re-studying the ray-finned fishes of the Chalk and specimens themselves were rendered very delicate London Clay using CT scanning, with the principal and difficult to examine. The loss of positional goals of better documenting their anatomy, relation- information associated with the disarticulation of ships and, through the use of biomechanical models specimens during preparation was exacerbated by developed for living fishes (e.g. Hulsey & Wain- the loss of individual bones (e.g. the jaws of Diplo- wright 2002; Collar & Wainwright 2006), ecology. mystus in Forey 2004: fig. 2). More generally, this This contribution provides context for this ongoing preparation approach is limited by the nature of research, reviewing current understanding of fishes matrix encasing fossils; although acid preparation from these two exceptional deposits. Examination is very effective with fish fossils from the Chalk, it of actinopterygians from the Chalk and London Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 ENGLISH CHALK AND LONDON CLAY FISHES Fig. 2. Detail of fossil fish skulls from the Chalk Group and London Clay Formation revealed by computed tomography (CT): (a–c) Argillichthys toombsi, NHMUK PV P 42519, London Clay Formation, Sheppey, Kent; (d–f)‘Sardinioides’ illustrans, NHMUK PV P 3977, Chalk Group, Burham, Kent. Models show: bones (white) visible external to matrix (brown) before segmentation of CT data (panels a and d); fossil specimen with matrix completely removed (panels b and e); and model of fossil with jaws and palate removed to reveal the branchial (green) and ventral hyoid (pink) arches. Clay has been intermittent following the major SMUC, Sedgwick Museum, University of Cam- twentieth-century monographs of Smith Woodward bridge, Cambridge, UK. (1902, 1903, 1907a, 1908, 1909, 1911, 1912a) and Casier (1966) (both of which produced major increases in the number of named fish species Geological context: Chalk Group from the British record; see Lloyd & Friedman 2013: fig. 2), meaning that important updates are High sea-levels and low continental relief limited dispersed throughout a large body of specialist liter- clastic deposition to regions deep within modern ature. Our goal is to provide an accessible summary continental interiors during the Late Cretaceous of current understanding of the Chalk and London and early Palaeogene (Mortimore et al. 2001; Mor- Clay actinopterygian faunas by reviewing a history timore 2011). Deposition in the expansive shelf of their study, basic geological context and evolu- settings of this interval was dominated by slow tionary significance. We close with a prospectus accumulation of the calcitic skeletons of plank- for future research on these deposits, which are tonic coccolithophorid algae. The resulting pelagic rightly recognized as Lagersta¨tten that represent carbonate – chalk – represents a distinctive and exceptional windows to fish diversity in the Late widespread feature of the Late Cretaceous–early Cretaceous and Eocene (Casier 1966; Patterson Palaeogene sedimentary record, with units found 1993a, b; Lloyd & Friedman 2013). across northern and central Europe, central Asia, Australia and the western interior of North America (Mortimore 2011). Institutional abbreviations The British record
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