Writhlington Geological Nature Reserve

Writhlington Geological Nature Reserve

Ed A. Jarzembowski

JARZEMBOWSKI, E. A. 1989. Writhlington Geological Nature Reserve. Proc. .Ge~l. Ass ..100(2), 219-34. The first comprehensive account is given of this ~opular fOSSIl site nearRadstock in Avon, formerly a colliery tip and now a temporary geological n~ture r~serve. Thehistory and geology of the tipped material (Upper Carbonifer~)Us: ~estphahan D) ,IS expl~re.d

and the significant fauna (dominated by terrestrial arthropods including insects and spiders') ISinterpreted.

Booth Museum of Natural History, Dyke Road, Brighton. BN] 5AA

1. INTRODUCTION

Writhlington is a village, divided into an Upper andLower portion, 1.5 km east of the town of Radstock inCounty Avon (formerly Somerset). Situated in thevalley of the Wellow Brook (Fig. 1), Lo~er

Writhlington was the site of one of the last workingcoal mines in the Bristol-Somerset Coalfield. Afterclosure in 1973, the colliery spoil heap or tip (nationalgrid reference ST 703553) continued to be awell-known haunt for palaeobotanists and othercollectors seeking plant compression fossils for whichit is internationally renowned (Prof. W. G. ChalonerF.R.S., pers. comm.). However, special interest inthe site developed in 1984 when reclamation work (forcoal) revealed that there was also a hith~rto

unrecognised fauna of land arthropods, especIaI.lyinsects. Speedy action was needed to collect fossilsbecause the rock, which had taken over 140 years toaccumulate, was due to be reworked and landscapedwithin a year or so ( Jarzembowski, 1985a). Thanks. tothe enthusiastic help of numerous volunteers workingweekends, the largest collection of British Carboniferous insects was assembled as well as otherinteresting fossils. Writhlington Geological NatureReserve (W. G. N. R.) was created.incorporati~g arock store (Fig. 1) to allow collecting to contmuewhen reclamation work ceased. This article is the firstcomprehensive account of the finds fr~m the salvageoperation and wor~ on the ~eserve until Augus~ 1988;it is perhaps fitting that it should appear m thecentennial volume of the Association's Proceedingssince the G.A. has provided financial support for theconservation and documentation of the site andmoreover much of the collecting has been done byamateur geologists: the success of the project is atribute to their efforts.

2. GENERAL GEOLOGY

The hills around Writhlington are carved in gentlyinclined early Mesozoic rocks which rest disconformably on a buried, eroded surface of folded andfaulted Palaeozoic strata) Welch, Crookall & Kell-

away, 1948; Welch, Kellaway, Green, Trotter, Lawrie& Pocock, 1962; Williams & Chapman, 1986).Coal-bearing deposits of Upper Carboniferous ~ge

occupy a synclinal basin around Radst.ock, Wnthlington lying in the eastern part of the basin (Moore &Trueman, 1939). In 1829, a colliery shaft was sunk atLower Writhlington in the valley bottom where theMesozoic cover is thinnest. As in other parts of thebasin the shallower coals of the Radstock Formationwere' worked first (Fig. 2). Shortly after 1894, theshaft was extended down through the Barren Redbeds to coals of the Farrington Formation (Down &Warrington, [1971]). Both coal-bearing formationswere worked during the first quarter of this century,but by 1960 only one seam (No. 10 in Farrington) wasworked, some 0.5 km underground, and this continued until closure (Allen, 1977). The galleries wereextensive, linking up with Kilmersdon Colliery 1 kmsouth of Radstock. So much spoil was tipped thatplant fossils collected on the surface of both tips afterclosure were generally attributable to the 'roof shales'(mudstones) overlying the No. 1~ co~1 (Allen, 197.1).Reclamation work changed the situation by exposmgearlier tipping. However, at Writhlington it is likelythat only material from the lower part of theFarrington Formation has survived because the centreof the tip is red and oxidised. The old tipped materialappears to have been burnt out by early World Wa~ II(Station Officer T. J. Coles, pers. comm) by. whichtime only this formation was worked, but dunng thewinter of 1984/5 steam could be seen rising fromfreshly exhumed grey mudstones showing thatcombustion had not ceased. Coal seams other thanNos. 5, 6 and 10 had been finally abandoned here by1949, most of them as early as 1911, and their spoilwas thus liable to have been destroyed. Two otherconsiderations suggest that the arthropod faunadescribed below is from the roof of No. 10 seam.Firstly, comparable horseshoe crabs and a trigonotarbid have been described from above the laterallyequivalent No.9 seam at Kilmersdon (Ambrose &Romano, 1972). Secondly, during reclamation work atKilmersdon tip the author found other landarthropods (a phalangiotarbid, protorthopteran and

219

220 E . A . JARZEMBOWSKr

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Peasedown

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Fig. 1. Sketch maps to show location of (A) Writhlington Geological Nature Reserve and (B) the rock store (broad arrow) .

several cockroaches) particularly in a Cyperites-richlithology which is so abundant at Writhlington (seebelow). These finds are consistent with the No. 10coal having been much worked latterly at bothlocalities (Allen, 1977). However, irrespective of theexact horizon, all the Writhlington coals belong to theWestphalian D stage of the Upper Carboniferous(Ramsbottom, Calver, Eagar, Hodson, Holliday,Stubblefield & Wilson, 1978). By elimination, thearthropod fauna could be from the middleWestphalian D of Cleal (1985), approximately 306.5million years Before Present (Leeder, 1988).

British Coal (South Wales Area) records show thatthe Farrington coals vary in average thickness from0.46 m (Rock Vein) to about 0.84 m (No.6 and No.10 seams) , the latter often subdivided by partings ofmainly inorganic sediment or mineral matter (ironcarbonate). The coals are underlain by seat-earth(fireclay) and roofed by mudstone which may coarsenin grain size and contain plant debris . Theunderground workings were over a wide area , butonly a small thickness of sediment would have beenexcavated to win the coal, at most one to two metresover seams and two to three metres in roadways (Mr.K. R. Doonan (Reading) , pers. comm.), The tippedmaterial therefore represents large but thin slices ofstrata. The animal fossils occur almost invariably in agrey, laminated mudstone. The fossiliferous blockscan be divided into three slightly overlapping'sublithologies' (Mr . J . A. Todd (Chichester) , pers.comm.). The Cyperites-rich sublithology is the mostimportant for land arthropods and is characterised by

numerous grass-like leaves of arborescent lycopods(giant c1ubmosses) . (When uncompressed , the leavesare actually 'butterfty'-shaped (Rex , 1986) and suchcross-sections may be seen sometimes where themudstone has been well impregnated with ironcarbonate). The leaves usually criss-cross the beddingplanes, but are occasionally current-aligned, and areoften associated with isolated lycopod sporophylls(fertile leaves) and sometimes cones.

3. COLLECI1NG mSTORY

There have been a number of G. A. excursions to theRadstock area but these were mainly to examine thelate Triassic-early Jurassic strata e.g. at WrithlingtonQuarry (Sollas, 1880; Richardson, 1910; Tutcher,1919, 1929). The Liassic exposures have beensummarised recently by Donovan & Kellaway (1984).Allen (1977) gave checklists of Carboniferous plantsthat may be collected around Radstock (includingLower Writhlington) of which many may be identifiedusing keys in Chaloner & Collinson (1975). Bolton(1911) described some bivalves from the Upper CoalMeasures of Writhlington whilst commenting that,unlike plants, animal remains are scarce in theBristol-Somerset Coalfield.

In his summary of Carboniferous insects, Wallis(1938) mentioned only two as having come from theRadstock area and none from Lower Writhlington. Inthe British Museum (Natural History) there are twospecimens from the latter locality, incomplete wings ofa cockroach (In . 64587) and protorthopteran (In .

WRITHLINGTON GEOLOGICAL NATURE RESERVE 221

RADSTOCK

BARRENRED

FARRINGTON

Great

Middle

SlyvingUnder LittleBull

mo

100

Rock

5/Middle

6/Deep Middle

10(=8,9)

W.G.N.R. is 12 in one block). At the G.A. AnnualReunion in 1984, the West Sussex Geological Society(W.S.G.S.) reported that the formerly derelict tip wasbeing speedily reworked for coal and seemed worthinvestigating, especially as the protorthopteran findwas unusual (Flitton, 1984). A preliminaryinvestigation by the author after the reunion yieldedmore insects than had hitherto been found there(Jarzembowski, 1988); in the meantime, W.S.G.S.and the Harrow & Hillingdon Geological Societyoffered help with searching this large site. Otherorganisations soon joined in (see acknowledgements)and Mr. Peter Austen (Seaford) kindly assumed therole of hon. field secretary. By the G.A. AnnualReunion in 1985, more Carboniferous insect fossilshad been recovered from the tip than had hithertobeen found in the U.K. (Jarzembowski, 1986). Thepalaeoentomological interest was supplemented bythe discovery of other arthropods plus manywell-preserved plant compression fossils of which Mr.Austen has the largest collection. In the meantime,reclamation work had slowed down due to externaleconomic factors and it was now possible to take stockof the situation. The tipped material consisted ofmudstone blocks of variable size and hardness set in amixture of debris, shale and slurry. In addition, therewere small amounts of coal and sandstone, a few smallironstone nodules and remains of recent industrialarchaeology including pine pit props, miningmetalwork and blocks of local limestone evidentlyfrom former colliery buildings. The reprocessingincluded size sorting of material and the harder, largerblocks were separated first and stock-piled for use asroad metal. Like the smaller pieces, these blocks werefossiliferous; they also had the advantage of enclosinglarger areas of bedding plane and were more resistantto weathering. With the financial backing of the G.A.and legal!conservation expertise of the West LondonWildlife Group (W.L.W.G.), 3000 tons of thismaterial were purchased. When reclamation workfinished, the blocks were relocated on site in areserved area on the S.E. side of the tip. WrithlingtonGeological Nature Reserve was thus established in1987, enabling the collecting to be extended for afive-year period.

Fig. 2. Section of Lower Writhlington Colliery showing coalsworked. Left: Formations; right: coal veins (named) andseams (numbered). Stippled: Triassic (Keuper Marl). Basedon abandoned mines information, British Coal andRamsbottom et al., 1978.

64605) presented by Dr. Andrew Scott (LondonUniversity) and Mr. Harry Woolgar (Shoreham) in1979 and 1982 respectively. These were consideredfortunate chance finds because of the general scarcityof insects in the British Coal Measures. (My average isbetween one and two a day; the all time record at

4. THE FAUNA

Depositories of figured and cited material areindicated thus: LL, Manchester Museum; R, BritishMuseum (Natural History); 0148-, Booth Museum ofNatural History; followed by specimen number andcollector's name. All specimens are from W.G.N.R.unless otherwise indicated.

(a) MoUuscs (Fig. 3)

These are uncommon at Lower Writhlington andrepresented by non-marine bivalves belonging to the

222 E. A. JARZEMBOWSKI

Fig. 3. Anthraconauta tenuis (Davies & Trueman) . A well preserved specimen lacking only a small part of the antero-ventralmargin (LL. 7986. Jim Greenwood) .

Fig. 4. Cochlichnus trace (014871. K. W. Abineri) mm scale divisions.


genera Anthraconaia and Anthraconauta which havebeen studied in detail (Dr R. M. C. Eagar(Knaresborough) pers. comm.). They are associatedoccasionally with Cyperites and Insecta.

(b) Nematodes (Fig. 4)

These are represented by sinuous trace fossilsbelonging to the ichnogenus Cochlichnus andconsidered to be the locomotion/feeding trails ofnematodes (round worms) (Dr. P. G. Hardy (BristolUniversity) & Dr J. E. Pollard (ManchesterUniversity) pers. comm .).

Cochlichnus may be associated occasionally withKouphichnium, Arachnida and Insecta (see below)although there is no evidence to suggest a feedingrelationship.

(c) Arthropods

(i) Merostomes (Figs. 5 & 6)These comprise body and trace fossils of horseshoecrabs (xiphosurids, xiphosurans or limulids). Nobodies have been found associated with tracesalthough the latter show telson (tail) and 'pusher'(appendage) imprints as in typical limulid trackways(Drs. Hardy & Pollard, pers. comm.). The longgrooves , representing the drag marks of telsons, aresometimes interrupted suggesting temporary lift of theanimal; the 'pushers' (on the fifth pair of feet) oftenshow as few as two good blade imprints giving a

Fig. 5. Euproops prosoma-opisthosoma (014865, SueBallard) , mm scale divisions.

distinctive inverted-V shaped track (Fig . 6). In thefigured specimen there are two track ways and theanimal(s) 'walked' from bottom right to top left.

No body fossils have been found yet with the telsonintact as described by Ambrose & Romano (1972)from Kilmersdon but one example (014858, J. A.Todd) is enrolled, i.e. with the opisthosoma(hindbody) flexed under the prosoma (carapace). Thewalking traces (Kouphichnium) are usually in'unfossiliferous' blocks except for the occasionallycopod leaf but may be associated with otherichnofossils including Pelecypodichnus (see below)and Cochlichnus. Body fossils (Euproops) may beassociated with insects; the former include E.kilmersdonensis Ambrose & Romano (Mr. S. F.Morris, British Museum (Natural History), pers.comm.) although Fisher (1979) considers this speciesto be a possible synonym of E. danae (Meek &Worthen) .

(ii) Arachnids (Figs. 7 & 8)In order of decreasing frequency these are represented by Phalangiotarbida (=Architarbida), Trigonotarbida and Araneida. The first two are extinctorders and the last is the spiders. Phalangiotarbids aremost commonly preserved in dorsal aspect and thusshow some superficial resemblance to trilobites (Fig.7) . This order is represented by at least three generaof which Phalangiotarbus is most common (Mr. B.Beall (Field Museum of Natural History) pers.comm.). Trigonotarbida are represented byEophrynus, including E. jugatus described originallyfrom Kilmersdon (Ambrose & Romano, 1972). Thisgenus has a distinctly tuberculate dorsal aspect (Fig.8); the ornamentation obscures the basic segmentednature of the animal but some idea of the generalform may be obtained from British Museum (NaturalHistory) (1975: pI. 63, fig. 6). Araneida are knownonly from a single prosoma.

Arachnids (phalangiotarbids) may be found associated with Cyperites, insects and Cochlichnus.

(iii) Crustaceans (Figs. 9-11)Two classes are represented at W.G.N.R.: Ostracodaand Conchostraca. The former is known only fromsmall trace fossils belonging to an undescribedichnotaxon (Drs. Hardy & Pollard, pers. comm.) . Theostracod traces consist of resting marks andlocomotory/feeding trails, the former indicated bysmall pits and the latter by light grooves (Fig. 9). Thetraces may be associated with coprolites.

Conchostracans (clam shrimps, Fig. 11) arerepresented by occasional valves (carapaces , Fig. 10)which superficially resemble small bivalve molluscsand are sometimes fragmented. There are also smallburrows (Pelecypodichnus) which look like 'dimples'or 'pimples' on bedding surfaces and may be


Fig. 6. Xiphosurid trackways: Kouphichnium alJ. uariablis (Linck), (014879, author & Peter Austen). mm scale divisions.

associated with Kouphichnium and insects. Thepimples or casts can be quite numerous and mayappear bifid under a handlens. No body fossils havebeen found associated with the traces although theyagree with the work of Conchostraca in form and sizealthough small mollusc activity cannot be excluded(Drs. Hardy & Pollard, pers. comm.). Some dimplesand pimples are due to other causes e.g. rootlets.However, these are usually less rounded in shape andmay contain carbonaceous material.

(iv) Myriapods (Fig. 12)Giant millipedes (Arthropleura) are known atW.G.N.R. from a single rosette (leg) plate associatedwith Cyperites.

(v) Insects (Figs. 13-16)In order of decreasing frequency, they are Blattodea,Protorthoptera and Palaeodictyopteroidea. The insect

remains are carbonised, rarely pyritised and may beassociated with trace fossils, horseshoe crabs,phalangiotarbids, Conchostraca and Mollusca.

Blattodea (Cockroaches) are the most commoninsects and animals to be found at W.G.N.R. Theyare represented usually by detached wings, especiallyforewings, but bodies and body parts also occur,including those of the young stages (nymphs). Unlikein the Wealden (Jarzembowski, 1984) detached claviare uncommon suggesting faster burial of thecockroaches. Lutz (1984) showed that clavi (analareas) become separated from the rest of the forewingat an early stage of decay whilst the dead insect is stillfloating on the surface of a lake. The richly veinedinsect wings have a superficial resemblance to thedetached leaves (pinnules) of seed ferns (pteridosperms) and true ferns (pteridophytes) (Jarzembowski, 1985b; 1987). They can be distinguished usingthe four pointers in larzembowski (1988) of which the


Fig. 7. Phalangiotarbus alongside Cyperites (Length of body23 mm; 014846, Brigid Jarzembowski).

symmetry test has the widest application. (In general,leaves are bilaterally symmetrical about their longaxes, wings are not). Additional differences include:

-fossil wings generally appear smoother and'crisper' than compressed fossil pinnules;

-fossil wings often show a fine crenulation of theanterior wing margin (Bolton, 1933; fig. 8);

-fossil wings are rarely depressed down the middleand curled along the edge.Bodies are rare and the wings are often in the folded(rest) position (Fig. 14b). The most distinctive bodyparts are the rounded shield-like pronota (Fig. 14a).Preliminary sorting of the cockroach forewings hasbeen attempted using Carpenter's (1954) simplifiedclassification. The extinct families Archimylacridaeand Mylacridae are represented, the former predominating. The pronota of these two families differin shape (Bolton, 1921-22) and this is seen in theWrithlington material.

The nymphs comprise 4.25% of the cockroachremains. They are readily distinguished from the

adults by the postero-laterally directed wing pads(developing wings) which often show the beginningsof venation (Jarzembowski, 1987: fig. 3. The wingpads on this specimen (collected by Peter Austen)also clearly illustrate the slight distortion affecting'roof shale' specimens). Where the nymphal remainshave become completely dissociated, the wing padscan be clearly seen to be continuous with the thoracicterga (body wall), a form of development (heterometabolism) characteristic of living cockroaches (Schneider, 1984). Nymphal pronota are sometimes splitlongitudinally providing evidence of emergence. Afew nymphs show the remains of cerci (pairedposterior appendages) which are short in livingcockroaches (Fig. 16) but long and filamentous inCarboniferous species (Handlirsch, 1906-08: pI. 18).

The Protorthoptera are of historic interest becauseit was their discovery that led to the investigation ofthe site and subsequent finds (section 3). Protorthoptera are possibly polyphyletic and the least satisfactorily defined of the extinct insect orders. TheWrithlington material includes a body with foldedwings and a nymphal wing pad provisionally attributedto this group. Palaeodictyopteroids are scarce andrepresented by some isolated wing remains of theextinct orders Palaeodictyoptera and Megasecoptera.

(d) Vertebrates (Figs. 17 & 18)

Vertebrate remains are uncommon at W.G.N.R.Bolton (1911) recorded a fish scale from shalesassociated with the Rock Vein at the top of theFarrington Formation. No vertebrate body fossilshave been found during the course of this work and,as discussed above, the shale examined by Bolton hasprobably been long burnt out on the tip. However,cartilaginous fish are evidently represented by eggcases (Palaeoxyris, Fig. 17). These fossils are stillconsidered to be problematical by some people (e.g.Thackray, 1984) but have been comprehensivelystudied by Mueller (1978) who favoured a piscineorigin. Tetrapods (reptiles and amphibians) arerepresented by an isolated footprint (Fig. 18; Milner,in prep.).

(e) Coprolites and ?chew marks

A few bedding planes have been found strewn withflattened carbonaceous cylinders some 4 x 1 mm andinterpreted as coprolites (Drs. Hardy & Pollard, pers.comm.). They may be associated with insects andostracod traces but are too large to be the product ofeither.

Fossil leaves, especially of the pteridosperm (seedfern) Neuropteris are often found with irregularlydamaged margins. The majority of these can beattributed to breakage during collection or prior toburial, but a few might belong to Phagophytichnus


Fig. 8. Eophrynus opisthosoma showing dorsal (tuberculate) and ventral (segmented) detail (014882 W. Stedman). mm scaledivisions.

Fig. 9. Ostracod trails and ovoid resting traces preserved as ridges (hypichnia). (014880, author). Actual size of beddingsurface 41 x 24 mm.


Fig. 10. Anomalonema carapace between Cyperites (014869, author). mm scale divisions.

Fig. 11. General habitus (form) of Recent conchostracanshowing internal soft parts. Actual size of carapace5x8.5mm.

Fig. 12. Leg (rosette) plate of Arthropleura (014847, JohnAllen). mm scale divisions.


Fig. 13. Wings and part of body Blattodea: Mylacridae (014844, J. A. Todd). Maximum width of left forewing 10 mm.

van Ameron 1966, an ichnogenus considered torepresent the feeding activity of insects.

5. DISCUSSION

During Upper Carboniferous times the AtlanticOcean had not yet formed and the Radstock Basinwould have been part of the Euramericanpalaeoequatorial belt. The non-marine Upper Carboniferous is typically portrayed as a forested lowlandcoal swamp environment. However, peat accumulation at Lower Writhlington had ceased and the futurecoal was submerged beneath mud-laden waters beforethe fossil biota (plants and animals) was entombed.That burial was quick, is suggested by some plantdebris lying at an angle to the bedding and,moreover, by the occurrence of lycopod stumpspreserved 'in the round'. The stumpssometimes showevidence of original horizontal bedding and evencompression parallel to the long axis indicating anupright position at burial. (A good example of a

lycopod stump from W.G.N.R. is in the SomersetCounty Museum, Taunton). Some of the biota fromthe 'roof shales' could therefore represent the remainsof one or more buried forests. Other organisms couldhave been transported from adjacent environmentsalong with the sediment. In addition, theinundation(s) would have created new habitats forvarious organisms, some of which left their traces inthe mud. The rotted, hollow lycopod stumps couldhave provided homes or traps for some animals as inNova Scotia (Ferguson, 1988). However, the stumpshave only yielded plant debris at W.G.N.R., althoughfew have been sampled so far because the mudstoneinfill is commonly cemented with iron carbonate andvery hard.

The terrestrial arthropods at Writhlington, especially Blattodea and Arachnida, tend to occur withlycopod litter (leaves, cones, sporophylls) althoughthe Protorthoptera are also found in other bioticassociations (Mr. Todd, pers. cornm.), The commonlycopod in the 'shales' is Lepidodendron and Sigillaria


Fig. 14. Blattodea: Mylacridae with wings folded in rest position (B) and pronotum (A) separated a short distance from therest of the body (014845 (B), Tony Nevard). Length of pronotum 5.5 mm, body 15 mm.

is rare (Mr. Austen, pers. comm.) which suggests thatthe trees grew in a damp swamp by comparison withthe early Pennsylvanian (early Westphalian) ofAlabama (Gastaldo, 1987). Evidence is growing thatpteridosperms and pteridophytes preferred elevated,drier habitats on the swamp margins (Gastaldo, fig. 2)and animals too were probably not uniformlydistributed in coal-forming basins as suggested by the

Fig. 15. Detached blattodean nymphal wing pad (014874,Joyce Austen). Maximum length 8 mm. See also Fig. 16.

frequency of various groups at W.G.N.R. (Fig. 19).Blattodea, Phalangiotarbida, Protorthoptera and Trigonotarbida are the most common taxa, suggestingthat they were well represented in the localcommunities although Protorthoptera could be amixture of local and marginal species. Blattodea andProtorthoptera specimens with folded wings show thatthese insects, at any rate, were not blown off coursewhilst in transit.

Phalangiotarbids are the most common arachnidswhich is broadly consistent with their presumedpreference for wet lycopod forests based on NorthAmerican occurrences (Mr. Beall, pers. comm.). Likeother terrestrial arthropods, Eophrynus specimensusually show some dissociation of body parts, but thepreservation of appendages (e.g. legs) as inphalangiotarbids suggests little transport. Blattodeaare by far the most dominant animals at Writhlingtonand are known from mature and immatureindividuals suggesting that they lived locally. Thefrequency of Blattodea is similar to the lateWestphalian coalfields of Pennsylvania where they canbe 90% of all insects found (Carpenter, 1980) and


Fig. 16. General habitus of Recent blattodean nymphshowing location of wing pad and associated body wall(shaded) for comparison with Fig. 15. (c, cercus). Actualbody length 25 mm.

evidently show a correspondingly high diversity(Richardson, 1956). The classical locality forWestphalian D insects is Mazon Creek, Illinois wherehowever, Protorthoptera are more diverse thanBlattodea, a situation tentatively attributed toenvironmental factors by Richardson. He consideredthat the Mazon Creek terrestrial fauna lived amongsta more open and better drained coastal vegetationdominated by large pteridosperms rather thanlycopods. Palaeodictyopteroids, mostly Palaeodictyoptera, are one of the most important insectgroups at Mazon Creek which is consistent with theavailability of pteridosperms as food (e.g. seereconstruction by Ponomarenko, 1980) rather thanRichardson's presumed aquatic habits of theseinsectsfor which there is no morphological evidence. Asmight be expected palaeodictyopteroids, includingPalaeodictyoptera, are rare at Writhlington. Otherrare terrestrial arthropods include Araneida whichgenerally have a poor fossil record (Selden, 1984).The great size of arthropleurids suggests that theywould have been represented by fewer individualsalthough they are considered to have inhabitedlycopod forests (Rolfe, 1985a). Protodonata (giantdragonflies) are conspicuous by their absence. Theseevocative insects are represented in the RadstockBasin by a solitary specimen found on the now

Fig. 17. Ridged fish egg capsule: Palaeoxyris (014849,author). Maximum width 6 mm.

landscaped Tyning tip (Bolton, 1914). Protodonataare equally scarce in the late Westphalian of NorthAmerica where only four specimens have been foundrepresenting the same number of species and all fromdifferent localities (Carpenter, 1980). Protodonatawere large insects, some of which were giants withconsiderable wingspans and were perhaps sporadicallyassociated with more open situations. Their absence at


Fig. 18. Outline of a tetrapod footprint preserved as apositive hypichnia (R.l1034, author). Actual size 63 x29mm.

W.G.N.R. cannot be attributed to size selection as theremains of large Palaeodictyoptera have been found .

By analogy with present day species, Blattodeawould have subsisted on a variety of plant and animalfoodstuffs including scavenging , whereas the extinctphalangiotarbids and trigonotarbids are considered tohave been predators (Mr. Beall , pers. comm.; Rolfe,1985b). It is interesting to note that , of the presumedforest dwellers , B1attodea are more common thanarachnids (Fig. 19) which is consistent with their likelylower position in the food chain . CarboniferousProtorthoptera included forms as diverse as specialised predators (Carpenter, 1971) and spore feeders(Scott & Taylor, 1983) perhaps reflecting theunnatural composition of this order. Outside theforest , and in the absence of flying vertebrates at thisperiod, Protodonata could have been the top aerialcarnivores, perhaps taking protorthopterans andspecialised plant-sucking palaeodictyopterans alongswamp margins such as levees (raised river banks).Direct evidence from the Radstock Basin thatProtorthoptera were involved in predation is suggested by the colour pattern preserved on theforewing of Narkeminopsis eddi from the formerKilmersdon colliery tip (Jarzembowski, 1988). Thetransverse banding on the wing suggests camouflage,an interpretation supported by a possible modelprovided by Cyperites. The shadows cast by the longnarrow leaves on an elongate object would have hadthe visual effect of breaking up its true outline andgiving it a banded appearance. Such a naturaldisruptive pattern displayed by a resting insect wouldhelp to conceal it. Arachnids too would have soughtconcealment and Lamont (1969) has proposed that thetuberculate appearance of the dorsal (upper) surface

of Eophrynus was 'droplet' camouflage i.e. thetubercles modelled water drops in damp Carboniferous forests. However, the tubercles formsymmetrical patterns in Eophrynus and the patternsshow subtle differences in the three known species(Brauckmann, Koch & Kemper, 1985). Furthermore,examination of vegetation after rain or in mist showsthat water droplets do not form symmetrical patternsand are soon shed by the waxy cuticle . 'Mimesis'(mimicry) therefore seems unlikely in this instancejust like supposed leaf mimicry in Blattodea(Jarzembowski, 1987). Another interesting suggestionis that the crenulation on Blattodea forewingsrepresents a stridularium (stridulatory file/soundproducing organ) (Durden, 1972). However, this isnot supported by crenulation on the hindwing too atWrithlington, a relatively fragile wing in life in anycase.

The bivalves and trace fossils suggest that themudstones at Writhlington were deposited in atemporary lake (Drs. Hardy, Pollard & Eagar , pers .comm.) but terrestrial organisms predominate overaquatic ones . This could be due to the thin 'roofshales' recording only the initial part of the inundationwhen much forest debris would have been availableas well as water-borne material. Rare roots (Stigmaria) and rootlets in the mudstones suggest that clastic(mud) swamp environments may overlie the 'roofshales '. The most common aquatic animals arexiphosurids which were probably scavengers byanalogy with Recent species (Barnes , 1968). It hasbeen suggested that fossil horseshoe crabs differedfrom their living relatives and lived in trees (Fisher ,1979) but the evidence from Writhlington(Kouphichnium) shows that the crabs frequentedmuddy lake bottoms. Euproops' aquatic habits arefurther supported by an enrolled example (section4(c)i) , a posture Fisher (1977) earlier interpreted as adefence reaction by a swimming crab encountering apredatory fish or amphibian. Such vertebrates areknown or suspected at Writhlington and otherinstances of quick burial (plant remains) are indicatedabove. Filter feeders (bivalves, conchostracans) areuncommon possibly due to sedimentation. Smallsurface detritus feeders evidently include ostracods(section 4(c) 3) and the presence of nematode wormsis of interest because they are abundant animals in soiland mud ecosystems at the present day . Most livingnon-marine round worms are less than a millimetrelong, although marine ones can reach 50 mm (Barnes,1968). The Writhlington finds include traces producedby individuals which were larger than living species ,e.g. 014881 (Joyce Austen) has an approximatewavelength of 65 mm! However, gigantism is knownin other Carboniferous animals such as certainarthropods and is therefore plausible in otherinvertebrates at this time. Thus the fossils fromW.G.N.R . not only provide some insight into Upper

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Carboniferous non-marine life at one locality but alsointo 'coal swamps' generally.

6. FUTURE WORK

W.G.N.R. was established on a temporary basis andmay have two years or less to run after theAssociation celebrates its centennial volume . It istherefore important that the 'rock store' continues tobe well used for research and education as well asgeneral collecting. Organised visits will be publishedin the Association 's Circular and further informationon the site, including access, can be obtained fromPeter Austen, 3 Bromley Road , Seaford , East Sussex,BN25 3ES, (please enclose large S.A.E. ).

In the longer term , many of the finds--especially

arthropods-s-will need to be described and figured asthey have added considerably to our knowledge of theBritish Carboniferous fauna. Work on bivalves,phalangiotarbids , trace fossils and animal/plantassociations is in hand and a Special Part of theProceedings is already being planned . The numerouscockroach remains will exercise the newer classifications by Durden (1969) and Schneider (1983) ofthis difficult but stratigraphically useful orde r. Mr.Todd (pers . comm. ) has recorded 16 plant generaassociated with animal remains, but the Austen'herbarium' is yet to be studied. Another interestingarea is that of plant/insect interaction in early times(Scott & Taylor , 1983). The abundant fossil plantsmight furnish more direct evidence on this elusivesubject, especially if animal activity can be


distinguished definitely from the vagaries offossilisation. A provisional picture of the palaeoenvironment has been sketched above but needsdeveloping and testing. And even if we don't find allthe answers, then, like many visitors to Writhlington,we shall have enjoyed the fun of the chase.

ACKNOWLEDGEMENTS

I am grateful to the above quoted workers andorganisations for information and assistance; toBurrows Bros Ltd. (Chesterfield) and Avon CountyCouncil for facilitating the establishment ofW.G.N.R.; to the Nature Conservancy Council forturning over the rock store; to Radstock Fire Stationfer combustion history; to the Royal Society andPalaeontological Association for financial assistance toW.L.W.G. towards leaflet production and conservation work respectively; to Dr. W. D. I. Rolfe (RoyalScottish Museum) for identifying Fig. 12; to Brigid

Jarzembowski for help with artwork; to Ms. J.Buckwell for typing the manuscript; to Harold Taylor(Liverpool) for photographic work; to the BritishGeological Survey (B.G.S.) and Geological Societyfor library facilities; and to members/staff/students ofthe following organisations for help with salvagecollecting: Essex Rock & Mineral Society; theAmateur, Bath, Brighton & Hove, Hertfordshire,Mole Valley, Open University, Reading, Sidcup andWest Sussex Geological Societies; the GeologischeKring Tellus; the Geologists' Association and LocalGroups (Brent, Essex, Farnham, Harrow & Hillingdon, South Wales, West of England); the OxfordGeological, Southampton Geological Field Study andWest London Wildlife Groups; the Medway andSouthampton Lapidary and Mineral Societies; theBath Geology, Bristol, British (Natural History) andSomerset County Museums; Nationwide GeologyClub; Bristol, London (Imperial and Royal Holloway& Bedford New Colleges) and Reading Universities.

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Writhlington Geological Nature Reserve