earth and environmental sciences
Paleobotany, palynology, Precambrian paleobiology, and the origin of land plants. I am interested in the fossil evidence of the algal-plant transition; the origin of basal eukaryotic supergroups, and the role of phytoplankton in the Devonian extinction. For a more complete description of ongoing research, please see the Paleobotany Laboratory website at Weston Observatory.
EESC1146: Origin and Evolution of Life (Spring 2017)
EESC3335: Topics in Geobiology (Spring 2017)
Current Collaborative Projects
Cryptospores from Ordovician and Cambrian rocks of Saudi Arabia - CIMP-ARAMCO Project Paleobiology of the Nonesuch Shale and the Torridonian Group - with C. Wellman, Sheffield Cambrian Cryptospores and the origin of land plants - with W. Taylor, Wisconsin Eau-Claire Biomarkers of the Nankoweap Butte section, Grand Canyon - with C. Hallman group, Bremen Palynology of Triassic/Jurassic boundary - with Bas van de Schootbrugge, Utrecht.
M.S. Alumni and Projects
Paleoecology of Some Glaucony Bearing Units of the Middle and Upper Cambrian of Laurentia. (2008)
Effects of the Evolution and Expansion of the Grassland Biome on Miocene Climate: A Modeling/palynology Study. (1999)
Wellman, C.H. and P.K. Strother, 2015, The Terrestrial Biota Prior to the Origin of Land Plants (embryophytes): A Review of the Evidence. Palaeontology, May 2015, doi: 10.1111/pala.12172.
Strother, Paul K., Traverse, M. Vecoli, 2015, Cryptospores from the Hanadir Shale Member of the Qasim Formation, Ordovician (Darriwilian) of Saudi Arabia: Taxonomy and Systematics. Review of Palaeobotany and Palynology, 212: 97-110.
Wacey, D., M. Saunders, M. Roberts, S. Menon, L. Green, C. Kong, T. Culwick, P.K. Strother, and M.D. Brasier, 2014, Enchanced Cellular Preservation by Clay Minerals in 1 Billion-year-old Lakes. Scientific Reports, 4: 5841-5841.
Graham, L.E., P. Arancibia-Avila, W.A. Taylor, P.K. Strother, and M.E. Cook, 2012, Aeroterrestrial Coleochaete (Streptophyta, Coleochaetales) Models Early Plant Adaptation to Land. American Journal of Botany, 99: 130-144.
Strother, P.K., Battison, L., Brasier, M. Wellman, C., 2011, Earth's Earliest Non-marine Eukaryotes. Nature, 473: 505-509.
Strother, P.K., T. Servais, and M. Vecoli, 2010, The Effect's of Terrestrialization on Marine Ecosystems: The Fall of CO2. In Vecoli, M., G. Clement, and B. Meyer-Berthaud (eds.), The Terrestrialization Process: Modelling Complex Interactions at the Biosphere-Geosphere Interface. Geological Society of London, Special Publications, 339: 37-48.
Taylor, W. A. & P. K. Strother, 2009, Ultrastructure, Morphology, and Topology of Cambrian Palynomorphs from the Lone Rock Formation, Wisconsin, USA. Review of Palæobotany and Palynology, 153: 296-309.
Strother, P. K., 2008, A Speculative Review of Factors Controlling the Evolution of Phytoplankton During Paleozoic Time. Revue de micropaléontology, 51: 9-21.
Beck, J. H. & P. K. Strother, 2008, Spores and Cryptospores from a Silurian Section near Allenport, Pennsylvania. Journal of Paleontology, 82(5): 857-883.
Strother, P. K., 2008, A New Cambrian Acritarch from the Nolichucky Shale, Eastern Tennessee. U.S.A. Palynology, 32: 205-212.
Strother, P. K. G. D. Wood, W. A. Taylor & J. H. Beck, 2004, Middle Cambrian Cryptospores and the Origin of Land Plants. Memoirs of the Association of Australasian Palaeontologists, 29: 99-113.
Baldwin, C. T., P. K. Strother, J. H. Beck & E. Rose, 2004, Palaeoecology of the Bright Angel Shale in the Eastern Grand Canyon, Arizona, U.S.A. Incorporating Sedimentological, Ichnological and Palynological Data, 213-236. In The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. McIlroy, D. (ed.). Geological Society of London, Special Publications, 228.
Creating a Taxonomy of Cambrian Cryptospores
Strother, P.K., Commission Internationale du Microflore du Paleozoique, University of Bergen, Norway, September 2015
Problematic palynomorphs extracted from shales from the Lower Cambrian Rome Formation and the Middle Cambrian Conasauga Group in eastern Tennessee are classified as cryptospores: they possess laminated wall ultrastructure, and were shed in polyads that reflect successive meiosis during endosporogenesis. Similar lamellated spore-wall ultrastructure, which is found in Ordovician - Devonian cryptospore dyads, has recently been confirmed in the living basal liverwort, Haplomitrium gibbisae (Steph.) Schust., the only living land known to produce spore dyads. The Cambrian cryptospores are highly plesomorphic, which has made initial attempts at creating a taxonomy somewhat taxing. Spore wall surfaces are generally smooth, without ornamentation; some new taxa are characterized by mottled walls which reflect their underlying multilaminate ultrastructure. In some instances both dyads and tetrads occur within a single spore mother cell (SMC) wall. It is also clear, from cryptospore packets that are attached in regular geometries, that the same plany was producing differing numbers of spores as the end result of reduction division. This fact, in combination with populations of cryptospore packets that have retained their SMC walls, provides a basis for establishing a highly-lumped taxonomy. The weight of evidence indicates that the Cambrian cryptospores were shed by thalloid sporophytes belonging to lineages of (aeroterrestrial) charophytes that were actively evolving in subaerial settings. This conclusion is consistent with Bower's theory of the antithetic origin of the plant sporophyte and with recent studies in bryophyte sporogenesis which predict that spores evolved prior to the evolution of a somatic sporophyte phase.
Evolution in Precambrian Terrestrial Ecosystems
Strother, P.K., 4th International Paleontological Conference, Mendoza, Argentina, October 2014
Most evidence of life on land during the Precambrian comes from geochemical studies, but two geological deposits, the Nonesuch Shale (Michigan, USA) and the Torridonian Sequence (Scotland), provide direct evidence of the organisms that inhabited non-marine habitats approximately 1 billion years ago. These are lacustrine ecosystems which contain some cyanobacteria, including species whose colonial habit mimics that of Microcystis aeruginosa, but which otherwise appear to be dominated by unicellular eukaryotic remains. Individual cells can be quite large, and multicellular forms are scarce. Morphological asymmetry in cell form, including attachment features, indicates that protists had adapted to benthic settings. Rare, small dorsiventral thalli could be the remains of early amphibious gametophytes, although this would considerably pre-date the origin of true land plants. The occurrence of Moyeria cabotti, which is clearly euglenoid in character, establishes that the supergroup Excavata is ancient. Specimens of Moyeria showing whorl reduction were probably photosynthetic, so their presence is indirect evidence of the prior origin of the green algae by this time. Multicellular balls of cells appear to be related to the opisthokonts, establishing a Mesorproterozioc origin to the clade as well. Ecologically it is not possible to rule out that cyanobacteria were still the primary producers at 1 Ga. The direct evidence of photosynthetic algae, is by inference only - there are no unique morphologies that establish the photosynthetic nature of many of these eukaryotic microfossils. Given a wide range of unicellular morphotypes however, one would assume that a fair portion of the microfossils recovered from these deposits would have been primary producers, i.e. algae. Indeed, the number of morphotypes from these deposits far exceeds that found in coeval marine settings. This leads to the conclusion that non-marine settings provided a refuge for eukaryotes during the 1800 to 800 Ma period of oceanic anoxia dictated by geobiological studies. In addition, habitat heterogeneity associated with non-marine settings, may have been an important selective driver of speciation during this time. At the very least, the fossil record of terrestrial settings at the Meso-Neoproterozoic boundary supports recent phylogenomic studies suggesting a terrestrial origin to the primary endosymbiotic acquisition of the chloroplast.
Paleoproterozoic Prokaryotic Palynomorphs
Strother, P. K., The International Biogeoscience Conference, Nagoya, Japan, November 2013
Introduction: The transition from prokaryotic cell structure represents the most fundamentally profound evolutionary transition in the history of life on Earth. The fossil record provides a first order constraint upon the time of this transition, which is currently set between 1900 and 1700 Ma (Lamb et al., 2009; Peng et al., 2009). Shale samples from two distinct environments were sampled from ca. 2.0 Ga rocks in the Belcher Islands, Clarke Island and the Richmond Gulf (Canada). Typically, palynomorphs recovered from acid maceration are described as acritarchs, a term which carries with it the connotation of eukaryotic affinity - we generally do not think of either eubacteria or archebacteria as capable of producing large cells with robust cell walls. None of the palynomorphs recovered from these samples retains the distinct vesicular (walled) character associated with walls of younger eukaryotic palynomorphs (Peng et al., 2009). In spite of large size, it is possible to interpret all of these finds as being of a prokaryotic nature.
Results: In some cases, spherical to sub-spherical palynomorphs appear to be composed of interlocking granulated and highly carbonized organic matter. Similar granular microspheres can be found in associated silicified stromatolites. Some apparently multicellular spheroids are also preserved as palynomorphs. At the Richmond Gulf site, organic films and granular compressions, some approaching the size of Grypania are found. The microfossils and mesofossils recovered from the Belcher and Richmond Gulf Groups are composed of granular, black, organic matter which is quite distinct in texture from palynomorphs recovered from younger macerations. Similar, granular organic microfossils from Latest Mesoproterozoic rocks have been interpreted as being of prokaryotic origin (kah et al., 2012). These fossils are also composed of highly carbonized organic matter and show no specific characters, other than size, that support an affinity with the Eucarya.
Discussion: The occurrence of palynomorphs characterized by granular textured walls, suggests that they are the remains of degraded prokaryotes and associated eps, rather than eukaryotes. The significance of this observation is that acid maceration procedures associated with palynology may be capable of recovering organic structures and microfossils which are prokaryotic in nature. This means that we should no longer assume that the recovery of a palynomorph assemblage implies a eukaryotic provenance to that assemblage. In particular, the use of the term, acritarch, with its implication of planktonic algal affinity, should be used with caution when describing such remains. These findings are consistent with both molecular clock and fossil evidence that place the origins of the eukaryotes between 1900 to 1700 Ma. These results indicate the eukaryotic cell probably evolved after 2.0 Ga.
References: Kah, L.C., Bartley, J.K., Teal, D.A., 2012, Precambrian Research, 200-203, 82-103. Lamb, D.M., Awramik, S.M., Chapman, D.J., Zhu, S., 2009, Precamb. Res., 173, 93-104. Peng, Y., Bao, H., Yuan, X., 2009, Precamb. Res., 168, 223-232.
Evidence of Trophic Collapse as a Forcing Factor in the Late Devonian Mass Extinction
Strother, P.K., 52nd Palaeontological Association Annual Meeting, University of Glasgow, Scotland, December 2008
Acritarch species richness yields a first order metric of marine primary productivity of large phytoplankton in the Palaeozoic oceans. Acritarchs decline smoothly over a period of 100 Myr (ca. 425 Ma to 325 Ma), from a Silurian high of 27 genera/Myr to 1 genus/Myr. The robustness of this data set yields a unique opportunity to look at the Devonian mass extinction as caused by partial trophic collapse in marine ecosystems, based on a cascading effect of declining large phytoplankton. The loss of phytoplankton as a food resource should have had a more direct effect on those organisms living entirely in the water column than those in benthic communities. This allows for a simple predictive model which has two components: 1) the cause of extinctions would have been entirely gradual, representing a long-term forcing gradient, and 2) the zooplankton and nekton, as members of the neritic and pelagic marine realm, should have suffered greater levels of extinction than benthic marine organisms. While it is difficult to find a simple metric to document this latter prediction, three groups of neritic/pelagic organisms - graptolites, chitinozoans and fishes - do exhibit major changes in their evolutionary history at the end of the Devonian.