Interglacial coleoptera from Bobbitshole, Ipswich, Suffolk

G. RUSSELL COOPE

CONTENTS

x The fauna 333 2 Environmental implications of the fauna 337 (A) Local environment of deposition . 337 (~) Climate 338 3 Comparison of the coleopteran and botanical data from Bobbitshole 339 4 Comparison of the fauna with other known interglacial faunas 339 5 References 340

SUM MARY An assemblage of twenty one named species of the area at the present day with average July Coleoptera is described from the type locality temperatures of about 20°C; about 3°C above of the Ipswichian interglacial at Bobbitshole, those for southern England today. There is no Suffolk. This assemblage can be assigned to the evidence of increased climatic continentality. boundary between pollen zones e and f of the Compared with other interglacial faunas, this interglacial. All species live today in western assemblage differs markedly from those of the Europe• They indicate that the deposits were Hoxrfian interglacial but bears a striking laid down in a eutrophic lake or pond with a resemblance to the Ipswichian assemblage rich peripheral reed swamp. The climate of the from the excavations in Trafalgar Square. times was considerably warmer than that in

TaF. interglacial deposits at Bobbitshole near Ipswich have been the subject of an intensive study by West (1957) and they have subsequently become the type section for the Eemian interglacial in the British Isles. The deposits were first exposed during the construction of a sewage works for Ipswich Corporation and whilst the excavations were open, a small sample of the organic silt containing remains was collected by Mr H. E. P. Spencer of the Ipswich Museum. These fossils represent twenty one named species plus a number that can only be identified to the generic level. Though numerically unimpressive, they provide detailed evidence of the sedimentary environment and also the climatic conditions at the time of deposition of the interglacial beds. This evidence can be compared with that from the plant remains studied by West. The assemblage of Coleoptera provides a basis for the correlation of these deposits with other interglacial deposits in Britain.

I. The fauna The specimens discussed below are deposited in the Ipswich Museum. Their modern ecological requirements and, where significant, their present day distri- butions are given below.

Jl geol. Soc. Londo vol. x3o , 1974, PP. 333-34 °. Printed in Northern Ireland.

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CARAB I DAE Feronia vernalis Panz. one head, one pronotum and one fragmentary right elytron. This species is found abundantly in marshy places on the margins of more or less eutrophic pools or by slowly flowing water. It seems to prefer a substrate of clay or sandy clay. Though dominantly a species of open conditions, it can tolerate some shade as it has been recorded on banks under Alnus glutinosa. More usually it prefers an abundant growth of Carex or moss, other than Sphagnum. The species is common over most of the British Isles but is rarer in Scotland. It is widespread in Europe chiefly south of latitude 62 ° . Colliurus melanura Payk. six heads. This is a pronounced reed swamp species, found on the margins of eutrophic lakes especially where there is a substratum of soft clay or gyttja. It is more frequent in the outer part of the Phragmites zone; on the large rafts of dead reeds from the previous year. In the winter, and during periods of high water, it takes refuge in the hollow stems of these reeds. Lindroth (I 945, P. 572) gives Phragmites as the 's first preference in Sweden with Typha latifolia and to a lesser extent, Glyceria spectabilis as alternatives. In other parts of the continent the preference seems to be for T. latifolia. In Britain this species is restricted to the southern districts of England and Wales and in Europe it does not extend further north than latitude 61°. Oodes gracilis Villa. four pronota and several fragments of elytra. In complete accord with the previous species, O. gracilis is found exclusively by eutrophic pools with an abundant growth of vegetation chiefly Phragmites, Carex and Typha latifolia. O. gracilis does not now live in Britain but it has a widespread distribution in central and southern Europe and, apart from one northerly outpost near Stock- holm, it is not found north of 55 ° .

DYTISCIDAE Colymbetes sp. elytral fragment. A carnivorous water beetle found most frequently in stationary or slowly moving eutrophic water. It is widespread and common over all of Europe. Cybister lateralimarginalis Deg. fragment of elytron. This large carnivorous water beetle is found in more or less open water in ponds and lakes. Though isolated records exist for this species in sv. England, it has not been found recently and it is now not generally accepted as a living British species. As it is a strong flier, it may have reached these shores unaided from the continent, but it seems unable to establish itself here in modern times. Its present status has been summarized by Balfour-Browne (i95o , p. 288). On the continent it is widespread over central and southern areas and in Scandinavia it only reaches the southern tip of Sweden (Skgne) with a northern outpost near Stockholm.

GYRINIDAE Gyrinus sp. two pronota. These are the familiar 'whirligig' bettles, predatory species that require open surfaces of water, either standing or flowing. They are common and widespread over all of Europe.

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HYDROPHYLIDAE Hydrophilus sp. one fragmentary pronotum. This fragment is indistinguishable from H. piceus L. which is largely a pond species found in central and southern Europe and extending as far north as southern England and the extreme south of Scandinavia. Since several other species are to be found in southern Europe a precise identification of the fossilis not possible. Coelostoma orbiculare F. three left elytra, one right elytron. This species is found in shallow standing water with decaying plant refuse upon which both imago and larva feed. It is widespread and common in England but somewhat local in Scotland. On the continent it is widespread except for the extreme north.

ELATERIDAE Melanotus sp. two heads. The larvae of this genus are found in rotten wood. It is widespread and common throughout all Europe.

DRYOPIDAE Dryops sp. two pronota. Found most frequently under stones or logs in wet places. This genus is widespread throughout all Europe.

CUCUJIDAIg Airaphilus elongatus Gyll one pronotum. Little is known about the life history of this species. It is usually found in wet places in vegetable debris. It has a rather scattered distribution in central and southern Europe ranging as far north as southern Fennoscandia. It is not found living in the British Isles today.

TENEBRIONIDAE Opatrum sabulosum L. one head. A species of dry sandy places where it probably lives on dead vegetable matter. It is widespread in central and southern Europe extending as far north as Lat. 62°N in Finland.

SCARABAEIDAE Caccobius schreberi L. one head. This species is chiefly associated with ungulate dung. It is widespread and common in southern Europe but becomes much rarer in the north where it has been found as far north as Sk~ne in southern Sweden. It does not live in the British Isles today. Onthophagus opacicollis d'Orb, two male heads. This is a southern European dung beetle that is particularly common in the eastern Mediterranean countries. Its range extends across southern Europe to southern Spain and as far north as southern Hungary and southern France. Onthophagus taurus Schrb. one female head. This dung beetle is common throughout central and southern Europe but is rare in the north where its range extends as far as Gotland. It has been recorded from southern England but its present status is obscure and it may be extinct in the British Isles today. Aphodius sp. two heads and one pronotum. These distinctive fragments seem to come nearest to the subgenus Ammoecius; the heads have two well developed

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projections on the anterior margin which is curved downwards between them. There is a transverse ridge across the clypeus. These fossils bear similarities to the southern European and North African species A. elevatus Oliv. but they differ in having the area between the transverse ridge and the anterior margin polished and very finely punctured instead of granulate. The transverse ridge is also much shorter. In these respects the fossils agree with the Moroccan species A. dentatus A. Schmidt, but they differ from this species in being slightly larger and in having shallow crater like pits at the margins of the clypeus. These fossils are unnamed. Melolontha melolontha L. one mandible. This is the familiar Cockchafer whose larvae live at the roots of plants, often in grassy places. The adults frequently eat the leaves of deciduous trees. The species is widespread and common throughout all of Europe as far as Lat. 6o°N. Valgus hemipterus L. one head. A species associated with wet rotten wood of deciduous trees. Though widespread in central and southern Europe, this species is much rarer in the north and ranges only as far north as Denmark. It is absent from the British Isles today. Cetonia aurata L. fragmentary elytron. This is the familiar 'rose chafer' whose larvae live underground in plant debris and whose adults are found on flowers. It is common throughout Europe but is much rarer in the north. Dorcusparallelopipedus L. fragmentary left elytron. This is the small stag beetle whose larvae bore into dead deciduous wood. It is widespread throughout Europe as far north as Lat. 6o°N.

CHRYSOMELIDAE Donacia impressa Payk. one pronotum, one left elytron. All species of Donacia are phytophagous and feed on aquatic plants. D. impressa is found chiefly on Carex sp. Reitter (I912 , p. 76) records it on Carex acuta and paludosa. It is local in England but not recorded from Scotland. Donacia cinerea Hbst. three pronota, two fragments of elytra. This species is usually found on Sparganium, Typha latifolia and Phragmites commun#. It is nowhere abundant in Britain, where it occurs only as far north as Northumberland. On the continent its chief area of distribution lies south of Lat. 62 °N. braccata Scop. one head, two pronota, two fragments of elytra. This species appears to be confined almost entirely to Phragmites communis. Today it is local and on the whole rare, though it is sometimes abundant especially near the coast. The species is confined to the South and sE England and on the continent is not found north of Lat. 6O°N. Plateumaris sericea L. fragments of elytra. This is an almost ubiquitous species found on many aquatic plants. It occurs all over Britain and on the continent its range extends to the extreme north.

CURCULIONIDAE Bagous collfgnensisHbst. one head and thorax, one left and one right elytron. This is an aquatic weevil that lives on Equisetum limosum (Diekmann, 1964). It is wide- spread but rare in Europe as far north as Lat. 58°N.

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Notaris scirpi F. one left and one right elytron. This weevil lives on emergent vegetation such as Carex, Typha and Scirpus. It is found throughout Europe as far north as Lat. 60°N. Eubrychius velutus Payk. one left elytron. This is an aquatic weevil associated with Potamogeton, Hippuris and Myriophyllum. It is found throughout Europe south of the Arctic Circle.

2. Environmental implications of the fauna

A) THE LOCAL ENVIRONMENT OF DEPOSITION Although the assemblage of fossil Coleoptera from Bobbitshole is evidently a very small sample of an otherwise rich insect fauna, it provides a consistent picture of the depositional environment of the organic silts. It is clear that we are dealing with deposits laid down in a shallow eutrophic lake or pond, the margins of which were becoming heavily overgrown with marsh vegetation. The presence of Eubrychius velutus suggests that, within the lake itself, its preferred food plant Myriophyllum was growing. The availability of open water is indicated by the large dytiscid water Colymbetes and Cybister lateralimarginalis and also by Hydrophilus, the largest of the European water beetles. Areas of water clear of floating leaf plants are essential for the surface-hunting Gyrinus. Apart from these aquatic beetles, a large proportion of the species in this assemblage is associated with the marshy edges of pools. It is a peculiarity of this fauna that the largely carnivorous Carabidae, so important an element in most fossil assemblages of beetles, are here represented by only three species. Each of these is, however, characteristic of the margins of standing water. Two of them, Colliurus melanura and Oodes gracilis are members of the feed swamp fauna and are represented here by at least six and four individuals respectively, the highest frequencies in this assemblage. Amongst the phytophagous species, the dominance of Donacia and Plateumaris is also suggestive of a reed swamp but only Plateumaris braccata seems to be fastidious about its choice of food plant, preferring Phragmites communis. The occurrence of the aquatic weevil Bagous collignensis indicates that the marsh also supported Equisetum limosum. Decaying plant refuse at the water's edge would have provided habitats for Coelostoma orbiculare. A group of three species, Melanotus sp., Dorcus parallelopipidus and Valgus hemip- tersus, is indicative of dead wood in the vicinity of the pool. In the case of the latter species, water sodden wood is its chief preference. Three species in this assemblage are indicative of habitats further afield. Cetonia aurata has larvae that live in accumulations of vegetable debris on drier land, incidentally the usual habitat of Airaphilus elongatus also, but the adult is a very active flier often found on flowers and it is thus likely that the species is an acci- dental inclusion in this assemblage. The same interpretation can be put upon the occurrence of Melolontha melolontha whose larvae live on land at the roots of many plants but whose adult flies readily, feeding on the foliage of deciduous trees. Each of these species is represented here by a single fragment.

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A curious feature of this faunal assemblage is the presence of four species of dung beetle. All these species are active fliers which breed on land away from the immediate vicinity in which the deposits accumulated. Their presence here must also be accidental. The relatively large numbers in this sample must indicate a very considerable abundance of these species on the drier land adjacent to the pool, implying the abundance of the dung chiefly of large herbivorous mammals. The unexpected increase in the inorganic content of the sediment towards the top of the section at Bobbitshole and the accompanying fall in the proportion of tree pollen in the spectrum (West 1957, p. 25) might well be attributed to the trampling and browsing activities of these large mammals reducing the local vegetation cover and increasing the soil erosion.

B) THE CLIMATE Climatic interpretations based on fossil data rely heavily upon the present day geographical distributions of the species concerned. In the Bobbitshole assemblage, six (29%) out of a total of 21 named species, are no longer found living in the British Isles. These are Oodes gracilis, Cybister laterali- marginalis, Airaphilus elongatus, Caccobius schreberi, Onthophagus opacicollis and Valgus hemipterus. Amongst the unidentified fragments from this site there are several that clearly do not belong to any species of the present day British fauna, suggesting that the exotic element in the fossil assemblage was even greater than that given above. All the recognized species are widespread in central and southern Europe today and though many of them have ranges that extend as far north as the southern extremity of Scandinavia, they become exceedingly rare there and are associated with thermally favoured localities. For example, Lindroth (19¢3) has shown how Oodes gracilis, in its northern outpost near Stockholm, is locally restricted to sites with high summer temperatures. The dung beetles from Bobbitshole have particular climatic significance. In cool temperature regions the dung beetle fauna is dominated by species of Aphodius. This is the situation in Britain today. In regions with hotter climates, for example in southern Europe, the scarabaeines such as Onthophagus become the most important dung beetles. The Bobbitshole assemblage falls clearly into this latter category. Indeed one species of Onthophagus (0. opacicollis) is exclusively Medi- terranean (Balthasar 1963). There can be thus little doubt that the suite of dung beetles could find acceptable habitats only in a climatic regime considerably warmer than in Britain today. Taken as a whole the Bobbitshole Coleoptera comprise a typical west palae- arctic assemblage of species that would be found today only in regions where the average July temperature reached about 2o°C, that is about 3°C above that of southern England now. Winter temperatures need not have differed much from those experienced at the present time in southern England. Thus, though the seasonal variation in temperature may have been greater than it is in this country at the moment there is no evidence from the fauna of any marked increase in climatic continentality.

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3. Comparison of the Coleopteran and botanical data from Bobbitshole

Before a comparison can be made between these environmental interpretations and those made by West from palaeobotanical data, there is the problem of relating the horizon from which the insect fossils came to the stratigraphy described by him in his original account of the site (West I957). Lithologically the insect bearing sample was a silty clay mud with abundant macroscopic plant remains and fresh water mollusca. There can be thus little doubt that the sample came from West's stratum C. However, this stratum spans most of West's pollen spectrum and a more precise correlation with his pollen zones is needed if a meaningful comparison is to be made with the botanical data. The great profusion of 'seeds' suggests that the sample came from either pollen zone e or f. Nutlets of Cerato- phyllurn demersum and the fruit stones of Sparganium ramosurn were both abundant, suggesting a correlation with the boundary between pollen zones e and f. This correlation is reinforced by the local environment that can be inferred from both the beetle and the macroscopic plant data. Both provide a picture of a richly eutrophic lake which at the boundary between zones e andfwas becoming over- grown to give a reed swamp. The Coleoptera support and amplify the conclusion reached by West (op. cir. p. 2I) that "The distributional evidence (of the plants) taken as a whole would seem to point to a conclusion that during zoner (and perhaps also in zone e, where Hydrocharis (one seed), Stratiotes pollen and Salvinia were all found) the summers were rather warmer than at the present day." It would seem from the geographical distributions of the Coleoptera, that the summer temperatures at Bobbitshole were already as warm as those in southern central Europe today by the very beginning of pollen zone f. The presence at this time of a forest whose composition was largely made up of Pinus and Quercus might at first sight seem anomalous in the context of such high summer temperatures. However, the pollen data do not permit the identification of the species concerned and it may be that southern European trees were involved in the curves of the two genera in the pollen spectrum. It is nevertheless tempting to surmise that, had these high summer temperatures persisted for longer, the flora might well have taken on a much more southern European aspect with the incoming of yet more thermophilous species into the British Isles.

4. Comparison of the insect fauna with other known interglacial faunas

So far only insect faunas from Pleistocene deposits in the British Isles have been studied in adequate detail for meaningful comparison. At the moment three inter- glacial periods are generally recognized here: the Cromerian, the Hoxnian and the Ipswichian.

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Unfortunately the insect fauna of the Cromerian interglacial is inadequately known at the moment and thus comparisons with that from Bobbitshole cannot yet be made. Known insect assemblages from the Hoxnian Interglacial deposits differ markedly from that from Bobbitshole. Thus the fauna from Nechells, Birmingham, described by Shotton & Osborne (1965) has little in common with this assemblage. This difference may be in part due to the different local environment there, namely a rather acid woodland pond. However, the Nechells fauna resembles in many respects the insect assemblage currently being investigated from the 'peat' bed at the type site at Hoxne, stratum D of West (I956). If this similarity of Hoxnian faunas and the contrast between them and Ipswichian insect assemblages is eventually found to be consistent, it may well be possible to recognize empirical differences that will enable the Coleoptera to be used to distinguish between the deposits of these interglacials. The only other insect assemblage that bears any resemblance to that from Bobbitshole is the unpublished fauna from Trafalgar Square which has been independently ascribed to the Ipswichian interglacial (Franks et al. I958). The parallelism between these two assemblages is, however, precise. Almost all taxa recognized in the Bobbitshole fauna are represented in that from Trafalgar Square, but there the southern exotic species are joined by others of similar distribution not yet found at Bobbitshole. The Trafalgar Square sample was, how- ever, much larger and the richness of its insect fauna is almost certainly merely a reflection of sample size. The dung beetle assemblage is dominated by the same scarabaeines and in this respect both faunas are unique among known interglacial insect assemblages. On the basis of their Coleoptera alone there can be little doubt that these two deposits are of the same age.

5. References BALFOtm-BRow~, F. x95o. British Water Beeries. Roy. Soc. Lond. ~. BALTHASAR, V. x963. Monographie der Scarabaeidae und Aphodiidae der palaearktischen Region, 2, Pragh. Dm~N, L. x964 . Die mitteleuropaischen Arten aus der Gattung Bagous Germ. Ent. Blatt 66, 8-xII. F~a~xs, J. W., StrrCLIFFF, A. J., KEmcsy, M. P. & CooPE, G. R. i958. Haunt of elephant and rhinoceros: the Trafalgar Square of 1ooo00 years ago--new discoveries. The Illustrated London News I o I t-IoI3. LINDROTH, C. H. x943. Oodes gradlis Villa. Eine thermophile Carabide Schwedens. Notulae Entomol. 22, xo9-x57. r945, Die fennoscandische Carabidae. Eine tiergeographische Studie. t, 2 Goteborgs If. Vetensk. o. Vittern Samh. Handl. B 6. R~ITTER, E. t912. Fauna C,ermanica, 4, Stuttgart. SHOTTON, F. W. & OSBORNE, P. J. I965. The fauna of the Hoxnian interglacial deposits of Nechells, Birmingham. Phil. Trans. Roy. Soc. Lond. Ser. B 245, 357-378. W~ST, R. G. 1956. The Quaternary deposits of Hoxne, Suffolk. Phil. Trans. Roy. ~o¢. Lond. Ser. B 239, 265-356. -- 1957. Interglacial deposits at Bobbitshole, Ipswich. Phil. Trans. Roy. Soc. Lond. Ser. B 24 x, t-3 x. Received 9 October x973; read 2o February 1974. Geoffrey Russell Coope, D.Sc. Ph.D., F.G.S., Department of Geology, University, Edgbaston~ Birmingham 15.

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