Michał Kowalewski

Spatial and Environmental Variation in the Fossil Record of Drilling Predation: A Case Study from the Miocene of Central Europe

Abstract Drilling predation presents a rare opportunity to quantify ecological interactions in the fossil record. Most large-scale studies have focused on temporal rather than spatial patterns. However, spatial variability patterns may both mask secular trends and provide important insights into geographic and environmental gradients in predation. To explore spatial patterns in predation, bulk samples of mollusks were collected from middle Miocene (Burdigalian and Langhian) marine deposits of Europe, including multiple sites from two adjacent bioprovinces: the Boreal Province and Paratethys. Two facies were sampled: fine-grained and coarse-grained siliciclastics. The sampling scheme allows for a comparison of drilling predation at the local scale (within provinces), regional scale (between provinces), and between facies (within and between provinces). In the Miocene of Europe, statistically significant spatial variations in drilling-predation patterns occur locally, regionally, and among facies (these variations can be either masked or exaggerated when the samples are pooled into coarser analytical groupings). Regardless of the taxonomic resolution of the analysis, inter-regional and facies variation between samples is significant and on occasions exceeds 20%. The sample-level pattern of variation in drilling intensity is notably consistent for pooled data and for each mollusk class, but major differences exist at finer taxonomic scales of families and genera. Escalation parameters (proportion of failed and multiple predatory attacks) also vary significantly between the provinces. In contrast, drill-hole size and site distributions display remarkably consistent patterns across samples regardless of the region, environment, composition of potential prey and predator, observed drilling intensity, and levels of escalation parameters. This suggests that stereotypy in predatory behavior can be displayed by higher taxa and may be independent of the environment, geography, and prey type. The dramatic differences between intensity patterns and stereotypy patterns indicate that the scale and nature of spatial variability may vary notably among different predation parameters. Thus, whereas behavioral stereotypy appears to be stable, the drilling intensity and escalation parameters display variability levels that are comparable to the temporal variations observed among samples collected over evolutionary time scales. The spatial variation in the fossil record of all relevant predation parameters should be evaluated independently, and controlled for, before any large-scale temporal trends are inferred.

Abundant Brachiopods on a Tropical, Upwelling-Influenced Shelf (Southeast Brazilian Bight, South Atlantic)

Abstract Rhynchonelliform brachiopods were diverse and often dominant benthos of tropical seas in the Paleozoic. In contrast, they are believed to be rare in open habitats of modern oceans, especially at low latitudes. This study documents numerous occurrences of rhynchonelliform brachiopods on a modern tropical shelf, particularly in areas influenced by upwelling. Extensive sampling of the outer shelf and coastal bays of the Southeast Brazilian Bight revealed dense populations of terebratulid brachiopods (>103 individuals / m2 of seafloor) between 24° and 26°S. On the outer shelf, brachiopods are more abundant than bivalves and gastropods combined. However, brachiopod diversity is low: only four species belonging to the genera Bouchardia, Terebratulina, Argyrotheca, and Platidia were identified among over 16000 examined specimens. Brachiopods occur preferentially on carbonate bottoms and include two substrate-related associations: Bouchardia (40–70% CaCO3 weight content) and Terebratulina-Argyrotheca (70–95% CaCO3). All four species display a broad bathymetric range that contrasts with a narrow depth tolerance postulated for many Paleozoic rhynchonelliforms. The most abundant populations occur in the depth range between 100 and 200 m, and coincide with zones of shelf-break upwelling, where relatively colder and nutrient-rich water masses of the South Atlantic Central Water are brought upward by cyclonic meanders of the South Brazil Current (a western boundary current that flows poleward along the coast of Brazil). This is consistent with previous biological and paleontological studies that suggest upwelling may play a role in sustaining brachiopod-dominated benthic associations. The presence of abundant brachiopods in the open habitats of the tropical shelf of the western South Atlantic contrasts with current understanding of their latitudinal distribution and points to major gaps in our knowledge of their present-day biogeography. The ecological importance of rhynchonelliform brachiopods in modern oceans and their role as producers of biogenic sedimentary particles may be underestimated.

SEQUENCE STRATIGRAPHIC ANATOMY OF DIVERSITY PATTERNS: LATE QUATERNARY BENTHIC MOLLUSKS OF THE PO PLAIN, ITALY

Abstract The influence of sequence stratigraphic (base-level driven) processes on patterns derived from the fossil record is receiving increasing attention. This study explores the stratigraphic anatomy of diversity patterns across two late Quaternary fourth-order sequences deposited on the Po Plain (Italy) over the last 150 ky (i.e., the two most recent glacial-interglacial cycles). The rich mollusk fauna, dominated by extant forms, preserved as a part of well-understood eustatic cycles, offers a testing ground for exploring how climate-driven sea-level changes influence sample diversity, diversity turnover, and higher-order diversity patterns within and across systems tracts and sequences. These two fourth-order depositional sequences were densely sampled from three cores. The data (152 species and 22777 specimens from 29 Holocene and 19 Pleistocene samples) were analyzed using single-sample and multisample rarefaction techniques. In all three cores and for both cycles, sample-level diversity decreased upward within sequences: the late transgressive systems tract samples displayed the highest equitability and richness, and the highstand systems tract samples displayed the lowest diversity (the trend primarily reflects the increase in the dominance of most common species in highstand systems tract samples). This pattern is likely due to a combination of ecological, environmental, and taphonomic processes. Multisample rarefaction indicates that species turnover is more limited in transgressive phases of both depositional cycles. This trend may reflect increasing environmental heterogeneity of marginal habitats averaged within shallowing-upward successions or decreasing time averaging associated with increasing sedimentation rates during highstand systems tract phases of the cycles. The sequence and multisequence diversity levels are lower than those observed within individual late transgressive systems tracts, indicating that species turnover was minimal both within as well as across the last two glacial-interglacial cycles. This study shows that species richness and equitability patterns of the most common mollusk species track closely the sequence stratigraphic architecture of late Quaternary successions of the Po Plain.

Sieves and Fossils: Effects of Mesh Size on Paleontological Patterns

Abstract Bulk samples are among the foremost sources of quantitative data retrieved from the fossil record. However, such samples are not sieved in a uniform way, even among research projects with a very similar research focus. Several studies recently have demonstrated the sensitivity of paleontological patterns to changes in sieve size and underscored the importance of controlling for mesh size in paleontological analyses. Building on previous work, this study exploits a large dataset of Miocene mollusks that is fortuitously suitable for exploring the effect of mesh size: dimensions of each fossil were measured, all samples were acquired with fine screens (≤1 mm mesh), and data for numerous paleoecological and taphonomic variables were obtained for each specimen. This large dataset was sieved artificially (i.e., subsampled in computer simulations) to explore the effects of mesh size. The results show that paleontological variables, from taphonomic and paleoecological parameters to diversity indices, can fluctuate, to various degrees, as a function of mesh size. Some parameters (e.g., evenness indices) appear remarkably invariant to mesh size, while others (e.g., encrustation rate) can vary dramatically with a small change in mesh size. Most importantly, even when the compared datasets are sieved uniformly with the same standard mesh size, outcomes of comparative analyses can lead to disparate conclusions when that standard size is changed. The mesh-size sensitivity observed here for a wide assortment of paleontological patterns points to ubiquitous influence of body size on taphonomic, ecological, and evolutionary patterns and underscores the importance of developing sampling strategies and/or corrective analytical measures for making data more comparable in terms of mesh size across and within studies. Future research also should concentrate on evaluating secular trends in size-filtering aspects of extraction methods used to acquire quantitative samples throughout the Phanerozoic fossil record.

COMPARATIVE ANALYSIS OF DRILLING FREQUENCIES IN RECENT BRACHIOPOD-MOLLUSK ASSOCIATIONS FROM THE SOUTHERN BRAZILIAN SHELF

Abstract Over 14,000 specimens—5,204 brachiopods, 9,137 bivalves, and 178 gastropods—acquired from 30 collecting stations (0 to 45 m depth) in the Ubatuba and Picinguaba bays, southern Brazil, were compared for drilling frequencies. Beveled (countersunk) circular-to-subcircular borings (Oichnus-like drill holes) were found in diverse bivalves but also in the rhynchonelliform brachiopod Bouchardia rosea—a small, semi-infaunal to epifaunal, free-lying species that dominates the brachiopod fauna of the southern Brazilian shelf. Drill holes in bivalve mollusks and brachiopods are comparable in their morphology, average diameter, and diameter range, indicating attacks by a single type of drilling organism. Drill holes in brachiopods were rare (0.4%) and found only at five sampling sites. Drillings in bivalves were over 10 times as frequent as in brachiopods, but the average drilling frequency was still low (5.6%) compared to typical boring frequencies of Cenozoic mollusks. Some common bivalve species, however, were drilled at frequencies up to 50 times higher than those observed for shells of B. rosea from the same samples. Due to scarcity of drilled brachiopods, it is not possible to evaluate if the driller displayed a nonrandom (stereotyped) site, size, or valve preference. Drilled brachiopods may record (1) naticid or muricid predation, (2) predation by other drillers, (3) parasitic drillings, and (4) mistaken or opportunistic attacks. Low drilling frequency in brachiopods is consistent with recent reports on ancient and modern examples. The scarcity of drilling in brachiopods, coupled with much higher drilling frequencies observed in sympatric bivalves, suggests that drilling in brachiopods may have been due to facultative or erroneous attacks. The drilling frequencies observed here for the brachiopod-bivalve assemblages are remarkably similar to those reported for Permian brachiopod-bivalves associations. This report adds to the growing evidence for an intriguing macroecological stasis: multiple meta-analytical surveys of present-day and fossil rhynchonelliform brachiopods conducted in recent years also point to persistent scarcity and low intensity of biotic interactions between brachiopods and drilling organisms throughout their evolutionary history.

BODY SIZE ESTIMATES FROM THE LITERATURE: UTILITY AND POTENTIAL FOR MACROEVOLUTIONARY STUDIES

Abstract Images in the monographic literature represent an important but relatively untapped resource for paleontologists. In particular, they could provide vast amounts of body size data. It is possible, however, that images of specimens represent a biased sample of the fossil record. Thus, the quality of these data must be assessed before body size estimates from the literature can be used in analyses. Two complementary datasets were constructed for a group of bivalve and brachiopod species from the Paleozoic and the Cenozoic. The monograph dataset consisted of length measurements taken from all unique images of a species in a monograph. The counterpart bulk dataset consisted of comparable measurements taken from a set (n > 10) of bulk-collected specimens of the same species acquired from the same locality as those figured in the monograph. These paired datasets were used to assess the quality of monographic data. Bias direction and magnitude were assessed by using the bulk sample of a species as an estimate of its underlying size-frequency distribution. Bias was estimated for each monographed specimen by calculating its percentile-value in relation to the size-frequency distribution for that species. All species groups had mean values within the 70th to 85th percentile range, indicating a significant bias toward monograph specimens that are larger than the mean of the bulk sample. The consistency of bias was evaluated by comparing the monograph sample mean to the bulk sample mean for each species. When compared in bivariate scatter plots, all species groups yielded significant regression lines with slopes near unity, indicating highly consistent, yet predictable, bias in each case. This trend persisted when the data were grouped taxonomically, geographically, or by year of monograph publication. These results indicate that size measurements of monographed specimens of bivalves and brachiopods consistently record similar size classes for most species. This bias is easy to remove and doing so renders size data from images in monographs useful for macroevolutionary studies of body size.

Actualistic Taphonomy: Death, Decay, and Disintegration in Contemporary Settings

When Leonardo da Vinci contended that fossil shells of Monferrato (Lombardy, Italy) were not left there by the biblical deluge, he argued the point by observing that neither live bivalves nor their empty shells possibly could have traveled 250 miles from the Adriatic to Monferrato in 40 days (MacCurdy, 1938; Cadee, 1990). Five centuries later, the approach pioneered by the Tuscan scholar has become a discipline in its own right: it will be referred to here as Actualistic Taphonomy. Taphonomy denotes the study of fossilization processes: a search for principles governing the transition of organismal remains from the biosphere to the lithosphere (Efremov, 1940). Actualistic denotes the study of present-day patterns and processes in search for clues helpful in investigating their historical records. Practitioners of Actualistic Taphonomy collect observations on death, decay, and burial of organisms in contemporary settings to aid and guide interpretations of diverse data offered by the fossil record. This special issue of PALAIOS includes eight case studies representing a diverse cross-section of the research themes of modern actualistic taphonomy. All projects have been conducted in the same study area (San Juan Islands, Washington State, USA), and represent the efforts of students who attended a 5-week field course offered in summer 2002 at Friday Harbor Laboratories of the University of Washington (Fig. 1). The fact that the eight projects offer such a diverse spectrum of research themes despite the similarity in geographic setting and logistics is an excellent demonstration of the remarkable intellectual breadth of actualistic taphonomy. FIGURE 1 —Diverse taphonomic research settings available around the San Juan Islands. (A) A sample of live and dead invertebrates obtained by dredging off the coast of San Juan Island (photograph by Adam Tomasových). (B) The well-sorted sand tidal flats of False Bay, San Juan Island; a few miles …

POTENTIAL PALEOECOLOGIC BIASES FROM SIZE-FILTERING OF FOSSILS: STRATEGIES FOR SIEVING

Abstract The methods by which fossils are extracted from sediments can alter their observed size-frequency distributions, which can in turn alter observed paleoecologic patterns. Building on previous work, this study uses virtual sieving (i.e., replicated via subsampling on a computer) to test the effects of size filtering on the apparent ecologic composition of a database of Miocene mollusks in which the size of every specimen was measured. When simulated mesh sizes varied by nearly an order of magnitude (2–10 mm), the apparent relative abundances of tiering, motility, and feeding categories varied substantially in some individual bulk samples. Not surprisingly, the extent to which variations in mesh size affected the ecologic proportions of a sample depended in part on its size-frequency distribution. If the goal is to characterize the ecology of adult assemblages, the chosen mesh size should not be so small that juveniles dominate the results or so large that a majority of specimens are excluded. For many molluscan assemblages, 2–4 mm should often be appropriate. For preexisting data sets composed of heterogeneously collected data, there is a positive result: averaging samples together to produce a mean view of ecologic composition tends to remove the more egregious effects of the size-filtering bias. Thus, comparisons of the ecologic composition of single samples may be sensitive to mesh-size effects, but comparisons of regional or global faunas are likely more robust, and variations in size filtering may not be an obstacle to large-scale, secular comparisons of ecospace use. Measuring ecologic importance using biomass instead of abundance also reduced the effects of the mesh-size bias by reducing the influence of small-bodied individuals on ecologic proportions.

Bouchardia rosea, a vanishing brachiopod species of the Brazilian platform: taphonomy, historical ecology and conservation paleobiology

Dead-live faunal comparisons can offer powerful data to detect natural or human-induced population changes in the late Holocene. Here, we document dead–live comparisons for death assemblages of the brachiopod Bouchardia rosea in nearshore (0–45 m) environments along the northern coast of São Paulo State, Brazil. The sampling programme included 30 stations (14 at Ubatuba, 16 at Picinguaba bay). The bottom was sampled via Van Veen grab sampler, and also dredged. Out of 30 stations, 22 yielded brachiopods. The fidelity estimates were obtained by direct comparisons of live biota with dead shells. A total of 6627 brachiopods were recovered, 5339 (80.6%) from Ubatuba and 1288 (19.4%) from Picinguaba. Out of these, 6621 (99.9%) were empty, dead shells, while only six individuals (0.1%) were found alive, all in the Picinguaba Bay. These results suggest extremely poor dead–live compositional fidelity for B. rosea assemblages. The spatial data suggest that the distribution of B. rosea accumulations has been highly patchy in the region, whereas the great scarcity of live brachiopods may point to a recent decline in local populations. Several lines of evidences indicate that changes in water temperature, nutrient availability, population history and even pollution, may have all affected spatio-temporal dynamics of B. rosea populations.

QUANTITATIVE TAPHONOMY OF A TRIASSIC REPTILE TANYTRACHELOS AHYNIS FROM THE COW BRANCH FORMATION, DAN RIVER BASIN, SOLITE QUARRY, VIRGINIA

Abstract The Virginia Solite Quarry occurrence of exceptionally abundant and uniquely preserved specimens of the tetrapod Tanytrachelos ahynis offers an opportunity to quantify multiple aspects of vertebrate taphonomy. Presence or absence of 128 skeletal elements and of 136 skeletal variables were recorded for 99 specimens from two distinct layers within the quarry—lake cycles 2 and 16. Anatomical completeness, or the percent of bones and variables present in a specimen, is low in spite of protection given by anoxic bottom waters from predators and scavengers; the median specimen preserves 14.5% of bones and 11.8% of measured variables. Specimen size, soft-tissue preservation, and postexhumation weathering have no significant effect on specimen completeness; soft-tissue preservation has a significant impact on degree of articulation. Tanytrachelos specimens with heterotopic bones are not significantly more complete than those lacking such bones; this quantitative pattern reinforces independent qualitative taphonomic evidence supporting a biological rather than taphonomic interpretation of the two morphotypes. Lake cycles 2 and 16 differ significantly in terms of articulation and anatomical completeness when anatomical specimen completeness has been corrected for postdepositional faulting. Preservation frequency of bones and variables, or the percent of specimens in which a bone or variable is present, varies greatly but is low with substantial removal of smaller skeletal elements and preferential preservation of such hindlimb elements as femora. Low anatomical specimen completeness and positive correlation between bone size and frequency of preservation both indicate specimen disturbance by minor hydraulic currents. Taphonomic patterns support a low-to-moderate-depth depositional environment, which is shallower than the original reconstruction.