November 4, 2013 at 3:26 pm

Hembree Makes Five Presentations at GSA, One with Student

Ohio University faculty made an impact with 23 presentations at the Geological Society of America’s 125th Anniversary Annual Meeting & Exposition Oct. 27–30 in Denver.

Mike Hils ’14M & Dan Hembree presented on BEFORE THE WEB: NEOICHNOLOGY OF BURROWING SPIDERS. Hils is a master’s student in Geological Sciences in the College of Arts & Sciences.

True spiders (Order Araneae) first appear during the Carboniferous, but fossils of infraorders Mygalomorphae and Araneomorphae do not appear until the Triassic. Although burrowing is considered to be a primitive trait, fossil burrows attributed to spiders are known mainly from the Pleistocene. This may be due to a failure to recognize fossil spider burrows. While many modern mygalomorph and some araneomorph spiders burrow in soil, there are few studies on the morphology of their burrows. This study aims to determine the range of burrow morphologies produced by spiders and to determine if burrow morphology is changed in response to environmental stresses. Two species of burrowing spiders were studied: the mygalomorph Gorgyrella inermis (South African trapdoor spider) and the araneomorph Hogna lenta (field wolf spider). Both species are obligatory burrowers that exhibit different predatory behaviors; G. inermis ambushes prey from its burrow entrance whereas H. lenta leaves its burrow to actively hunt. The morphology of each species’ burrows was determined by placing individuals in sediment-filled terraria for intervals of 14 and 30 days. The composition and moisture content of the sediment was modeled after the natural conditions of each species. Subsequent 30-day trials exposed each spider to sediments of increasing clay content and density and increased or decreased moisture content. At the end of each trial the spiders were removed from their burrows and the burrows were cast. Burrow casts were described and measured for the number of surface openings, maximum depth, tunnel width and height, width-to-height ratio, circumference, slope, total length, complexity, and tortuosity. Both species produced vertical shafts, but H. lenta burrows had one to two surface openings whereas G. inermis had only one. The burrows of G. inermis were deeper and lined with more silk than the burrows of H. lenta. Increasing sediment density produced shallower burrows for H. lenta and no changes for G. inermis. Both species were unable to burrow when sediment was drier than 35%. The results of this study may be used to assist in the recognition of fossil burrows produced by early spiders in units where body fossils are absent and to enable better paleoecological and paleoenvironmental interpretation of units containing fossil burrows.

Dr.  Royal Mapes, Dr. Daniel Hembree, & others presented on THE NAUTILUS DEATH CENOTE. Hembree is Associate Professor of Geological Sciences in the College of Arts & Sciences.

Exploration of a cenote on Lifou (Loyalty Islands, South Pacific) revealed more than 35 empty shells of the cephalopodNautilus macromphalus in saltwater on the cenote floor, ~35-40 meters below the piezometric surface. This is the first known occurrence of modern Nautilus shells in a karstic system. The shells are scattered and oriented randomly on the sloping scree of the cenote floor. Most are mature individuals and are unbroken with faded brown stripes. Some have cemented carbonate mud partly filling the umbilical opening and body chambers. Seven shells were collected for analysis. These shells have a chalky outer surface but no mineral precipitates. No other organisms, living or dead, were observed on the Nautilus shell surfaces, attached to the limestone rubble, or anywhere in the cenote. Radiocarbon dating of the shells indicated ages of 6380 ± 30 to 7095 ± 30 y BP, making these the oldest Nautilus shells known since the Pleistocene. The 238U series radionuclides210Pb (half-life = 22.3 y) and 226Ra (half-life = 1600 y) were also measured and generally showed radioactive equilibrium between these nuclides, consistent with their old radiocarbon ages. At least one specimen showed excess 210Pb, however, suggesting an age of <100 y. Correcting the 226Ra activities for decay yielded 226Ra activities much greater than those found in living Nautilus. Exposure to high activities of 222Rn and 226Ra in the salty groundwater of the cenote likely altered the activities originally incorporated into the shells. The taphonomic pathway of this Nautilus death assemblage is only partly understood at this time. Human placement of the shells in the cave is rejected based on the radiocarbon age and geometry of the cenote. The restricted radiocarbon ages of the shells suggest that a connection to the adjacent marine waters existed for ~700 years and Nautilus occasionally entered from the seaward site through a flooded karstic system. Unable to find the exit, they were trapped and died. After ~6400 y BP, the connection with the adjacent ocean was lost. This unique occurrence provides a minimum age for the appearance of Nautilus in the Loyalty Islands and provides insight into fossil cephalopod occurrences in karstic environments.


Yes, bioturbation is a major process in the evolution of soils and landscapes based on plant and animal trace fossil evidence in paleosols through deep time, if not THE major process. Bioturbation plays a role in the production of organic material (plants and roots), mixing (animal behavior), and the creation of macropores and macrochannels (active and open plant root channels and animal activity) in the vadose zone. Soils, because of their physical and biological components and biophysicochemical activities, are also referred to as the critical zone—where physical materials and biomass are transformed into soils and its nutrients made available to the community, whose boundaries range from the top of the canopy to the groundwater. Continental strata in deep time record the concomitant evolution of continental bioturbation and paleopedogenesis that is intimately tied to depositional systems and postdepositional conditions in the critical zone. In deep time, ichnofossils (microbial, plant, and animal interactions with each other and physical media) and paleosols together form ichnopedologic facies that record environmental variables and their effects across gradients of time, lithology, disturbances, biological activity, and topography. The study of modern animal bioturbation rates and patterns in soils and landscapes demonstrates the vast amount of work done to mix sediment and create pores and channels into which materials and fluids can be translocated and soil structure produced. Field and laboratory experiments observing and quantifying the burrowing activity of animals demonstrate the great amount of work animals can do in a short amount of time in a particular three-dimensional space. Results of these studies are manifest in the rock record as ichnopedologic facies that record the significance of bioturbation in the evolution of soils and landscapes through time through (i.e., stratigraphic record). Since the Ordovician, ichnopedologic facies became increasingly more diverse, abundant, and penetrative from mid to late Paleozoic, through the Mesozoic and into the Cenozoic. From the Permian to the Neogene, a large number of ichnopedologic patterns are similar to those seen today. Thus, bioturbation mediates biological, pedological, and hydrological processes from micro- to macroscales.


Research continues to demonstrate that ichnofossils produced by terrestrial and freshwater-aquatic organisms provide distinct and important information on the physicochemical processes unique to the continental realm. Such information enhances the use of ichnology by providing empirical to quantitative information for reconstructing and modeling past environments, ecosystems, and climates. Ichnofossils in marine and continental settings can appear similar in morphology; however, they record physicochemical characteristics unique to each depositional setting and the postdepositional conditions. The dominant controlling factor in continental settings is the groundwater profile, and the vadose zone is where most activity takes place. The best way to understand organism-media (=substrate) and organism-organism interactions in continental settings is to study them in the field and laboratory while being produced under controlled conditions. Observations of organisms while making traces and casting their traces in the field can relate behaviors visible on the surface and the three-dimensional (3D) morphospace that burrow complexes occupy below the surface. Similarly, these organisms can be collected and their subterranean behaviors observed in experimental setups under controlled settings, such as grain size, moisture, media consistency and density, and slope. Locomotion and excavation behaviors can be recorded through digital video to understand the movements that produce them. Resultant traces from these behaviors can also be scanned with a multistripe laser triangulation scanner and manipulated in 3D editing software for a range of semiquantitative and quantitative analyses, which can be used to improve morphological and statistical analyses of modern and ancient traces for biological, ichnotaxonomic, pedological, environmental, and hydrological interpretations. Digital models can be made tangible with 3D printers and shared with others for research and teaching. Traces in terrestrial settings are intimately associated with the critical zone and pedogenesis. The degree of pedogenesis in relation to sedimentation rate and basin dynamics can be used to interpret landscape evolution and production of significant stratigraphic surfaces: short- to long-term periods of stability.


Our knowledge of the burrows produced by modern continental animals is limited. This makes the interpretation of continental ichnofossils difficult and inhibits our understanding of ancient soil ecosystems despite the presence of plant and animal trace fossils in even Early Paleozoic paleosols. Actualistic studies of living animals in the field and laboratory provide the data that make trace fossils invaluable to paleoecological and paleoenvironmental reconstructions. These studies allow for the interpretation of tracemakers, associated behaviors, and the environmental factors that influenced burrow production. The goal of this project is to determine how well burrows produced by known continental tracemakers engaged in known behaviors under controlled environmental conditions can be differentiated on the basis of morphology alone. This project involved the analysis of scorpion, whip scorpion, millipede, centipede, salamander, and skink burrows produced in a laboratory setting. The burrows include a diverse assemblage of shafts, ramps, U-, J-, W-, Y-shaped and helical burrows, mazeworks, and boxworks. Qualitative burrow descriptions include basic architecture, shape, orientation, internal structure, and surficial features. Quantitative descriptions include depth, slope, total length, tunnel width, height, and circumference, complexity, and tortuosity. On average, each animal species produced three distinct burrow morphologies, although there was overlap in basic burrow architectures between taxonomic groups. The quantitative aspects of the burrow morphologies were compared using nonparametric similarity and distance indices as well as cluster analyses to determine if the burrow casts could be effectively differentiated based upon their tracemakers, behaviors, and environmental conditions. By using multiple properties of burrow morphology to compare the burrows statistically, the burrows could be separated by different behaviors and tracemakers. Levels of similarity were highest amongst animals with similar morphologies, burrowing techniques, and behavioral patterns. Differences due to environmental conditions were minimal. The results from these experiments provide an assessment of our ability to reconstruct ancient soil ecosystems based on trace fossil morphology.


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