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Large-bodied, semiaquatic herbivorous mammals have been a recurring component of most continental ecosystems throughout the Cenozoic. Identification of these species in the fossil record has largely been based on the morphological similarities with present-day hippopotamids, leading to the designation of this pairing of body type and ecological niche as the hippo ecomorph. These morphological characters, however, may not always be diagnostic of aquatic habits. Here, enamel δ13C and δ18O values from living hippopotamuses were examined to define an isotopic signature unique to the hippo ecomorph. Although δ13C values do not support unique foraging habits for this ecomorph, living and fossil hippopotamids typically have low mean δ18O values relative to associated ungulates that fit a linear regression (δ18Ohippopotamids = 0.96 ± 0.09·δ18Ofauna − 1.67 ± 2.97; r2 = 0.886, p < 0.001). Modeling of oxygen fluxes in large mammals suggests that high water-turnover rates or increased water loss through feces and urine may explain this relationship. This relationship was then used to assess the aquatic adaptation of four purported hippo ecomorphs from the fossil record: Coryphodon (early Eocene), Moeritherium and Bothriogenys (early Oligocene), and Teleoceras (middle–late Miocene). Only fossil specimens of Moeritherium, Bothriogenys, and large species of Coryphodon had δ18O values expected for hippo ecomorphs; δ18O values for Teleoceras and a small species of Coryphodon were not significantly different from those of the associated fauna. These results show that the mean δ18O value of fossil specimens is an effective tool for assessing the aquatic habits of extinct species.
Taphonomic signatures on modern bivalve shells, such as traces of drilling organisms, encrusters, fragmentation, and abrasion function as indicators of environmental differences on Belize atoll reefs. Glovers Reef, Lighthouse Reef, and Turneffe Islands are three adjacent Caribbean atolls showing variations in geomorphology, lagoonal depth, sedimentation, mangrove growth, sea-grass cover, and exposure to winds and currents, as well as differences in their lagoonal development and age. A variety of bivalve assemblages characterize lagoonal subenvironments and also mirror the above-mentioned environmental variations. Taphonomic signatures, such as shell-size distribution, disarticulation, sorting, boring traces, encrustations, fragmentation, and abrasion, were identified on bivalve shells from a total of 111 surface sediment samples. Shell-size distribution and sorting of right and left valves indicate in situ deposition of populations on each atoll. Increasing residence times of shells on the sediment surface due to decreasing sedimentation rates from Turneffe Islands to Lighthouse Reef to Glovers Reef cause an increase in taphonomic shell signatures.
Four environmental provinces are distinguished in the deep South China Sea based on ichna and their relationship to the Pinatubo 1991 ash accumulation. Scolicia ichnofabrics along the Philippine Islands are in sand-prone, greenish, oxygen-deficient deposits to ∼3500 m water depth. Abundance and size of Scolicia appear to be related to quantity and quality of benthic food, respectively. Scolicia producers intensely bioturbate the 1991 ash; below this level, Phycosiphon, Planolites, and Thalassinoides may occupy different tiers. In mud-prone deposits Palaeophycus, Planolites, Thalassinoides, and local Zoophycos (including Spirophyton-like Zoophycos) are present. In the Manila Trench, turbidites are sparsely bioturbated. To the west, Thalassinoides ichnofabrics are found in slowly deposited, deeply oxidized sediments containing little organic matter; Fe- and Mn-oxides lead to their induration. The area west of ∼118°E is affected by upwelling and intense wind mixing, where the Nereites ichnofabrics are present. The Nereites producers feed preferably just above the redox boundary. Following blooms, however, temporary surface feeding is documented by 1991 ash in the burrows. The high benthic food content and the vertical movements of the Nereites producers probably prevented the production of graphoglyptids. Below this level Planolites and Thalassinoides are present. The 1991 ash is bioturbated to some degree where hyperpycnites provide a soft surface layer and some benthic food, in particular along the Philippines. Where such deposits are lacking, the 1991 ash is nearly unbioturbated. Where ample organic matter reaches the seafloor, surface trails have been observed, especially along the Philippines slope and the area affected by upwelling and intense wind mixing.
Examination of remains of Callinectes sapidus deployed in several depth and environmental settings in the Bahamas and Gulf of Mexico as part of the Shelf and Slope Experimental Taphonomy Initiative project revealed that all specimens were uniformly and strongly degraded except those in brine-seep settings. Fragmentation and loss of cuticular material at all sites was correlated to the degree of calcification within the cuticle of different skeletal elements as observed in the undeployed specimens. Claws, tips of the last anterolateral spine, and mandibles were the most durable remains. In brine-seep areas, extraordinary preservation yielded articulated skeletal elements and some soft tissue. Examination of the cuticle in control specimens with cross-polarized light and computed tomographic scanning documents the correspondence of high degrees of calcification with portions of the exoskeleton remaining after deployment.
An exceptionally preserved subadult specimen (JRF 115H) of a hadrosaurid, Brachylophosaurus canadensis, from the Judith River Formation near Malta, Montana, contains abundant plant fragments concentrated within the body cavity. We examined the taphonomy of the carcass and analyzed the gut-region material to test whether the organic remains represent fossilized gut contents. The dinosaur was buried in a fluvial channel setting, and the excellent articulation, integument impressions, and lack of scavenging indicate rapid burial. The organic material occupies a volume of at least 5750 cm3, and comparable material is not found outside the carcass. The carcass contents include ∼63% clay, ∼16% undetermined matrix, ∼12% organic matter, and ∼9% larger inorganic clasts—mostly 50–100 μm quartz grains. Most of the organics appear to be mm-scale leaf fragments. The most parsimonious explanation for the presence and composition of the gut-region material is that much of the plant fossils represent reworked brachylophosaur ingesta influenced by flowing water that entered through openings in the carcass and introduced clay. The evidence strongly suggests that the hadrosaurid ate significant quantities of leaves and processed them into small pieces. This study provides baseline information for analyzing other cases of putative gut contents in herbivorous dinosaurs.
SHE analysis for biozone identification (SHEBI) is a new technique that identifies abundance biozones (ABs) by accumulating species abundance data along a time series, recalculating species richness (S), the information function (H), and the equitability index (E) with the addition of each sample. Boundaries are drawn between ABs where SHE analysis detects a change in either (1) the population structure or (2) the assemblage's species composition, species having joined or left the community in quantities that affect the evenness of the distribution of species abundances. This study uses foraminiferal data from two Miocene sections on Trinidad (Cipero Formation, Catapsydrax stainforthi Zone; San José Calcareous Silt, Globorotalia acostaensis Zone) to test if top-downward or bottom-upward analyses indicate the same AB boundaries. The results differ. In the Cipero there are no matches between AB boundaries determined by bottom-up and top-down SHEBIs. In the San José Calcareous Silt, only some boundaries match. It is recommended that SHEBI proceed in the order in which the samples in the ABs were deposited, treating the ABs as successive ecostratigraphic units. Intriguingly, no matter whether ABs were determined by bottom-up and top-down SHEBIs, SHE community structure investigations indicated logarithmic series population structures. A graphical technique for determining the species responsible for the change in ABs reveals that a peak in the per sample percentage abundance of Nuttallides umbonifera in the Cipero Formation is offset by one sample from the AB boundaries it engendered, marking a temporary decrease in nutrient flux.