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.

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.

Stakeholder interests have spurred the reintroduction of the critically endangered populations of Chinook Salmon to tributaries upstream of Shasta Dam, in northern California. We released two groups of acoustically tagged, juvenile hatchery, late-fall Chinook Salmon to determine how juvenile salmon would distribute and survive. We measured travel times to Shasta Dam, and the number of fish that moved between locations within Shasta Reservoir. We used mark-recapture methods to determine detection and apparent survival probabilities of the tagged fish as they traveled through five reaches of the Sacramento River from the McCloud River to San Francisco Bay (~590 km) over the two 3-month observation periods. After our first (February) release of 262 tagged fish, 182 fish (70%) were detected at least once at the dam, 41 (16%) were detected at least once downstream of Shasta Dam, and 3 (1%) traveled as far as San Francisco Bay. After the second (November) release of 355 tagged fish, only 4 (1%) were detected at Shasta Dam. No fish were detected below Shasta Dam, so we could not estimate survival for this second release group. The first release of fish was fortuitously exposed to exceptionally high river flows and dam discharges, which may have contributed to the more distant downstream migration and detection of these fish — though other factors such as season, diploid versus triploid, and fish maturation and size may have also contributed to release differences. The reported fish travel times as well as detection and survival rates are the first estimates of juvenile salmon emigration from locations above Shasta Dam in more than 70 years. This information should help inform resource managers about how best to assess juvenile winter-run Chinook Salmon and assist in their reintroduction to watersheds upstream of Shasta Dam.

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