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Preexisting fossil collections, often the only source of data from sites that are no longer accessible, have been widely used in systematics but underutilized in quantitative paleontological studies. Here, the potential utility and limitations of materials obtained from preexisting collections is explored using a paleoecological case example (confamilial predation by drilling naticid predators). Specimens of the gastropod Cochlis pseudoepiglottina were collected from a single locality (Nidolères outcrop, Pyrénées-Orientales Département, southern France) of an unnamed, early Pliocene unit; the site is currently inaccessible. A statistical analysis of 183 specimens, representing three separate collections, indicates that these datasets are quantitatively consistent and provide interpretable numerical data on various aspects of drilling predation patterns. Despite various limitations, the results indicate that (1) intense confamilial predation affected C. pseudoepiglottina; (2) drilling attacks may have been size selective; (3) the frequency of failed attacks recorded by incomplete drill holes was high; and (4) the ratio of successful attacks declined dramatically with increase in snail size, suggesting a strong size-refuge effect. Our interpretation is hampered by the exclusion of the smaller size classes of C. pseudoepiglottina and a lack of bulk-sampled, assemblage-level quantitative data on all fossil taxa at this taxonomically diverse site. Nevertheless, the results provide a useful addition to previous literature on drilling predation, including quantitative data that are potentially applicable in meta-analytical compilations (e.g., prey effectiveness). Despite limitations, preexisting collections—especially those representing fossil sites that no longer exist or are inaccessible—can yield useful quantitative data.
Bryozoa exhibit some broad phylogenetic patterns in skeletal carbonate mineralogy that have previously been elucidated based on material from Australasia, Europe, North America, South Africa, and Antarctica. A new dataset from 19 locations in the Patagonian fiord region of Chile adds 93 specimens and 23 species to the mineralogical information on this highly variable phylum, as well as providing a comparison with generalizations made to date. Most species, genera, and families from Chile are of similar mineralogy to their worldwide counterparts, but a few are surprising. Chilean Membranipora isabellana and Diastopora sp. are both 100% aragonite despite belonging to taxa that are dominantly calcitic. Adeonella patagonica and Adeonella sp. are the only species exhibiting bimineral skeletons, from 6 to 100% calcite, a much greater range than was previously known for this genus and the Adeonellidae. Skeletal mineralogy has been tested in only 95 of the 323 families in the Bryozoa. We are, nevertheless, able to make some generalizations. For example, stenolaemates are almost always low-Mg calcite, and ascophoran cheilostomes are the most variable and mineralogically complex group. The capacity to generalize about bryozoan mineralogy is necessary in the face of increasing pressure on biomineralization from ocean acidification.
Leaf margin analysis (LMA) is a widely used method that applies present-day linear correlation between the proportion of woody dicotyledonous species with untoothed leaves (P) and mean annual temperature (MAT) to estimate paleotemperatures from fossil leaf floras. Previous works demonstrate that LMA shows regional constraints and to date, no equation has been modeled directly from Chinese forests. Fifty humid to mesic Chinese forests were chosen to understand the relationship between percentage of untoothed leaf species and MAT in China. Consistent with previous studies, the Chinese data indicate that P shows a strong linear correlation with MAT, but the actual relationship is a little different from those recognized from other regions. Among the several currently used LMA equations, the one resulting from North and Central American and Japanese data, rather than the widely used East Asian LMA equation, yields the closest values to the actual MATs of the Chinese samples (mean absolute error = 1.9 °C). A new equation derived from the Chinese forests is therefore developed, where MAT = 1.038 27.6 × P. This study not only demonstrates the similarity of the relationship between P and MAT in the Northern Hemisphere, but also improves the reliability of LMA for paleoclimate reconstructions of Chinese paleofloras.
Gyrolithes burrows reflect fluctuating salinity in incised valleys that were filling when estuarine circulation was established during Holocene transgression in a mesotidal setting off southern Vietnam. Gyrolithes burrows were produced in stiff mud, but they postdate burrows with diffuse outlines formed in soft mud, and they predate burrows of the Glossifungites suite that represent fully marine conditions. The latter are filled with and overlain by marine sand and shell debris deposits. The pore-water composition of the Gyrolithes host sediment supports these findings while exhibiting only 75%–95% of marine chloride values. Gyrolithes is restricted to low-gradient parts of the inner shelf. In narrow confined valleys, an estuarine circulation was established and a temporally lengthy omission ensued while fluvial and tidal currents interacted. The absence of Gyrolithes in other parts of the study area is explained by the steep gradient of incised valleys. This might have resulted in accelerated currents in the incised valleys precluding the Gyrolithes trace maker. Alternatively, environmental conditions resulting from rapid sea-level rise, including increased mud deposition, might have been unfavorable for Gyrolithes producers. No Gyrolithes burrows were found in areas where normally thin marine transgressive deposits rest directly on Pleistocene paleosols.
Paleontologists have identified patterns of stability in the diversity and composition of communities over millions to tens of millions of years within the fossil record. It is unclear, however, what processes are responsible for controlling the stability observed in these communities—for example, local species interactions within communities, local species-environment relationships, immigration of species from the regional biota. This study tests whether the taxonomic composition of local brachiopod paleocommunities occupying a slope environment across a ∼40 km2 region remains temporally uniform over a 5.4 myr interval of time recorded by the Pinery, Rader, Lamar, and Reef Trail Members of the middle Permian (Capitanian) Bell Canyon Formation (BCF). Two third-order sequence boundaries have been previously recognized in this formation, indicating episodes of environmental disruptions related to sea-level fall within the basin that can induce habitat tracking or immigration events from other basins. Presence-absence data analyzed by cluster analysis, ordination techniques, and rank-occurrence plots demonstrate that compositional turnover occurs within the BCF. Change in composition of the Lamar Member paleocommunities documents the replacement of established brachiopods with new taxa, including the immigration of two new brachiopod genera from outside North America, indicating the influence of regional-scale effects on community assembly. The results based on metacommunity models suggest that dispersal plays an important role in the assembly of brachiopod paleocommunities in the Delaware Basin. Results also indicate that fossil communities provide useful information for interpreting placement of sequence boundaries and the magnitude of disruption.
An analysis of five Holocene sediment cores from Belize atoll lagoons has revealed a possible mass mortality of the Caribbean sea urchins Diadema antillarum and Echinometra sp. during 6400–6100, 4000, and 1300 yr BP. Event layers were identified by quantifying echinoid fragments in Holocene sediments. Peaks of echinoid abundance were dated radiometrically. There are two explanations for the fact that echinoderm-rich layers cannot be correlated among the three atoll lagoons. First, die out was not as widespread as the 1983–84 event that led to mass mortality of Diadema in the Caribbean. Possibly, local environmental transitions in lagoonal circulation patterns and changes in temperature and precipitation in the study area were responsible for echinoid mass mortality in the Holocene of Belize. Second, echinoid mass mortality is not necessarily implied in the composition of contemporaneous reef sediments. Comparable studies on Holocene corals in the area also suggest that turnover events have repeatedly occurred during the past several thousand years, however, recent events were unprecedented in their significance. Potential limitations of this study refer to taphonomic bias as imposed by callianassid shrimp burrowing.
Whale corpses on the modern seafloor host particular communities that benefit from the large amounts of available labile organic matter. The study of these communities has revealed the presence of the siboglinid annelid Osedax that feeds on bone tissue by means of a symbiotic relationship with heterotrophic bacteria. Here we report the presence of tubular borings in a fragment of the neurocranium of a fossil baleen whale found in lower Pliocene rocks of southeastern Spain. They are formally described as Trypanites ionasi isp. n. The fossil borings can be assigned to annelid or sipunculid worms and may constitute the first evidence of an Osedax-like osteophagous behavior in the fossil record of cetaceans. Nevertheless, the definitive assignment to Osedax is not possible until we have more information on the morphology of modern siboglinid borings.
We report on a large burrow cast with skeletal contents from Lower Triassic strata of the Palingkloof Member of the Balfour Formation, which forms the lowermost portion of the Lystrosaurus Assemblage Zone (LAZ) of South Africa. The burrow cast is similar to large burrow casts previously described from the LAZ that were identified as large-scale Scoyenia domichnia. It is the first large burrow cast from the LAZ found to contain diagnostic fossil bone. The burrow cast is a relatively straight, subhorizontal (inclined ∼12°), dorsoventrally compressed tube consisting of an entry ramp and living chamber; the entrance to the burrow is not preserved and there is no evidence that the ramp formed a spiral section. The skeletal material comprises a single, partial, disarticulated skeleton of a juvenile animal that can be assigned with confidence to the dicynodont genus Lystrosaurus. Whereas similar large-diameter burrow casts from strata slightly higher in the LAZ have been attributed to Lystrosaurus, we present an alternative hypothesis that a carnivorous tetrapod constructed the burrow. Our preferred hypothesis is supported by the observation that the interred Lystrosaurus skeleton is too small to be the maker of this particular burrow, by the general observation that carnivorous tetrapods construct relatively straight burrows, and by the partial, disarticulated state of the skeleton, which we interpret as the remains of larded prey. We suggest that akidnognathid theriodonts of the genera Moschorhinus or Olivierosuchus, the most conspicuous large predators of the LAZ, were the constructors of large-diameter, subhorizontal burrows.