Late Pleistocene environmental changes indicated by fossil insect faunas of the English Midlands ANNE MORGAN Morgan, Anne: Late Pleistocene environmental changes indicated by fossil insect faunas of the English Midlands. Boreas, Vol. 2, pp. 173-212. Oslo, 31st Decem- ber 1973. Twenty-five fossil insect assemblages are described from discrete lenses of or- ganic material in a gravel sequence at Four Ashes. The youngest date of 30,500 years B.P. obtained on the organic materia1 has confirmed that the till overlying the gravels is Late Devensian (Weichselian) in age. The analyses of the insect faunas have shown conclusively for the first time the existence of climatic changes in one geographic area during the Early and Middle Devensian in Britain. Some of the earliest insect faunas can be correlated with the Br0rup Interstadial, when boreal forests existed in the English Midlands. It is suggested that a cold period prior to 43,000 years ago (but post-Br~rup) may have caused the elimination of the trees, because around 40,000 years ago the insects indicate that there was a rapid climatic amelioration when it was warm enough for trees to grow again in that area. Around 36,000 years ago there was another climatic deterioration when the thermophilous insect species were replaced by a large number of arctic stenotherms and a tundra type of environment. This cold period lasted for at least 6,000 years and probably became increasingly severe with the approach of the main Devensian ice advance sometime after 30,500 years B.P. Anne Morgan, Department of Geology, University of Birmingham, Birmingham, B15 ZTT, England (present address : Department of Biology, University of Waterloo, Waterloo, Ontario, Canada), 27th September, 1973. During the past fifteen years a number of papers have been published (Coope 1959; Coope et al. 1961 ; Coope et al. 1971) documenting past climatic re- gimes at scattered localities throughout the British Isles. Although most of these papers deal with the Devensian (Weichselian, Wisconsinian) period, they inevitably relate to a fraction of time during that interstadial. When the first samples were analysed from the gravel pit at Four Ashes, it was again thought that the insect assemblages (and thus the gravels) rep- resented one phase of the Middle Devensian. However, over fifty additional samples were collected from this gravel pit during the period April 1967 to January 1970 as they became exposed in the working face. When the beetles were investigated from these additional sites, it became obvious that there were several distinct faunal assemblages indicating a variety of environments ranging from tundra, through boreal forest to warm open ground situations. Radiocarbon dating also confirmed that the gravel sequence had been de- posited over a minimum period of thirteen thousand years of the Middle Devensian. Thus, for the first time, it has been possible, using fossil beetles, to trace a series of climatic fluctuations at one geographic location over a long period of time during the Early and Middle Devensian. 12 - Boreas 2:4
Transcript
Late Pleistocene environmental changes indicated by fossil insect faunas of the English Midlands A N N E M O R G A N
Morgan, Anne: Late Pleistocene environmental changes indicated by fossil insect faunas of the English Midlands. Boreas, Vol. 2, pp. 173-212. Oslo, 31st Decem- ber 1973.
Twenty-five fossil insect assemblages are described from discrete lenses of or- ganic material in a gravel sequence at Four Ashes. The youngest date of 30,500 years B.P. obtained on the organic materia1 has confirmed that the till overlying the gravels is Late Devensian (Weichselian) in age. The analyses of the insect faunas have shown conclusively for the first time the existence of climatic changes in one geographic area during the Early and Middle Devensian in Britain. Some of the earliest insect faunas can be correlated with the Br0rup Interstadial, when boreal forests existed in the English Midlands. It is suggested that a cold period prior to 43,000 years ago (but post-Br~rup) may have caused the elimination of the trees, because around 40,000 years ago the insects indicate that there was a rapid climatic amelioration when it was warm enough for trees to grow again in that area. Around 36,000 years ago there was another climatic deterioration when the thermophilous insect species were replaced by a large number of arctic stenotherms and a tundra type of environment. This cold period lasted for at least 6,000 years and probably became increasingly severe with the approach of the main Devensian ice advance sometime after 30,500 years B.P.
Anne Morgan, Department of Geology, University of Birmingham, Birmingham, B15 ZTT, England (present address : Department of Biology, University of Waterloo, Waterloo, Ontario, Canada), 27th September, 1973.
During the past fifteen years a number of papers have been published (Coope 1959; Coope et al. 1961 ; Coope et al. 1971) documenting past climatic re- gimes at scattered localities throughout the British Isles. Although most of these papers deal with the Devensian (Weichselian, Wisconsinian) period, they inevitably relate to a fraction of time during that interstadial.
When the first samples were analysed from the gravel pit at Four Ashes, it was again thought that the insect assemblages (and thus the gravels) rep- resented one phase of the Middle Devensian. However, over fifty additional samples were collected from this gravel pit during the period April 1967 to January 1970 as they became exposed in the working face. When the beetles were investigated from these additional sites, it became obvious that there were several distinct faunal assemblages indicating a variety of environments ranging from tundra, through boreal forest to warm open ground situations. Radiocarbon dating also confirmed that the gravel sequence had been de- posited over a minimum period of thirteen thousand years of the Middle Devensian.
Thus, for the first time, it has been possible, using fossil beetles, to trace a series of climatic fluctuations at one geographic location over a long period of time during the Early and Middle Devensian.
12 - Boreas 2 : 4
174 Anne Morgan
Location and geology of Four Ashes The Four Ashes gravel pit is located at latitude 52” 40’ 13” N and longitude 2” 7‘ 24” W (Fig. 1). The National Grid Reference is 916.082 (SJ. 90/NW). The detailed stratigraphy of this area has been described by Alan V. Morgan (1973); consequently it is proposed to give only a general description of the geology where it is directly related to the organic deposits. At the Four Ashes gravel pit there was a threefold succession of Triassic bedrock, sands, and gravels with an overlying Irish Sea till. A typical sequence is shown in Fig. 2. The organic material occurred sporadically throughout the gravels, from hollows in the bedrock surface to just below the overlying till. When it occurred in the bedrock hollows it was usually underlain by a few centi- metres of sand and gravel.
Fig. 1 . Location of Four Ashes.
Material and methods Samples were collected from 48 separate lenses within a radius of about 200 metres (Fig. 3). A minimum of 4 kg was collected from each locality, although in many cases larger quantities were obtained for dating and for botanical analyses. The lithology of the lenses varied considerably from detritus muds to grey clays, and the amount of material washed to obtain an adequate fauna differed accordingly. In all, about 500 kg were processed and of this approximately 200 kg were analysed in detail.
The separation of the fossils from the inorganic fraction was more or less consistent for all the Four Ashes sites and follows the flotation method de-
Late Pleistocene environment and insects 175
Fig. 2. Four Ashes pit show- ing Late Devensian till over- lying gravels.
Fig. 3. Location of sample sites.
176 Anne Morgan
scribed by Coope (1968a). All the fossils are stored in the Geology Depart- ment at the University of Birmingham.
14C dates were obtained from eight separate localities at Four Ashes. Samples of each were collected from a clean exposure and a full acid and alkali pretreatment was given to them, except those from localities 2 and 3 which were treated with acid only.
~ ~~ ~
Sample Birmingham Lithology of sample Date in Years B.P. Reference number number
Arthropod fossils were obtained from 48 separate lenses, but only the fos- sils from 25 lenses have been examined in detail. Appendix I shows the distribution and frequency of all the species in these 25 samples. The ar- rangement of the sites in the faunal list is based on the fact that most of the 25 fossil assemblages fall naturally into one of three well defined groups. The fauna from locality 44 was small and inconclusive, but its unique floral assemblage is of particular interest and indicates that it probably belonged to an interglacial period prior to the Devensian. For completeness of the record it is described in Appendix 2.
As mentioned above the fossil faunas have been divided into three separate groups. This grouping is based mainly on the presence or absence of certain species, but stratigraphy can also be correlated with this to a limited extent. In the analyses of the faunal groups ecological information has been used from the following references :
(a) Coleoptera (general): Fowler (1887-1891); Joy (1932); Portevin (1929-
As far as possible, all components of the ecology have been considered in the analysis of each fossil assemblage. For simplicity, those faunas which look alike will be considered together in one of three groups. General habitat preferences are described and specific food plants are listed where known.
Group 1 faunas
The two faunas (from localities 9 and 10) which have been classified under Group 1 were collected from rich detritus muds lying directly on bedrock (see Fig. 3 for locations). These faunas are clearly characterised by six species of Coleoptera, each unique to this group and each associated with trees. These are as follows:
Olophrum rotundicolle . . . . . . . . . . . . . . . . . . . .sometimes under loose bark. Dorcatoma sp. ........................ .in fungi on decaying trees. Pissodes sp. ........................... .coniferous trees. Scolytus ratzeburgi .................... .exclusively in Betula, usually B. alba and B.
verrucosa, and rarely B. pubescens. Blastophagus piniperda . . . . . . . . . . . . . . . . . . usually in Pinus sylvestris, less frequently in
other species of Pinus. Picea excelsa, Abies, and Larix. (Adults feed on shoots and breed in weakened or fallen trees.)
Many of the commonest Carabidae such as Patrobus assimilis, Agonum ,fuliginosum, Pterostichus nigrita and P. diligens are eurytopic species, al- though they are often common in humus-rich areas. P. diligens usually indi- cates a rather acid substrate, and it is interesting to note that this species is twice as common as P. nigrita in locality 10. All the species mentioned above are often associated with Trechus rivularis to-day, as they are in the fossil assemblage. T. rivularis is nearly stenotopic to broken wood swamp, usually with strong shade provided by Betula, A l m s or Salix, and domi- nantly Sphagnum vegetation.
Many of the staphylinids, such as Arpedium brachypterum, Pycnoglypta lurida (Fig. 4) and Boreaphilus species, which are normally very common in Middle Devensian sites, are here represented by relatively low numbers. Nevertheless, their occurrence again indicates the presence of some leaf litter, such as Salix and other vegetable debris.
178 Anne Morgan
Fig. 4. Pycnoglypta lurida head and pronotum ( x 98).
A weevil, which is unique to this faunal group, is Meleus sp., although it is not certain what it feeds on. Reitter (1916) states that members of this genus gnaw young conifer plants, whilst Hoffman (1954) records Rumex alpinus as the food plant of one species.
Other plants are indicated by the following phytophages : Simplocaria metallica . . . . . . . . . . . . . . . . . . . moss and liverworts (including Marchantiu
Adding together all the Chrysomelidae and Curculionidae, they represent 19.5 per cent of the total fauna (205 individuals) in locality 10, and 8.6 per cent of the total fauna (126 individuals) in locality 9.
The presence of thirty-five individuals of Hydraena at locality 10 indicates that some aquatic habitats were present, but the general scarcity of other water beetles indicates the minor role of water in this environment. Hydrobius fuscipes suggests stagnant pools and Helophorus species could indicate any- thing from small temporary puddles to more open areas of water. I n locality 9 the abundance of Limnius tuberculatus infers that running water existed in the region at some time.
The overall view of the vegetation which emerges from the two faunas in Group 1 is that of coniferous forests represented mainly by Pinus and Picea, together with Betula and possibly Salix. This environment is also suggested by the presence of Pinus, Picea, and Betula pollen in the deposit. Amongst the forested areas there must have been acid, mossy swamps and perhaps small pools with sedges growing around them. There is very little evidence of a rich herbaceous vegetation or of bare open ground.
Group 2 faunas
The faunas from this group came from deposits of differing lithologies, ranging from felted detritus peats to grey clays (localities 4, 8, 12, 15, 19,
Late Pleistocene environment and insects 179
Fig. 5 (left). Helophorus nubilus pronotum ( x 62). Fig. 6 (right). Helophorus nubilus pronotum ( x 287) showing ornament between median and submedian ridges.
22, 34). All of them, however, have been found in the lower parts of the gravel sequence, usually near the bedrock, and rarely more than one metre above it (see Fig. 3 for location of faunas).
The characteristic feature of the faunas in this group was that they all contained a large number of phytophagous beetles, and the majority of these plant feeding species did not occur in the assemblages of Groups 1 or 3. However, none of these phytophagous species was associated with trees as in Group 1.
The Carabidae from the Group 2 faunas are mostly eurytopic, but the majority are somewhat hygrophilous, showing a preference for damp, shaded situations. Dyschirius globosus and Pterostichus diligens, both relatively com- mon in this faunal group, are found today in every type of moist to wet biotope. Another typical member of this faunal group is Pterostichus nigrita which, although it is eurytopic, tends to avoid barren sand and gravels, in preference for soil with some loam or humus in it, such as that developed under Alnus. Both Trechus rivularis and T. secalis are also found in damp, shaded situations where the soil has a good humus content.
Fig. 7. Oxytelus gibbulus pronotum ( x 95).
180 Anne Morgan
Fig. 8. Sitona flavescens head ( x 62).
A few species in the faunas of Group 2 attest to more open conditions. Amara quenseli and Otiorrhynchus arcticus occur on more or less sandy soils with only sparse vegetation, and Calathus melanocephalus prefers open grass- land.
Very few Agonum species occurred anywhere at Four Ashes, but Agonum consimile is of interest in locality 12. This carabid is restricted to the margins of standing water, always where the soil is soft and the vegetation rich. A base-poor soil is suggested indirectly by the weevil Micrelus ericae, which feeds on Erica species - most of these are described as calcifuges by Clapham, Tutin & Warburg (1962).
There is no evidence of large bodies of open water in the area at this time, although the presence of a few Dytiscidae in each fauna suggests that perhaps small pools existed. Most of the hydrophilid species which are found in these Group 2 faunas such as Coelostoma orbiculare, Sphaeridium scarabaeoides, and Chaetarthria seminulum are found in damp vegetation or mud, and the Helophorus species (Figs. 5 and 6) are notorious for their colonisation of temporary pools.
Several species of Staphylinidae are also restricted to these Group 2 faunas (Fig. 7) and most of them live in vegetable debris. However, some, such as Platystethus arenarius and Oxytelus laqueatus, spend much of their life in dung. The large numbers of Aphodius and the presence of Cercyon melanocephalus also infer that dung was available in the area, although some of the Aphodius species may have been living in vegetable refuse.
Many of the phytophagous species can be associated with particular host plants, and these are listed below to give some idea of the vegetation which was growing in Four Ashes area during part of the Devensian.
There are several other phytophagous species in Group 2 such as Phaedon sp., Phyllotreta sp., Haltica sp., Psylliodes sp., Apion spp., and Gymnetron sp., to which no specific host plants can be ascribed. The total number of phytophagous individuals (i.e. Chrysomelidae, Curculionidae and Byrrhidae) expressed as a percentage of the total fauna at each locality is given below.
In general, the plant feeding species comprise about 20 per cent of each fauna in Group 2. Locality 8 is somewhat lower, but it will be seen later that this fauna also has other peculiar features. All figures are, of course, minimum estimates since unidentified members of other families may also be plant feeders.
Another interesting component which is characteristic of these Group 2 faunas is that nearly all of them contain the yellow & black segments of syrphid flies. Such flies are normally found hovering over flowers. The caddis, Phryganea obsoleta, is also found in one of these faunas, but in none of the others at Four Ashes.
I n summary, the environment indicated by the Group 2 faunas is one with a fairly luxuriant vegetation of mosses, aquatic and semi-aquatic plants around small pools. The substrate in these swampy areas seems to have been rich in humus and slightly acid. There was also a certain amount of vege- table debris and dung. Away from the marshy places, there was a little open, sandy or gravelly ground, some grassland, and quite a variety of plants. The Coleoptera of the faunas in Group 2, however, indicate that this environ- ment remained entirely treeless, except for perhaps dwarf birch and willow.
182 Anne Morgan
Group 3 faunas
These faunas came from deposits of differing lithologies and they occuked at all levels in the gravel sequence (localities 2, 3, 13, 14, 16, 20, 23,24,27, 29, 31, 36, 40, 41, 45). One of them (locality 16) was almost on bedrock, but the majority were 1 m or more above bedrock (see Fig. 3 for locations).
The assemblages of Group 3 are characterised by very few plant feeders but by a large number of beetles which live on tundra or similar open ground situations.
Bembidion hasti lives on barren gravelly banks, usually along rivers, but may be found by lakes and pools on the tundra. Bembidion virens is also associated with barren, gravelly areas and is a marked hygrophile, always living near still or flowing water. Open ground with dry and moderately moist soil is suggested by Pterostichus adstrictus and Amara torrida, although neither of these species usually lives above the tree line. Amara alpina, which is more common than the two previously mentioned species in most of the Group 3 faunas, is a true alpine and tundra species and lives in a variety of barren habitats. Carabus maeander, which was only found in one Group 3 fauna, suggests more or less moist ground, with Carex and other fairly high vegetation. Damp, mossy, or sedgy areas are indicated by Diachila arctica and Elaphrus Iapponicus. The latter is typically found in wet moss near cold streams where the water is neutral to alkaline, rather than acidic. Diachila polita is also a tundra species, but is less hygrophilous than D . arctica and prefers peaty soil or moist mud around Carex pools. Another species showing a preference for damp surroundings is Pelophila borealis which is always found in exposed, sunny positions near water where the soil is soft and humus-rich. Pelophila borealis lives on the true tundra, but it is also found below tree line often in the same areas as Patrobus septentrionis. Open sandy areas are indicated by Aegialia sabuleti, but from the low per- centages of other Scarabaeidae which are coprophilous there was apparently very little dung.
Fig. 9 (left). Helophorus sibiricus pronotum ( x 46). Fig. 10 (right). Helophorzcs sibiricus pronotum ( X 290) showing ornament between median and submedian ridges.
Late Pleistocene environment and insects 183
Fig. 1 1 (left). Boreaphilus henningianus head ( X 87). Fig. 12 (right). Boreaphilus nordenskioldi head ( x 87).
All the above-mentioned species, plus several others (Pterostichus kokeili, Carabus menetriesi, Miscodera arctica, and Bembidion aeneum), are exclusive to the faunas in Group 3. Not one of them is found in Groups 1 or 2.
In general, water beetles are rare in Group 3, although there are several Helophorus species of which obscurellus and sibiricus (fennicus auctt.) (Figs. 9 and 10) are the most significant.
Amongst the Staphylinidae, Arpedium brachypterum, Olophrum fuscum, Pycnoglypta lurida, Acidota quadrata, and Boreaphilus henningianus (Fig. 1 1) and B. nordenskioldi (Fig. 12) reach much higher numbers in these Group 3 faunas than in either Group 1 or 2. I n contrast, such taxa as Oxytelus, Platystethus, Lesteva, and Aploderus which were so common in faunas of Group 2 are completely absent from Group 3.
Two of the Group 3 faunas also had the jaws, thoracic appendages, and
Fig. 13. Lepidurus arcticus supra- anal plate ( x 55). Note median spines.
184 Anne Morgan
Fig. 14. Lepidurus arcticus : (A) apodous segment ( x 28); (B) part of furca ( x 38); (C) endite of appendage ( x 23).
diagnostic abdominal segments of Lepidurus arcticus (Figs. 13 and 14). This small crustacean is usually found in shallow, sparsely vegetated pools in northern latitudes.
Compared with Group 2 faunas there are very few phytophagous species in Group 3. Those that are present infer a monotonous vegetation cover, predominantly composed of moss, grass, and semi-aquatic plants as shown below. Simplocaria metallica . . . . . . . . . . . . . . . . . . . moss. Simplocaria semistriata . . . . . . . . . . . . . . . . . . . moss. Byrrhus spp. ......................... .moss. Plateumaris sp. Notaris aethiops ........................ Sparganium ramosum, Menyanthes sp., and
Rhynchaenus flagellum and R . foliorum . . . . . Salix cinerea, S. alba, S. caprea, S. aurita, S.
........................ Carex and other sedges.
sedges.
ceae, and Graminae.
viminalus, and probably other Salix species.
The percentages of the phytophages in each of the Group 3 faunas are shown below. As before, these figures are obtained mainly from the Byrr- hidae, Chrysomelidae, and Curculionidae. It is interesting to note that the dominant weevils of the Group 3 faunas are Rhynchaenus jlagellumlfoliorum, Otiorrhynchus nodosus, and Notaris aethiops. There is not a single specimen of Otiorrhynchus ligneus, Strophosomus faber, or Sitona jlavescens which were so common in the Group 2 faunas. Locality 2 3 13 14 16 20 23 24 27 29 31 36 40 41 45 Total individuals in faunas 522 1188 14 62 173 150 37 22 56 18 24 40 46 33 376 Percentage phytophag- ous spp. in faunas 4% 9% 7% 8% 3% 11% 10% 31% 21% 0% 12% 10% 24% 9% 2%
Late Pleistocene environment and insects 185
These figures show that the percentage of plant feeding beetles in the larger Group 3 faunas is generally between 2 and 11 per cent, but fluctuates from 0 to 31 per cent in the smaller ones. However, it seems reasonable to assume that the larger faunas give a truer indication of environmental conditions and so greater emphasis will be placed on the results from these, than from the smaller faunas. Indeed, from the whole of Group 3 the phytophages only amount to 7.5 per cent, in marked contrast to 20.5 per cent in Group 2.
The overall view of the Four Ashes area from the Group 3 faunas is of an open, rather barren environment. The vegetational cover must have been low and mainly composed of moss and grass, with various aquatic and semi- aquatic plants growing in the moister areas around small, perhaps imper- manent pools. There were certainly no trees.
The climate
T h e interpretation of climate from an assemblage of fossil insects is not a simple process. Invariably it is possible to detect a general tendency for the modern distributions of the species in the fossil fauna to be dominantly more southern or more northern than the fossil locality is at the present day. It is even possible to give a subjective interpretation of the degree of 'norther- liness' or 'southerliness', but it is not easy to quantify these data. In previous analyses of fossil faunas (Coope & Sands 1966; Coope 1968a; Morgan 1969) considerable weight has been given to the occurrence of members of the family Carabidae in the vegetational zones of Scandinavia. Representative faunas from the three groups at Four Ashes have been analysed in this way, using absolute numbers, and the resulting histograms (Fig. 15) show that
I ECENO i-loo 7.
I u UPPER ALPINE ZONE c CONIFER ZONE
M MIDDLE ALPINE ZONE Q (IuERcus ZONE
L LOWER ALPINE LONE F FAGUS ZONE
CROUP 2
II 11111 _.1ll11 LOC 4164!!293) looc 121.8]!290)
Loc 3[86](8asl Lac 16[7]i l401
U M L B C ~ F U M L B C Q F Loc 20[9](1l71
U M L B C Q F
Fig. 15. Histograms showing distribution of Carabidae in floral zones.
186 Anne Morgan
faunas from Groups 1 and 2 are most suited to conditions likely to prevail below treeline, whereas those from Group 3 are much better suited to condi- tions aboae the treeline.
This method of analysis, however, does have several inherent problems, and these have been discussed more fully elsewhere (Morgan 1970). Basically, it is very difficult to correlate the boundaries of vegetation zones with cli- matic boundaries. Moreover, this method involves only one family of Cole- optera, and so the relative abundance of other families, which may be equally determined by climatic factors, is not taken into consideration.
A further attempt, therefore, has been made to devise a more objective method of climatic assessment which includes the entire fauna, and not only the Carabidae. This method is based on the understanding that insect dis- tribution is governed to a large extent by thermal factors and that maps of modern distributions thus reflect the thermal requirements of a species. I n general, this assumption seems justified in the light of work by entomologists on modern insects. For example, Lindroth (1969) states : ‘Macro-climate, above all temperature, is no doubt a master agent governing geographical distribution.’ Indeed many authors have found a close correlation between the distribution of an insect and temperatures during some part of the year (Predtentchenskii 1928; Cook 1929; Pepper 1938; Messenger 1958; Dani- levskii 1965, 1970). Those species with a wide distribution in Europe are no doubt eurythermal and thus of little use in determining more precise climate regimes. Those species with a more restricted distribution are prob- ably stenothermal, and these are the ones which will be considered in a further analysis of the Four Ashes faunas.
Accepting that temperature is the overriding factor in determining the distribution of an insect species, the use of stenotherms for the deduc- tion of climate from fossil assemblages still has several inherent dif- ficulties. Temperature can exert its influence at any time during the life history of an insect and in a vast number of ways, T h e following discussion is intended to point out some of these ways and to show that the rather crude analysis which I have used may be disguising many hidden factors. However, until more detailed information is available for the living species it is difficult to analyse the fossil faunas more completely, and we can only hope that future research will help to alleviate this problem.
The time of year at which the influence of temperature is strongest prob- ably varies from species to species. I n assessing the climate regime at Four Ashes, more importance has been given to summer temperatures since the northern limits of thermophilous species are more nearly paralleled with summer isotherms than they are with those of winter. The determination of winter temperatures is more difficult, but Danilevskii (1965) points out that the importance of these temperatures should not be overlooked, since ex- cessively cold winters may fall below the frost resistance of the diapause stage, or warm winters may be responsible for its reactivation. These factors must be borne in mind when analyzing some of the arcticstenothermas-
Late Pleistocene environment and insects 187
semblages from Four Ashes for which the assessment of summer temperature becomes more difficult.
T h e main problem when relying on the distributional analysis of a fauna is gathering adequate information of the total species range. Hansen et al. (1960) provide a fully documented list of Fennoscandian occurrences, but several species such as Pterostichus blandulus, P . kokeili, Carabus maeander and Boreaphilus nordenskioldi are absent from this area. Our knowledge of the distribution of such species, therefore, depends on the availability of collecting records. Thus a species may be considered as an ‘arctic’ steno- therm because it has a northern distribution, although it may actually live in climatically continental areas where the July temperature could be as high or higher than present day Britain. Nevertheless, it seems that there must be some factor which is restricting such species to places like Kanin, Novaya Zemlya, and eastern Siberia. This factor appears to be the contj- nentality of the climate, and this in itself is a valuable guide to assessing the climatic regime from a fossil assemblage.
Another factor which is of importance when considering these species from northern latitudes is the influence of day length on their distribution, although this is thought to be of minor importance. If a species, now living in northern latitudes of Europe or Siberia, was able to survive in Britain during the Devensian, day length can hardly be a significant factor. Downes (1965) states, ‘. . . the wide north-south ranges of many insects show clearly that a particular response to photoperiod is not a deeply entrenched specific attribute.’ In general, the important requirement for an insect is the number of day degrees available during the summer period (Uvarov 1931). Thus, the assessment of palaeoenvironment by comparison with northern areas to- day where day degrees are far less, despite the longer photoperiod, is more likely to lead to an underestimation of the actual summer temperatures. (This problem, of course, is avoided to a certain extent when analyzing the faunas by the ‘floral zone method’.)
Many authors stress the necessity to consider the micro-habitat tempera- tures (Cloudsley-Thompson 1952; Henson & Shepherd 1952), but as Smith (1954) points out, within the macroclimate there are heterogeneous groups of smaller climates, and all micro-weather is ultimately controlled by the general weather. Possible exceptions to this may be beetles which live in dung or decaying refuse. Fortunately these species were not common amongst the stenotherms at Four Ashes, but if they do occur in other faunas and this method of analysis is used, their inclusion should be carefully considered. Similarly those species dependent on specific host plants may not be reflecting temperature. Several of the Four Ashes stenotherms are phytophages, but none seem to be closely associated with one plant, but rather with a variety. Their inclusion therefore, seems justified. I t is often thought that modern species are controlled by the distribution of the host plant, but Pepper (1938) has shown that this is not necessarily so, and that it is more often temperature which is the limiting factor.
188 Anne Morgan
Bearing all these factors in mind it is thought that the distribution of the stenotherms within a fossil assemblage gives some idea of the area where the majority of the fauna finds climatic conditions acceptable.
The entire distributional range of the Four Ashes species extends from northern Siberia, throughout Fennoscandia and other parts of Europe, as well as Britain. On the basis of their present day distribution records the stenotherms of the Four Ashes faunas have been divided into four categories as follows:
.
Primary cold stenotherms (- -) . . . . . those species which are mainly restricted to areas north of the Arctic Circle in Fennoscandia, or to mountainous or climatically continental areas further south. None of these species are found living in Britain to-day, and some do not come any further west than the Kanin Peninsula.
Secondary cold stenotherms (-) . . . . . those species which, in Britain, are restricted to northern or mountainous areas. If non-British these species are usually widespread in Fennoscandia, but many are absent from the southern third.
Secondary warm stenotherms (+) . . . . . those species with a predominantly southern distribution in Scandinavia, but with scattered occurrences further north.
Primary warm stenotherms (+ +) . . . . those species confined to southern Sweden (south of 62" N), southern Finland (south of 64' N), and the extreme southern part of Norway. Where they continue northwards, these species only follow the coast of the Gulf of Bothnia. Many which occur in Britain are restricted to the south of the country.
Thus all the species with restricted modern ranges have been placed into one of the above categories. The total number of individuals in each of the stenotherm categories has then been added up and expressed as a percentage of the total specifically identified individuals of each fauna. T h e percentage of warm and cold stenotherms within each fauna may then give an indication of the thermal environment for the period in which these species lived. This enables each of the twenty five faunas to be compared with each other in a qualitative way.
The next consideration is to what extent these differences may be related accurately to the climate of that time. Theoretically it should be possible to make some general correlations with the climatic regime of the area in which the predominant type of stenotherms now occur. As already mentioned, day length is a minor problem in this regard, but the degree of oceanicity or continentality is rather more important. If a species appears to avoid the entire west coast of Norway, and is restricted to north-east areas of Fenno- scandia or north European Russia, this is thought to be indicative of a preference for more continental conditions. Similarly a species which is found dominantly in coastal areas is taken as evidence of more oceanic con- ditions. According to the oceanic index of Kotilainen (in I indroth 1949), continentality increases in Sweden north of 60" N, and in Finland north of a line running from 63" N in the west to 62" N in the southeast. The greatest degree of continentality in both Sweden and Finland is beyond 65" N. This index has been used as a further guide in the assessment of conditions indicated by the various stenotherms.
As before, the faunas of Four Ashes are retained within Groups 1, 2, or 3 for simplicity. Each Group is considered separately, giving the types
Late Pleistocene environment and insects 189
and percentages of stenotherms which the individual faunas contain and the climate that they suggest.
Group 1 faunas ( f ~ o m localities 9, 10)
T h e stenothermic species of Group 1 fall into the following categories:
The numbers of individuals in these groups expressed as percentages of the total identified individuals are as follows.
Total number Locality of identified Percentage Percentage Percentagc Percentage
individuals of - - of - of + of + + 10 154 0 33 0 1 9 81 0 39 0 0
Both localities 235 0 35 0 0.8
These faunas are characterized by the predominance of - stenotherms and, from the definition given previously, this may indicate a climate similar to northern Britain or central Fennoscandia. Since there are n o - stenotherms there is unlikely to be a climatic correlation with northern Europe, and the scar- city of warm stenotherms excludes a southern climatic regime. In addition many species in Faunal Group 1 tend to avoid the western seaboard of Scandi- navia, which suggests that some degree of continentality must be inferred. In general, the best climatic 'fit' seems to be that found in central Sweden or Finland between 60" N and 65"N, where the average July temperatures are 14 "-16 "C.
In order to analyse each fauna more precisely in Group 2, the same method has been adopted as for Group 1. The percentages for each category of stenotherms are shown below.
Total number Locality of identified Percentage Percentage Percentage Percentage
individuals of - - of - of + o f t + 4 8
12 15 19 22 34
All localities
293 130 290 116 359 52
157 1397
14 58 15 9
49 10 11 26
2 0 2 0 0 6 4
1.5
1.5 2 9 5 1 2
13 8
In the Group 2 faunas there is again a total absence of - - stenotherms, but the ++ and + stenotherms become significant. The average percentage of - stenotherms is 26 per cent but localities 8 and 19 are somewhat dif- ferent in having 58 and 49 per cent respectively, and these will be discussed later. The majority of the faunas in Group 2 suggest a climatic regime of southern or central Fennoscandia with average July temperatures around 15 O or 16 "C. Added to this, the stenotherms in this group indicate only a moderate degree of continentality.
Group 3 faunas
The stenotherms of the faunas in this group (localities 2, 3, 13, 14, 16, 20, 23, 24, 27, 29, 31, 36, 40, 41, 45) fall into the following categories:
The striking feature of all these faunas is the total lack of warm stenotherms (except locality 40), and the abundance of cold stenotherms. Several of the faunas are small, but climatic inferences are based mainly on those faunas containing more than 100 specifically identified individuals. The smaller faunas will be discussed later. The average total percentages of the cold
192 Anne Morgan
stenotherms in these larger faunas is 80 per cent of the total identified species, which means there are very few eurythermal species. It also means that the faunas as a whole must represent a more northern type of climate than those described previously. If only the Fennoscandian distribution of these species is considered then the average July temperatures would be assessed at 10 " to 13 "C, but if some of the non-European species are con- sidered this temperature could be put as low as 4 "C or as high as 16 "C. For example, Boreaphilus nordenskioldi (Fig. 12) is known from such widely scattered places as Novaya Zemlya (average July temperature 4 "-6 "C) to Shigansk on the Lena River (average July temperature 14 "-16 "C). Several other species in these Group 3 faunas are not known to occur further west than the Kanin Peninsula, and these may also tolerate moderately warm summers. Without doubt these faunas indicate a continental climate with very cold winters, but I am rather reluctant to infer an exact summer tem- perature from them. According to their occurrences in the vegetation zones, the Carabidae suggest a July average not much higher than 10 "C, but their modern geographic distributions show that several species can tolerate tem- peratures well above or below this. However, the overall assemblage in each of these Group 3 sites indicates that a climate having a July average of 10 "C is probably one which most of the species would find acceptable.
Comparison of the Four Ashes faunas with other Devensian faunas
As shown above, the organic deposits at Four Ashes fall into three more or less distinct groups, each with characteristic faunas. In this section it is proposed to compare similar faunas from elsewhere in Britian with those at Four Ashes. I t is not possible to compare the complete faunal range at Four Ashes with a similar range elsewhere, since no single site with such a variation has yet been described. I t is for this reason that a comparison of specific sites at Four Ashes must be made with a number of individual sites in widely separated geographical localities
Group 1 faunas
The faunas from localities 9 and 10 at Four Ashes are very similar to that from Chelford described by Coope (1959), but due to its smaller size locality 9 will be omitted from this discussion. Both locality 10 and Chelford contain many of the same species, and these species are rare or absent from other faunas at Four Ashes. For instance, Trechus rivularis, Patrobus assimilis, Ptevostichus nigrita, P. diligens, Agonum fuliginosum, Hydraena riparia and Olophrum rotundicolle are particularly common in both locality 10 of Four Ashes and at Chelford. In addition, both sites are characterized by two scolytids, Blastophagus piniperda and Scolytus ratzeburgi, which have not been recorded from any other fauna at Four Ashes, nor indeed from any
Late Pleistocene environment and insects 193
Middle Devensian fauna in Britain. These scolytid beetles feed and live on coniferous trees and thus suggest that the locality 10 fauna at Four Ashes lived during a similar, forested period of the Early Devensian as did the Chelford fauna.
The pollen spectrum of Pinus, Picea and Betula from locality 10 is also very similar to that described from Chelford by Simpson & West (1958). According to Dr. W. Zagwijn (pres. comm. 1970) the Picea pollen from Four Ashes is a small grain resembling that from the Brorup deposits in Holland dated at about 60,000 years B.P. (Andersen 1961; Andersen, De Vries & Zagwijn 1960).
Group 2 faunas
There is, at present, only one described fauna in Britain which is similar to the faunas of Group 2 at Four Ashes. This fauna was obtained from an organic band in a gravel sequence at Upton Warren (Coope, Shotton & Strachan 1961), and was 14C dated at around 42,000 years B.P. The faunas from both Upton Warren and Group 2 at Four Ashes contain relatively thermophilous species and lack the arctic stenotherms so typical of the Group 3 faunas. Some of the notable species which they have in common include Georyssus crenulatus, Crypticus quisquilius, Sitona jlavescens (lepida) and Otiorrhynchus ligneus. None of these species are present in any of the faunas of Groups 1 or 3 at Four Ashes, and all are moderately southern at the present day. Nevertheless, some differences do exist.
Upton Warren contains three species, Amara torrida, Agonum sahlbergi, and Syncalypta cyclolepidia, which are all confined to northern or moun- tainous areas today. The present southern limit of Amara torrida may only represent a dynamic limit (Lindroth pers. comm. 1970). Agonum sahlbergi has been recorded from the banks of the River Clyde, but its survival there is dubious (Lindroth pers. comm. 1970). T h e Upton Warren fauna also contains several other species which have a moderately northern distribu- tion and these include Dyschirius septentrionum, Amara erratica, Amara interstitialis and Pterostichus adstrictus. None of these more northern species are found in the Group 2 faunas of Four Ashes.
Whatever the reason for these few northern forms in a predominantly southern fauna, it seems strange in the light of recent work with Late Devensian faunas. In these there is very little ‘overlap’ of northern and southern species despite the rapid climatic changes which were occurring at this time (Coope et al. 1971). Also it is notable that this overlap of northern species has not been picked up in any of the Four Ashes faunas of Group 2. Nevertheless, their overall similarity with the Upton Warren fauna is in- disputable and this is further substantiated by the range of radiocarbon dates which have been obtained.
Group 3 faunas
The majority of the Group 3 faunas at Four Ashes are closely comparable
194 Anne Morgan
with the faunas from Brandon (Coope 1968a) and Great Billing (Anne Morgan 1969). They are all characterized by their numerous arctic steno- therms and the total lack of more thermophilous species. Pterostzihus blandulus, P . kokeili, Dinchila polita, Helophorus sibiricus, Helophorus obscurel- lus, and Boreaphilis nordenskioldi are some of the northern species which all these faunas have in common. Such species are absent from the Group 1 and 2 faunas at Four Ashes.
The fauna from Fladbury (Coope 1962) is also rather similar to the Four Ashes faunas of Group 3. The only difference is that the Fladbury fauna contains the weevil Otiorrlzynchus ligneus, which is usually more common in the Group 2 faunas at Four Ashes. 0. ligneus is now confined to southern Scandinavia and is usually associated with more thermophilous fossil as- semblages, although it did occur in one Group 3 fauna (loc. 40) at Four Ashes and it has been recorded from another site amongst arctic stenotherms (Coope pers. comm. 1970). These apparently anomalous occurrences remain unexplained.
I t should be emphasized that both the faunas and the radiocarbon dates for these widely separated sites are quite similar. This will be discussed later.
Environmental changes at Four Ashes Climatic changes
The fact that the Four Ashes faunas can be compared with individual faunas deposited under different climatic regimes, at different times in the Deven- sian at widely separated geographic localities, indicates the degree of climatic fluctuation that occurred here during gravel deposition. Out of the twenty- five sites which have been analysed in detail from Four Ashes, eight have been radiocarbon dated. These eight sites were specifically chosen for age determination, since they contained the climatically different faunal assem- blages which were characteristic of the three Faunal Groups. Using these dates in combination with the stenothermal categories which were defined above, it is possible to postulate a chronology of the climatic fluctuations which took place at Four Ashes and elsewhere during the Devensian period. Bearing in mind the relatively large standard deviation which is obtained for these Middle Devensian dates, it is impossible to be precise about the time of the climatic changes. However, the occurrence of deposits having similar dates and similar faunas at Four Ashes suggests that it may be valid to base a chronology of climatic fluctuations on these dates.
Since some of the smaller samples were possibly inadequate, only those containing more than 100 specifically identified individuals are used here. All these faunas together with four dated faunas from elsewhere in the Midlands have been placed in a tentative chronological sequence as shown in Fig. 16. The residual columns opposite the stenotherms of each fauna
Late Pleistocene environment and insects 195 - 0
45 +STENOTHERMS 0 0 3 - 8 1
19 I - 12 m I I 34 w P U W B 7 4- P
16 0 20 0 9 - 10 I = CH H I I
___)
+ + STENOTHERMS
28 000
15 I 1
Fig. 16. Suggested chronology of the Four Ashes faunas. The varying proportions of stenotherms reflect climatic changes during the Devensian. The open bars indicate percent- age of eurytherms. GB-Great Billing; BR-Brandon; UW-Upton Warren ; CH-Chelford.
represent the remainder of the species (at that locality) which do not come under the present definition of a stenotherm. The climatic changes which took place during the deposition of the Four Ashes gravel sequence will now be outlined, starting with the oldest faunas.
Gravel deposition is actually thought to have started sometime during the Ipswichian Interglacial, although the insect remains from this site were so few that no climatic deductions could be made from them (see Appendix 2). The earliest faunas which provide any evidence of the climate are thought to be Early Devensian in age. The beetles from localities 9 and 10 lying at the base of the gravel sequence indicate the presence of boreal forest con- ditions at some early period. As pointed out previously these faunas are very similar to that from Chelford. The latter was originally 14C dated 57,000 years B.P. by the enrichment method (Simpson & West 195S), but later re-calculated to 60,800 years B.P. (Vogel & Zagwijn 1967). Localities 9 and 10 from Four Ashes have not been dated, but on faunal evidence they are almost certainly of an equivalent age to the Chelford deposit which in turn was thought to be equivalent to the Brplrup Interstadial deposits of Holland (Simpson & West 1958; Vogel & Zagwijn 1967). From Fig. 16 it can be seen that these faunas from Four Ashes, like that from Chdford, lack nearly all the extreme cold (- -) stenotherms, and are mainly com- posed of - stenotherms and eurytherms. Probably at this time the climate in the English Midlands was moderately continental with July temperatures around 14 O- 16 "C.
Following this period there appears to have been a climatic deterioration represented by the fauna from locality 20 at Four Ashes. In this fauna there is a high proportion of all the cold stenotherms, a complete absence of warm stenotherms and only a few eurytherms. A continental climate is, therefore,
196 Anne Morgan
implied and probably one having moderately cool summers. The assemblage from locality 20 was dated in excess of 43,500 years B.P. and was notable due to the abundance of Lepidurus arcticus (Figs. 13 and 14) which is to-day found only in arctic regions. This crustacean was also found in locality 31 at Four Ashes, but the age of this particular deposit is unknown. Lepidurus arcticus has been recorded from Zone I11 of the Late Devensian (Mitchell 1957) when the climate apparently underwent a similar deterioration (Os- borne 1972). As shown in Fig. 16, locality 16 has been placed in the same period as locality 20, although this has not been confirmed by radiocarbon dating. Faunally it is indistinguishable from all the colder Group 3 localities, but from its stratigraphic position on bedrock, it is possible that it belongs to this postulated early cold phase. However, bearing in mind the complexity of the gravel sequence it could equally well belong to a later phase, so it cannot be assigned to any chronological position with absolute certainty. Moreover, the infinite date obtained for locality 20 could mean that this cold phase occurred prior to the B r ~ r u p Interstadial, and until these older materials can be dated more accurately the absolute chronology of climatic changes during the Early Devensian must remain tentative.
Following this apparent early cold phase there was an amelioration of the climate. Three deposits at Four Ashes (localities 4, 34, 12) all with relatively thermophilous faunas have been dated at 42,500,40,000 and 38,500 years B.P. respectively, and it is thought that one more fauna (locality 15) is approximately the same age. A similar fauna from Upton Warren (Coope et al. 1961) has also been dated around 42,000 years B.P. (As shown in Fig. 16 all these faunas are characterized by their lack of northern and continental species (- - stenotherms), low proportions of - stenotherms and the rela- tive predominance of warm stenotherms. During this period the insects of these Group 2 faunas suggest that the climate became less continental and that the summers were somewhat warmer. However, the landscape remained treeless since there were no wood-eating insects and no tree pollen was found in the preliminary pollen samples.
A ground beetle of particular interest at this time at Four Ashes was Calathus melanocephalus, which always had a clear red pronotum. This is thought to have some climatic significance since the same species at Brandon always had a black pronotum (Coope 1968a), and the Brandon fauna is similar to the colder Group 3 faunas of Four Ashes. Greenslade (1968) notes that colour variants of C . melanocephalus exist in Scotland to-day. Those having a clear red pronotum consistently occur below 260 m, whereas those individuals with a dark red to black pronotum are found above 260 m where annual temperatures are lower. According to Lindroth (pers. comm. 1970) the black varieties in Scandinavia occur along the west coast, whereas those on the east of the mountains have red pronota. Lindroth thinks that humidity may be an important factor controlling the colour of the pronota, although it is interesting to note that the summer temperatures do tend to be higher inland than on the coast.
Late Pleistocene environment and insects 197
Following the chronological sequence shown on Fig. 16 the faunas from localities 8 and 19 would appear to indicate a slightly cooler climate than that of the previous period. Unlike the other faunas of Group 2, those of localities 8 and 19 have much higher proportions of cold stenotherms (-) and lower proportions of warm stenotherms. The fauna of locality 19 is somewhat unusual because it contains relatively large numbers of Arpedium brachypterum and Pycnoglypta lurida, both of which are normally found in association with more northern species than they are in this fauna. Never- theless, both these species are recorded in Zone I1 of the Late Devensian when the climate was definitely not cold (Anne Morgan 1970; Osborne 1972). They are also widely distributed in Scandinavia to-day, so they are certainly not indicative of extreme cold. Unfortunately, neither locality 8 nor 19 was dated, so they cannot be fitted into any absolute chronology, but on faunal grounds they would indicate a cool period just before or just after the 'optimum' which occurred around 40,000 years B.P.
Sometime after 38,000 years B.P. there appears to have been a climatic deterioration at Four Ashes (Fig. 16) when conditions became much more continental. This caused the elimination of the thermophilous species (+ + and + stenotherms) and the re-immigration of the more northern and east- ern ones (-- and - stenotherms). The low number of eurytherms in these faunas (as shown by the residual columns to the right of Fig. 16) suggests that there were very few species with a wide temperature tolerance. The early part of this deterioration may be represented by locality 3, dated at 36,300 years B.P. when several tundra species are present, together with some species which are not found above the tree-line today except in coastal areas. The remainder of the larger Group 3 faunas are thought to date from the period after 36,000 years B.P., although they have not all been dated. Localities 2 and 45 were dated at 30,655 and 30,500 years B.P. respectively, and both were rather similar to the faunas from Great Billing (Anne Morgan 1969) and Brandon (Coope 1968a). During this period around 30,000 years B.P. the insects indicate that the landscape became more open and that the July average temperatures were probably about 10 "C, although with the increased continentality it is difficult to make an accurate assessment of these.
Despite the fact that the smaller faunas have not been included in this chronology, they cannot be considered to be irrelevant. The general paucity of insects in the deposits of localities 13, 14, 23, 24, 27, 29 and 31 may be due to severe climatic conditions when temperatures became unfavourable for the majority of species. Indeed, sparse assemblages are typical of the arctic today (Downes 1962, 1964), and in such areas staphylinids are often the predominant species. This situation occurs in some of the smaller faunas at Four Ashes where staphylinids are virtually the only beetles present. These sparse faunas may represent the last phases of insect colonisation in the Four Ashes area, before the imposition of polar desert conditions prior to the advance of the Late Devensian ice.
198 Anne Morgan
Correlations with known climatic jkctuations elsewhere in Europe
The Early Devensian boreal forest phase at Four Ashes can almost certainly be correlated with the B r ~ r u p Interstadial in the Netherlands (Andersen, De Vries & Zagwijn 1960; Andersen 1961). According to Andersen (1961) the July temperature for this period was 13 "-15 "C, which is in fairly close agreement with the estimate of 14 "-16 "C at Four Ashes.
It is not quite so easy to correlate the early cold phase at Four Ashes with similar episodes elsewhere, because I cannot be certain which side of the B r ~ r u p Interstadial this phase occurred. Andersen (1961) postulates a 'cold substage' prior to the Rodebaek Interstadial, another between the Rodebaek and Brorup, and yet another after the B r ~ r u p Interstadial. During these cold substages the pollen spectrum from the B r ~ r u p Hotel Bog shows both dwarf and tree Betula, Juniperus, and Populus, with July temperatures from 12 "C to less than 10 "C (Andersen 1961). These low temperatures correspond closely to those suggested for the early cold period at Four Ashes.
In addition there appears to be evidence from various other sites in the Netherlands of a cold period between 52,000 and 43,000 years B.P. Van der Hammen et al. (1967) record six deposits dated at 51,600 (GrN4289), 50,800 (GrN-4252), 46,250 (GrN-1718), 45,600 (GrN-3177), 43,600 (GrN- 3221) and 43,500 (GrN-1715) years B.P. T h e pollen diagrams from these deposits indicate '. . . a toundra vegetation almost devoid of trees' and '. . . support the view that the toundra phase of the Lower Pleniglacial started some time before 50,000 years ago and lasted until about 44,000 years B.P.' (van der Hammen et al. 1967). Vogel & Zagwijn (1967) refer to this period as 'a relatively mild phase' (i.e. not polar desert) but they state: 'It must be stressed, however, that conditions during that phase still remained severe. . .'. It would, therefore, be tempting to correlate this phase of the Lower Pleni- glacial (the Moershoofd Interstadial) or the period prior to it in the Nether- lands with locality 20 at Four Ashes dated in excess of 43,500 years B.P.
Further evidence of a climatic deterioration in the early part of the Devensian between 50,000 and 60,000 years B.P. is also provided by various deep sea cores (Rosholt et al. 1961 ; Emiliani 1966). These cores are con- sistent in showing a warm pre-Br~rup phase and a cold post Brmup phase.
The climatic fluctuations shown to have occurred during the Middle Devensian at Four Ashes cannot be easily correlated with those elsewhere in Europe. In the Netherlands, van der Hammen et al. (1967) have evidence of two interstadials during this period. These are the Denekamp between 32,000 and 29,000 years B.P. and the Hengelo from approximately 39,000 to 37,000 years B.P. T h e existence of these interstadials was based on dated deposits containing higher percentages of Betula pollen than at other times in the Pleniglacial. From evidence of Late Devensian sequences in Britain (Coope et al. 1971) it appears that insects show a faster response to changes in climate than do plants. If this is so, the amelioration which the Coleoptera reflect at Four Ashes around 40,000 years B.P. may possibly correspond to
Late Pleistocene environment and insects 199
the Hengelo Interstadial in the Netherlands. However, at Four Ashes there does not appear to have been another amelioration after 38,000 but rather a gradual deterioration with the approach of the maximum glaciation. No deposits have been found yet at Four Ashes which can be correlated with the Denekamp Interstadial of the Netherlands or with the Paudorf Inter- stadia1 of Austria (Vogel and van der Hammen 1967). I t is, nevertheless, interesting to note than an insect fauna from Peelo (33,000 years B.P.) in the Netherlands (Coope 1968b) corresponds very closely to those at Four Ashes of approximately the same age.
Vegetational changes
From the macroscopic plant remains at locality 44 it appears that Ilex and Alnus were, at one time, very common at Four Ashes (see Appendix 2). Since Ilex has not been recorded from any Early Devensian deposits, except as derived pollen (Andersen 1961), it seems that an interglacial period is represented at the base of the Four Ashes gravel sequence. This probably corresponds to the Ipswichian Interglacial, and it is unlikely to have been the later part (zones g, h and i) when Picea and Pinus had replaced most of the thermophilous trees (Jessen & Milthers 1928; Iversen 1944), because no coniferous pollen has been found in the samples so far examined.
Following this interglacial episode all the more thermophilous types of trees gave way to forests of Pinus, Picea, and Betula. Subsequent to this boreal forest phase there is no further evidence of trees, but it is not clear what caused their elimination. One possible explanation could be the jm- position of more severe climatic conditions. Such a deterioration may be represented by locality 20 at Four Ashes, dated in excess of 43,500 years B.P. and having a characteristic assemblage of arctic stenotherms. If this cold period did exist around 50,000 years ago and if it lasted for several thousand years it may have forced the trees completely out of Britain and into southern Europe. Even in southwest France during the 'last part of the Full-glacial', Oldfield (1964) found no tree pollen, and he postulated that some of the thermophilous trees may have survived this period even further south in Iberia. At Four Ashes the insects indicate that the open and treeless conditions existed for the rest of the Middle Devensian, despite the marked amelioration which occurred around 40,000 years B.P. At this time the July average was about 15 "C (that is, about 5 "C above the normal timber limit). Thus temperature is unlikely to have been the factor preventing the growth of at least some trees in this area.
Despite the consistently treeless landscape during the Middle Devensian, the plant feeding insects show some interesting fluctuations which may reflect changes in the herbaceous vegetation of this period. By taking the percentages of phytophages (Chrysomelidae and Curculionidae) from each of the larger faunas and plotting all these in order of increasing abundance, it is found that the percentages increase in those sites having relatively more
200 Anne Morgan
45 16 2 20 8 3 34 12 4 19 15 Fig. 17. Percentage of plant feeding beetles in the Four Ashes faunas.
thermophilous faunas (Fig. 17). In the ‘cold’ faunas the few phytophagous species that are present indicate little more than grass, sedges and low wil- lows. In the ‘warm’ faunas there is not only an increase in numbers, but also an increase in species. For example, Otiorrhynchus clavipesjfuscipes, 0. ligneus, Strophosomus faber, Sitona jlavescens, Notaris acridulus, Micrelus ericae, and Alophus triguttatus are all additional species found in the warm faunas and absent from the cold ones. This illustrates another interesting point, that the increase of phytophages is due to Curculionidae rather than to Chrysomelidae, but the reason for this is not clear.
The variations of modern phytophagous insects in relation to climate has been observed by Mani (1962) in the Himalayas, where they gradually decrease with the increasing severity of the climate at high altitudes. Similarly, Downes( 1964) noted a decrease of plant feeders in the Canadian Arctic, and he also found that this was not directly attributable to the availability of plants. At Lake Hazen the species of vascular plants outnumbered the insects by 3 to 1 and further north at Isachsen the proportions of plants to phytophages was 48 to 1. It, therefore, seems that cliniate is the major factor controlling the number of phytophagous species in a particular area. This may well be the case at Four Ashes where several of the Curculionidae are confined to southern Sweden to-day. This also seems to be true for other Devensian sites. For example, a Middle Devensian deposit from Derryvree in Ireland (Colhoun et al. 1971) contains an assemblage of dominantly northern species of Coleoptera with very few phytophages, whereas the presence of large numbers of plant fossils indicates that there was sufficient vegetation to provide food for the insects. Thus, a decrease of phytophagous species seems to be good evidence for an increasing severity of the climate, but is not necessarily indicative of a reduced vegetational cover.
Late Pleistocene environment and imects 201
Origin of the organic material One of the most important findings in this study at Four Ashes has been that in each of the twenty-five sites examined the fauna is ecologically dis- tinct with absolutely no signs of mixing, even though they were all collected within a radius of 200 m or less. Because of the restricted geographic area in which they were found and because there is a distinct lack of amplitude in the topography of the region around Four Ashes, there is every reason to believe that the climatic changes reflected by the faunal assemblages are real fluctuations and not just reflections of the micro-climatic requirements of different species. It, therefore, seems worthwhile to comment on this further and to consider some of the factors which led to the deposition of discrete organic lenses within a single gravel sequence over such a long period of time.
The Four Ashes gravels, in which the organic deposits occur, are mainly composed of quartzite pebbles derived from the Bunter Pebble Beds which outcrop 3 km east of the (1970) pit. Under the predominantly periglacial conditions which are believed to have existed throughout much of the Early and Middle Devensian, mass wastage of these deposits would have been pronounced. However, during this long period of aggradation at Four Ashes, small scale erosion must also have been occurring (A. V. Morgan 1973) and this would be expected to have created an ‘ideal’ situation for the derivation and re-deposition of fossiliferous material. Nevertheless, each of the faunal assemblages has been shown to be consistent, both ecologically and climatically.
Derivation has long been a problem with Quaternary botanists, particu- larly when assessing the status of typically interglacial plants such as Carpinus in Middle Devensian floras. Locality 44 at Four Ashes presented a similar problem, since it contained a typically interglacial flora, and yet all the other deposits from the gravel sequence were Early or Middle Devensian in age. The insects in this material were sparse and fragmentary, suggesting that they had been exposed prior to burial or that they had been transported and broken. On the other hand, there were well preserved leaves of Ilex which suggested to Dr. Zagwign (pers. comm. 1970) that the material had not been transported. In addition, there were abundant cones, seeds and pollen of Alnus, and it is unlikely that all three parts of the same species would be re-deposited from elsewhere in such abundance. On this criterion locality 4 4 is unlikely to have been derived and other factors such as its apparent ecological consistency and position on bedrock, would tend to substantiate this conclusion. The fragmentary nature of the insects may simply be due to a short period of exposure to the air during which they would almost certainly have broken up very rapidly. Also, if this interglacial material had been washed out from elsewhere, it might have been expected to have been re-deposited in other parts of the gravel sequence amongst deposits of Middle Devensian age. This does not seem to have happened.
202 Anne Morgan
At Four Ashes, where some of the organic lenses were less than 1 m apart, both the interglacial and Early Devensian deposits were at the base of the gravels and, during the period 1967-1970, never appeared higher up amongst the later deposits. T h e type of Early Devensian material at locality 10, would have been particularly easy to detect if it had been derived into other material, because it contained several wood dwelling insects and also abundant tree pollen. Even more surprising perhaps is the fact that there is a consistent ecological picture from each of the Middle Devensian faunas, even though they represent several different climatic regimes. Furthermore, the deposits containing these faunas are often separated by only a few metres of gravels, both vertically and laterally, and even those that have been dated span a period of a t least 13,000 radiocarbon years.
The majority of the Four Ashes deposits, therefore, are considered to be in situ assemblages of plants and insects, representing accumulations or or- ganic material in the local braided stream environment. For example, locality 4 was a felted peaty material containing extraordinarily high numbers of Carex nutlets and many Coleoptera which live on Carex and similar types of plants. Such close ecological conformity almost certainly represents ma- terial which has grown and died virtually in situ. Other samples may not have ‘grown’ in the site of accumulation, but they contain material which was probably blown or washed in from the local surroundings. In the treeless regions of the arctic to-day, wind is clearly a powerful agent in concentrating organic debris in any small depression in the landscape. Similarly, during the Spring thaw, the run-off would have swept the previous years growth together and this inevitably would have incorporated some insects from a short distance away.
This now leads to the question of why there has been no derivation and re-deposition during the 30,000 or more years of gravel accumulation ? One important factor is that, insects make rather poor derived fossils. Not only are they destroyed by fungi, but they are particularly vulnerable to wetting and drying because they warp and crack so easily.
Another factor which may be partially responsible for the absence of re- deposition is the geographic location of Four Ashes. Even to-day this area is high on the watershed, and it is probable that the amount of water avail- able from the attenuated headwaters of the Proto-Saredon Brook would have been more reduced during the Devensian.
Conclusions
(1) Gravel deposition at Four Ashes spans a period from at least 60,000 years B.P., until about 30,000 years B.P., and probably extends back to the Last (Ipswichian) Interglacial.
(2) Deposition of the organic material took place in a predominantly ag- grading environment. No derivation or re-deposition of faunas appears to
Late Pleistocene environment and insects 203
have taken place, since each lens of organic material contains an ecologically conformable assemblage of insects. None of the interglacial or Early Deven- sian material on bedrock has been incorporated into the later deposits, and none of the faunas has any climatically incompatible species.
( 3 ) A method has been devised using the modern distributions of the steno- thermic species in these faunas to analyse the type of climate acceptable to each of the assemblages of Coleoptera at Four Ashes. This method, in com- bination with the distribution of the Carabidae in the vegetational zones, has shown that several climatic fluctuations occurred during the deposition of the gravel sequence. Radiocarbon dating has helped to provide a chronolo- gical framework for these different climatic periods which are as follows:
(a) An interglacial period (probably Ipswichian) when such plants as Zfex and Alnus were present. (This interpretation was based wholly on the botanical evidence, since only a sparse insect assemblage was recovered).
(b) An early Devensian phase when the Coleoptera indicate the presence of Pinus, Picea and Betulu in the area. The average July temperatures are estimated to have been 14 "-16 "C and the climatic regime of moderate continentality. The deposits of this period have been correlated with the Brcarup Interstadial.
(c) An early cold episode prior to 43,000 years B.P. when the climate became more conti- nental and the July temperature dropped to around 10 "C. The fauna of this age is domi- nated by a crustacean Lepidurus arcticus and the majority of Coleoptera are arctic stenotherms This colder period may have been before the Brcarup Interstadial, but it is more likely that it occurred afterwards and was the main factor responsible for the elimination of the trees from the Midlands and probably from Britain.
(d) An amelioration leading to a relatively warm episode around 40,000 years B.P. During this period all the northern and more continental species, which had been present in the earlier cold phase, were eliminated and more thermophilous species became established. The July average temperature probably reached 15 "-16 "C. The climate became less continental, although the winters may still have been moderately cold.
( e ) Another cold phase from 36,000 years B.P. until at least 30,000 years B.P. when the climate again became more continental and the average July temperatures were perhaps depressed to around 10 "C. There was an elimination of the thermophilous species and a return of the arctic stenotherms. The absence of dates later than 30,000 years B.P. at Four Ashes may indicate the imposition of polar desert conditions preceding the maximum advance of the Irish Sea ice.
(4) Despite the apparently climatically favourable period around 42,000 years B.P. the landscape remained open and treeless.
(5) Although the landscape remained devoid of trees throughout the Middle Devensian at Four Ashes there were fluctuations in the proportions of phytophagous species. During the warmer episodes the phytophages were relatively more numerous than in the colder periods. These changes are thought to have been due to climatic factors, rather than to the availability of food plants.
(6) This examination of a number of fossil insect assemblages from Four Ashes has shown conclusively for the first time the existence of several climatic fluctuations during the Early and Middle Devensian within a re- stricted geographical area.
204 Anne Morgan
Acknowledgements. - I would like to thank Dr. G. R. Coope and Mr. P. J. Osborne for their constant advicc throughout this project, and Professor F. W. Shotton and Dr. G. R. Coope for reading the manuscript. I am also grateful for the repeated access to the collec- tions allowed to me at the British Museum of Natural History, and the generous loan of specimens from the Zoological Institute in Lund. In particular, I would like to thank the people who have helped me with insect identifications: Dr. R. Angus (Helophorus), Dr. M. Campbell (Micropeplus), Mr. P Hammond (Staphylinidae), Professor C. Lindroth (Carabidae) and Mr. R. Thompson (Curculionidae). Finally I wish to thank my husband, who collected most of the samples and helped me with the preparation of the diagrams and photographic plates.
A P P E N D I X 1
The nomenclature in the faunal list that follows is taken mainly from Hansen et al. (1960), supplemented where necessary by Kloet & Hincks(l945).Where there is more than one species of a particular genus, they are listed alphabetically, The sampling localities are arranged in Faunal Groups 1, 2, and 3 (which are explained in the text) to show boththesimilarityof species content within one group and how each group differs. The numbers represent the minimum number of individuals, based on the maximum of heads, pronota of elytra. The detailed records of these skeletal parts are kept in the Geology Department at the Univer- sity of Birmingham.
* Aphodius sp. A has recently been identified as a Tibetan species, Aphodius holdereri Reitter (Coope 1973 in Nature 245 (5424), 335-336).
A P P E N D I X 2
Notes on the interglacial site a t Four Ashes (locality 44)
The description of locality 44 has been excluded from the main part of the paper mainly because the insect fauna was so meagre that it precluded any
Late Pleistocene environment and insects 209
climatic interpretations being based on it. However, preliminary analyses of the plant fossils by the author and others, have indicated that this siteis of interest and as such it is described in this appendix.
Despite the fact that large quantities (21 kg) of this organic material were washed and sorted, only a few poorly preserved insect remains were recov- ered. The identified fragments are listed here as a record, although they tell very little about the environmental history of the deposit. Bembidion sp. . . . . . . . . . . . . . . . . . . . . . . . . . . l head Hydrophilidae gen indet . . . . . . . . . . . . . . . . . elytral fragments Lathrobium sp ........................ . 2 heads Limnius sp ............................ 2 heads
The most interesting finds from this site include the wood and some of the plant macrofossils. T h e pieces of wood were commonly about 30 cm in length and 15 cm in diameter. Some of the smaller pieces were sectioned and examined by Miss Allison Loader of the Botany School, Cambridge. She found that there were at least two types of wood present, one of which was definitely Alnus and the other probably Taxus (pers. comm. 1969). The presence of Alnus and Taxus wood was also later confirmed by Miss Ann Conolly at the University of Leicester (pers. comm. 1970). She noted that some of the Taxus were ‘odd’, but she thought this was probablydueto them being twigs.
Also present in the organic material were large numbers of complete Alnus cones and well preserved leaves and fruit stones of Ilex. Since these seemed important finds, some of the plant remains were sent to Mrs. G. Wilson of the Botany School, Cambridge. The following taxa were identified and according to Mrs. Wilson (pers. comm. 1969) they form a temperate fen-wood assemblage.
A preliminary pollen sample was also prepared, and a brief examination by Dr. W. Zagwijn revealed that Alnus and Quercus grains were predominant, with some Pinus, Polypodium, Typlza and Betula.
Such an assemblage of plants almost certainly indicates that interglacial conditions existed in the Four Ashes area prior to the deposition of the Devensian gravels. There is a possibility that this interglacial material may have been derived from elsewhere upstream and re-deposited during Early Devensian times. However, the presence of well preserved holly leaves would tend to preclude this. It is hoped that a future study of the pollen and plant remains from this particular site will help to elucidate the very early environmental history of the Four Ashes region.
2 10 Anne Morgan
R E F E R E N C E S
Andersen, S. T. 1961 : Vegetation in the Early Weichselian Glacial (Last Glacial). Danm. Geol. Unders. Ser. 2 , 75, 1-175.
Andersen, S. T . de Vries, H. & Zagwijn, W. H. 1957: New investigations of interglacial fresh-water deposits in Jutland : A preliminary report. Eiszeitalter und Gegenwart 8 ,
Angus, R. B. 1970: A revision of the beetles of the genus Helophorus F. (Col. Hydrophilidae) subgenera Orphelophorus d'orchymont, Gephelophorus Sharp and Meghelophorus Kuwert. Acta 2001. Fenn. 129, 62 pp.
181-186.
Balfour-Browne, F. 1940, 1950, 1958: British Water Beetles 1, 2, 3. Ray SOC, London. Balthasar, V. 1963-1964: Monographie der Scarabaeidae und Aphodiidae der Pa1aearktische:z
Orientalischen Region, 1 ,2 ,3 . Prague, Tschechoslowakische Akademie der Wissenschaften. Bevan, D. 1962: Pine Shoot Beetles. Forestry Commission leaflet 3. Britton, E. B. 1956: Scarabaeoidae. Handbooks for the Identification of British Insects, V.
pt. 11. London: Roy. Ent. SOC. Clapham, A. R., Tutin, T. G. & Warburg, E. F. 1962: Flora of the British Isles. 2nd ed.
Cambridge University Press. Cloudsley-Thompson, J. L. 1952 : Microclimates and the distribution of terrestrial arthro-
pods. Ann. Rev. Ent. 7,.199-222. Colhoun, E. A., Dickson, J. H., McCabe, A. M. & Shotton, F. W. 1972: A Middle Mid-
landian freshwater series at Derryvree, Maguiresbridge, County Fermanagh, Northern Ireland. Proc. R. SOL. Lond. B 180, 273-292.
Cook, W. C. 1929: A bioclimatic zonation for studying the economic distribution of injurious insects. Ecol. 10, 282-293.
Coope, G. R. 1959: A Late Pleistocene insect fauna from Chelford, Cheshire. Proc. R. SOC. Lond. B 151, 70-86.
Coope, G. R. 1962: A Pleistocene coleopterous fauna with arctic affinities from Fladbury, Worcestershire. Q. Jl . Geol. Soc. Lond. 118, 103-123.
Coope, G. R. 1967 : The value of Quaternary insect faunss in the interpretation of ancient ecology and climate. In Quaternary Paleoecology, 359-380, ed. E. J. Cushing and H. E. Wright. Yale University Press.
Coope, G. R. 1968a: An insect fauna from Mid-Weichselian deposits at Brandon, War- wickshire. Phil. Trans. Roy. Soc. Lond. B 254, 425-456.
Coope, G. R. 1968b: Insect remains from Mid-Weichselian deposits at Peelo, Netherlands. Mededel. Rijks Geol. Dienst. 20, 1-5.
Coope, G. R. 1970: Interpretations of Quaternary insect fossils. Ann. Rev. Ent. 15, 97-120. Coope, G. R., Morgan, Anne & Osborne, P. J. 1971: Fossil Coleoptera as indicators of
climatic fluctuation during the last glaciation in Britain. Palaeogeography, Palaeoclima- tology, Palaeoecology 10, 87-101.
Coope, G. R. & Sands, C. H. S. 1966: Insect faunas of the last glaciation from the Tame Valley, Warwickshire. Proc. R. Soc. Lond. B 165, 389-412.
Coope, G. R., Shotton, F. W. & Strachan, I. 9161 : A Late Pleistocene fauna and flora from Upton Warren, Worcestershire. Phil. Trans. Roy. Soc. Lond. B 244, 379-421.
Danilevskii, A. S. 1965: Photoperiodism and Seasonal Development of Insects. 283 pp. Oliver and Boyd, Edinburgh and London.
Danilevskii, A. S., Goryshin, N. I. & Tyschenko, V. P. 1970: Biological rhythms in ter- restrial arthropods. Ann. Rev. Ent. 15, 201-244.
Downes, J. A. 1962: What is an arctic insect? Can. Ent. 94, 143-162. Downes, J. A. 1964: Arctic insects and their environment. Can. Ent. 96, 279-307. Downes, J . A. 1965: Adaptations of insects in the arctic. Ann. Rev. Ent. 10, 257-274. Duffy, E. A. J. 1953: Scolytidae and Platypodidae. Handbooks for the Idzntificatiox of
British Insects, V, 15. London: Roy. Ent. SOC. Emiliani, C. 1966 : Paleotemperature analysis of Caribbean Cores P6301-8 and P6301-9
and a generalised temperature curve for the past 425,000 years. J. Geol. 73, 109-124. Fowler, W. W. 1887-1891 : The Coleoptera of the British Islands. 1, 2, 3, 4 , 5. London: Reeve
and Co. Freude, H., Harde, K. W. & Lohse, G. A. 1964: Die Kufer Mitteleuropas. 1. Krefeld:
Goecke and Evers.
Late Pleistocene environment and insects 21 1
Greenslade, P. J. 1968 : Habitat and altitude distribution of Carabidae (Coleoptera) in Argyll, Scotland. Trans. R. Ent. SOC. Lond. 120, 39-54.
van der Hammen, T. Maarleueld, G. C., Vogel, J. C. & Zagwijn, W. H. 1967: Stratigraphy, climatic succession and radiocarbon dating of the Last Glacial in the Netherlands. Geol. Mijnbouw. 46, 79-95.
Hansen, V., Klefbeck, E., Sjoberg, O., Stenius, G. & Strand, A., revised by Lindroth, C . H. 1960 : Catalogus Coleopterorum Fennoscandiae et Duniae. Entomologiska Sallskapet, Lund.
Henson, W. R. & Shepherd, R. F. 1952: The effects of radiation on the habitat tempera- tures of the lodgepole needle miner, Recurvaria miller : Busk (Gelechiidae : Lepidoptera). Can. Jl. Zool. 30, 144-153.
Hoffman, A. 1950, 1954, 1958: Colioptires Curculionides: Fauna de France. 52, 59, 62. Paris : Lechevalier.
Iversen, J. 1944: Viscum, Hedera and Ilex as climate indicators. Geol. Foren. Forh. Stock- holm 66, 463-483.
Jeannel, R. 1941, 1943, 1949: Colioptires Carabiques: Fauna de France 39, 40, 51. Paris: Lechevalier.
Jessen, A. & Milthers, V. 1928 : Stratigraphical and paleontological studies of interglacial fresh-water deposits in Jutland and northwest Germany. Danm. Geol. Unders. Ser. ZZ 48, Copenhagen.
Joy, N. H. 1932: A Practical Handbook of British Beetles. 1, 2. Edinburgh: H. F. and G. Witherby.
Kloet, G. S. & Hincks, W. D 1945: A Check List of British Insects. Stockport: Kloet and Hincks.
Lindroth, C. H. 1944, 1945, 1949 : Die fennoscandischen Carabidae. Eine tiergeographische Studie. 1, 2, 3. Goteborgs K. Vetensk. Vitterh. Samh. Handl. ( 6 ) , Ser. B , 4.
Lindroth, C. H. 1961, 1963, 1966, 1968, 1969: The Ground Beetles of Canada and Alaska. Entomologiska Sallskapet, Lund.
Mani, M. S. 1962: Introduction to High Altitude Entomology. London: Methuen. Messenger, P. S. 19.58: Bioclimatic studies with insects. Ann. Rev. Ent. 4, 183-206. Mitchell, G. F. 1957: Late-glacial finds of Lepidurus arcticus (Pallas) in the British Isles.
Morgan, Anne 1969: A Pleistocene fauna and flora from Great Billing, Northamptonshire,
Morgan, Anne 1970: Weichselian Insect Faunas of the English Midlands. Unpublished Ph.
Morgan, A. V. 1973: The Pleistocene geology of the area north and west of Wolverhampton,
Oldfield, F. 1964: Late-Quaternary deposits at Le Moura, Biarritze, southwest France.
Osborne, P. J. 1972: Insect faunas of Late Devensian and Flandrian age from Church
Pepper, J. H. 1938: The effect of certain climatic factors on the distribution of the beet
Pope, R. D. 1953 : Coccinellidae and Sphindidae. Handbooks ,for the IdentiJication of British
Portevin, G. 1929, 1931, 1935: Histoire naturelle des Colioptires de France. 1, 2 , 3. Paris:
Predtentchenskii, S. A. 1928: [Locustu migratoriu L. in central Russia. Rep. Bur. Appl.
Reitter, E. 1908-1916: Fauna Germanica. Die Kafer des Deutschen Reiches. 1-4, Stuttgart:
Rosholt, J. N., Emiliani, C., Geiss, J . , Koczy, F. F. & Wangersky, P. J. 1961: Absolute
Rudinsky, J. A. 1962: Ecology of Scolytidae. Ann. Rev. Ent. 7 , 327-348. Sands, C . H. S. 1964: Coleopterous Faunas from Late Pleistocene Deposits of the Tame Valley,
Warwickshire. Unpublished Ph. D. thesis, University of Birmingham. Shotton, F. W., Blundell, D. J. & Williams, R. E. G. 1968: Birmingham University radio-
carbon dates 11. Radiocarbon 10 ( 2 ) , 200-206.
Nature 180 (4584), 513.
England. Opusc. Ent. 34, 109-129.
D. thesis, University of Birmingham.
Staffordshire, England. Phil. Trans. Roy. SOC. Lond. B 265, 233-297.
New Phytol. 63, 374-409.
Stretton, Shropshire. Phil. Trans. R. SOC. Lond. B 263, 327-367.
webworm Loxostege sticticallis L. I. North America. Ecology 19, 565.
Insects, V , p t . 7, London: Roy. Ent. SOC.
Lechevalier.
Ent. Leningrad. 3, 113-199.1 (cited from Uvarov, 1931).
Lutz.
dating of deep-sea cores by the Paz3'/ThZ30 method. J . Geol. 69, 162-185.
2 12 Anne Morgan
Shotton, F. W., Blundell, D. J. & Williams, R. E. G. 1970: Birmingham University radio-
Shotton, F. W. & Williams, R. E. G. 1971: Birmingham University radiocarbon date V.
Simpson, I. M. & West, R. G. 1958: On the stratigraphy and palaeobotany of a Late Plei-
Smith, R. F. 1954: The importance of the microenvironment in insect ecology. r. Econ.
Strand, A. 1946 : Nord-Norges Coleoptera. Trornsa Mus. Arsh. (Naturhist. A v d . ) 67, 1-629. Thompson, R. T. 1958: Phalacridae. Handbooks for the Identification of British Insects.
Tottenham, C. E. 1954: Staphylinidae. Handboks for the Identification of British Insects.
Uvarov, B. P. 1931: Insects and climate. Trans. Ent. SOC. Lond. 79, 1-232. Vogel, J. C. & van der Hammen, T. 1967: The Denekamp and Paudorf Interstadials.
Vogel, J. C. & Zagwijn, W. H. 1967: Groningen radiocarbon dates VI. Radiocarbon. 9,
carbon dates IV. Radiocarbon 12 ( 2 ) , 385-399.
Radiocarbon 13 (2) , 141-156.
stocene organic deposit at Chelford, Cheshire. New Phytol. 57, 239-250.
