Dávid, Árpád

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DÁVID ÁRPÁDPALAEO-OECOLOGICAL AND PALAEO-PATHOLOGICAL OBSERVATIONS ON UPPER OLIGOCENE MOLLUSCS (EGER, HUNGARY)ABSTRACT: The most noteworthy geological exposure in North-Hungary can be found in Eger (Hungary). The Upper-Oligocenebeds in the claypit of the former "Wind" brickworks have anabundant fossil content.On the basis of scientific investigations of remains of molluscs,the author has made a series of palaeoecological andpalaeopathological observations. The quantity and preservation ofthe shells, the various forms of symbiosis, the bio-erosive activity ofcaustic sponges, the presence of Bryozoan-colonies, the traces ofboring-bivalves, the perforation-marks of predatory snails, cicactriescaused by crabs all refer to a former shallow-water marineenvironment.INTRODUCTIONA famous geological outcrop in North-Hungary can be foundin Eger, in a brickyard's clay-pit situated at the south-east part of thetown. The 120 m thick deposits are mentioned as the "Wind factory"beds in the special literature.Four stratigraphic units can be distinquished in this section: 1.Glauconitic-tufiltic sandstone and marl. 2. The glauconitic-tuffiticseries is overlain by Molluscan Clay. 3. Alternating beds ofsandstone and clay of shallow-sublittoral origin. 4. Series of littoraland lagoonal coarse sand and clay.33In associate with these layers, rich flora and fauna can be foundhere in a good preservation. The strata, that were deposited duringthe regression of the Upper Oligocene sea, through T. BÁLDI's andhis colleauges' activity got into the palaeontological literature as the"Egerian stage" (BÁLDI, T. 1973.)TREATMENT OF THE SUBJECTDuring the scientific investigations of the comparatively wellpreserved Molluscan fossils the author has won numerouspalaeoecological and palaeopathological observations /DAVID, A.1987., 1991/. The Molluscan remains had been collected mainlyfrom the "x" layer /Silty fine molluscan sand/ and the "k" layer/Limonitic friable sandstone/.Palaeoecological observations The fact that there are a lot of abraded, deficient, or brokenshells and valves among the collected remains indicates a seashoreenvironment. Owing to the surf, the shells of dead or living creatureswere knocked to each other and fell to pieces. In this case, the burialwas preceedcd by transportation. The embedding was allochtonous.The proximity of the shore is proved by the presence of plantremains, too.Dentalium simplex (Michelotti) remains belonging to theScaphopoda class also refer to an allochtonous embedding. They lieparallel with the laminae of the covering stone.After the animals' destruction, the tests must have been drifted intothe lower parts of the sublittoral zone by the streaming water. The author has collected shell-fishes in large quantities, whichwere embedded intact into the sand of the fonner bottom. It signsthat they were buried rapidly by the deposition of sand. The animals'decay was caused by the burial, or they were buried immediatelyafter their death at the place where they dwelt. I have studied thesame phenomenon in the case of Anadara, Crassatella, Pitar andPolymesoda species.The author could observe oyster-beds which mark littoral andshallow sublittoral environment. The single oysters formed banks by34growing to one another (epoechia) (BOGSCH. L. 1968.). Because ofthe favourable conditions they were crowded in great masses and itaffected frame deformation in a number of cases. The disfigurementof the oyster-shells might cause the animal's destruction in extremecircumstances.The author studied another type of symbiosis in the case anAthleta rarispina (Lamarck) specimen and alittle oyster-colony. Oneof the oysters has both valves. The mouth of the Athleta is notcovered by the oysters' shell. So, presumably, the oysters werecarried by the snail. The Athleta was a large-figured, thick-shelledgastropod, which followed predatory way of life. It might have beennot too difficult for it to carry the oysters. And the oysters, howevercould participate in the residues of the gastropod's nutriment. Thistype of symbiosis is called commensalism.The author have found oyster-shells on an Egerea collectiva (Gábor) specimen, too. Its aperture was covered by the oyster-colony. This proves that the Egerea had become extinct before theoysters settled on it.The symbiosis of the Ostrea sp. is not limited to one, or twospecies only. I could observe similar occurrences in case of othergastropods, too. These are the following: Turricula reguláris(Köninck, Polinices josephinia olla (De Serres), Turritella beyrichi percarinata (Telegdi-Roth), Galeodes basilica (Bellardi), Globularia gibberosa callosa (Noszky) The oysters live attached in one place on the solid sea-bottom(cementation). In the present case, mainly shells of died gastropodsserved as a bottom for its larvae. The mostly broken, deficient androlled shells indicate that the decay of the snails didn't take placelocally.The streaming water caused them to get to the place where theoyster larvae settled on them. It explains how the shell of theTurritella, which otherwise lives within the bottom sediments couldget among the tests of the other gastropods. Owing to the flowingwater the sedimentation was paused, or was not significant. It wasfavourable for the sessile habitude oysters. Conclusion can be drawnfrom the form of the bivalves for the changes or peridicity of thecurrent. The rounded forms are characteristic of such simpleorganisms that live in a relatively undisturbed envrionment.35The greatest part of the valves of the large-statured oysters aredensely pierced, the small borings indicate the activity of caustic-sponges which belong to the Family Clionidae. These borings are notonly signs of liaerosion but of dwelling structures (domichnia), too.Openings limited to the surface of the valve indicate that the boringswere mode in the shell of a living animal, reducing its solidity. Boredvalves having pore openings on the inner surface or on both sideswere empty. The larvae of the sponge settled onto the internal part ofthe shell after the oyster's death. The persence of these marine borersrefers shallow-water enviroment (WARME, E. J. 1975).The author has, also studied another type of overgrowth(epoechia), on a shell of Babylonia eburnoides umbilicosiformis (T.-Roth). I could observe a small worm-colony forming crust on thesurface of the shell. The tubes of the worm-colony were filled andaffixed to the snail-horn with limonite. The aperture of the shell wasnot covered by the worms. It seems possible that the colony wascarried by the snail until its destruction. As a consequence of thedisplacement the worms, which otherwise led a sessile a way of life,they had more chance to obtain their food. Overgrowth producessynoechia among the associated two species.In the course of my investigations I have found shells withborings of cirriped larvae in many cases: Babylonia eburnoides umbilicosiformis (T.-Roth), Athleta rarispina (Lamarck), Turricula reguláris (Köninck), Egerea collectiva (Gábor), Hadriana egerensis(Gábor).On the surface of the shells openings of various numbers canbe seen, but neither of them are perforated by the larvae.Cirripeds belonging to Genus Balanus compose solid skeletonand live attached in one place. In our case the cirriped is settled onthe valve of an Ostrea cyathula (Lamarck). There is a small cone-frustum type specimen on the Balanus. The presence of Ostreaindicates a rather strongly agitated water and a very slow andfrequently interrupted sedimentation. Here the rock barnacle couldfind the suitable living conditions: nutriment, oxygen, protectionfrom burying. After all, the decay of the two associated speciesmight be caused by the fast coverage with limonitic sandy silt. Itrefers to the well preservation of the cirriped's test.The author could also observe Bryozoa remains on twoMollusc species. In the first case the thin Bryozoa-colony encrusted36the shell of an Athleta rarispina (Lamarck). The zoarium is aroundthe aperture of the gastropod. Presumably after the animal'sdestruction, the shell lay upwards with its mouth on the sea-bottom.It functioned as a firm basis for the Bryozoa larvae so that the colonycould develop. The other side of the shell is bare and eroded. I havefound a small Bryozoa-colony on the valve of an Ostrea cyathula (Lamarck), too. The occurrence of Bryozoas indicate shallow-waterregion. The encrusting species refer to agitated water (GÉCZY, B.1985.) In my opinion, the Bryozoa-colonies in both cases, by reasonof the colony's structure, and the thick walls and rounded aperture ofthe zoecia, belong to the Genus Electra.The author managed to observe charasteristic traces of boring-bivalve (Teredo sp.). Teredo is especially adapted for wood boring.In this case drift wood were exavated by them. During thefossilization the organisms did not endure. But their borings werefilled in and cemented by limonitic sand. The tubes areapproximately 0,5 cm in diameter. Since the tubes wound by fits andstarts in the former driftwood, presumably, great number of borerscould be in it. It signs that the bivalves often had to go round eachother. The driftwood itself mouldered and vanished already, onlysome coalified pieces remind us of the feeding and dwelling place ofthe former borer-bivalves. These organisms may occur in most of thefossil communities because of the transportation of the currents.Palaeopathological observations While investigating fossils I could observe traces of predatorysnails. The activity of these gastropods can be qualified in twodifferent ways: it can be a palaeopathological symptom form theviewpoint of the prey, and on the part of the gastropod it can be a feeding trace (TASNÁDI-KUBACSKA, A. I960.). I could study borings of predatory snails in case of species belonging to the ClassGastropoda, Scaphopoda, Bivalvia.The species are as follows:Gastropoda: Polinices catena helicina (Brocchi), Polinices josephinia olla (De Serres), Athleta rarispina (Lamarck), Turritella beyrichi (Hofmann s. str.) Turritella beyrichi percarinata (T.-Roth), Turritella venus margarethae (Gaäl), Natica millepunctata tigrina (Defrance), Turris duchasteli (Nyst), Hadriana egerensis (Gábor), 37Hinia schlotheimi (Beyrich), Ringicula aurículata paulicciae (Morlet),Scaphopoda: Dentalium simplex (Michelotti),Bivalvia: Corbula basteroti (Homes), Corbula gibba (Olivi), Pitar polytropa (Anderson), Nucula mayeri (Hörnes), Ostrea cyathula (Lamarck). There are two kinds of borings. According to the scientificinvestigations this indicates the activity of two different species.1. The cylindriform and cone-shaped boreholes are made bymuricid gastropods.2. The borings which converge toward the center of the inneropening sign the activity of naticid gastropods (BISHOP,G.A. 1975).The author could collect numerous fossil claws. I supposed thatI could discover the feeding traces of crabs, too. I have found twogastropod shells with signs of crab's activity. The shells belong tothe next species: Ampullina crassatina (Lamarck), Turricula reguláris (Köninck). In case of both specimen we can see thecharacteristic damage, the extreme opening, which begins at themouth of the gastropod and extends over several whorls. Suchdamage to the snail is caused by crabs to reach the soft parts of thebody. The dimensions of the openings show that the meeting withthe crabs was fateful for both gastropods.These observations refer to a former shallow-water marineenviroment.Similar phenomenon can be studied under recent conditions inthe coastal regions of subtropical and mediterranean seas.38LITERATURE CITED1. BÁLDI, T. (1973): Mollusc fauna of the Hungarian Upper Oligocene (Egerian). Akadémiai Kiadó, Budapest, 511 p.2. BISHOP, G. A.: Trace of predation. in: Frey, E.W.(ed.), TheStudy of Trace Fossils. Springer Verlag, Berlin-Heidelbert-New-York, pp. 261-281.3. BOGSCH, L. (1968): General Palaeontology Tankönyvkiadó,Budapest, 281 p. (in Hungarian)4. DÁVID, Á. (1987): Paleo-oecological and Palaeo-pathologicalObservations on Upper Oligocene Molluscs MalakologiaiTájékoztató, 7:5-10. The Natural Science Section of MatraMuseum, Gyöngyös (in Hungarian)5. DÁVID, Á. (1991): New Palaeo-oecological observations onUpper-Oligocene Molluscs Malakológiai Tájékoztató, 11:12-14(m Hungarian)6. GECZY, B. (1985): Palaeontology Tankönyvkiadó, Budapest, 453p. (in Hungarian)7. TASNÁDI-KUBACSKA, A. (1960): Palaeopathologia MedicinaKiadó, Budapest. 230 p. (in Hungarian)8. WARME, E. J. (1975): Borings as trace fossils and the process ofmarine bioerosion. In: Frey, E. W. (ed.) The Study of TraceFossils. Springer Verlag, Berlin-Heidelberg-New York, pp.181-227.39

Palaeo-oecological and palaeopathological

observations on upper oligocene molluscs(Eger,Hungary)

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Palaeo-oecological and palaeopathological observations on upper oligocene molluscs(Eger,Hungary)

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