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Examination of the mechanisms involved in the construction of present-day vegetative deposits along coastal waterways has made it possible to establish depositional patterns that can be compared with those found in similar environments in geologic time. These patterns include not only the composition and transport of the debris but also an estimation of the time involved in its deposition. Six sites with active deposits of plant macrodebris in the coastal basin of the Itanhaém River, São Paulo State, Brazil, were used in the study. In the central portion of the basin, the interior coastal plain is covered with restinga forest (dense, wet tropical forest of low altitudes), while the lower portion consists of mangrove swamps. The coast reflects anthropogenic intervention, and only a few scattered remnants of precolonization dune vegetation remain. The results after three years of study suggest that the accumulation of plant macrodebris in the middle and lower portions of the basin is parautochthonous, since only the leaves of genera typical of the restinga forest and mangrove swamp, respectively, were found. Along the coast the accumulations involved a mixture of parautochthonous and allochthonous elements. On the levee of the Branco River and within the mangrove swamp, deposition was slow, and many of the elements decayed quickly; such accumulations show little potential for preservation and eventual fossilization. A different site, however, reveals the rapid deposition of thick layers of plant debris, presumably associated with storms, and these accumulations are preserved for long periods, constituting good candidates for possible fossilization.
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.
Cheilostomes dominate bryozoan faunas today and are the only order of bryozoans to have evolved aragonitic, calcitic, and bimineralic skeletons. New XRD analyses of 177 recent species and 34 Cretaceous–Eocene species are combined with published data to probe the mineralogical evolution of cheilostomes. This is undertaken with particular reference to the effects of the late Paleogene transition from calcite to aragonite seas believed to have been driven by the increasing Mg/Ca ratio in seawater. Aragonite was absent from all of the Cretaceous and Paleocene cheilostomes analyzed, even though most came from deposits preserving aragonitic mollusk shells, but was detected in four distantly related cheilostomes from the middle Eocene (Lutetian). Examples of cheilostomes preserved as partial molds, however, suggests that bimineralic species with aragonitic outer skeletal layers may have originated as early as the Maastrichtian. A strong latitudinal gradient was evident in cheilostome mineralogy, with the proportion of aragonitic and bimineralic recent species increasing towards the tropics. Unfortunately, relatively few low-latitude bryozoans have been described from the Cretaceous and Cenozoic fossil record, where aragonitic species are likely to be most numerous and may have their oldest occurrences. A combined database of cheilostome mineralogy shows aragonite to be widely distributed across Cheilostomata, occurring in numerous genera and families belonging to the three most diverse subgroups (Flustrina, Umbonulomorpha, and Lepraliomorpha) as well as one genus of Malacostegina. In spite of the lack of a robust phylogeny for cheilostomes, it is clear that aragonite has evolved independently on multiple occasions, the earliest acquisitions antedating the onset of aragonite seas, although apparently accelerating after this transition.
A polycotylid plesiosaur (Dolichorhynchops sp.), recently discovered in the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale in Glen Canyon National Recreation Area, southern Utah, is associated with 289 gastroliths. This specimen is significant due to the general lack of gastroliths associated with most short-necked plesiosaur skeletons. The skeleton (MNA V10046) was excavated from a stratigraphic interval of marine shale that does not contain coarser-grained material. The stones were generally concentrated in one area of the skeleton, with the majority situated near the back of the skull. The stones are mainly composed of dark grey chert, are smooth and well rounded, and have varying degrees of polish. The majority of the stones are spherical in shape and are likely fluvial in origin. The gastroliths from this animal are similar in shape and number to those documented from elasmosaurid plesiosaurs. The gastroliths from MNA V10046, however, are much smaller and weigh considerably less than most elasmosaurid stomach stones. Given the lack of comparative material from other short-necked plesiosaurs, the size and mass differences are attributed to differences in function of gastroliths between long- and short-necked plesiosaurs.
Here we report on the frequency, shape, and position of sublethal, predatory-induced breakage on shells of the common pterineid bivalve genus Ptychopteria from the Middle Devonian of New York. Twenty-six of the 115 well-preserved shells of Ptychopteria examined displayed evidence of at least one repair scar. The capacity to retract the vulnerable mantle deep within the shell and squeeze the valve margins together tightly to seal the shell enabled Ptychopteria to sustain marginal shell damage that was often severe. Repair scars resemble traces made by modern shell-breaking predators, especially decapod arthropods. Stereotyped positioning of the repair scars on the posterior portion of the valve also suggests active selection of an attack site by unknown shell-breaking predators. The relatively high repair frequency for Ptychopteria supports a growing body of evidence that suggests predation pressure intensified in the middle Paleozoic.
We report on the first record of a pterosaur from Alaska. This record consists of a single manus track from the lower part of the Upper Cretaceous Cantwell Formation in Denali National Park, Alaska, United States, making this the northernmost occurrence for this group of reptiles. The specimen is from deposits that record a low-lying floodplain with small lakes and ponds, dissected by small channels that fed a larger tributary stream on an active fan lobe. The dominant vegetation was comprised of conifers with an understory of ferns and horsetails.
A trace fossil with its putative in situ maker, a redlichiid juvenile of Eoredlichia intermediaLu, 1940 from the lower Cambrian (Series 2) Chengjiang fauna, southwestern China, is reported here. Evidence for biogenetic linkage of the trail to the trilobite includes their close, integrated association, in situ preservation, and consistent dimensions. Analysis from Scanning Electron Microscopy further strengthens this argument. Preservation mechanism and fidelity loss in the trail are considered. In light of functional morphology, a nektonic-benthic transition in modes of life is inferred for meraspides of Eoredlichia.