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Evidence of Bioerosive Structures in Quaternary Glaciomarine Sediments from Southwestern Iceland
Abstract
The Late Weichselian marine and glaciomarine sediments occurring in many places along the coast of Iceland are rich in invertebrate fossils, especially mollusks and barnacles. A diverse ichnofauna, constituted especially by bioerosional traces documenting the activity of predators and animals that use the host shell for attachment or the construction of dwellings, was identified at the localities of Ósmelur, Saurbær, and Brekkubakkar in southwestern Iceland. The ichnotaxa identified include Anellusichnus circularis (Santos, Mayoral, and Muñiz), Caulostrepsis isp., Centrichnus concentricus (Bromley and Martinell), Clionolithes isp., Finichnus peristroma (Taylor, Wilson, and Bromley), Finichnus isp., Sedilichnus asperus (Nielsen and Nielsen), Sedilichnus cf. excavatus (Donovan and Jagt), Sedilichnus gradatus (Nielsen and Nielsen), Sedilichnus smiley isp. nov., Sedilichnus ovalis (Bromley), Sedilichnus paraboloides (Bromley), Sedilichnus simplex (Bromley), and Sedilichnus spongiophilus (Müller).
Bioeroded gastropod, bivalve and coral specimens (n = 570) were collected from the Jazan area, Saudi Red Sea coast, from which 22 ichnospecies of 8 ichnogenera were identified and illustrated. These traces were produced by clionid sponges (Entobia geometrica, E. ovula, E. cf. goniodes, E. cretacea, E. laquea, E. cf. paradoxa and E. isp.), duraphagous drillers (Oichnus ovalis, O. paraboloides, O. simplex and O. isp.), endolithic bivalves (Gastrochaenolites cf. dijugus, G. lapidicus, G. torpedo and G. isp.), polychaete annelids (Caulostrepsis taeniola, C. isp., Maeandropolydora sulcans, M. isp. and ?Trypanites isp.), acorn barnacles (Rogerella isp.), and vermetid gastropods (Renichnus isp.). The seashells act as hard substrate for colonization by serpulid worm, bivalves, bryozoans, and barnacles. Ichnogenus Entobia was most abundant (56.1%), followed by Gastrochaenolites (25.4%), Caulostrepsis (5.3%), Trypanites (4.2%), Maeandropolydora (3.2%), Oichnus (2.8%), Renichnus (1.9%), and Rogerella (1.0%). Oichnus occurred on the thin-shelled and smooth molluscs, while most Gastrochaenolites borings were found in the larger and thicker seashells as a suitable substrate for the settlement of polychaetes, lithophages, naticids, mytilids, and vermetids. Presence of annelid traces among radial ribs and at the siphonal areas of bivalves is indicative of nutrient capturing from water flow during the lifetime of these bivalves, within a shallow, high energy marine environment, where disarticulation, fragmentation, and abrasion of the seashells were abundantly observed.
Iceland and Faroe Islands represent a classical example of an area fully formed by volcanic activity. Their geological history goes back to the Lower Palaeogene when the northern part of Mid-Atlantic Ridge was active in the area of hotspot expression. Thick effusions and sheet intrusions of tholeiitic plateau basalts of Palaeogene age are characteristic for the Faroe Islands. Undersea volcanism which continuously cropped up and extruded the surface began in the Middle Miocene. The sequence of volcano-stratigraphic units with numerous volcaniclastic sedimentary layers is typical for both regions. However, there is one significant difference – in Iceland the marine and coastal deposits dominate but in the Faroe Islands mostly freshwater sediments are concerned.
Marine fauna is often preserved in the Icelandic sediments, for example Bivalvia, Gastropoda, Scaphopoda, Cirripedia, Annelida etc. In non-marine ecosystems, fossil plants, which locally form coal layers, dominate. Freshwater and terrestrial animals are much rarer. Fossil records of animal activities have not been studied there yet; however, their information potential has a great potential. Before the research presented in here, only three ichnologic papers were published and in several others the traces are only marginally mentioned.
No animal fossils from the Palaeogene age have been discovered in the Faroe archipelago yet, the same goes for the trace fossils. The only knowledge relates to the fossil plants. From the period after the end of the volcanic activity the finds of fossils are mostly limited to the Holocene age, except the Eemian wood fragments from the unique locality on the Borðoy Island.
In 2012–2018, a detailed paleontological research was carried out in the above mentioned European part of Arctic and Subarctic. Various bioerosion traces of Weichselian age were identified in the glaciomarine sediments, which remained after mechanic damages on shells of mollusc or barnacle, caused by the activity of predators; or after attachment of epibiotic organisms (e.g. Anellusichnus, Caulostrepsis, Centrichnus, Clionolithes, Finichnus and Oichnus), a lot of traces of locomotion were also found on the surface or inside sediment (will be published in the coming years). Resting traces and escape traces were also found here in the marine and also freshwater environments (Miocene).
It is not surprising that the marine ichnoassemblages show the worldwide geographic range; on the other hand, the lacustrine trace fossils are mostly endemic (Helminthoidichnites, Mammillichnis, Thorichnus igen. nov. and Vatnaspor igen. nov.).
In the Faroe Islands, the character of the Palaeogene landscape and ecosystems was quite well known based on the knowledge about the fossil plants and lithology of the volcaniclastic sediments. However, the proof of the animal presence was still missing. Although expected, the finding of Helminthoidichnites isp. and ?Palaeophycus isp. on the Eysturoy Island was important. Another but significantly younger trace fossils (Teredolites) were identified in the wood fragments comes from gyttja coastal cliffs of Eemian age. Terminal deposit place of driftwood in the lake basin connected with sea allows a big discussion about principal directions of sea currents in the last interglacial, despite their origin in high seas. The youngest confirmed traces come from the late Holocene soil profile. These are rhizoliths that testify the change of the landscape in the age of first human settlement of Faroe Islands. At present, the trace fossils mentioned above represent the first and only occurrence of trace fossils on the Faroe Islands.
A remarkable diversity of bioerosion trace fossils is reflected by the plethora of ichnotaxa that has been proposed for these structures during the past two centuries. Bioerosion traces include microborings, macroborings, grazing traces, attachment etchings, and predation traces. They occur in calcareous, siliceous, osteic, and xylic substrates, and are known or interpreted to be produced by tracemakers as diverse as bacteria, fungi, algae, invertebrates, and vertebrates. This review presents the status quo of an inventory of all bioerosion ichnotaxa currently recognized as valid, comprising 123 ichnogenera and 339 ichnospecies, including 45 combinationes novae, the majority of which on account of fossil sponge bioerosion traces for-merly grouped within the sponge biotaxon Cliona. In addition, the spelling of several ichnotaxa has to be corrected, leading to eight nomina corrigenda, and three cases of primary or secondary homonymy require establishing nomina nova, i.e., the new ichnogenus name Irhopalia replacing Rhopalia Radtke, 1991, as well as the new ichnospecies names Entobia morrisi replacing E. glomerata (Morris, 1851) and Entobia tuberculata replacing E. mammillata Bromley and D’Alessandro, 1984, respectively. Ichnotaxa of dubious or invalid nomenclatural status currently include an additional 76 ichnogenera and 157 ichnospecies. The invalid ichnogenus Ipites is herein reinstated as new ichnogenus. Considering that only four valid (and one invalid) ichnofamilies had previously been established for bioerosion ichnotaxa, we here introduce a suite of 14 addi-tional ichnofamilies: GASTROCHAENOLITIDAE, TALPINIDAE, ENTOBIAIDAE, PLANOBOLIDAE, ICHNORETICULINIDAE, SACCOMORPHIDAE, CENTRICHNIDAE, RENICHNIDAE, PODICHNIDAE, GNATHICHNIDAE, CIRCOLITIDAE, OICHNIDAE, BELICHNIDAE, and MACHICHNIDAE. During the past five decades, the number of valid bioerosion ichnotaxa has more than quadrupled, reflecting a boost in bioerosion research, but also indicating the need for ichnotaxonomic consolidation in concert with a revision of key ichnogenera. In this context, the aim of this overview is to call for feedback from the research community in order to foster completeness of this list and to provide ichnotaxonomic stability. Furthermore, we want to raise awareness of the existence of the listed ichnotaxa, many of which obviously have remained unconsidered or forgotten for a long time.
Dendritic and/or rosetted microborings in calcareous and osteic skeletal substrates have a diverse trace fossil record, spanning most of the Phanerozoic, whereas the ichnodiversity of comparable bioerosion traces produced in modern seas is rather limited. The most prominent occurrences are known from Devonian brachiopods and from Upper Cretaceous belemnite rostra. Ichnotaxonomically, they are comprised within one of the few ichnofamilies established to date, the Dendrinidae Bromley et al., 2007. As an outcome of the present revision of this ichnofamily, the plethora of 84 ichnospecies established within 25 ichnogenera since the erection of the type ichnogenus Dendrina Quenstedt, 1849 was considerably condensed to 22 ichnospecies included in 7 ichnogenera, based on a coherent morphological categorisation and ichnotaxobasis assessment. The suite of ichnogenera now subsumed within the Dendrinidae includes Dendrina Quenstedt, 1849; Clionolithes Clarke, 1908; Calcideletrix Mägdefrau, 1937; Dictyoporus Mägdefrau, 1937; Abeliella Mägdefrau, 1937; Nododendrina Vogel et al., 1987; and Pyrodendrina Tapanila, 2008. New combinations thereby concern Dendrina dendrina (Morris, 1851) comb. nov., Clionolithes pannosus (Solle, 1938) comb. nov., C. alcicornis (Vogel et al., 1987) comb. nov., C. convexus (Hofmann, 1996) comb. nov., Calcideletrix anomala (Mägdefrau, 1937) comb. nov., C. fastigata (Radtke, 1991) comb. nov., Dictyoporus balani (Tavernier et al., 1992) comb. nov., Nododendrina europaea (Fischer, 1875) comb. nov., N. incomposita (Mägdefrau, 1937) comb. nov. and N. paleodendrica (Elias, 1957) comb. nov. Investigation of new material and a reassessment of 63 dendrinid microborings previously addressed in informal nomenclature allowed the establishment of two complementing ichnogenera, Rhopalondendrina igen. nov. and Antodendrina igen. nov., and eight new ichnospecies, comprising Pyrodendrina arctica isp. nov., P. belua isp. nov., P. villosa isp. nov., Rhopalondendrina avis igen. et isp. nov., R. acanthina igen. et isp. nov., R. contra igen. et isp. nov., R. tigris igen. et isp. nov. and Antodendrina ligula igen. et isp. nov. In densely bioeroded calcareous substrates, different dendrinids and other bioerosion traces may be found in direct contact with each other, forming composite trace fossils, but some of these associations appear rather systematic in nature and could be the work of the same tracemaker under different behavioural modes, thus forming compound trace fossils. In these cases, however, the distinction between the two concepts remains largely equivocal. Dendrinid microborings are primarily found in living and dead calcareous skeletal substrates of bivalves, brachiopods, belemnites and corals, with complementing records from six other substrate types. Facing considerable sampling artefacts, evidence for true substrate specificity or symbiotic relationships is inconclusive as yet, whereas there is direct evidence for post-mortem infestation in several cases, such as the diverse dendrinid associations in Upper Cretaceous belemnite guards. Despite a wealth of available interpretations, the actual biological identity of the dendrinids’ tracemakers remains largely speculative. The most convincing evidence has been put forward in support of foraminiferans as the producers of Nododendrina, and excavating micro-sponges producing Clionolithes and some Calcideletrix. Since most of the dendrinids are found in aphotic (palaeo-)environments, these two principal types of organotrophic tracemakers are also potential candidates for the other ichnogenera. With regards to evolutionary patterns through geologic time, strong adaptive radiations are evident from the ichnodiversity of dendrinid ichnospecies in the Early to Mid-Palaeozoic, reflecting the “Ordovician Bioerosion Revolution” (sensu Wilson & Palmer 2006) and the “Mid-Palaeozoic Precursor of the Mesozoic Marine Revolution” (sensu Signor & Brett 1984), respectively, and in the Mesozoic, coinciding with the prominent “Marine Mesozoic Revolution” (sensu Vermeij 1977). This pattern mimics that of other micro- and macro-bioerosion trace fossils and is interpreted as a reflection of increased predation pressure and consequent infaunalisation. For extinction events, in turn, a differential effect is recorded in that the first four of the “Big Five” mass extinctions appear not to have had any noticeable effect on dendrinid ichnodiversity, whereas the end-Cretaceous mass-extinction resulted in a 77% drop following the Cretaceous peak ichnodiversity of 13 dendrinid ichnospecies.
In a Late Pleistocene/Holocene glaciomarine/marine sequence, a minimum of 115 taxa, macrofossils and trace fossils, are recognized on the basis of 690 samples from gravity cores from Andfjorden (nine) and Malangsdjupet (one).The biostratigraphy is proposed on the basis of reconstructions of autochthonous macrofaunal assemblages. A total of seven zones are defined, five in the Pleistocene and two in the Holocene, the ages of which are estimated by radiocarbon datings. In ascending order the zones are: Mixed Assemblage-zone, Barren Interzone, Arctinula greenlandica Assemblage-zone (before 14,000 yr B.P.), Yoldiella intermedia Assemblage-zone (14,000-13,000 yr B.P.), Bathyarca glacialis Assemblage-zozne (13,000-yr. B.P.), Bathyarca glacialis-Kelliella miliaris Interval-zone (10,000-ca. 7800 yr B.P.) and Kelliella miliaris Assemblage-zone (ca. 7800-present). The Bathyarca glacialis Zone is divided into three faunules: I (13,000-12,000 yr B.P.); II (12,200-11,100 yr B.P.) and III (11,100-10,000 yr B.P.).The palaeoecology of the faunal succession is elucidated by means of the sample-frequency method. Two major environmental events have influenced the faunal history. The first was the onset of the deglaciation of the thoughs, the second the intrusion of the Norwegian Current, bringing warm saline Atlantic water into the troughs at 10,000 yr B.P. The Pleistocene fossils demonstrate an Arctic macrofaunal succession from a low-order stage to a high-order equilibrium stage that is in principle identical to that of a modern faunal development in fjords following a disturbance causing anoxia. An estimated polychaete/mollusc ratio together with changes in sediment influx, depositional rates and grain size of substrate, indicate the presence of different energy regimes, where the inner and outer reaches of Andfjorden are compared.About 10,000 yr B.P. a major faunal change took place. The previous Arctic fauna was replaced by a Boreal fauna which developed into the modern fauna. The most important factor causing the replacement, and renewed faunal succession, were probably the rise in temperature and salinity as well as an increase in nutrient supply, brought about by the intrusion of the Norwegian Current.A comparison with shallower shelf areas indicates a somewhat different faunal composition in the Pleistocene brought about by different depositional environments. However, a similar major faunal change took place at 10,000 yr B.P. and there are fewer discrepancies among the Holocene faunas. Regional comparison indicates that some of the phases in the development of the fauna probably are rather local while other have a more regional nature.
The ichnogenera Caulostrepsis Clarke and Maeandropolydora Voigt are re—examined and redescribed on the basis of new material from Cretaceous deposits at Ivö (Sweden) and in particular from Pleistocene deposits from southern Italy. The morphological differences between the two ichnogenera are explained as having originated by different modes of substrate penetration. Maeandropolydora's gallery is extended from the end of one limb (axial boring), whereas Caulostrepsis's gallery advances at the vertex (lateral boring). Combinations of the two processes give rise to intermediate forms: Caulostrepsis contorta, in which lateral boring prevails and Maeandropolydora decipiens, in which axial boring is predominant. Structures that are U—shaped or produced by elaboration of this basic U—plan (C. contorta) are referred to the ichnogenus Caulostrepsis; the ichnospecies are separated according to presence/absence of vane, pouches, apertural pits and apertural grooves. The different ichnospecies of Maeandropolydora are characterized by presence or absence of pouches or by galleries tending to run in pairs
On the western side of the Tjornes Peninsula in North Iceland a long sequence of fossiliferous marine sediments, basalts, and diamicitites records the climatic history of the North Atlantic during the Pliocene and Lower Pleistocene. The Pliocene Tjornes beds are divided in three biozones; the Tapes Zone (oldest), the Mactra Zone, and the Serripes Zone (youngest). The Tjornes beds consist mainly of marine silt- and sandstones but there art, also several fossiliferous terrestrial beds in the lower part. The marine faunas in the Tapes and Mactra Zones are mainly boreal, but during the deposition of the Serripes Zone the fauna greatly diversified with immigration of Pacific molluscan species with more arctic elements. They reached the North Atlantic at 3.6 Ma after migration through the Bering Strait coeval with closing of the Central American Seaway. Marine molluscs of Pacific ancestry it? the Tapes and Mactra Zones post-date also the first opening of the Bering Strait. In the Breioavik Group, diamictite beds alternate with volcaniclastic mudrocks and sandstones, and basaltic lava flows. Fourteen lithological cycles are identified in the Breidavik Group each one starting with a diamictite interpreted as lodgement tillite and ending with terrestrial sediments and lava flows. Interbedded marine fossiliferous mudrocks and sandstones contain arctic to boreal faunal assemblages. The oldest cycle in the Breioavik group was probably deposited about 2.5 Ma, just after the Gauss/Matuyama polarity reversal.
Introduction Tests of large-sized Late Cretaceous holasteroid echinoid genera, such as Echinocorys Leske and Hemipneustes L. Agassiz, uncommonly preserve growth reactions to invasive interactions with settling, cementing and boring invertebrates, and lesions caused by vertebrates, that occurred during the life of the echinoid (for example, Donovan and Jagt, 2002; Donovan et al., 2008). There may be subtle evidence that infestations manifested themselves in vivo. The corollary of this is that infestations not associated with test modifications are interpreted as having occurred, most probably, post mortem, but prior to final burial of the echinoid test. The naked test of a dead echinoid on a soft chalk bottom may have provided a hard substrate and would thus have facilitated those benthic invertebrates that were obligate encrusters or borers, such as certain groups of bivalve and brachiopod, and most bryozoans, but would have been of limited or no interest to predatory vertebrates. There is ample evidence that species of these superficially burrowing holasteroid echinoids, both dead and alive, hosted a wide range of infesting organisms (for example, Joysey, 1959; Voigt and Soule, 1973; Donovan and Jagt, 2005; Jagt et al., 2007; Neumann and Wisshak, 2006; Wisshak and Neumann, 2006). Herein, we describe an unusual attachment trace on a test of Echinocorys, one of the commonest and most widely distributed echinoid genera in the Upper Cretaceous of Europe. The specimen is deposited in the collections of the Natuurhistorisch Museum Maastricht, The Netherlands (NHMM). NL-2300 RA Leiden, The Netherlands <donovan@naturalis.nnm.nl> + Natuurhistorisch Museum Maastricht (SCZ), de Bosquetplein 6-7, NL-6211 KJ Maastricht, The Netherlands <john.jagt@maastricht.nl> # Molenberg 4, NL-6191 KM Beek, The Netherlands <paul.dols@planet.nl> The tests of large holasteroid echinoids provided hard substrates that could become infested, both before and after death, by a range of invertebrates during the Late Cretaceous. A specimen of Echinocorys gr. conoidea (Goldfuss) from the (late Maastrichtian) upper Lixhe 1 Member, Gulpen Formation, of the Lixhe area, Belgium, preserves an elongate pentagonal scar. This trace fossil is non-penetrative and is probably the result of shallow embedment of an unmineralized, sessile invertebrate (a sea anemone?) on the test of the live echinoid. The elongation in an adapical-abapical direction may reflect the normal morphology of the producing species or was perhaps a plastic response to environment. Abstract Bulletin of the Mizunami Fossil Museum, no. 36 (2010), p. 51–53, 2 figs. © 200, Mizunami Fossil Museum Fig. 1. Outline map of the study area (redrawn and simplified after Jagt, 1999, fig. 1; Donovan and Jagt, 2004, fig. 1), showing political boundaries (dashed lines), rivers and canals (solid lines), the city of Maastricht and the Lixhe area. The inset map of The Netherlands, Belgium and Germany shows the approximate position of the main map (box).
The examination of 730 borings within 88 brachiopod hosts form the Middle Devonian of central New York State revealed four ichnospecies belonging to three ichnogenera that have taxonomic histories riddled with confusion, controversy and contradiction. New observations of the ichnotaxa question long-held views of a simple morphologic differentiation between sponge borings and worm borings. Clionoides Fenton and Fenton, 1932 is here considered a sponge boring, which is comprised of a complex, multi-dimensional system of tunnels, shafts, canals, microterraced bowlshaped structures and cone extensions, and is a senior synonym of Paleosabella (McCoy 1855) and Vermiforichnus Cameron, 1969a. Clionolithes Clarke, 1908 is a sponge boring possessing a rosette, branching network extending from a central node and is a senior synonym of Nododendrina Vogel et al., 1987 and Ramodendrina Vogel et al., 1987. The creation of Canaliparva circularis n. ichnogen. n. ichnosp. is needed to accommodate simple, vertically oriented, U-shaped tunnels that are indicative of worm activity. Paleoecologic evidence supports a commensal relationship between the endoliths and hosts based upon boring site frequencies in the hosts, boring patterns and five inter-specific co-occurrences between traces. These new data suggest greater diversity and ecologic complexity in ichnofaunal paleocommunities from the Middle Devonian than previously recognized.
The Middle Eocene to Middle Miocene White Limestone Group of Jamaica contains a common and diverse, poorly to well-preserved microboring ichnofauna, namely Centrichnus eccentricus Bromley & Martinell, Curvichnus pediformis isp. nov., Dendrorete balani Tavernier, Campbell & Golubic, Dipatulichnus rotundus Nielsen & Nielsen, Entobia volzi Bromley & D’Alessandro, Entobia isp. cf. E. ovula Bromley & D’Alessandro, Entobia isp. forms A and B, Fossichnus solus Nielsen, Nielsen & Bromley, Maeandropolydora elegans Bromley & D’Alessandro, Maeandropolydora sulcans Voigt, Oichnus asperus Nielsen & Nielsen, Oichnus excavatus Donovan & Jagt, Oichnus gradatus Nielsen & Nielsen, Oichnus ovalis Bromley, Oichnus paraboloides Bromley, Oichnus simplex Bromley, Oichnus isp., Planobola microgota Schmidt, Podichnus centrifugalis Bromley & Surlyk, Ramosulcichnus biforans Hillmer & Schulz, Reticulina elegans Radtke, Scolecia filosa Radtke, Scolecia maeandria Radtke, Stellatichnus radiatus Nielsen & Nielsen, Trypanites fimbriatus (Stephenson), Trypanites solitarius (Hagenow), Trypanites weisei Mägdefrau, and one example each of an unnamed crescent-shaped and a sub-horizontal to undulatory boring. These ichnospecies are distributed within three formations, the Somerset, Moneague and Montpelier formations, of the White Limestone Group. The majority of these microborings are preserved in the foraminifers Lepidocylina spp. within the Somerset Formation.
New etching trace fossils produced by the attachment of balanid barnacles on fossil molluscs, mainly bivalves, from the Upper Miocene of Cacela (southern Portugal) and Lower Pliocene of Huelva (southwestern Spain) are described. These traces are named as Anellusichnus n. igen. due to the ring-like shape of the scars. Two ichnospecies are recognized: A. circularis n. isp., consisting in a circular scar defined by a discoloured area or by a circular to subcircular trench and A. undulatus n. isp. that has a sinuous perimeter reflecting the undulate pathway of the furrow and a flat shelf etched into the substrate. Within the outer furrow both can display a cluster of circular, oval or subpolygonal concentric lines. A. undulatus n. isp. shows several morphologies that correspond to different ontogenetic stages.
Bioerosion on shells of a brachiopod-bearing thanatocoenosis dredged on red-coral sea-bottom (depth 100 m, 12 miles off the southwestern coast of Alborán Island, Spain) was analyzed. Although low, the intensity of predation was noticeable. Predation drill holes belonging to the ichnogenera Oichnus simplex, O. paraboloides and O. ovalis were recognized. They were probably produced by Muricidae and Marginellidae (gastropods) and octopod cephalopods, respectively. Oichnus ovalis was more common on Terebratulina retusa. A strong selectivity with respect to species, valve, and size was noted. Terebratulina retusa, especially small individuals, was preyed upon more often than any other species. The central portion of both valves was attacked more frequently than expected by chance.
This study describes bioerosion traces ascribed to either predation or endo- and epibiont activity in twenty assemblages from the Mediterranean region and Paratethys, spanning in age from Eocene to Recent. Statistical analysis of the distribution of bioerosion traces among genera and assemblages revealed that there is higher drilling predation intensity on smaller species. Larger species seem to be primarily affected by non-drilling predators. Greatest variety in types of bioerosion could be related to species’ ecology and body size. Both major categories of bioerosion (etchings and traces of predatory activity) vary considerably among samples. Different genera show significant differences in the frequency of different bioerosion types. Shell size seems a major factor contributing to these differences.
The taxonomic treatment of trace fossils needs a uniform approach, independent of the ethologic groups concerned. To this aim, trace fossils are rigorously defined with regard to biological taxa and physical sedimentary structures. Potential ichnotaxobases are evaluated, with morphology resulting as the most important criterion. For trace fossils related to bioerosion and herbivory, substrate plays a key role, as well as composition for coprolites. Size, producer, age, facies and preservation are rejected as ichnotaxobases. Separate names for undertracks and other poorly preserved material should gradually be replaced by ichnotaxa based on well-preserved specimens. Recent traces may be identified using established trace fossil taxa but new names can only be based on fossil material, even if the distinction between recent and fossil may frequently remain arbitrary. It is stressed that ichnotaxa must not be incorporated into biological taxa in systematics. Composite trace fossil structures (complex structures made by the combined activity of two or more species) have no ichnotaxonomic standing but compound traces (complex structures made by one individual tracemaker) may be named separately under certain provisions. The following emendations are proposed to the International Code of Zoological Nomenclature: The term ‘work of an animal’ should be deleted from the code, and ichnotaxa should be based solely on trace fossils as defined herein.
The new combined attachment and feeding trace fossil Oichnus halo isp. n. is described from oral surfaces of Campanian and Danian Echinocorys tests. It shows striking conformity with traces produced by Recent eulimid gastropods of the genus Thyca parasitising the asteroid Linckia laevigata. The trace is characterised by a central penetration surrounded by the eponymous circular groove. The occurrence of Oichnus halo isp. n. in the Campanian is contemporaneous with the first appearance of eulimid gastropods in the fossil record and indicates that the eulimid–echinoderm parasitic interaction was already established in the Late Cretaceous.
A large number of Quaternary foraminiferans, collected from several localities worldwide, show evidence of bioerosion in their tests. These bioerosion traces confirm that predation and parasitism of benthic foraminiferans are widespread phenomena in modern and fossil marine environments. Also, single borings related to different chambers in the tests of planktonic foraminiferans support the hypothesis that one or several unknown planktonic organisms prey on living foraminiferans. A healed boring observed on the test of a planktonic foraminiferan indicates that at least some planktonic foraminiferans survive the attack of the unknown predator. The occurrence of one of the traces, Fossichnus solus igen. et isp. nov., suggests that its distribution is controlled by environmental parameters. Fossichnus solus isp. nov. is distinguished by a single groove having a circular to oval outline and most likely represents an attachment structure. Alternatively, as F. solus isp. nov. forms part of a developmental sequence that may result in Oichnus simplex, it could be interpreted as an abandoned predation trace. Other bioerosion structures are recorded for the first time. A sieve-shaped boring is left in open nomenclature because of its rarity. A crescent-shaped hole and a groove-shaped hole are left in open nomenclature as Oichnus aff. asperus and O. aff. paraboloides, respectively. Fossichnus solus isp. nov. is quite common within its temporal and geographical area of distribution. Therefore, this ichnospecies has a potential usefulness as a palaeoecological marker. However, the sieve-shaped boring, Oichnus aff. asperus, and O. aff. paraboloides all occur very rarely and therefore are of limited palaeoecological use at present.
The crustal break-up between Eurasia and Greenland during chron 24r, the subsequent growth of deep ocean basins, and regional continental uplift provide a geometric framework that have influenced circulation patterns and sedimentation/erosion on local and regional scales. Cenozoic tectono-magmatic events may also have affected the chemical and physical properties of the oceans and atmosphere, yielding a potential global impact. The events include: 1) Syn-rift uplift, followed by a massive, transient magmatic pulse during break-up and initial sea floor spreading. The magmatism resulted in emplacement of onshore and offshore flood basalts accompanied by regional ashfalls. There is a temporal correspondence with the terminal Paleocene deep-sea extinction event and the earliest Eocene greenhouse. Enhanced atmospheric CO2 levels, leading to polar warming and changing patterns of deep water formation, may have affected the global environment. 2) Emplacement of extrusive complexes during break-up, which combined with a segmented plate boundary, controlled circulation of Paleogene waters in the Norwegian-Greenland Sea. This led to late Paleocene-early Eocene shallow basins with poor regional water mass exchange. Deep basins formed in the middle Eocene, creating regional surface water interaction, but deep water was isolated throughout the Paleogene. The present deep water exchange through the Norwegian-Greenland Sea is a Neogene and Quaternary phenomenon, related to Fram Strait opening and subsidence of the Greenland - Scotland Ridge. 3) Neogene epeirogenic uplift of the Fennoscandian landmass and inner shelf region. This tectonic uplift was probably initiated in Late Oligocene and continued through the Pliocene. Deep erosion of the landmass generated huge late Neogene sedimentary wedges along the eastern Norwegian-Greenland Sea margin. The uplift appears to be contemporaneous with Northern Hemisphere climatic deterioration.
Four marine molluscan species that migrated to Iceland during the deposition of sedimentary sequences on the north side of Snaefellsnes, western Iceland, at about 1.1 Ma, are not living in Iceland today. Three of these species are arctic and reached the area during an Early Pleistocene deglaciation. The fourth is thermophilic and arrived during the following interglacial, together with several littoral species now living in Iceland. The arctic species probably migrated to Iceland from the west or northwest due to a southward shift of the cold and euhaline East Greenland Current to the Icelandic west coast. At that time the Polar Front was lying considerably south of Iceland, but then followed a periodic northward shift of the front. The fact that the arctic species did not reach northern Iceland at this time may indicate a rapid shift of the Polar Front across the north coast of Iceland that minimized the influence of the East Icelandic Current during the deglaciation. Several thermophilic littoral species that migrated to western Iceland during the following interglacial did not reach northern Iceland. They came from the south or southeast during strengthening of the warm Irminger Current. However, the current's influence on the Icelandic north and northeast coasts was probably limited because of mixing with colder water masses with reduced salinity from the East Icelandic Current.
Two characteristic and common trace fossils, lightly etched into the surfaces of skeletal substrates in marine environments, are named Centrichnus eccentricus igen. et isp. nov., and C. concentricus isp. nov. respectively. The first is new, not having been described in recent or fossil material before. It corresponds to the attachment scars produced by anomiid bivalves where they anchor their unique calcified byssus to the substrate. C. concentricus, on the other hand, is well known but hitherto has not been named. It corresponds to the etching scars produced beneath verrucid cirripedes on calcareous substrates.
Bioerosion was studied at Vardo, N Norway, Only those substrates that were composed of carbonate (skeletal material) were found to be attacked by organisms. The bioeroding community is dominated by boring algae, which have entered almost every grain. Most surfaces have been rasped by patellid gastropods and some by regular echinoids. Boring sponges, annelids and phoronids are less common, whereas bivalve and, possibly, sipunculid borings were not recorded. The bioeroding community is thus impoverished, in comparison with warm-water communities, and this impoverishment is probably due to the low water temperature. -Authors
Small round pits and holes in fossil skeletal material are found in a wide variety of invertebrate substrates from diverse environmental settings. They are associated with parasitism, predation and commensal attachment. Four ichnogenera have been proposed for these trace fossils: Sedilichnus Muller, Oichnus Bromley, Tremichnus Brett and Fossichnus Nielsen, Nielsen and Bromley. Previous authors have established that Tremichnus is a junior synonym of Oichnus. Herein we show that Oichnus and Fossichnus are junior synonyms of Sedilichnus. Sedilichnus, as defined herein, includes 10 ichnospecies. Sedilichnus spongiophilus, S. simplex, S. paraboloides, S. ovalis, S. coronatus, S. gradatus, S. halo, S. asperus, S. excavatus and S. solus. Consistent with previous work Sedilichnus ichnospecies are defined solely by morphological criteria and not by a priori assumptions regarding depositional environment or tracemaker. Thus, this ichnotaxon is recognized in both marine and continental settings on a wide variety of invertebrate skeletal tests. As is true with many ichnotaxa, Sedilichnus ichnospecies represent end-members in morphological spectra, however each ichnospecies is clearly differentiable from the others. Sedilichnus spongiophilus are circular, non-penetrative pits in shells. Sedilichnus paraboloides are penetrative holes with spherical paraboloid forms and typically have larger external openings and smaller internal openings. Sedilichnus simplex are simple cylindrical borings that have both penetrative and non-penetrative forms. Sedilichnus coronatus differ from other forms by the presence of an etched or granular halo surrounding the boring. Sedilichnus gradatus have two concentric parts, an outer boring and an inner shelf of smaller diameter. Sedilichnus ovalis and S. asperus are both oval in outline differing in the presence of tapering paraboloid margins in S. ovalis and margins perpendicular to the substrate in S. asperus. Sedilichnus excavatus and S. solus are primarily non-penetrative and differ from other Sedilichnus by the presence of central, raised bosses or platforms. These two ichnospecies differ in the shapes of their external walls and the proportional thickness of the bounding groove.
Predators of extant decapod crustaceans are fairly well known, but unlike many other invertebrate clades, not much is known regarding predation evidence found on fossil decapods. Herein, we provide an overview of such predation and expand upon this through an extensive study of fossil decapod specimens from multiple museum collections. Thus far most examples of predation come from drill holes and stomach contents; bite marks, incisions or irregular holes, and possible regurgitated material are also known. The currently recognized predators of decapods in the fossil record are fish, plesiosaurs, ammonites, octopods, and gastropods. We also provide new evidence of unambiguous drill-hole predation in decapods, based on 33,593 nonmoldic Cenozoic (middle Eocene– Holocene) decapod remains originating from Europe, Asia, and North America, indicating that drilling predation in decapods is more common than currently recognized. Drill holes attributed to octopods (ichnotaxon Oichnus ovalis) and gastropods (O. simplex and O. paraboloides) were found in carapaces and appendages from the Pliocene of the Netherlands, the Pleistocene and Pliocene of the United States (Florida), and the Pleistocene and early Miocene of Japan. Six drill holes attributed to octopods were found in epifaunal and semiburrowing crabs; three drill holes attributed to gastropods were discovered in semiburrowing and epifaunal crabs, and in a burrowing mud shrimp; and the producer of two other drill holes in epifaunal crabs is unknown. Other possible drill holes occur in decapods from the Holocene and early Miocene of Japan and the late Eocene of the United States. Drill-hole predation intensities in decapod faunas by stratigraphic formation are low (#2.7%), at least in part due to multiple biases such as preservation and molting.
The propagating rift model has resolved discrepancies that occur when rigid plate tectonic models are applied to the Pangea configuration of the continents, and furnish a number of guidelines for the process of continental breakup. Continents do not drift apart instantaneously in a rigid manner, but rather permit an ocean to form by means of a propagating rift. This rifting occurs in a manner resembling crack propagation, progressing in a direction that is normal to that of the regional least compressive stress. Hotspot tracks and other regions of weakened lithosphere act as stress guides for the rifting. The model also predicts that the continental-oceanic boundary is not an isochron, but rather becomes younger in the direction of rifting. Extension along the continental margin is a minimum at the initial rifting point, and reaches a minimum at the furthest extent of the rift.
A survey of the large number of scallops from the Plio-Pleistocene shell beds of Florida held in the collections of the Florida Museum of Natural History has revealed that a proportion have been penetrated by drillholes of the ichnospecies Oichnus ovalis, which may be attributed to predatory octopods. Only large individuals had been drilled. Drillhole positioning was highly stereotyped, most being located on the ‘upper’ left valve, between ribs and directly into the adductor myostracum. Such stereotypy indicates that the octopods concerned were highly accustomed to taking scallop prey and also that the complex predatory behavior seen in modern octopods was already in place by the Pliocene. Such stereotypic patterns suggest that scallops from these localities were frequently the victims of octopod attack.
Animal bioerosion trace fossils upon mineral substrates are analyzed from the point of view of the Seilacherian ethological classification. Several of the currently accepted ethological classes: cubichnia, fugichnia, repichnia, fodinichnia, agrichnia, calichnia and aedificichnia are not represented in these substrates. This fact points out a lower behavioral diversity of hard substrate trace fossils when compared with soft sediment trace fossils. Bioerosion traces can be classified in just five classes: domichnia, pascichnia, equilibrichnia, praedichnia and fixichnia. Fixichnia is here erected to gather superficial etching scars resulting from the anchoring of fixation of sessile epiliths by means of a soft or skeletal body part. Praedichnia and fixichnia are exclusive of the bioerosion realm.
The proximity of a hotspot to a spreading center may result in the channeling of asthenosphere to the section of rise crest closest to the hotspot. This produces more basalt and thicker crust at these locations, thus forming a plateau over time. The geometric constraints of such a model predict a unique orientation, location, and age progression for a plateau formed by this mechanism. The hotspot will channel material to the closest part of the rise; therefore the orientation of the plateau will differ from that of a hotspot track by the component of absolute motion perpendicular to the rise axis. The plateau will be symmetric with respect to the location of the rise axis at the time of formation. Also, the age progression of the plateau will be contemporaneous with the age of formation of the seafloor on either side because the plateau is seafloor, just with thicker crust. A set of reconstructions based upon magnetic isochrons and a fixed hotspot reference frame is presented for the Norwegian-Greenland Sea as a means of evaluating the model's predictions. By locating the Iceland hotspot, reconstructing the relative positions of the Greenland and European plates, and then assuming material would be channeled from the hotspot to the closest section of the rise crest, we can trace the tectonic evolution of the Greenland-Faeroe and Voring plateaus. The model is able to locate the plateaus, explain their orientations, and predict an age progression that satisfies observed age determinations. The analysis demonstrates that both plateaus could have been formed by the Iceland hotspot with the Greenland-Faeroe Plateau being in effect a continuation of the Voring Plateau, which was cut off due to transform motion between the northern and southern spreading centers.
Endobenthic animals, which reside within the sea bottom, include stationary suspension feeders, mobile deposit feeders and both stationary and mobile carnivores. Their activities, especially with regard to dwelling, feeding, walking/crawling and resting/nesting, are recorded as trace fossils.Abundance, diversity and density of some kinds of trace fossils allow interpretation of the population strategies of the trace-makers in terms of opportunistic (r-selected) and equilibrium (K-selected) strategies. Opportunistic ichnotaxa tend to be faciesbreaking traces, which are highly localized in low-diversity, high-density trace fossil associations in rocks representing environmental extremes (e.g., variable salinities, harsh temperatures, low oxygen levels or shifting substrates). Equilibrium ichnotaxa usually are restricted to particular sedimentary facies and are characteristic of high-diversity, low-dominance trace fossil associations in sediments reflecting stable, predictable environmental conditions.The most important environmental factors influencing the composition of trace fossil assemblages in marine settings are bathymetry, substrate, oxygen and hydrodynamic energy. The four factors are closely interrelated, because as water depth increases, there is a general decrease in sediment grain size and hydrodynamic energy of the depositional environment. As depth below the water—sediment interface increases, the firmness of the sediment (due to compaction and dewatering) increases and the oxygen content of interstitial waters drops drastically.Marine ichnofacies are largely substrate-controlled. Soupgrounds are water-saturated, incompetent substrates typified by highly compressed and usually unidentifiable burrows. Softgrounds commonly contain numerous distinctive burrows and are zoned bathymetrically by the Skolithos, Cruziana, Zoophycos and Nereites Ichnofacies. Firmgrounds are characterized by stiff, compacted sediments, in which traces of the Glossifungites Ichnofacies are excavated. Hardgrounds are cemented substrates, in which bioerosion traces of the Trypanites Ichnofacies are bored. Woodgrounds are woody materials that have been exposed to the sea and bored by bivalves, which produce characteristic traces of the Teredolites Ichnofacies. Tiering of endobenthic communities is common and is related to substrate preference of the burrowers and oxygen stratification of interstitial waters.
The geological history of octopus is virtually unknown, owing to lack of a preservable skeleton, Several octopod Species today are known to drill holes in prey animals for the injection of venom. These borings incipient trace fossils that have good fossilization potential. and arc named Oichnus ovalis isp. nov. Their abundance ill Pliocene assemblages suggests that they will be recognized elsewhere in tertiary and perhaps older assemblages, providing greatly needed data oil the earlier range and feeding habits of octopus.
Published in the journal Ichnos (unrecognized by ResearchGate).
An ichnotaxonomic revision is given of the two ichnogenera Oichnus Bromley 1981 and Tremichnus Brett 1985. The following ichnotaxa are retained: O. simplex, O. paraboloides and O. ovalis. Abandonment of T. paraboloides, T. cysticus, T. minutus, T. puteolus and Tremichnus isp. aff. T. puteolus is proposed herein. Several specimens of O. simplex and O. paraboloides are present in the studied tests.Bioerosional structures have been observed in more than 600 out of 30,000 tests of Pliocene to late Holocene benthic and planktonic foraminiferans. A new ichnogenus, Stellatichnus igen, nov., is proposed herein to include star‐shaped holes. This ichnogenus comprises one ichnospecies, Stellatichnus radiatus isp. nov. Its overall shape seems to be related to substrate thickness.Three new ichnospecies of Oichnus are also defined. O. coronatus isp. nov. is distinguished by a halo of surficially etched substrate, but is otherwise similar to O. simplex. O. asperus isp. nov. is characterized by openings with irregular elongate‐oval outlines. The distinctive feature of O. gradatus isp. nov. is its two interconnected subcylindrical components. Dipatu‐lichnus igen. nov., which contains D. rotundus isp. nov., comprises pairs of circular holes.These bioerosional structures are interpreted as representing the ethologic categories praedichnia and domichnia. Biological affinities of the tracemakers are unknown.
Three ichnospecies of Oichnus Bromley occur in tests of the large holasteroid echinoid Hemipneustes striatoradiatus (Leske) in the type area of the Maastrichtian (Upper Cretaceous) in The Netherlands and Belgium; Oichnus simplex Bromley (penetrative), Oichnus paraboloides Bromley (nonpenetrative and showing two distinct morphologies), and Oichnus excavatus isp. nov. (nonpenetrative). The two distinct morphologies of O. paraboloides (both shallow, one with a central boss) are gregarious, but do not occur together on the same specimens, suggesting they were generated by different taxa. Oichnus paraboloides with a central boss occurs on H. striatoradiatus from the upper Nekum Member, Maastricht Formation (Maastrichtian, Upper Cretaceous). Tests of the host echinoid are smaller in the overlying Meerssen Member, Maastricht Formation, where they are infested by O. excavatus, the largest borings considered herein, which have concave walls and a large central boss. Blisters inside tests from the Meerssen Member show that this infestation occurred when the echinoid was alive. It is postulated that producers of these borings in H. striatoradiatus may have been genetically related and increased in size during the Maastrichtian even as the host echinoids showed a size decrease. This size increase in H. striatoradiatus was genetic and cannot be related to increase in size of borings.
The presence of organisms whose bodies have low preservation potential may be deduced by searching for the traces produced by them. The addition of predatory gastropods and soft-bodied epizoans to Quaternary marine faunas dominated by bivalves was facilitated by an examination of borings in bivalve shells. Borings attributed to predatory gastropods (ichnogenus Oichnus) were observed in shells of Astarte spp., Hiatella arctica and Macoma calcarea. Astarte, Hiatella and Macoma were preyed upon in preference to other members of a diverse suspension-feeding bivalve community. Borings attributed to epizoans (ichnogenus Cautostrepsis) were observed in bivalve shells (Astarte spp. Hiatella arctica), calcareous algae and limestone clasts. Biotic interactions revealed by trace fossils are employed, for the first time, to reconstruct the trophic structure of arctic Quaternary marine benthic faunas. ▭ Arctic molluscs, palaeoecology, Oichnus, Caulostrepsis.
The research history and geological problems of the stratigraphy of Late Pleistocene rocks in Reykjavík, Iceland are reviewed. New data are presented on the stratigraphy and palaentology of the sedimentary record. The Reykjavík sequence rests unconformably on reversed polarity rocks of Early Pleistocene age and includes tillites as well as marine mudrocks and sandstones, terrestrial diamictites, conglometrates, sandstones and lignites. These rocks are exposed along the coasts of Reykjavík and have also been penetrated by several boreholes. The lithostratigraphy, climatic indicators and available dates indicate that the Weichselian glaciation of the area was preceded by an ice free interval with climate that was comparable to the present one in South Iceland. The so called Fossvogur beds and deposits in Seltjarnarnes indicate three glaciations of the area after the last interglacial.
Some encrusting cheilostome bryozoans etch a pattern of small pits into hard calcareous substrates, especially calcitic and aragonitic shells of molluscs. These patterns, herein described as Leptichnus ichnogen. nov., comprise pits which are sub-circular to elongate in cross section and are found in either uniserial (L. dromeus isp. nov.) or multiserial arrangements (L. peristroma isp. nov., the type species). Each pit corresponds to the location of a single zooid in the bryozoan colony. The oldest known Leptichnus is Late Cretaceous (Maastrichtian), the trace fossil first becomes common in the Cenozoic, and at least nine modern cheilostome genera produce incipient Leptichnus. Leptichnus can be the only evidence remaining of encrusting cheilostomes following taphonomic or diagenetic loss of their calcareous skeletons. The mechanism by which bryozoans etch into their calcareous substrates is unknown but is almost certain to be chemical and necessitates having windows in the basal walls of the zooids which permit contact with the substratum beneath. Etching may result in better adherence to the substrate, giving protection from abrasion and bioerosion.
Sedimentary facies, foraminifera, and molluscs are used to reconstruct environmental conditions during the accumulation of the 1.5 Ma Svarthamar Member unit from the Tjörnes sequence, North Iceland. The Tjörnes sequence and the Breidavík Group in particular contains a unique record of Cainozoic glacier variations in the North Atlantic. This is reflected in lithological variations where marine and terrestrial sediments are intercalated between lava flows and pyroclastic rocks on Tjörnes Peninsula. Our results from the Svarthamar Member show that the lithological cycle from glacial to proglacial and then to shallow marine sedimentation coincide with faunal succession, reflecting a change from arctic to boreal arctic or even boreal conditions in the sea around Iceland just after the Olduvai event of the Matuyama. The amplitude of this climatic cycle is comparable to the Late Pleistocene glacial-interglacial cycles in the North Atlantic. This indicates that the North Atlantic current crossed the Greenland-Iceland and Iceland-Faroe ridges during interglacial periods resulting in a periodic northward shift of the polar front during at least a part of the Early Pleistocene.
Late Cainozoic Floras of Iceland. 15 million years of vegetation and climate history in the Northern North Atlantic
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