Research in the Hembree Lab

Department of Geological Sciences, Ohio University

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My research interests primarily lie with the interaction of sedimentological and biological processes. I am interested in animal-substrate interactions in ancient and modern continental (or “non-marine”) environments. These interactions are preserved in the fossil record as trace fossils. Trace fossils provide an in situ record of ancient biodiversity, ecology, and environment. The study of trace fossils, therefore, provides vital information for accurate paleoenvironmental reconstructions. As sensitive indicators of environmental and climatic change, ichnofossils are also useful for detailed sequence stratigraphic analysis.

In my research, I interpret the paleoenvironmental, paleoclimatic, and paleoecological significance of paleosols and ichnofossils preserved in the geologic record. This involves not only the study of paleosols and continental trace fossils throughout geologic time but also the experimental study of burrowing behaviors of extant terrestrial annelids, arthropods, amphibians, and reptiles. My current research projects involve the study of the influence of climate changes on ancient soils and soil ecosystems including those of the Pennsylvanian of southeast Ohio, Permian of eastern Kansas, and the Eocene to Miocene of Colorado and Wyoming.

I am interested in recruiting motivated Masters students interested in these research areas. For more information see News and Opportunities.

Continental Ichnology
My research in continental ichnology has covered a range of geologic time and depositional settings. My research on Paleozoic vertebrates of Kansas has involved the study of the aestivation burrows of the lysorophid amphibian, Brachydectes elongates, from pond deposits within the Lower Permian Speiser Shale. These burrows represent the earliest evidence of aestivation behavior by tetrapods in the fossil record. This behavior allows aquatic and semi-aquatic animals to survive long periods of time without water and has become common among extant amphibians and reptiles. Along with the detailed study of the surrounding paleosols, associated ichnofossils and body fossils, these aestivation burrows provide evidence for the interpretation of seasonality in the Permian of the North American midcontinent.	Top view of in situ lysorophid burrow casts in an ephemeral pond deposit of the Permian Speiser Shale, eastern Kansas.	Lysorphid burrow casts (Torridorefugium eskridgensis) containing skeletal material excavated from the Permian Speiser Shale.
My dissertation research covered a more recent period of paleoenvironmental change, the late Eocene and early Oligocene. I completed a detailed study of the ichnofossils associated with paleosols in the White River Formation of northeastern Colorado (Hembree and Hasiotis, 2007). These deposits contain the fossils of a number of burrowing vertebrate groups, including the Amphisbaenia, an order limbless lizard common in modern tropical environments. The paleosols of the White River Formation contain a diverse assemblage of continental ichnofossils including those produced by dung beetles (Pallichnus and Macanopsis), bees (Celliforma), ants (Parowanichnus), earthworms (Edaphichnium), wasps, beetles, plants, and vertebrates. I used the lateral and vertical changes in the distribution of ichnofossils to interpret paleoenvironmental changes in the sedimentary basin. Along with ichnofossils I have also applied paleopedologic and sedimentologic principles to determine which environmental changes within the basin were due to autogenic and allogenic processes.	Large rhizoliths (fossil roots) preserved in an Oligocene paleosol from northeast Colorado. Small, elliptical fecal pellets within an Oligocene paleosol. These are interpreted as earthworm fecal pellets.	System of interconnected burrows and chambers interpreted as a dung beetle nest. Preserved within an Oligocene paleosol. Cross sectional view of a dung beetle brood burrow in an Oligocene paleosol.
I am currently studying Pennsylvanian continental ichnofossils from the paleosols of southeast Ohio. The Pennsylvanian world contained all of the animals that comprise modern soil ecosystems. The most abundant of these soil organisms were the arthropods. Pennsylvanian fossils of arthropod detritovores include millipedes, arthropleurids, mites, and insects all of which would have engaged in feeding and dwelling behaviors in the soil based on comparisons with modern examples. Fossils of arthropod herbivores include flying insects. These organisms would have had temporary interaction with the soil through the production of such reproductive structures as nests or brood burrows. Fossils of arthropod predators include scorpions and arachnids. Modern arthropod predators construct burrows for use as dwellings, temporary resting places, and reproduction. Pennsylvanian amphibians and early reptiles, such as microsaurs, temnospondyls, and cotylosaurs, likely constructed burrows for use as dwellings, temporary nests, and possibly aestivation.	Ichnofossils interpreted as millipede burrows from the Pennsylvanian Casselman Formation, southeast Ohio.	Rhizoliths from paleosols of the Pennsylvanian Casselman Formation.
My research in continental ichnology also involves experimental work with modern organisms. Through detailed field observation and laboratory experiments with modern burrowing animals, continental tracemakers and their trace morphologies may be correlated to: 1) such substrate conditions as soil texture, moisture, and organic content; 2) depositional environments; and 3) such climatic factors as temperature and precipitation. I have established an animal burrowing laboratory that includes such burrowing animals as tarantulas, scorpions, and millipedes. The goal of this research is to develop a database that provides qualitative and quantitative paleoenvironmental data for variations in continental trace fossil type and morphology. For more information on this research click here.	Giant African millipedes (Lophostreptus rutilans) used in burrowing experiments.	Casts of spiral burrows produced by African millipedes burrowing in loose, organic-rich sediment.
Paleopedology
The study of paleosols is important to geologists and biologists alike. Paleosols provide unique evidence for interpreting ancient terrestrial ecosystems, environment, and climate. They also provide some of the best evidence of the evolution of terrestrial ecosystems as well as the interaction of terrestrial organisms and the substrate. I have used paleopedology extensively along with my studies of continental ichnology. My research has included the study of paleosols from the Pennsylvanian and Permian of Kansas, Oklahoma, and Ohio, the Triassic of Colorado, the Eocene of Wyoming, and the Oligocene of Colorado, South Dakota, Nebraska, and Wyoming. In addition, by studying the characteristics of modern soils in Kansas through field work and laboratory analysis, the pedogenic features preserved in these paleosols have been used to interpret specific paleoenvironmental and paleoclimatic conditions. My current research on Pennsylvanian paleosols of Ohio incorporates a heavy field component in addition to laboratory analyses, including the determination of bulk chemistry, clay mineralogy, and stable isotope ratios. There is an extensive record of Pennsylvanian paleosols in southeastern Ohio. Exposures of the Allegheny and Conemaugh groups in particular allow for both lateral and vertical analyses of the strata. One 30 m section, for example, contains 10 different paleosols interpreted as four different types based on parent material, pedogenic modification, and ichnofossils.	Miocene paleosols in northeast Colorado.	Pennsylvanian paleosols in southeast Ohio.
Reptile Paleobiology
The members of the Reptilia possess many significant evolutionary adaptations for life in a variety of continental environments. These adaptations are extremely useful in paleoenvironmental and paleoclimatic studies. Such adaptations include extensive morphological modification, from body elongation to complete loss of limbs, for fossorial lifestyles. Many of my current projects involve the fossil record, ichnology, phylogeny, paleoecology, and biogeography of amphisbaenians. North American fossil amphisbaenians are present in Paleocene to Miocene deposits of Colorado, Nebraska, South Dakota, and Wyoming. I have completed a paleobiogeographic study of the Amphisbaenia using worldwide occurrences of both fossil and modern taxa (Hembree, 2006). This study has indicated that the origin of this group, whose fossils appear only in the Paleocene, may extend as far back as the Triassic. I have also completed a phylogenetic study and reclassification of the North American family of amphisbaenians, the Rhineuridae (Hembree, 2007). This study has involved the reexamination of fossils collected since the end of the nineteenth century and resulted in the clarification of many taxonomic irregularities. Finally, my study of the Amphisbaenia has involved the study of living amphisbaenians including variations in their burrowing behavior to changes in temperature, moisture, and substrate conditions (Hembree and Hasiotis, 2006). The ecology of the modern amphisbaenians, therefore, provides an excellent analog for interpreting the paleoecology of the fossil forms. The study of these living animals, then, can help in interpreting changes in the paleoenvironments and paleoclimate of North America during the late Paleogene and Neogene. My study of the Amphisbaenia is ongoing as are studies of other modern reptile groups that are either entirely fossorial or facultative burrowers.	Amphisbaena camura, a living amphisbaenian. Skull of Rhineura floridana, a North American amphisbaenian. Revised phylogeny of North American amphisbaenians.	Cast of an amphisbaenians burrow system excavated in a 10 gallon aquarium. Branching tunnels in an amphisbaenians burrow complex produced in the lab. Push marks preserved on the surface of the tunnels in the amphisbaenians burrow complex. These surficial structures provide clues to determine both the excavation method and tracemaker.
Paleozoic Tetrapod Evolution and Paleoecology
The early evolution of tetrapods has been another major area of interest in my research. Fossils generally classified as amphibians, or non-amniote tetrapods, continue to comprise a diverse, paraphyletic assemblage of lineages that seem to resist further resolution. Recent phylogenetic work, however, has begun to clarify some of these relationships. The fossils of these organisms preserve the initial modifications necessary for life on land. Their evolution can be used to interpret paleoenvironmental change in their habitats. In light of the modern biodiversity crisis, studying such reactions would help biologists and paleontologists understand how current life may be affected my modern environmental change. Eastern Kansas provides extensive outcrops to study, all containing abundant fossils of Pennsylvanian and Permian tetrapods. My research to date has involved Early Permian ephemeral pond communities and their responses to environmental changes through both brief time periods (10s to 100s of years) and geologic time (Hembree et al., 2004). These deposits preserve complete, articulated fossil specimens of early tetrapods which are also ideal for use in phylogenetic studies.	Articulated lysorophid skeletons from the Permian Speiser Shale, eastern Kansas.	SEM photos of fossils collected from a Permian ephemeral pond including lungfish teeth, unidentified tetrapod teeth, ostracodes, and charophytes.
Copyright © 2007 Daniel Hembree Last revised: 4/2008