earth and environmental sciences
Paleobotany, palynology, Precambrian paleobiology, and the origin of land plants. We are especially excited to be working on new discoveries of Cambrian cryptospores, evidence that land plants evolved much earlier than previously thought. For a more complete description of ongoing research, please see the Paleobotany Laboratory web site at Weston Observatory.
GE 146 - Origin & Evolution of Life (Spring 2009)
GE 335 - Topics in Geobiology (Spring 2009)
GE 330 - Paleobiology (Spring 2010)
CURRENT GRADUATE STUDENTS AND PROJECTS
David Li Quantification and analysis of micro-burrows in the Consasauga Group in eastern Tennessee.
M.S. ALUMNI AND PROJECTS
Paleoecology of some glaucony bearing units of the Middle and Upper Cambrian of Laurentia.
Effects of the evolution and expansion of the grassland biome on Miocene climate: a modeling/palynology study. (1999)
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.
Evidence of trophic collapse as a forcing factor in the Late Devonian mass extinction.
Strother, P. K. 2008.
Acritarch species richness yields a first order metric of marine primary productivity of large phytoplankton in the Palæozoic oceans. Acritarchs decline smoothly over a period of 100 Myr (ca. 425Ma 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.
52nd Palæontological Association Annual Meeting, 18-21 December 2008, University of Glasgow. Abstracts: 82.
Lower Palæozoic cryptospore ultrastructure and the origin of multilaminate sporoderm.
Strother, P. K.
Spores of embryophytic origin are traced back in time to the Middle Ordovician (Darriwilian), based on a benchmark of tetrahedrally arranged tetrads and spores broken out of such tetrads. Earlier spore-like palynomorphs appear to be organized as sets of dyads and dyad pairs—these are topologies that are not found in extant plants, so their evolutionary relationship with the embryophytes appears tenuous. For one thing, once the consistent association of four spores in tightly-held tetrads is lost, it is difficult to prove that such forms are the immediate products of meiosis. Recent investigations of Cambrian cryptospore ultrastructure by W. A. Taylor have yielded some answers about the potential affinities of Cambrian dyads—some of which retain ultrastructural details of some crown group liverworts. This implies that the Cambrian forms might well be ancestral to modern embryophytes. In terms of sporoderm evolution, it appears that the multilaminated walls of liverworts may have evolved through the fusion of uniformly thick distinct laminae. These laminae, in turn appear to result from sequential pulses of sporopollenin deposition that is derived centripetally, since multiple spore bodies become enclosed within synoecosporal walls. The topology of a newly described late Cambrian cryptospore is consistent with the concept of sporopollenin transfer from a hypothetical zygote wall to the walls of meiospores produced by DNA endoduplication rather than simple meiosis (a twist on a model proposed by Alan Hemsley in 1994). These observations, based on fossil spore morphology and topology, are being used to generate new hypotheses about evolution of both sporogenesis and meiosis itself during the algal-plant transition.
"Integrating evolution and development of pollen and spores: new perspectives," Linnean Society of London Palynology Specialist Group, Burlington House, Piccadilly, London. October 29, 2008.
Cryptospores and the evolution of sporogenesis in bryophytes.
Strother, P. K. & W. A. Taylor.
Axial plants are preceded in the geologic column by a 100 Myr record of cryptospore monads, dyads and tetrads. Cambrian dyads and tetrads are typically enclosed in a common synoecosporal wall comprised of one to three discrete laminae. Others possess multilaminate walls, similar to Riccia. Many Cambrian cryptospores are dispersed as dyads and dyad pairs; tetrahedrally-arranged meiospores do not appear in the fossil record until Middle Ordovician. The fossil record indicates that meiotic sporogensis evolved over time and was not a singular evolutionary event. This conclusion is supported by the work of Shimamura and others who noted in 2004 that the control of spindle formation (MTOCs) in bryophytes, varies from algal-like (centriolar) to higher-plant-like (diffuse). Embryophytes may have evolved from charophytes through the serial acquisition of structures (characters) associated with selection in subaerial habitats—a proposition that is also supported by recent discoveries of Cambrian fragmentary plant remains.
Joint meeting of the 6th International Association of Lichenologists and the American Bryological and Lichenological Society. Asilomar, California, July 13 - 17, 2008.
Cryptospores and the Origin of Land Plants
Paul K. Strother
Palæobotany Laboratory, Weston Observatory of Boston College, Department of Geology & Geophysics, 381 Concord Road, Weston, Massachusetts 02493 US
Evidence from microfossil cryptospores and small organic fossils (mesofossils) indicates that land plants (embryophytes) evolved prior to the Middle Cambrian. The earliest records of land plants are small cryptospore tetrads recovered from the Rome Formation in eastern Tennessee, USA. These are complemented by an extensive suite of cryptospore tetrads, dyads, polyads and monads recovered from several Middle to Upper Cambrian sites from both the eastern and western margins of the ancient Laurentian continent. Cryptospore wall ultrastructure varies from homogeneous to laminated, matching that seen in Caradocian (Ordovician) tetrads derived from putative sporangia of liverwort affinity and modern Riccia. Clusters of Cambrian cryptospores associated with recalcitrant tissues point toward an embryophytic rather than algal derivation. Small pieces of pseudo-cellular cuticles, similar to that seen in some Silurian preparations, have now been isolated. Recently discovered mesofossils of Upper Cambrian age are composed of a plexus of intertwined organic filaments. The filaments possess oblique cross walls, supporting their interpretation as the resistant protonemata of bryophytic gametophytes. A fair and balanced assessment of these fossils now supports the presence of a persistent subaerial bryophytic flora during most of the Cambrian. These new discoveries support the recognition of a persistent protonematal phase in plant life cycles as an important step in the evolution of plant adaptation to the terrestrial environment.
Paléobotanique et Evolution du Monde Végétal: Quelque Problèmes d'Actualité. Séminare International, Collège de France, Paris. May 23-25, 2007.