Daniel I. Hembree

The Trace-Fossil Record of Vertebrates

SUMMARY: The trace-fossil record of vertebrates contains behavioral evidence of fish, amphibians, reptiles, dinosaurs, mammals, and birds in continental, transitional, and marine paleoenvironments since the Devonian. The study of vertebrate trace fossils includes tracks, trails, burrows, nests, and such feeding traces as bite marks, coprolites, gastroliths, and regurgitalites. Behaviors recorded by these traces include various kinds of (1) locomotion, (2) dwelling, (3) aestivation, (4) breeding and nesting, as well as (5) acts of feeding, which also result in (6) digestion, (7) regurgitation, and (8) defecation. These trace fossils represent the interaction between a vertebrate and a medium, which includes softgrounds, firmgrounds, hardgrounds, plants, and other animals. Humans also have a trace-fossil record, and, like other vertebrates, produce numerous trace fossils that result from different kinds of behavior.

Amphibian burrows and ephemeral ponds of the Lower Permian Speiser Shale, Kansas: evidence for seasonality in the midcontinent

Abstract Burrows attributed to the lysorophid Brachydectes elongatus occur within a green mudstone lens in the Lower Permian (Wolfcampian) Speiser Shale (Council Grove Group) of eastern Kansas. The burrow-bearing unit consists of a 100 m long lens of massive, calcareous, silty mudstone with a maximum thickness of 35 cm. The lens also contains the fossils of fish, amphibians, reptiles, charophytes (Stomachara), and ostracodes (Carbonita). The mudstone lens pinches out laterally into red, pedogenically modified mudstone. The burrows occur in three layers. At the top of each layer is a subaerial exposure surface indicated by rhizoliths, mudcracks, and coarse-grained lags. The mudstone lens is interpreted as the deposit of a shallow, ephemeral pond. The burrows occur in three vertically and temporally separated clusters with concentrations up to 20/m2. The burrows show two types of architecture. Type I burrows are elongate, elliptical tubes 4–32 cm long and 2–7 cm in width. Type II burrows are short, elliptical tubes 1.5–3.5 cm in length and 2.5–5 cm in width. The burrow fill consists of a mudstone capped by sandy siltstone. Each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix. While similar to Permian lungfish burrows, the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils. The occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non-burrowed, massive mudstone indicates that burrowing occurred in response to episodic, perhaps seasonal, droughts on the Permian coastal plain. The lysorophid burrowing behavior is analogous to that of the extant amphibians Amphiuma sp. and Siren intermedia, which inhabit rivers and ponds in the southeastern USA.

PALEOSOLS AND ICHNOFOSSILS OF THE WHITE RIVER FORMATION OF COLORADO: INSIGHT INTO SOIL ECOSYSTEMS OF THE NORTH AMERICAN MIDCONTINENT DURING THE EOCENE-OLIGOCENE TRANSITION

Abstract Exposures of the upper Eocene to middle Oligocene White River Formation in northeastern Colorado contain ichnofossil-rich paleosols in a meandering alluvial system. The paleoenvironmental, paleoecological, and paleoclimatic significance of these paleosols and ichnofossils record the effects on soil ecosystems of the initial stages of global cooling in the late Eocene and early Oligocene. Previous studies of Eocene-Oligocene paleosols in Wyoming and South Dakota suggest a transition from woodland to grassland ecosystems in response to global cooling and drying. We describe four paleosol types from the study area. Type I paleosols include compound Entisols characterized by shallow networks of fine rhizoliths and ichnofaunal assemblages of Planolites isp., Pallichnus dakotensis, Macanopsis isp., Celliforma ficoides, and vertebrate coprolites. Type II paleosols are compound Inceptisols characterized by elongate rhizoliths and ichnofaunal assemblages of Planolites isp., Pallichnus dakotensis, Macanopsis isp., and vertebrate tracks. Type III paleosols are cumulative Inceptisols characterized by elongate rhizolith and ichnofaunal assemblages of Planolites isp., Pallichnus dakotensis, Macanopsis isp., Parowanichnus isp., Edaphichnium isp., and backfilled burrows. Type IV paleosols include composite Inceptisols characterized by large rhizoliths and ichnofaunal assemblages of Edaphichnium isp., Fictovichnus parvus, and wasp cocoons. The vertical transition from less-well-developed (Type I) to better-developed (Type IV) paleosols records decreasing rates of sedimentation and erosion, increasing rates of pedogenesis, and a transition in landscapes from grasslands to savannahs and woodlands. The effects of global cooling on the paleosols and soil biota, therefore, appear to have been buffered by basin-scale, autogenic, sedimentologic, and hydrologic processes.

TORRIDOREFUGIUM ESKRIDGENSIS (NEW ICHNOGENUS AND ICHNOSPECIES): AMPHIBIAN AESTIVATION BURROWS FROM THE LOWER PERMIAN SPEISER SHALE OF KANSAS

Abstract Burrows of the lysorophid amphibian Brachydectes elongatus occur in deposits interpreted as ephemeral ponds within the Lower Permian Speiser Shale of eastern Kansas. The burrows of B. elongatus have been previously recorded in the Lower Permian strata of Texas, Oklahoma, and Kansas, but have not been described in detail and an ichnotaxonomic designation has not been provided. Torridorefugium eskridgensis new ichnogenus and ichnospecies show two types of burrow architecture distinguished by width-to-length ratios. Type I burrows are elongate, elliptical tubes 4–32 cm long and 2–7 cm wide. Type II burrows are short, elliptical tubes 1.5–3.5 cm long and 2.5–5 cm wide. Both Type I and II burrows may contain coiled skeletons of B. elongatus. Torridorefugium eskridgensis occur in clusters of up to 45 burrows with maximum concentrations of 20/m2. The type specimens of Torridorefugium eskridgensis occur in a 40-cm-thick lens of calcareous mudstone that fills a 100-m-long paleodepression within a well-developed paleosol. The burrow clusters are capped by surfaces with evidence of subaerial exposure, and overlain by nonburrowed, massive mudstone containing the fossils of the charophyte Stomachara, the ostracodes Carbonita and Paraparchites, fish, amphibians, and reptiles. This succession suggests that lysorophids burrowed in response to episodic, perhaps seasonal, droughts on the Permian midcontinental coastal plain. Permian lysorophid burrowing behavior is analogous to that of the extant aestivating amphibians Amphiuma sp. and Siren intermedia that inhabit ephemeral rivers and ponds of the southeastern United States.

The Identification and Interpretation of Reptile Ichnofossils in Paleosols Through Modern Studies

Abstract The soil ecosystems of modern floodplains of North America, South America, the Caribbean, Africa, Europe, and western Asia are the habitat of a group of limbless, fossorial reptiles (Order Amphisbaenia). Although body fossils are relatively abundant in North American Paleocene and Neogene paleosols, no ichnofossils are attributed to these organisms, largely because the morphologies present in modern burrows have not been studied. Because ichnofossils tend to have a higher preservation potential than body fossils, knowledge of the architectural and surficial burrow morphologies of such burrowing vertebrates as amphisbaenians can lead to the knowledge of their true stratigraphic and geographic ranges. The behavioral responses of a common South American amphisbaenian to variations in soil composition, moisture, and cohesion were studied in the laboratory so that the architectural and surficial morphology of their burrows could be tied to these environmental changes. Qualitative and quantitative models were designed to describe the morphology of the amphisbaenian burrows and then used to distinguish them from other floodplain burrowers, including skinks, scorpions, and crayfish. Amphisbaenians were found to produce unique two- and three-dimensional biogenic structures that could be both distinguished from those of other organisms and tied to specific environmental conditions. From these data, variations in the morphology of amphisbaenian ichnofossils can provide more accurate interpretations not only of the paleoecology, paleoenvironment, and paleoclimate of floodplain paleosols but also of rates of sedimentation.

Neoichnology of burrowing millipedes: Linking modern burrow morphology, organism behavior, and sediment properties to interpret continental ichnofossils

Abstract Millipedes are known from body fossils as early as the Silurian, and they are an important part of modern global soil ecosystems. Little is known, however, of the morphology of millipede burrows in either the modern or the fossil record. The burrowing behavior and traces of two species of extant millipedes were studied in a laboratory setting. The goal of this research was to determine the connections between millipede morphology, burrow morphology, and media conditions. Specimens of Archispirostreptus gigas and Orthoporus ornatus were placed in large, sediment-filled terrariums. The sediment was varied in terms of texture, compactness, and moisture. Traces produced by the millipedes were then cast and described. The burrow morphology of each species was primarily controlled by trace-making behavior, including excavation methods and burrow occupation time. Orthoporus ornatus burrowed by excavation to construct subvertical shafts leading to terminal chambers occupied for several days to weeks. Archispirostreptus gigas burrowed by sediment compression to construct large-diameter, sinuous tunnels occupied for hours to days. Increasing the clay content, compaction, and moisture content of the sediment together served to inhibit burrowing. Specimens of A. gigas were unable to burrow into compact or clay-rich sediments, whereas specimens of O. ornatus were able to burrow into even firm clay. Neither species was able to burrow into water-saturated media. The study described in this paper aids in understanding the relationships among the morphology of terrestrial biogenic structures, organism size, organism behavior, and media conditions.

Modern Nautilus (Cephalopoda) taphonomy in a subtidal to backshore environment, Lifou (Loyalty Islands)

Abstract Thirty-two samples of submerged Nautilus macromphalus shells were recovered in 2008 from Lifou, Loyalty Islands in the South Pacific Ocean. Specimens were collected from carbonate-dominated sediment in water depths of 1–3 m. Some specimens were partly buried, whereas others rested on the seafloor. The majority of the specimens (66%) were recovered in a horizontal position, whereas 34% of the specimens were oriented vertically. Some specimens were pristine, with sharp color stripes and little encrustation by algae, cyanobacteria, or epizoans. The majority of specimens have substantial algal and cyanobacterial overcoats with some epizoans. In some specimens, the overcoats also trapped substantial amounts of carbonate sediment. Comparison of the 2008 collection of subtidal specimens to 43 beached Nautilus shells collected in 2002 from the same location reveals that the nearshore taphonomic pathways for drift cephalopod shells can be more complicated than published theoretical models suggest. Nautilus shells may or may not float directly to the beach. Shells not immediately deposited on the beach sink in the shallow water in a vertical position. Weight added by attached organisms and water infiltration, causes the submerged shells to eventually assume a horizontal position. Waves, currents, and bioturbation can then flip the shells over from side to side. Eventually submerged shells are buried, broken apart, or transported onto the beach. Beached shells that follow this taphonomic pathway have conspicuous algal coatings compared to those that simply float to shore. The Lifou subtidal population represents the first substantial modern externally shelled cephalopod collection from a shallow water environment to be analyzed to determine its taphonomic pathways. Conclusions from this analysis can be applied to nearshore deposits that contain externally shelled, fossilized cephalopods.

Neoichnology of the burrowing spiders Gorgyrella inermis (Mygalomorphae: Idiopidae) and Hogna lenta (Araneomorphae: Lycosidae)

Burrowing arachnids are important to modern soil ecosystems, but knowledge of these animals in ancient soil ecosystems is limited. In this study, two species of burrowing spiders were studied: Gorgyrella inermis (South African trapdoor spider) and Hogna lenta (field wolf spider). Individuals of each species were studied to investigate their burrowing techniques and behaviors and to categorize the morphologies of their burrows. Experiments were run with variations in sediment density and sediment moisture to evaluate the effects of environmental conditions on burrow morphology. Seven burrow architectures were produced by the spiders: vertical shafts, vertical shafts with terminal chambers, subvertical shafts, subvertical shafts with terminal chambers, Jshaped burrows, Y-shaped burrows, and isolated chambers. All burrow architectures share common features that make them identifiable as spider burrows. Sediment density and moisture had little influence on burrow morphology, but architecture diversity was greatest in sediments of moderate density and moisture. Results from this study show that spiders produce unique biogenic structures that can be distinguished from the burrows of other soil organisms. Data collected from this study can be used to better interpret the paleoecology and evolutionary history of spiders and soil arthropods. J. Michael Hils. Department of Geological Sciences, Ohio University, 316 Clippinger Laboratories, Athens, Ohio 45701, USA. jhils2@udayton.edu Daniel I. Hembree. Department of Geological Sciences, Ohio University, 316 Clippinger Laboratories, Athens, Ohio 45701, USA. Corresponding author. hembree@ohio.edu

Aestivation in the Fossil Record: Evidence from Ichnology

Aestivation is a physiological and behavioral response to high temperature or low moisture conditions. Therefore, it is typically not considered to be capable of being preserved in the fossil record. However, most aestivating organisms produce a burrow to protect themselves from the harmful environmental conditions that trigger aestivation. These structures can be preserved in the rock record as trace fossils. While trace fossils are abundant in the continental fossil record, few are definitively associated with aestivation. Interpreting aestivation behavior from fossil burrows requires a detailed examination and interpretation of the surrounding sedimentary rocks and comparisons with taxonomically and ecologically similar extant organisms. Currently, only four types of aestivation structures are recognized in the fossil record: Pleistocene earthworm chambers, Devonian to Cretaceous lungfish burrows, Permian lysorophid burrows, and Permian to Triassic dicynodont burrows. The trace fossil evidence suggests that aestivation evolved independently among continental organisms in several clades during the middle to late Paleozoic.

Neoichnology of the whip scorpion Mastigoproctus giganteus: Complex burrows of predatory terrestrial arthropods

ABSTRACT Soils contain complex ecosystems with a diverse micro- and macrofauna including arthropod predators. Our knowledge of arthropod predators in ancient soil ecosystems, however, is limited. This project involved the laboratory study of Mastigoproctus giganteus, or giant whip scorpion, to describe its burrowing behaviors and resulting burrow morphologies to aid the recognition of their burrows in the fossil record. Specimens were placed in sediment-filled terrariums for 14–60 days. Experiments were run with variations in sediment density and moisture to evaluate the effects of environmental conditions. The burrows were cast, described qualitatively and quantitatively, and then compared to each other and to scorpion burrows using nonparametric statistical methods. Six different burrow architectures were produced by the whip scorpions including vertical shafts, subvertical ramps, J-, U-, and Y-shaped burrows, and mazeworks. Despite these different architectures, the whip scorpion burrows possessed statistically similar properties that allowed them to be distinguished from burrows produced by scorpions. Sediment density and moisture had little influence on burrow properties but did affect the diversity of architectures produced. The greatest diversity of burrow architectures occurred in low-density sediment with moderate moisture levels. Results from this study show that whip scorpions produce unique biogenic structures possessing architectural and surficial properties that can be used to distinguish them from the burrows of other soil organisms. Data collected from these and similar experiments can be applied to ichnofossil assemblages found in middle Paleozoic to Pleistocene paleosols in order to better interpret the paleobiology and paleoecology of ancient soil ecosystems.