Nicole Bonuso

Phanerozoic trends in the global diversity of marine invertebrates.

It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.

ASSESSING THE ECOLOGICAL DOMINANCE OF PHANEROZOIC MARINE INVERTEBRATES

Abstract Ecological studies have revealed that the functional roles of dominant species in modern communities are often more important than overall diversity in governing community composition and functioning. Despite this recognition that abundance and diversity data are both required for a complete understanding of ecological processes, many paleoecological studies focus on presence-absence data, possibly because of concerns regarding the taphonomic fidelity of time-averaged fossil accumulations. However, the abundance of organisms in shell beds has been shown to provide a fairly accurate record of the living community, suggesting that the benefits of relative-abundance data should be reconsidered. Recognition of ecologically dominant species in local fossil assemblages should be based on counts of relative abundance and assessment of ecological role. Ecological dominance at larger spatial or temporal scales can be quantified using the mean rank order of a clade and the proportion of assemblages where the clade is present, providing unbiased, quantitative values for measuring the ecological importance of a clade. Their utility has been tested with three case studies encompassing a range of geographic and taxonomic scales, using a database of 1221 Ordovician–Paleogene quantitative fossil collections. The dominance metrics for rhynchonelliform brachiopods, bivalves, and gastropods broadly parallel anecdotal trends, even including some more detailed patterns documented by regional studies. An examination of substrate preferences for brachiopod and bivalve orders confirms the abundance of infaunal bivalves in siliciclastics and epifaunal bivalves in carbonates, but it also reveals intriguing patterns regarding substrate preferences among rhynchonelliform brachiopod orders. The final case study analyzed changes in dominance between early Mesozoic fossil assemblages from Tethys and Panthalassa, documenting significant geographic differences in the ecological importance of rhynchonelliform brachiopods and bivalves. These large-scale dominance patterns often approximately matched those inferred from diversity trends; however, there are also times when dominance was decoupled from diversity, indicating that further investigation of ecological dominance will provide additional insights into ecological influences on the Phanerozoic history of life. “Are most species simply passengers in ecosystems that are run basically by a few dominants?” (Worm and Duffy, 2003, p. 631)

Statistical testing of community patterns: Uppermost Hamilton Group, Middle Devonian (New York State: USA)

Abstract We present an extensive and rigorously controlled quantitative paleoecological study within an interval of inferred coordinated stasis. This Middle Devonian Hamilton Group study completes a 20-yr project by providing data within the unresolved upper Hamilton Group section. Together with other rigorously controlled studies, these data sets have the potential to address the larger question of coordinated stasis in the fossil record. We collected data from the Windom Member, Moscow Formation (uppermost Hamilton Group), to test different statistical approaches to define paleocommunities. We evaluate various techniques, including non-parametric multidimensional scaling and agglomerative hierarchical clustering to decipher community patterns. Additionally, we advocate regular use of cluster significance testing along with ANOSIM (i.e. analysis of similarities) when examining ecological data. Together these techniques test the significance of sample groups more rigorously than conventional testing (e.g. discriminant analysis or analysis of variance (ANOVA)). Our results indicate that communities within this upper Hamilton Group interval exhibit variable taxonomic membership within a relatively stable ecological structure.

Does coordinated stasis yield taxonomic and ecologic stability?: Middle Devonian Hamilton Group of central New York

Statistical tests of coordinated stasis within the Middle Devonian Hamilton Group demonstrate significant temporal changes in taxonomic composition and ecological structure of the macrofauna throughout a 5‐6 m.y. time span. The analysis, based upon a collection of .38,000 specimens obtained over a 20 yr period from the Hamilton Group of central New York, used highly controlled sampling techniques, applied within a single, well-defined lithofacies. Assemblages were tested for stability through time, as would be predicted by the model of coordinated stasis. Our results reveal that within at least one major Hamilton environment, taxonomic and ecological stability are not statistically significant and therefore do not support the hypothesis of coordinated stasis.

A TEST OF BIOGEOGRAPHICAL, ENVIRONMENTAL, AND ECOLOGICAL EFFECT ON MIDDLE AND LATE TRIASSIC BRACHIOPOD AND BIVALVE ABUNDANCE PATTERNS

Abstract Analysis of Middle Triassic data indicates that biogeography influences sample distributions, whereas depositional environment and stratigraphic position play secondary roles in governing sample patterns. During this time, taxa differed among biogeographic realms, while the general ecology remained the same: epifaunal benthos— pedunculate and epibyssate suspension feeders—dominate Middle Triassic samples much as they did in the Early Triassic. In contrast, Late Triassic data prove to be more complex in terms of ecology compared to Middle Triassic. Here, guild structure dictates the faunal patterns in addition to biogeographic realm and stratigraphic position, and an overall increase of infaunal life habits occurs—burrowing suspension and deposit feeders increase. Although diversity after mass extinction began to recover at the Early-Middle Triassic boundary, our results indicate that ecology remained stable through the Middle Triassic until the more modern life habits (e.g., infaunalization) increased in the Late Triassic. We conclude that the taxonomic and ecological differences among Late Triassic geographic regions recorded the initiation of a more mobile and infaunal life habit indicative of a modern lifestyle. Our results also indicate that this modernization did not necessarily unfold simultaneously and in coordinated fashion within regions and throughout time. Instead, details of guild expansion or stability may be region specific.

Patterns of fossil distributions within their environmental context from the Middle Triassic in South Canyon, Central Nevada, USA

Abstract The Middle Triassic records the return of diverse marine communities after the severe effects of the end-Permian mass extinction. This diversification leads to the Mesozoic/modern adaptive radiation resulting in substantial changes in marine communities in comparison to their Paleozoic predecessors. This analysis focuses on the faunal abundance, ecological patterns, and environmental interpretation of a Middle Triassic section in Central Nevada. Twelve bulk samples were collected. Visible fossils were identified and tallied from hand samples and thin-sections were used to aid in environmental interpretation. Beginning in the Late Anisian, we observed an ammonoid dominated to flat-clam, epifaunal dominated benthic community within a muddy, quiet, inner shelf depositional environment. Through time, epifaunal bivalves dominate within a middle shelf environment followed by an increase in infaunalization and shell-thickness. During this time the presence of oncoids and the reported finding of corals suggest the middle shelf environment gave way to a higher energy patch reef shelf edge environment. Finally, we observe epifaunal brachiopods communities at the top of our section deposited in a middle shelf environment. In sum, we observe the dominance of modern taxa (i.e., bivalves) with Paleozoic ecologies (i.e., epifaunal), followed by the dominance of modern taxa with Modern ecologies (i.e., infaunal, thick shells) and then a return to Paleozoic taxa (i.e., brachiopods) and Paleozoic ecologies within an overall transgressive environment.

A QUANTITATIVE STUDY OF BENTHIC FAUNAL PATTERNS WITHIN THE PENNSYLVANIAN AND EARLY PERMIAN

Abstract Using abundance data, this study explores quantitative patterns from marine benthos, including implications for paleogeography, depositional environment, stratigraphic position, taxonomic groups (brachiopod or mollusc), substrate preferences, and ecological niches. Twenty-nine brachiopod- and bivalve-dominated fossil assemblages from the Pennsylvanian and Early Permian of North and South America, Thailand, and Australia were analyzed from carbonate-platform environments; specifically, Nevada, Kansas, Oklahoma, Texas, Utah, New Mexico, Venezuela, Kanchanaburi (Thailand), and Queensland (Australia). Samples were categorized by paleogeographic location, depositional environment, and age to help differentiate factors controlling the faunal patterns. Pooled from primary and summary literature resources, 336,321 specimens were identified to genus level and classified in terms of taxonomic membership, substrate preference, and ecological niche. Data were analyzed using detrended correspondence analysis (DCA) and multi-response permutation procedure cross-validated a-priori categories (e.g., paleogeography, depositional environment, stratigraphic position, and specimen ecology). Multivariate analyses indicate that the separation between genera and the orthogonal trends implies that paleoecological patterns within the studied late Paleozoic faunal associations were influenced strongly by the abundance of sessile versus mobile faunal components.

SHORTENING THE GAP BETWEEN MODERN COMMUNITY ECOLOGY AND EVOLUTIONARY PALEOECOLOGY

Zeno of Elea, the ancient Greek philosopher, proposed a paradox that captures one of the challenges facing evolutionary paleoecologists: that which is in motion must arrive at the halfway stage before it arrives at its goal (Aristotle, 1984). Zeno describes a footrace between Achilles and a tortoise and explains that if Achilles, a fast runner, gives the tortoise a head start, he will never overtake the tortoise. Achilles must traverse a finite series of distances before catching the tortoise, but in the time it takes Achilles to achieve this distance the tortoise crawls forward a tiny bit farther. As a result, Achilles is forever chasing a tortoise he can never actually catch. This seeming paradox resembles one of the challenges facing evolutionary paleoecologists; that is, the ever-present challenge of keeping up with developments in modern community ecology—a swift opponent with a definite head start. Several major patterns of functional biology and life habits are well established for marine organisms throughout the Phanerozoic (Bambach, 1985, 1993; Sepkoski and Miller, 1985; Bottjer and Ausich, 1986). The lack of coherent theories to help understand these macroevolutionary trends, however, keeps evolutionary paleoecology a step behind (Jackson, 1988; Allmon, 1994; Allmon and Bottjer, 2001). The good news is that this paradox is not irresolvable. Perhaps evolutionary paleoecologists, like the mathematicians who used calculus to produce practical solutions to Zenos paradox, can use math to gain headway; for example, the mathematical model …