Daniel I. Hembree, PhD , Ohio University
During the past year I have undertaken experimental research of the burrowing behaviors of 16 different terrestrial arthropod taxa including four species of millipedes (Archispirostreptus gigas, Orthoporus ornatus, Narceus gordanus, Narceus americanus), six species of scorpions (Pandinus imperator, Hadrurus arizonensis, Heterometrus spinifer, Scorpio maurus, Smeringurus mesaensis, Uroctonus mordax), two species of whipscorpions (Phrynus marginemaculata, Mastigoproctus giganteus), two centipede species (Scolopendra alterans, Hemiscolopendra marginata), and two trapdoor spider species (Myrmekiaphila coreyi, Gorgyella sp.). I have also begun research on four vertebrate species including two species of skinks (Chalcides ocellatus, Mabuya multifasciata) and two species of salamanders (Ambystoma tigrinum, Abystoma opacum). With these species I have completed several series of experiments involving the alteration of substrate composition, soil moisture, and air temperature in 30, 56, and 75 gallon aquariums. These experiments have yielded many excellent burrow casts for each group of animals which have been measured and described and are currently being compared using nonparametric statistics.
The research so far has yielded new information on the way in which terrestrial arthropods construct burrows, how they behave below the soil surface, and how they alter the soil environment. For example, predatory terrestrial arthropods such as scorpions and whip scorpions, which have been generally regarded as minimally involved in soil processes, have been found to be capable of moving large volumes of soil and sediment. In the process, these animals improve the quality of the soil and alter the surface environment. Terrestrial arthropod detritivores such as millipedes have been found to produce large numbers of temporary to permanent open burrows up to 50 cm into the experimental soils. These burrows dramatically increase the permeability of these sediments even when they have been actively or passively filled.
Each species currently under study is represented by a unique array of burrowing methods and morphologies, some of which vary with changes in the soil environment. The methods the animals use to burrow have been found to have the greatest effect on their ability to handle changes in environmental conditions. Animals that are substrate excavators (physically move sediment particles from the subsurface to the surface) are able to burrow into the widest range of substrates (composition, consistency and moisture). These animals tend to inhabit regions with seasonal climates. Those animals that burrow by intrusion or compression (create openings by compacting sediment below the surface) tend to have more tightly constrained environmental requirements. These animals typically inhabit warm, wet environments.
The identification of the unique burrow morphologies produced by these terrestrial arthropods will be invaluable in identifying subaerial exposure surfaces where pedogenic overprinting is poorly developed or poorly preserved. In the Pennsylvanian strata of southeastern Ohio, the identification of continental ichnofossils has been very useful in locating sequence boundaries and lowstand deposits. The continental origin of many of these ichnofossils was difficult to determine until this experimental research was undertaken.
This grant has supported two graduate students as research assistants and two undergraduate students as laboratory assistants. Their duties have included daily animal care and laboratory maintenance as well as assisting in experimental setup, data collection, and the description of burrow casts. As part of this job I have been instructing these students on the field of ichnology and assigned readings to aid in their understanding of the project. The students have also been directly involved in the setup of the experiments and in the collection of data during the experiments. The two graduate students will be presented the current results of their research with the skinks and salamanders the 2011 Annual Geological Society of America meeting and are currently preparing manuscripts for submission to PALAIOS. Both undergraduate students are coauthors on a paper recently submitted to Palaeontologica Electronica.
I have presented results of this research at the Geological Society of America 2010 Annual Meeting and I will be presenting additional results of the GSA 2011 Annual Meeting where I will also be running a full day session on actualistic experimental research in paleontology. I currently have one manuscript in review and four manuscripts in preparation the last of which will be ready for submission by August 2012.
Despite the fact that my PRF UNI grant has been expended, work on this project will continue using equipment, animals, and other resources obtained through funds from the ACS. For example, a new graduate student starting work in my lab in 2011 will be assisting in research with three current and two new soil arthropod species designed to investigate the production and significance of simple cylindrical burrows in terrestrial deposits. Trace fossils of this type are very common in the geologic record but are poorly understood. In addition to the paleoecological and paleoenvironmental significance of this project, this research will also be designed to investigate the effect of simple cylindrical burrow on the porosity, permeability, and ultimately fluid flow through terrestrial mudstones.