The earliest fossil communities of macroscopic organisms are preserved in the Ediacara Biota. While many are difficult to classify into well-known phylogenetic groups, the exceptional preservation of these mostly soft-bodied forms, provides a plethora of material for comprehensive investigations of their biology and ecology. Exceptional deposits of the Ediacara Member from the Flinders Ranges and surrounding areas of South Australia yield abundant Ediacara Biota fossils ideal for such studies. The research presented below targets modular Ediacaran taxa, in particular the iconic and abundant fossil Dickinsonia. Patterns of growth and development in Dickinsonia are explained most parsimoniously via posterior addition of modular units and variable growth rates of units through development regulated to maintain an ovoid shape. Fossiliferous Ediacaran bedding plane surfaces, including the recently uncovered Alice’s Restaurant bed, highlight the heterogeneous distribution of taxa on the Ediacaran seafloor. Trace fossil evidence demonstrates that Dickinsonia and Yorgia were mobile, muscular organisms that fed on the organic mat through their ventral surface. Comparisons with other bilaterally symmetrical modular taxa suggests that many Ediacaran forms may have been mobile but did not engage in activities conducive to trace fossil preservation. Dickinsonia was bilaterally symmetrical, marked by distinct anterior/posterior and likely dorsal/ventral differentiation in addition to modules that met precisely at the midline. Taphonomic variants of Dickinsonia reveal that it was structurally resilient for a soft-bodied organism, highly extensible compared with most modern biopolymers, capable of elastic and plastic deformation, and composed of relatively thick, differentiated tissue. While many of these characters are consistent with bilaterians today this fossil probably represents an extinct clade within the Eumetazoa. This work establishes that the physiology and morphology of Dickinsonia were specifically suited to Ediacaran environments, and that departures from those unique conditions may have led to the ultimate disappearance of this taxa.

Capitalizing on the diverse pool of students and early geoscience exposure in Riverside County, the NSF Geopaths Geoscientist Development (GEODE) Program at UCR is designed to remove barriers, recruit, and retain underrepresented students into the geosciences, the least diverse of the STEM fields. We report the results from the GEODE Internship Program that offered 10-week paid student internships, providing the opportunity for students to be exposed to the geosciences through research experiences. The students agreed that participating in research increased their interest in conducting scientific research in the future, reporting benefits of new research skills, career preparation, and networking. The studies herein were conducted with the assistance of undergraduate interns, highlighting the potential for rigorous research while strengthening geoscience educational pathways and increase diversity in STEM. The analysis of sclerobionts is a powerful tool for understanding ecological relationships and their trace fossils provide opportunities to study organisms not well-preserved. We examined sclerobionts on Hyotissa hyotis oysters from the Miocene Latrania Formation near Ocotillo, California, an ancient shoreline of the proto-Gulf of California. We analyzed occurrences and abundance of sponges, polychaetes, bivalves, phoronids, and corals. Combining taxonomic diversity with encrusting intensity yielded a more accurate representation of the dynamics of a hard substrate community than diversity alone. An Entobia ichnofacies, this assemblage supports a model of sediment starvation in the fan-delta deposits of the Latrania Formation.

We examined sclerobionts on modern Mercenaria mercenaria bivalves from Shelter Island, New York, in the Peconic Bay, an estuary with a history of pollution and hypoxia. We analyzed occurrences and abundance of sponges, polychaetes, bryozoans, barnacles, and molluscan attachment scars. Encrustation occurred with similar intensities on both surfaces of the valves and the co-occurrence of both deep- and shallow-tiered borings indicated the shells were exposed predominantly to a low energy environment, with periodic reworking events. For community studies involving encrusters, we found no added benefit from including heavily fragmented shells with complete shells. If complete valves are unavailable, we suggest examining valves >50% complete will yield robust results.

We present the preliminary data on a sclerochronological and isotopic analysis of the Miocene oyster Hyotissa hyotis.

Dickinsonia, an iconic member of the Ediacara biota, is abundant in the Ediacaran deposits found at the Nilpena field site, South Australia. Despite exquisite preservation at this site, many specimens of Dickinsonia appear to be incomplete. Orientation measurements from specimens on fossil beds suggest that “missing pieces” are aligned irrespective of the axial orientation of Dickinsonia. The nonrandom orientation of incomplete specimens matches that of aligned structures found on two beds. The directionality of this feature suggests the molding of incomplete specimens under the influence of current activity prior to or during burial. This feature originates where part of a Dickinsonia was lifted off of the substrate during a storm event and sand was deposited beneath this lifted portion. This suggests that Dickinsonia was easily separated from the sea floor and was not attached to the substrate. This is consistent with the data suggesting that Dickinsonia was mobile. Examination of Dickinsonia costata demonstrates ranges in length from 3.6 mm to 167.4 mm and occurs in varying abundance within and across facies. Density data show that this organism preferred a relatively shallow water, fair-weather wave base habitat. The substrate dominated by fossils of Aspidella and Funisia limited the presence of D. costata. Ubiquitous Funisia in the absence of Aspidella preserves larger populations of D. costata, while juvenile forms occur preferentially in an inferred algal-dominated seafloor. The timing of depositional events controlled the maximum size ranges of D. costata, with small populations representing communities buried before they fully developed. The biology of D. costata is reflected in the overall right-skewed, log-normal size frequency curve, demonstrating a pattern of high infant mortality. A single bed contains more than half of the D. costata at Nilpena and the absence of cohorts within this large population is suggestive of continuous recruitment.

Tetrapod swim tracks attributed to reptiles occur abundantly throughout Lower to Middle Triassic deposits across the western United States. In central and southern Utah these swim track localities are stratigraphically restricted to the upper portion of the Torrey Member of the Moenkopi Formation. Here they show detailed features such as longitudinal striae and disc-shaped claw impressions that must have required specific substrate conditions in order to be produced and preserved. A suite of sedimentologic and ichnologic observations at several swim track localities demonstrates the widespread development and persistence of subaqueous firmground substrates buried by crevasse splay deposits in the interdistributary areas of a large lower delta plain. The heterolithic stratigraphy is typical of interdistributary bays and channels and generally consists of decimeter-scale fining-upward cycles of mud- and siltstone beds below the track-bearing horizons and thicker, massive or cross-bedded sandstones above. Siltstone and sandstone beds show low angle accretion sets, vary laterally in thickness, and commonly pinch out so that they cannot be correlated regionally. Common sedimentary structures indicate predominately quiet subaqueous conditions with periodic higher energy events. These include trough cross stratification, climbing ripples, rip-up clasts, and soft sediment deformation. Track surfaces often exhibit localized dewatering structures and load casts in addition to flute casts and current crescents indicating unidirectional current flow. Mudcracks are rare. The low diversity invertebrate ichnoassemblage is comprised of locally high densities of relatively diminutive traces and reflects stressed brackish water faunas. These characteristics are almost certainly augmented by delayed biotic recovery following the end-Permian mass extinction and resulted in extremely low degrees of bioturbation. This lack of biogenic mixing promoted semi-consolidation of dewatered mud substrates resulting in the widespread production and persistence of firmgrounds capable of recording and maintaining detailed swim tracks. The subsequent burial of these firmground surfaces under coarser-grained crevasse splay deposits resulted in sharp heterolithic contacts further facilitating the preservation of detailed track features.

The Ediacaran fossil taxon Attenborites janae was originally excavated in 2017 from the Ediacara Member of the Nilpena Ediacara National Park (Nilpena, Droser et al, 2018). Attenborites was described as a potentially pelagic organism that had undergone deflation during preservation. This thesis tests this hypothesis by examining the taphonomy and preservational morphology of Attenborites using an additional 55 specimens recently excavated from Nilpena. The life habit of Attenborites is determined by comparing the characteristics of known benthic Ediacaran organisms and evaluating the preservational morphology and taphonomy of Attenborites according to criteria for the preservation of early soft-bodied pelagic forms put forth by Young and Hagadorn (2010). It is concluded that Attenborites was most likely a pelagic organism, consistent with findings in the original description of Attenborites. This taxon is thus the first known macroscopic inhabitant of the pelagic realm. In identifying the life habit of Attenborites, criteria for identifying the preservation of Ediacaran pelagic taxa in the fossil record were created.This thesis was focuses on developing methods for the retrodeformation of deflated taxa and characterization of the in vivo morphology of Attenborites janae. Laser scans taken of the fossils in the field were simulated to inflate using the 3D modeling software Blender. This is a novel effort because no soft-bodied fossil taxon has ever been retrodeformed. This approach led to the characterization of then-living Attenborites as ellipsoid forms with relatively smooth surfaces and confirmed that the ridges found within the fossils are taphonomic features formed during deflation rather than true morphological features.

The Ediacara Biota represent a turning point in the evolution of life on Earth, signifying the transition from single celled organisms to complex, community forming macrobiota. The exceptional fossil record of the soft-bodied Ediacara Biota provides critical insight into the nature of this transition and into ecosystem dynamics leading up to the so-called “Cambrian Explosion”. However, the preservation of non-biomineralizing organisms in a diversity of lithologies goes hand-in-hand with considerable taphonomic complexity that often shrouds true ecological and biological signatures. We address the nature of this taphonomic complexity within the fossiliferous sandstones of the Ediacara Member in South Australia. Utilizing the most data-rich and well-preserved outcropping of the Ediacara Member, the Nilpena Station National Heritage Ediacara Fossil Site, we conduct a focused, taxon-level taphonomic characterization of the tubular organism Funisia dorothea. Funisia is the most abundant body fossil in the Ediacara Member, making its taphonomic characterization essential to the accurate interpretation of regional paleobiology and paleoecology. We identify two primary modes of Funisia population structure, cluster-type and surface-type packages, each of which exhibit distinct suites of taphonomic variation in individual Funisia. Within the two package types, four preservational modes of Funisia are identified: convex external molds, concave external molds, convex internal molds, and concave internal molds. Among macrofossils at Nilpena, this tiered preservational complexity is unique to Funisia; its systematic classification elucidates population-level biostratinomy at Nilpena as well as aspects of Funisia’s paleobiology and autecology.

The radiation of burrowing metazoans in the early Phanerozoic is commonly assumed to have dramatically altered the properties of marine sediment. The advent of biogenically-mediated sediment mixing, by profoundly impacting nutrient burial fluxes, organic carbon remineralization, seafloor oxygenation and sediment ecology, likely instigated Phanerozoic biogeochemical cycling. However, the timing of the development of mixed seafloor sediment has, historically, not been well constrained. Mixing has commonly been assumed, in the absence of data, to occur at the Precambrian-Cambrian boundary with the appearance of the index fossil and three-dimensional burrow Treptichnus pedum (the &ldquoCambrian substrate revolution&rdquo or &ldquoagronomic revolution&rdquo). Likewise, instances of exceptional preservation--preservation of near-surface structures of high taphonomic fidelity, including bioglyphic detail--have previously been anecdotally reported from lower Paleozoic trace fossil assemblages worldwide. However, it has hitherto been unknown to what extent this exceptional preservation characterizes the lower Paleozoic record as a whole.

Herein I present new ichnological, stratigraphic and taphonomic data suggesting that, although significant developments in infaunalization-- paleobiologically complex animal-substrate interactions, particularly burrow construction--occurred during the early Paleozoic, mixing remained suppressed throughout this interval. I demonstrate that shelfal sediment in the earliest Cambrian was essentially unmixed and that, even as late as the middle Ordovician--over 75 million years after the Precambrian-Cambrian transition and well after the appearance and diversification of supposedly deposit-feeding trilobites, seafloor shelfal sediment remained largely unmixed on a global scale. Moreover, lower Paleozoic heterolithic shelfal successions are also characterized by widespread exceptional preservation of shallow-tier ichnological assemblages and bioglyphic structures, implying formation and preservation in a cohesive, i.e. unmixed substrate. Bed-sole assemblages are preserved through syndepositional casting rather than intrastratally. Well-mixed intervals are typically of limited spatial extent; macro-scale depositional fabrics are largely undisrupted. These findings challenge the current assumption that mixing occurred with the first appearance of three-dimensional burrows and that early Paleozoic infauna were efficient sediment mixers. The protracted development of the mixed layer holds important implications for exceptional preservation in both the trace and body fossil records, for the structure of lower Paleozoic benthic ecosystems, and for the advent and development of modern-style biogeochemical cycling.

Here we reconstruct a new tubular, serially divided organism with a bilateral morphology from the Ediacaran of South Australia. The organism, Plexus ricei n. gen. n. sp., was a broadly curving tube that resided on the Ediacaran seafloor. Plexus ricei individuals range in size from 5 to 80 cm long and 5 to 20 mm wide, and are comprised of two main components: a rigid median tubular structure and a fragile outer tubular wall. Plexus ricei is preserved as an external mold on bed soles, and as a counterpart cast on bed tops in sandstones interpreted to represent deposition between storm and fairweather wave-base. The phylogenetic affinities of P. ricei are uncertain; P. ricei symmetry implies a bilaterian origin, but a lack of defined anterior and posterior ends precludes definitive assignment.

The Ediacaran Period, spanning 635 to 538 million years ago, marks a pivotal phase in life’s evolutionary history, showcasing early multicellular animal life. This thesis examines the remarkable fossil bed, 1T-F, from the Ediacara Member of the Rawnsley Quartzite at Nilpena Ediacara National Park, South Australia, offering insights into a shallow marine ecosystem during the Ediacaran period. 1T-F, preserving over 400 fossils across 16 metazoan-grade genera and numerous multicellular algae, exhibits remarkable ecological complexity and diversity. A detailed examination reveals a stable, low-energy environment that fostered diverse life forms. Comparative studies with other fossil beds emphasize 1T-F’s unique ecological dynamics, providing valuable insights into the evolutionary transitions preceding the Cambrian Explosion and enhancing our understanding of early multicellular ecosystems.

A new species of Middle Ordovician receptaculitid is described from the Arrow Canyon Range in southeastern Nevada. Ischadites n. sp. exhibits a unique gross morphology, large body size, small, numerous outer plates, and an exceptionally large aperture to body size ratio.