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Main Research in the Paleoecology Lab

Mary Droser's research addresses questions of ecological change through time and across intervals of major taxonomic turnover, particularly the Precambrian-Cambrian and Ordovician radiations. These questions can be addressed through a variety of tools including paleoecological levels, biofabrics (ichnofabric, shell beds, constructional fabrics), and studies of abundance and diversity. 

Recent Reseach Interests

Unlike taxonomic changes, it is impossible to “count” ecological changes.  However, ecological changes can be ranked in that some are larger than others.  In order to aid in evaluation of paleoecological changes, a series of paleoecological levels was developed. With colleagues (Dave Bottjer, Peter Sheehan, George McGhee), I am using this method to compare Phanerozoic mass extinction and radiations. The Precambrian-Cambrian radiation was one of the most significant events in the history of life.  Much of the evidence for this radiation comes from trace fossils and ichnofabrics. However, there has not yet been a systematic comparative study of the ichnological record through this interval at different localities. This is the focus of current work with Sšren Jensen and Jim Gehling.  

The Ordovician radiation established the Paleozoic fauna and resulted in a tripling of marine diversity. Late Cambrian communities are vastly different from Late Ordovician communities but the nature of how these changes took place remains unexamined. With colleague Peter Sheehan, Richard Fortey, and students (see  below), I am currently looking at the nature of ecological changes through this event. With Andy Gale I am additionally examining geochemical changes.  

Biofabrics are sedimentary rock fabrics that result from the interaction of physical and biological processes.  Biofabrics can be used for a variety of paleoecological issues including, as a proxy for examining changes in abundance or dominants within a habitat, changes in utilization of the infaunal habitat, nature of constructional fabrics.  Current work on biofabrics includes Triassic shell beds (with Dave Bottjer), Cretaceous ichnofabrics, and Precambrian-Cambrian ichnofabrics and shell beds.
 Nearly all of my research projects are heavily field based and aimed at finding ways to recognize ecological changes independent of, though incorporating, taxonomic data.

Post Docs

Sšren Jensen, Ph.D. Univ. Uppsala, 1993

Main Research Interests 

1. Discrete trace fossils and ichnofabrics in the terminal Proterozoic and Cambrian. Particular attention to the functional interpretation and morphologic reconstruction of trace fossils and the role of taphonomic processes on trace fossil morphology and diversity.

2. Problematic sedimentary structures, particularly in the terminal Proterozoic and Cambrian. My starting assumption is that the morphological complexity attainable by physical sedimentary structures traditionally has been underestimate, particularly under conditions of low bioturbation and in the likely presence of microbial mats.

3. Experimental production of animal trace fossils. This remains a dramatically under-explored source of information on the preservation of trace fossils and of animal behavior.

Anette Hšgstršm, Ph.D. 1998, Uppsala University

My main interests lies with various Palaeozoic problematic groups, especially the scleritome-bearing Machaeridia. A group that has remained largely unstudied despite being nearly ubiquitous in many Palaeozoic faunas. Machaeridians are known from the lowermost Ordovician to the mid Permian and has been reported from several parts of the world. Present work focuses on the life styles of machaeridians from different environments ranging from deeper outer shelf settings to shallow biohermal and reefal associations, the origin and phylogeny of the group, and exploring the possible use of machaeridians in stratigraphy and palaeogeography. Emphasis is on material from lower Palaeozoic deposits of Baltica, Arctic Russia, eastern North America and the Great Basin. Broader questions are aimed at, for example, understanding functional constraints of different scleritome types by comparing both fossil and recent morphologies.  

Graduate Students

Robert Gaines - BS, William & Mary, MS, University of Cincinnati

Dissertation Project Title: “Were Burgess Shale Faunas burrowed away? Exploring links between an expanding infaunal habitat and the decline of soft-bodied preservation”

 Bob’s research focuses on testing a hypothesis advanced by Allison & Briggs (1993, 1994), that soft-bodied constituents of the Burgess Shale fauna were essentially “burrowed away” from the fossil record by the rise of significant burrowing in the Early Paleozoic.  Burgess Shale faunas, Conveniently, the Great Basin of the Western US hosts an ideal succession of Lower Paleozoic strata upon which to address this question.   Bob is testing this hypothesis by tracking the invasion of the infaunal habitat in mudstone settings across the Cambrian & Ordovician, by examining multiple mudstone units deposited in a diverse array of environmental settings, and exhibiting a wide variety of preservational conditions.  Three of the ten known Lower and Middle Cambrian lagerstŠtten occur in Utah: the Middle Cambrian Spence Shale, Wheeler Shale, and Marjum Formation are all subjects of his  research. Additionally, Bob is working on the Lower Cambrian Latham Shale of the Eastern Mojave (California), and several other units which are not known to contain soft-bodied faunas: Middle Cambrian C-plus Shale (Nevada), Upper Cambrian Dunerburg Formation (Nevada), Upper Cambrian Whirlwind Formation (Utah), Lower Ordovician Al Rose Formation (California), Middle Ordovician Kanosh Formation (Utah), Middle Ordovician Swan Peak Formation (Utah).

Heather Moffat - AB, Smith College, MS, University of Southern California, MS, University of Rochester

 Heather's dissertation study examines the temporal, geographic and environmental distributions of fossil representatives of the prominent Pacific Coast sand dollar genus Dendraster.  Her work focuses on refining knowledge of the paleoenvironments and paleoecological communities associated with the genus throughout its evolutionary history from the Miocene through the Pleistocene.  Heather is interested in documenting the spatial and temporal patterns of environmental distribution and community structure for Dendraster.  Her field-based project examines Dendraster-bearing strata spanning the genus' geographic range,  from Oregon south to Baja California Sur(Mexico).  

In addition, Heather's dissertation will document degrees of eccentricity within and between the examined Dendraster assemblages. It has been proposed that degrees of eccentricity within Dendraster may correlate to environmental variations (see Raup, 1956; Stanton et al., 1979).  One aspect of Heather's dissertation is to test this hypothesis within fossil Dendraster assemblages for which she has detailed paleoenvironmental information to determine if there is a relationship between eccentricity of fossil Dendraster and the paleoenvironments which they inhabited.

Bill Phelps- BS(s), University of Utah

Bill's dissertation study examines the ecologic changes of soft-substrate level bottom marine communities across the Late Devonian mass extinction.  To assess these changes, he is examining biofabrics (biologically influenced sedimentary rock fabrics) in Late Devonian and Early Carboniferous limestones to obtain ecologic data such as species abundance and community dominance.  While the level bottom community has been studied taxonomically, no studies have attempted to examine it ecologically.  By utilizing biofabrics to study this extinction from an ecological view point, he hopes to gain a better understanding of the ecologic effects of this mass extinction, and suggest approaches for examining other mass extinctions.  This study will also have implications for modern conservation efforts, such as whether to preserve species or habitat.

Seth Finnegan - AB, University of Chicago

Seth is currently completing his MS here; in the fall he will be beginning work towards a Ph.D.  For his thesis, Seth is looking at paleoecological changes across the Lower-Middle Ordovician boundary in the classic Ibex area of western Utah.  This boundary has been the subject of increasing attention in recent years, and there is growing evidence that this interval may be of critical importance in the Ordovician reorganization of marine ecosystems (Droser & Sheehan, 1993, Miller & Foote, 1996, Westrop & Adrain, 1998, Li & Droser, 1999).  It has been suggested that major ecological shifts are concentrated around this period, but this has not been tested.  A particular controversy focuses on apparent changes in the abundance of  trilobites and brachiopods across the boundary. A detailed analysis of abundance data, often ignored in paleobiological studies, can lead to the recognition of important patterns of ecosystem change not apparent from taxonomic diversity data alone. Examination of abundance data is necessary if we are to comprehend the mechanisms, not just the patterns, of ecological shifts.  This is particularly true during episodes of rapid ecological change like the great Ordovician biodiversification event, which vastly increased the complexity of marine ecosystems.

Diana Thiel-BS, University of Delaware

Diana is beginning her thesis work studying brachiopod shell concentrations in the Great Basin.  Brachiopods were one of the most important elements of the Paleozoic Evolutionary Fauna.  They were in the Ordovician, what bivalves are to modern seas.   These organisms diversified significantly in the early Ordovician, but later, in the middle Ordovician, there is an enigmatic increase in brachiopod abundance that manifests itself as thick, laterally extensive shell concentrations, or beds. This apparent decoupling of increases in diversity and abundance necessitates a closer look at how radiations events proceed and will be the focus of her research. 

Diana will be working on the well preserved classic lower and middle Ordovician sections in the Confusion Range of west central Utah in the Lehman and Kanosh formations to answer a number of paleoecological and environmental questions.   These shell beds provide the unique opportunity to examine the nature of biotic diversification in an ecological and environmental framework over a period of time.

Recent papers by Post Docs and Graduate Students

Jensen, S. 1997. Trace fossils from the Lower Cambrian Mickwitzia sandstone,   south_central Sweden Fossils and Strata 42, 1_110.

Jensen, S. & Grant, S.W.F. 1998. Trace fossils from the Dividalen Group, northern Sweden: implications for Early Cambrian biostratigrapy of Baltica. Norsk Geologisk Tidsskrift 78, 305_317

Jensen, S., Gehling, J.G. & Droser, M.L. 1998. Ediacara_type fossils in Cambrian sediments. Nature 393, 567_569.

Jensen, S. & Mens, K. 1999. A Lower Cambrian shallow_water occurrence of the branching ‘deep_water’ type trace fossil Dendrorhaphe from the Lontova Formation, eastern Latvia. PalŠontologische Zeitschrift 73, 187_193.

Droser, M.L., Gehling, J.G. and Jensen, S. 1999. When the worm turned: concordance of early Cambrian ichnofabric and trace fossil record in siliciclastics of South Australia. Geology27, 625_628.

Jensen, S., Saylor, B.Z., Gehling, J.G. & Germs, G.J.B. 2000. Complex trace fossils from the terminal Proterozoic of Namibia. Geology 28, 143_146.

Budd, G.E. & Jensen, S. 2000. A critical reappraisal of the fossil record of the bilaterian phyla. Biological Reviews of the Cambridge Philosophical Society 75, 253-295.

 Brett, Brett, C.E., Moffat, H.A., and Taylor, W., 1997, Echinoderm Taphonomy, Taphofacies and LagerstŠtten, in Waters, J. and Maples, C., eds., Short Course on Echinoderms, Paleontological Society Special Paper, v. 3, p. 147-190.

Hšgstršm, A.E.S., 2000: Articulated lepidocoleid machaeridians from the Silurian of Gotland. GFF, 122(2), 219-226.

Hšgstršm, A.E.S., 1997: Machaeridians from the upper Wenlock (Silurian) of Gotland. Palaeontology, 40, 817-832.

Hšgstršm, A.E.S. & Taylor, W.L.: The machaeridian Lepidocoleus sarlei Clarke, 1896, from the Rochester Shale (Silurian) of New York State. Palaeontology in the press.

Ebbestad, J.-O. R. & Hšgstršm, A.E.S.,: Shell repair from failed predation in an upper Ordovician brachiopod. GFF in the press.

Budd, G.E., Hšgstršm, A.E.S. & Gogin, I.,: A Possible Cambrian Myriapod from Siberia. PalŠontologisches Zeitschrift, in the press.

Moffat, H.A. and Bottjer, D.J., 1999, Echinoid Concentration Beds:  Two Extreme Examples from the Stratigraphic Record, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 149, p. 329-348.