James H. Nebelsick

Drilling Predation on Recent Clypeasteroid Echinoids from the Red Sea

PALAIOS, 1999, V. 14, p. 127‐144 In contrast to mollusks, drilling predation on echinoids rarely has been investigated. Two minute clypeasteroid echinoids (Fibularia ovulum and Echinocyamus crispus) from the Northern Bay of Safaga, Red Sea, Egypt, were examined for drill holes using numerous samples collected from several bottom facies. Out of 1076 tests, 566 (52.6%) were drilled (45.8%-Fibularia ovulum, 70.7%-Echinocyamus crispus). The cylindrical shape of drill holes, their small size (mean diameter50.9 mm), acid-etching traces, and current biological knowledge suggest that these holes were produced by cassid gastropods. All holes are complete and unrepaired and tests with multiple holes are rare (6%) suggesting a very high success rate of predatory attacks. The other echinoids in the study area are rarely or never drilled. The minute clypeasteroids are preferred prey due, most likely, to their abundance and poor defensive mechanisms. Predation frequencies vary greatly, both within and across bottom facies, reaching up to 83%. Such variation may hamper reconstructions of the long-term patterns in the fossil record of drilling predation on echinoids. Drillhole outlines are highly variable due, most likely, to the presence of plate boundaries and pores in the prey tests. This suggests that such variation should not be used as sole evidence for presence of multiple predators or for variable predatory behavior. Predators drill preferentially the aboral (dorsal) side of the test (84.9%-F. ovulum, 99% -E. crispus), but do not appear size-selective. The drilling frequencies appear to be independent of the taphonomic state of the tests, suggesting that the preferential destruction of drilled tests during the pre-burial (biostratinomic) taphonomic phase is unlikely. The drilling frequencies in minute clypeasteroids are comparable with the highest frequencies previously reported for other modern echinoids, and are much higher than those typically reported for fossil echinoids as well as for other Recent and fossil prey of drilling predators.

Echinoid distribution by fragment identification in the Northern Bay of Safaga, Red Sea

Regular and irregular echinoid fragments from standardized bulk sediment samples from the Northern Bay of Safaga, Red Sea, Egypt, show a highly differentiated distribution which can be correlated to bottom facies type. The identification of echinoid fragments is possible upon comparison to living and complete skeletons, because of the numerous morphological features which characterize the test and spines. The distribution of fragments can be understood as a function of the presence of living taxa and taphonomic processes such as transport and time-averaging. The study of fragments should be useful in delineating the distribution of sea urchins in paleo-biological studies, despite the methodological size restriction, different taphonomic pathways of the diverse taxa, and limited habitat mixing

Multivariate hierarchical analyses of Miocene mollusk assemblages of Europe: Paleogeographic, paleoecological, and biostratigraphic implications

Mollusk-dominated fossil assemblages from the marine Miocene bioprovinces of Europe (the Boreal province and the Paratethys) were analyzed by using bulk samples collected hierarchically across several spatiotemporal scales. The study explores quantitative patterns recorded by benthic mollusk assemblages (including implications for paleogeographic, biostratigraphic, and paleoenvironmental patterns), and the relationship between spatiotemporal scale of analysis and levels of variability in paleontological data. A total of 8455 specimens from 23 samples were collected from siliciclastic sediments (clay and sand) at 12 localities from France, Belgium, the Netherlands, Germany, Poland, Austria, and Hungary. With the exception of one sample of Serravallian age from the southeastern North Atlantic, all samples came from Burdigalian and Langhian deposits of the Paratethys and the Boreal province. All specimens were identified to species level (297 species total), classified in terms of ecology, and analyzed by using multivariate and computer-intensive methods. The analyses focused on (1) bivalve/gastropod ratios, (2) diversity levels, (3) multivariate taxonomic and ecological patterns, and (4) multivariate Euclidean distances between samples compared at five different scales (within sites, within localities, within facies, among facies, among provinces). The bivalve/gastropod ratio is a highly volatile parameter; thus, its informative value is highly limited. The estimates of alpha diversity (sample species richness) standardized by rarefaction indicate that fossil assemblages of the Boreal province display higher diversity levels than those of the Paratethys. This result is consistent with the general tendency of isolated epicontinental basins to display impoverished fauna and may be due to geographic barriers limiting larval dispersal and to environmental instabilities inherent to marginal environments of epicontinental seaways. Rarefactions of pooled data indicate that, for both provinces, the taxonomic turnover among sites (beta diversity) accounts for 30%–40% of species diversity. Multivariate analyses indicate that biogeographic variation between the provinces is the most important factor controlling differences among samples, whereas facies type and stratigraphic position of samples play a secondary role. The strong biogeographic signature is consistent with recent paleogeographic reconstructions that suggest a lack of a direct marine connection between the two provinces at that time. The relatively poorer discrimination of mollusk assemblages across facies and biostratigraphic stages reflects the overriding role of the middle Miocene biogeography in controlling the composition of mollusk assemblages. The hierarchical multivariate analysis shows that with the increase in the scale of observation (within sites, within localities, within facies, among facies, among provinces), the average multivariate distance between samples increases continuously—new heterogeneities that add notable amounts of new variation exist at each scale of observation. The highest increase is observed for the “among provinces” comparison level, again indicating the major role of geographic sources of variation in the data. The hierarchical approach provides a rigorous way to quantify the effects of scale-dependent sources of variability on paleontological patterns.

The Stormy Path from Life to Death Assemblages: The Formation and Preservation of Mass Accumulations of Fossil Sand Dollars

Abstract Clypeasteroids can be very common in Recent, shallow water environments in a variety of biogeographic settings and represent important members of benthic invertebrate communities. Mass deposits of fossil clypeasteroids are also common and characteristic of many Cenozoic shallow water deposits. Their distribution and formation, however, has received much less attention than molluscan counterparts, although fossil examples are found within all three of the clypeasteroid suborders. A comparison of two mass deposits of scutellid clypeasteroids from the Miocene of the Mediterranean (Gebel Gharra section, Eastern Desert, Egypt; Alahan Section, Mut Basin, Turkey) shows common features, but also significant differences. Both were formed in high energy, coarse sandy, shoreface environments. The Gebel Gharra section consists of a thick, multi-event accumulation with numerous sedimentary features dominated by complete and fragmented skeletal remains of a single taxon (Parascutella). The accumulations in Alahan represents a single, thin, multi-taxon (Amphiope, Parascutella) deposit dominated by very well preserved, complete specimens. Both units are interpreted as proximal storm deposits based on the general sedimentary environment, clast relationships, and taphonomic features. Four factors contributing to mass deposits of clypeasteroid sea urchins in Cenozoic sediments include: (1) their gregarious nature with very high density populations; (2) their relatively robust skeletal morphology; (3) the high transport capacity of their flattened, low density skeletons; and (4) their habitat in shoreface environments which is conducive to physical concentrations of skeletal material. The presence of mass clypeasteroid accumulations is compared to other echinoderm deposits and discussed within the context of their rapid evolution in the Cenozoic.

Microfacies analysis and palaeoenvironmental interpretation of Lower Oligocene, shallow-water carbonates (Gornji Grad Beds, Slovenia)

SummaryThe microfacies and palaeoenvironment of Lower Oligocene carbonates of the Gornji Gradbeds from Slovenia are investigated. These beds form part of a transgressive succession overlying both terrigenous sediments (sand-stones and conglomerates) and marine carbonates of Eocene age as well as transgressing directly over Triassic lime-stones. They are followed by foraminiferal rich marls. The carbonates were investigated using multivariate statistical techniques on point counts of thin sections. They are dominated by poorly sorted biogenic rudstones with pack-/wackestone matrix; pack- and grainstones are subordinate. The biogenic components of the carbonates are dominated by coralline red algae (9 genera with 11 species), corals, small benthic, large benthic, and encrusting foraminifera as well as bivalves. Gastropods, bryozoans, brachiopods, echinoderms, serpulids, and green algae are subordinate. The well preserved components allow details pertaining to taxonomy, growth-forms and taphonomic features to be observed. The following carbonate facies are distinguished: 1) nummulitic, 2) bivalve, 3) foraminiferal—coralline algal, 4) grainstone, 5) coralline alga, 6) coralline algal—coral, and 7) coral facies. All the carbonate facies represent fully marine conditions within the photic zone. They are interpreted with respect to substrate composition and stability, water turbulence, terrigenous input and light.

Provenance analysis of Oligocene autochthonous and allochthonous coralline algae: a quantitative approach towards reconstructing transported assemblages

Abstract The Oligocene shallow-water carbonates of the Lower Inn Valley (Tyrol, Northern Calcareous Alps) contain a rich coralline algal flora. These carbonates are known from two distinct settings: (1) autochthonous limestones and (2) debris flows intercalated with deeper water marls. The carbonate facies are dominated not only by crustose coralline algae (Corallinaceae, Rhodophyta), but also by smaller and larger benthic foraminifers, bryozoans, corals as well as lithoclasts of Triassic origin. Five species of coralline algae are identified and described in detail: Lithoporella melobesioides , Lithothamnion sp. A, Lithothamnion sp. B, Mesophyllum sp., and Sporolithon sp. The distribution of algal taxa shows distinct relationships to non-algal biota and substrates: L. melobesioides preferably encrusts other coralline algae, Lithothamnion sp. A is found encrusting bryozoans, Lithothamnion sp. B encrusts corals, while Mesophyllum sp. grows directly on fine-grained, soft substrates. Besides the fact that algal taxa reveal close relationships to other components, it can also be shown that algal assemblages are highly correlated to carbonate facies types. Hierarchical cluster analysis based on the relative abundance of taxa reveals five coralline algal assemblages showing distinct distribution patterns among carbonate facies. While two of the assemblages are restricted to the debris flows, the other three were found in both debris flows and autochthonous occurrences. A correlation between algal assemblages and carbonate facies allows the following conclusions to be made: (1) Both coralline algal taxa in particular and algal assemblages as a whole show distinct relations to water depth (herein referred to as a summary of light conditions and hydrodynamic energy) and substrate relationships. This makes them potentially valuable indicators for palaeoecological reconstructions. (2) Most of the coralline algal assemblages in allochthonous occurrences (i.e. debris flow) can be traced back to facies patterns in autochthonous occurrences. This indicates that a thorough microfacies analysis combined with a systematic study of specific components can be very useful in the reconstruction of palaeoenvironments, even if these are not preserved in their original context. (3) Some of the coralline algal assemblages within debris flows cannot be traced to autochthonous facies and do not seem to reflect primary facies compositions as they contain an atypical mixture of algal taxa and other components. These are characterised by a relatively high abundance of lithoclasts (usually >20% of the components) and a high degree of fragmentation of coralline algae thalli.

Predation on Recent and Fossil Echinoids

Predator-prey interactions in marine ecosystems are documented in the fossil record by drill holes, repair scars, tooth marks and other structural damage left by durophagous (“hard-eating”) predators on skeletons of their prey. Previous paleoecological research focused primarily on benthic mollusks (e.g., Vermeij, 1977, 1983, 1987; Vermeij et al., 1980, 1981; Kitchell et al. 1981; Kitchell, 1986; Kelley and Hansen, 1993; Kowalewski et al., 1998; Dietl et al., 2000; Hoffmeister and Kowalewski, 2001; and numerous references therein). Other groups that received considerable treatment include brachiopods (e.g., Sheehan and Lesperance, 1978; Alexander, 1981, 1986, 1990; Smith et al., 1985; Baumiller et al., 1999; Harper and Wharton, 2000; Kowalewski et al., 2000; Leighton, 2001) and sessile echinoderms (e.g., Baumiller, 1990, 1993, 1996; Donovan, 1991a; Baumiller and Macurda, 1995). However, many important fossil groups of prey have been underrepresented in studies of predator-prey interactions.

Autochthonous facies and allochthonous debris flows compared: Early oligocene carbonate facies patterns of the Lower Inn Valley (Tyrol, Austria)

SummaryThis study presents a microfacies analysis and palaco-environmental interpretations of Early Oligocene carbon ates from the Lower Inn Valley Tertiary (“Unterinntal-Tertiär”) of Austria. The well preserved biogenic components allow detailed investigations of component relationships and controlling ecological parameters. The carbonates are dominated by coralline algae, corals, small and large benthic foraminifers, bryozoans and lithoclasts. Bivalves, gastropods, echinoderms, brachiopods and serpulids are subordinate. The limestones are present as A) autochthonous carbonates transgressing directly above the Triassic basement and B) allochthonous debris flows within deeper-water marls. These carbonates are found within the Paisslberg Formation. The Werlberg Member within this formation, pertains to the autochthonous carbonates and larger debris flows.Five facies types are separated following fabric analysis and statistical treatment (correlation, cluster analysis, principal components analysis) of semi-quantitative data consisting of component frequencies of thin sections. Facies distribution patterns are principally controlled by variations in substrate characteristics, turbulence and light along a depth gradient. Reconstruction of facies pattern distribution reveal both lateral and proximal-distal facies trends: coral-coralline algal facies, coralline algal facies as well as foraminiferal facies were situated in shallower environments, laterally adjacent to each other. These grade distally into coralline algal-bryozoan facies, bryozoan facies and finally into mollusc rich marls. Debris flows consisting of reworked material from all of the known facies (bioclastic packstone facies) is restricted to the debris flow and possible represents transport induced differentiation of components and grain size within distal debris flows.

Echinoid assemblages as a tool for palaeoenvironmental reconstruction – an example from the Early Miocene of Egypt

Abstract A rich Lower Miocene echinoid fauna has been investigated from Gebel Gharra, NW of Suez, Egypt. The ca 140 m long section consists of a siliciclastic lower part and a carbonate-dominated upper part. This corresponds to a general transgression/regression cycle. In all, 27 different echinoid taxa were recognised. The level of taxonomic identification varies depending on test completeness and preservation of specific morphological characters. The palaeoecology of the echinoids was inferred using a functional morphological approach and actualistic comparisons. A wide variety of ecological habitats are represented with the presence of regular as well as irregular sea urchins; epibenthic as well as endobenthic forms, as well as a wide range of interpreted burrowing depths for different irregular echinoids. Seven different echinoid assemblages were distinguished, which differ with respect to the species diversity, skeletal taphonomy and sedimentary environment: (1) the Parascutella Assemblage displays spectacular mass accumulations of sand dollars accumulated by proximal storm deposits and winnowing; (2) the Cidaroid–Echinacea Assemblage represents a slightly deeper, moderate-energy environment with a highly structured habitat and corresponding variety of regular and irregular sea urchins; (3) a Spatangoid Assemblage with a diverse fauna of burrowing echinoids; (4) the Transported Assemblage represents an allochthonous collection of echinoids from shallow-water, coarse sandy substrates; (5) the Mixed Assemblage representing a slightly shallower, low- to moderate-energy environment with reduced sedimentation rates; (6) a Clypeaster martini Assemblage characterising a shallow, higher-energy environment; (7) finally, the poorly diverse Phyllacanthus Assemblage from shallow-water carbonates. Diversity variations within the assemblages are correlated primarily to substrate variation, burrowing depths as well as taphonomic factors. The transgression/regression cycle is well reflected by the echinoid assemblages, which show a general deepening of depositional environment followed by shallowing upward tendencies.

Taphonomic comparison between Recent and fossil sand dollars

Abstract The taphonomy of a Recent and a fossil sand dollar are compared. The recent Echinodiscus auritus originates from a shallow-water carbonate environment in the Red Sea. The fossil Parascutella hobarthi is found in micaceous sands of the Lower Miocene Austrian Molasse Zone. Both species show strong similarities in constructional morphology including the flattened overall shape, details of the surface morphology as well as the presence of an internal support system. Three taphonomic features are remarkable different: (1) lethal and non-lethal predation (especially high in the recent E. auritus ; (2) encrustation of the test (especially by coralline algae in the fossil Parascutella ); and (3) radial cracking on implosion of the body cavity caused by sediment loading on the fossil tests. Differences in taphonomic signatures can be correlated with depositional environment (predation and encrustation) as well as factors related to burial of the fossil specimens (sediment loading and diagenesis).