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Deep-sea submersible observations made in the Bahamas revealed interactions between the stalked crinoid Endoxocrinus parrae and the cidaroid sea urchin Calocidaris micans. The in situ observations include occurrence of cidaroids within “meadows” of sea lilies, close proximity of cidaroids to several upended isocrinids, a cidaroid perched over the distal end of the stalk of an upended isocrinid, and disarticulated crinoid cirri and columnals directly underneath a specimen of C. micans. Guts of two C. micans collected from the crinoid meadow contain up to 70% crinoid material. Two of three large museum specimens of another cidaroid species, Histocidaris nuttingi, contain 14–99% crinoid material.
A comparison of cidaroid gut contents with local sediment revealed significant differences: sediment-derived material consists of single crinoid ossicles often abraded and lacking soft tissue, whereas crinoid columnals, cirrals, brachials, and pinnulars found in the cidaroids are often articulated, linked by soft tissue, and unabraded. Furthermore, articulated, multi-element fragments often show a mode of fracture characteristic of fresh crinoid material. Taken together, these data suggest that cidaroids prey on live isocrinids.
We argue that isocrinid stalk-shedding, whose purpose has remained a puzzle, and the recently documented rapid crawling of isocrinids are used in escaping benthic predators: isocrinids sacrifice and shed the distal stalk portion when attacked by cidaroids and crawl away, reducing the chance of a subsequent encounter. If such predation occurred throughout the Mesozoic and Cenozoic (possibly since the mid-Paleozoic), several evolutionary trends among crinoids might represent strategies to escape predation by slow-moving benthic predators.
Evolutionary trends observed over large clades have the potential to mask underlying trends that occur within their constituent subclades. A recent study of encephalization in the Caniformia (Carnivora, Mammalia) found evidence for an abrupt increase in median log-encephalization quotients (logEQs), indicating higher brain volume relative to body mass, at the end-Miocene, but gradual increase in the variance of logEQs. In this study, new endocranial volume estimates for fossil taxa in the well-sampled caniform subclade Canidae are reported. Using the encephalization data for the Canidae, hypotheses of evolution in encephalization allometries were tested with respect to canid phylogeny. The Akaike Information Criterion and likelihood ratios recovered support for a preferred hypothesis of the evolution of canid encephalization, which proposed two distinct allometric relationships: (1) a plesiomorphic grade of encephalization in the subfamilies Hesperocyoninae and Borophaginae and the paraphyletic canine genus Leptocyon, and (2) an apomorphic grade in the crown radiation of Caninae. This defines a shift in to higher encephalization, but without an associated change in the variance around the allometry. Increased canid encephalization coincides with a reorganization of the brain and the observed trend may reflect the evolution of complex social behavior in this clade.
We developed a new method to generate topographic maps of tooth crowns from X-ray synchrotron microtomographic data. Maps are drawn after cervix-plane orientation of tooth image stacks, without the need for a geographic information system. Classical topographic maps with contour lines are complemented by slope maps and angularity maps. Cartography allows precise comparisons of cusps morphologies, and quantification of the directions of cusp axis elongation and slope. Application of this method to muroid rodents with cricetine and murine dental patterns reveals clear-cut differences in cusps morphology that are indicative of the direction of the chewing movement, in agreement with wear facet analyses. Rodents with a murine dental pattern were derived from ancestors with a cricetine pattern, and their origin is associated with important changes in cusp morphology and organization. In order to understand such evolutionary change, our investigation is applied to a sample of extant and fossil muroid rodents that are characterized by either a murine dental plan or a cricetine one, or a dental pattern intermediate between those of cricetines and murines.
Examination of organismal characteristics which promote survivorship through both background and mass extinctions may reveal general ecological principles potentially critical to modern conservation efforts. This study explores survivorship of brachiopods, a highly diverse and abundant Paleozoic clade, through the mid-Permian to mid-Triassic interval, which includes the greatest mass extinction in the history of metazoan life. This interval of time separates two of the major Phanerozoic evolutionary faunas. In this regard, survivorship across any one extinction during the interval would not have been relevant if the survivor went extinct shortly after the extinction event; surviving background extinction is as important as surviving a mass extinction. Similarly, taxa that survived but failed to rediversify also were not major elements of the Mesozoic evolutionary fauna. Thus, the analysis aims to analyze survivorship not just across a single extinction but across the entire mid-Permian to mid-Triassic; only survivors through the entire interval can be the ancestors of the Mesozoic clades.
Fewer brachiopod genera survived the interval than did brachiopod clades, suggesting that pseudoextinction or insufficient sampling could be a problem in analyzing these extinctions; thus, survivorship analysis should be conducted at the clade level. Nine characteristics were examined for generic representatives of 20 North American brachiopod clades, five of which survived both Permian extinctions and the subsequent earliest Triassic transitional interval. Characteristics include both those that operate on global scales and those that operate on the higher-resolution scales of individuals and populations.
Survivors were significantly smaller and occurred less frequently than victims. Mean diversity of communities in which survivors were present was significantly greater. The finding that rare taxa belonging to high-diversity communities were more likely to survive runs counter to traditional predictions. However, these results are consistent with recent studies suggesting that higher diversity within a trophic level may create a buffer, as surviving taxa quickly occupy the vacant niche space of the victims. As size, abundance, and community diversity are all statistically related, the small size of survivors may be an artifact of reduced biovolume per taxon in a diverse community.
No significant relationship exists between global-scale processes and survivorship of brachiopods through the mid-Permian to mid-Triassic. The results suggest that ecological processes can strongly influence global extinction patterns.
The consensus view that the amount of rock available for sampling does not significantly and systematically bias Phanerozoic marine diversity patterns has broken down. How changes in rock availability and sampling intensity affect our estimates of past biodiversity has been investigated with a variety of new approaches. A number of proxies for the amount of rock available for sampling have been used, but most of these proxies do not rely directly on evidence from large-scale geological maps (maps that cover small areas) and accompanying memoirs. Most previous map-based studies focused on single regions or relied on small-scale synoptic maps. We collected data from published geological maps and memoirs from western Europe, Australia, and Chile, which we combined with COSUNA data from the United States to generate the first multiregional data set for investigating whether the global Phanerozoic marine diversity record is a true global record, or is instead biased toward North America and Western Europe as has long been suspected. Both short and long-term trends in variation in the amount of outcrop display limited correlation among the regions studied. A series of diversification models obtained better matches to observed fossil diversity from the European and U.S. records than for the Chilean and Australian records, further supporting suspicions that the global Phanerozoic diversity curve is disproportionately influenced by European and U.S. fossil data. These results indicate that future research into Phanerozoic marine diversity patterns should not continue to apply global eustatic curves as a proxy for rock at outcrop, but should use regional data on rock occurrence.
Temporal variation in sampling intensity and geologically controlled rates of fossil preservation distort macroevolutionary patterns in the fossil record. Here, we use a comprehensive, list-based compilation of taxonomically and stratigraphically vetted global crinoid genus occurrences to evaluate and correct for the effects of variable and incomplete sampling from the Ordovician through Early Silurian. After standardizing the number of occurrences or the number of biofacies used to estimate the stratigraphic ranges of genera and after adjusting rates of turnover to account for the incomplete preservation of true extinction and origination pulses, we find support for several important revisions to the macroevolutionary history of crinoids. First, in contrast to the uncorrected data, sample-standardized genus richness does not appear to increase by more than 20% after an abrupt Middle Ordovician (Harnagian) diversification. Second, the only significant short-term change in genus richness following the Harnagian increase is a ≥24% decline from the Rawtheyan to the Hirnantian. Third, volatility in rates of genus extinction is increased after adjusting for preservation and there remain significant peaks of extinction in the Rawtheyan, which marks the end-Ordovician extinction, and in the middle of the Early Silurian. Finally, significant increases in origination rates occur in the Early Silurian. These results reaffirm the importance of the end-Ordovician extinction for crinoids, but they also highlight the comparatively poorly sampled Early Silurian as a time of turnover among crinoids.
Crinoid genus extinction rates are positively correlated with area-weighted rates of sedimentary package truncation, suggesting that extinction may have been controlled by physical environmental changes, such as the contraction of unique epicontinental sea habitats. The lack of a correlation between genus origination and sedimentary package initiation reinforces this hypothesis and suggests that other factors, such as evolutionary innovations and biotic interactions during the Ordovician radiation, may have been more important in controlling the diversification of crinoids.
The Caune de l'Arago Cave (southern France) has yielded one of the best preserved and best documented sedimentary successions of the European Middle Pleistocene (Oxygen Isotopic Stages 14 to 12). Herbivorous ungulates (horse, reindeer, red deer, fallow deer, bison, musk ox, argali, and tahr) are well represented in the three major stratigraphic units CM1, CM2, and CM3. CM1 and CM3 correspond to cold and dry climate and CM2 represents temperate and humid environmental conditions. Dental microwear and mesowear analyses were performed for the ungulates from CM1–3 to test whether these methods of dental wear evaluation were suitable for detecting climate-driven changes in the dietary resources of the Arago ungulate community. We found that both dental mesowear and microwear indicate dietary traits and their relationship to climatic conditions as reflected by vegetation cover and community structure. In all units, even if some species seem to share habitats or resources, it appears that the overlap in their feeding ecology is very low. The CM1 and CM3 units, where pollen analysis indicates that the climate was cold and dry, show the lowest diversity in dietary traits. The CM2, where climate is known to be more temperate and humid, the spectrum of dietary traits is large—grazers, browsers, and mixed feeders are present.
Principal components analysis (PCA) of 21 shell parameters (geometry, sculpture, aperture shape, and suture complexity) in 597 L. Devonian to L. Triassic ammonoid genera (spanning ∼166 Myr) shows that eight basic morphotypes appeared within ∼20 Myr of the first appearance of ammonoids. With one exception, these morphotypes persisted throughout the Paleozoic, occurring in ∼75% of the ∼5-Myr time bins used in this study. Morphotypes were not exclusive to particular lineages. Their persistence was not just a product of phylogenetic constraints or longevity, and multiple iterations of the same morphotypes occurred at different times and in different groups. Although mass extinction events severely condensed the range of morphologic variation and taxonomic diversity, the effects were short lived and most extinct morphotypes were usually iterated within 5 Myr. The most important effect of mass extinctions on ammonoid evolutionary history seems to have been their role in large scale taxonomic turnovers; they effectively eliminated previously dominant orders at the Frasnian/Famennian (F/F) (Agoniatitida), the Devonian/Mississippian (D/M) (Clymeniida), and the Permian/Triassic (P/T) (Goniatitida and Prolecanitida) extinctions. Survivors varied from two (P/T) to four (D/M) and five genera (F/F). These events generated sharp reductions in morphologic disparity at the D/M (58%) and at the P/T (59%), but there was a net increase at the F/F (38%). There was no obvious survival bias for particular morphotypes, but 64% are interpreted to have been Nautilus-like nektobenthic. The recurrence of particular combinations of morphology and their strong independence of phylogeny are strong arguments for functional constraint. Intervals between mass extinctions seem to have been relatively static in terms of morphotype numbers, in contrast to numbers of genera. Significant decreases in genus diversity (54%) and morphologic disparity (33%) commenced in the mid-Permian (Wordian/ Capitanian boundary), well before the final P/T event.
It has recently been argued that barren intervals of marine sedimentary rock are less common in the Cenozoic than in the Paleozoic, and that this arises as a direct consequence of widespread epeiric seas and the prevalence of dysaerobic conditions at such times. We show, using an independent and more direct measure of rock outcrop through time in western Europe, that barren marine sedimentary rocks do become less frequent toward the present, but that this is not linked to any epeiric-seas effect. The proportion of barren to fossiliferous rock outcrop correlates well with the inferred Phanerozoic marine diversity curve (although more so in the Paleozoic than in the post-Paleozoic), and shows no correlation or only a weak negative correlation with area over which the sediments have been deposited. We therefore concluded that the Phanerozoic trend in fossiliferousness most likely records the degree to which space is occupied in the shallow marine realm.