Lunules have evolved independently in several groups of clypeasteroids, including the Rotulidae, Astriclypeidae, Mellitidae and Scutasteridae. In this paper, only the monophyletic assemblage Monophorasteridae plus Mellitidae is considered. Lunules result from modifications of the growth patterns of test plates which bring about changes in relative growth in specific directions. It is unnecessary to postulate resorption of the test. Ambulacral lunules, which are known to have hydrodynamic functions, originated as part of a series of changes: 1) bifurcation of food grooves, 2) formation of pressure drainage channels, 3) lobulation of the ambitus (as in Monophoraster), 4) complete lunule formation. The anal lunule shares the hydrodynamic function but arose separately, as a developmental aberration. The position of the periproct is highly variable but it is most commonly located at the junction of suture lines, at plate corners. In Scutella it is located between the first and second post-basicoronal plates. In Monophoraster the periproct is located further forward, between the first post-basicoronal plates, and the small anal lunule occupies the junction point between first and second post-basicoronals. It is hypothesized that the anal lunule originated as an all-or-nothing event following the forward migration of the periproct and failure to resume normal plate growth at the sutural junction point between first and second post-basicoronal plates. Its walls were derived from paired interambulacral supports. The hypothesis is discussed in connection with the ontogenetic formation of the anal lunule in living mellitid sand dollars.

The fossil conchs of ammonoids provide valuable information about the life habits of this extinct group. A new conch measurement, the apertural surface area (ASarea), is introduced here along with modeled sizes of the buccal mass and the hyponome, based on ratios of these organs in comparison with the aperture height from the Recent Nautilus pompilius. A principal components analysis was performed using the three main characters: (1) apertural surface area index (i.e., the ratio of the apertural surface and the conch diameter), (2) buccal mass area index (i.e., the ratio between the buccal mass area and the ASarea), and (3) coiling rate of the conch. It revealed an ecomorphospace where life history traits can be tentatively assigned to species of the Ammonoidea. In this morphospace, Recent Nautilus has a marginal position, being one of the ectocochleate cephalopods with best properties for active life (capacity for handling large food items, rather good mobility). In contrast, most ammonoids possessed, at comparable conch sizes, much smaller buccal apparatuses and hyponomes, suggesting a more passive life history with reduced mobility potential and reduced capacities for larger prey items.

The coastal environment of the Changjiang delta has been influenced by recent anthropogenic activities such as dam construction and increased sewage and fertilizer inputs. Previous work examined the compositional shift of marine plankton to assess ecological impacts of these activities on marine ecosystems in the Changjiang discharge area. Here we used benthic marine ostracodes collected in the Changjiang estuary and the adjacent East China Sea in the 1980s and the 2010s, respectively, to investigate temporal changes of the benthic community and controlling factors for the benthic fauna. Our results revealed more shoreward distribution of some well-known offshore ostracode species in the 2010s compared with the 1980s and a relatively more important role for environmental processes (e.g., bottom-water temperature, bottom-water salinity, and eutrophic conditions of surface water) than spatial processes (e.g., the flow of ocean currents) in structuring ostracode compositions. The temporal changes in the ostracode community are likely attributable to the combined effects of reduced fresh water and sediment discharge and eutrophic conditions of the Changjiang due to the many dams constructed along the Changjiang and population expansion in the Changjiang Basin. Results of redundancy analysis and variation partitioning suggest that ocean currents facilitated environmental filtering of ostracode species such that they could disperse to preferred environmental conditions. These findings highlight the potential uses of marine microfossils to better understand ecological impacts on benthic ecosystems in vulnerable Asian mega-deltas and provide insights into the integration of metacommunity concepts in disentangling dynamics of marine benthic communities.

Although extinction risk has been found to have a consistent negative relationship with geographic range across wide temporal and taxonomic scales, the effect has been difficult to disentangle from factors such as sampling, ecological niche, or clade. In addition, studies of extinction risk have focused on benthic invertebrates with less work on planktic taxa. We employed a global set of 1114 planktic graptolite species from the Ordovician to lower Devonian to analyze the predictive power of species’ traits and abiotic factors on extinction risk, combining general linear models (GLMs), partial least-squares regression (PLSR), and permutation tests. Factors included measures of geographic range, sampling, and graptolite-specific factors such as clade, biofacies affiliation, shallow water tolerance, and age cohorts split at the base of the Katian and Rhuddanian stages.

The percent variance in durations explained varied substantially between taxon subsets from 12% to 45%. Overall commonness, the correlated effects of geographic range and sampling, was the strongest, most consistent factor (12–30% variance explained), with clade and age cohort adding up to 18% and other factors <10%. Surprisingly, geographic range alone contributed little explanatory power (<5%). It is likely that this is a consequence of a nonlinear relationship between geographic range and extinction risk, wherein the largest reductions in extinction risk are gained from moderate expansion of small geographic ranges. Thus, even large differences in range size between graptolite species did not lead to a proportionate difference in extinction risk because of the large average ranges of these species. Finally, we emphasize that the common practice of determining the geographic range of taxa from the union of all occurrences over their duration poses a substantial risk of overestimating the geographic scope of the realized ecological niche and, thus, of further conflating sampling effects on observed duration with the biological effects of range size on extinction risk.

It has been shown in laboratory experiments that viruses can transfer DNA from the host cell to other cells and even to those of another species. In nature such transfers could facilitate convergent evolution. Studied cases of convergent evolution indicate that a gene might be successfully transferred to another species to produce a similar phenotypic effect as frequently as once per 1–10 ma and the effects of gene transfer on evolution in general are likely to be considerable. There are many constraints on the cases of convergent evolution that might be considered as possible examples of gene transfer. First, both co-occurrence in space and time of the taxa in question and presence of complete reproductive isolation must be assessed. Further, both the limited space available in a virus particle and the necessity that the transferred DNA functions well in both mitosis and meiosis in heterozygotic individuals indicate that only rather short pieces of DNA would be expected to be transferred. This limits the possible effects of any gene transfer. Examples of convergent evolution in five Siluro-Devonian conodont lineages are briefly presented and assessed in terms of possible mechanisms of convergence.

A thorough understanding of how communities respond to extreme changes, such as biotic invasions, is essential to manage ecosystems today. Here we constructed fossil food webs to identify changes in Late Ordovician (Katian) shallow-marine paleocommunity structure and functioning before and after the Richmondian invasion, a well-documented ancient invasion. Food webs were compared using descriptive metrics and cascading extinction on graphs models. Richness at intermediate trophic levels was underrepresented when using only data from the Paleobiology Database relative to museum collections, resulting in a spurious decrease in modeled paleocommunity stability. Therefore, museum collections and field sampling may provide more reliable sources of data for the reconstruction of trophic organization in comparison to online data repositories. The invasion resulted in several changes in ecosystem dynamics. Despite topological similarities between pre- and postinvasion food webs, species loss occurred corresponding to a minor decrease in functional groups. Invaders occupied all of the preinvasion functional guilds, with the exception of four incumbent guilds that were lost and one new guild, corroborating the notion that invaders replace incumbents and fill preexisting niche space. Overall, models exhibited strong resistance to secondary extinction, although the postinvasion community had a lower threshold of collapse and more variable response to perturbation. We interpret these changes in dynamics as a decrease in stability, despite similarities in overall structure. Changes in food web structure and functioning resulting from the invasion suggest that conservation efforts may need to focus on preserving functional diversity if more diverse ecosystems are not inherently more stable.

The process of evolution and the structures it produces are best understood in the light of hierarchy theory. The biota traditionally is described by either the genealogical Linnaean hierarchy or economic hierarchies of communities or ecosystems. Here we describe the Bretskyan hierarchy—a hybrid eco-genealogical hierarchy that consists of nested sets of different-sized, usually polyphyletic communities of interacting individuals separated from other such communities in space and time at multiple scales. The Bretskyan hierarchy consists of elements that have both genealogical and economic properties and functions—situated between, and connecting the elements of, the economic hierarchies (Vernadskyan) and the genealogical (Linnaean) hierarchy. The described hierarchy at lower tiers is populated by holobionts, individuals composed of multiple polyphyletic lineages integrated by functional interactions or biotically fabricated structures, such as membranes. At larger spatial tiers and longer time scales, the members of the Bretskyan hierarchy are of a more diffuse nature, partially due to the small size and relatively short duration of us as observers of larger and longer-lasting structures, here described as geobiomes. Their individuality is externally forced and directly tied to the spatial and temporal physical structures of our planet. These are sub-bioprovinces and bioprovinces—large and effectively isolated spatiotemporal structures of biota integrated internally by coevolution and individuated externally by a hierarchy of barriers. Gaia is here understood as the largest eco-genealogical individual compartmentalized by the outer space of the Earth and integrated at long time scales by biotic interactions and plate tectonic mixing of biota. The existence of a hierarchy of barriers and multilevel allopatry suggests that geographic isolation takes part not only in individuating species lineages, but also in producing coherent complexes of separate lineages forming bioprovinces at multiple space and time scales. The sizes, configurations, and durations of Bretskyan units are directly tied to geodynamics, demonstrating the central role of the physical planet in the processes of individuation and merging of geobiomes and the control of coevolution, and all its ramifications, at multiple space and time scales. The Bretskyan hierarchy also allows the integration of previously unconnected themes—“egalitarian” major transitions in individuality (e.g., eukaryogenesis) and some of the megatrajectories in the history of life—into a single theoretical framework of spatial and temporal scaling of eco-genealogy. The pervasive scaling of geodynamical processes and the direct connection of geodynamics to the dynamics of Bretskyan units allows us to formulate conjectures on the scales and limits of spatial and temporal contingency and competitiveness of biotas in evolution.

Three features that provide information on the paleobiologic significance of fossulae in North American Late Ordovician solitary rugose corals are (1) irregularities in shape and position of the outer wall, (2) discontiguous septal growth lamellae, and (3) foreign objects incorporated into interseptal chambers within the corallum. Outer wall irregularities indicate that portions of a polyp could detach from the calice and could contract and expand radially by a significant amount and for prolonged periods of time during ontogeny, especially in the vicinity of the alar and cardinal fossulae. Discontiguous lamellae indicate that the polyp could detach from septa and contract laterally, especially in the cardinal fossula. This began with the onset of maturity and probably reflects reproductive activity. Ostracodes are the most common foreign objects in these coralla and are usually situated within or near the cardinal and alar fossulae. In the most likely hypothesis accounting for their presence, a live ostracode entered the calice when one side of the polyp temporarily detached from the corallum and contracted radially. It became trapped upon expansion and reattachment of the soft parts. The polyp moved upward in its corallum by detachment and uplift of the aboral surface. In a less likely hypothesis, the ostracode was captured by the coral for food and came to rest on the floor of the central cavity. It was incorporated into an interseptal chamber when the polyp moved upward in its corallum by atrophy of the aboral surface and formation of a new base above the object. In either hypothesis, portions of the polyp in the cardinal and alar fossulae probably functioned throughout ontogeny for water circulation in the central cavity, and for the intake of food and/or ejection of undigested material through the mouth. Taxonomic, stratigraphic, and paleobiogeographic variability in frequencies of the three features may indicate differences in the necessity and/or ability of polyps to perform these functions involving the fossulae. This could be a reflection of environmental and/or genetic factors.

Finite element modeling (FEM) has been used to evaluate microstructure-controlled stability of selected eggshells of Indian dinosaurs. Our study suggests that under static load the eggshell microstructure of Megaloolithus cylindricus displays a low magnitude of tensile stress over most of the spherolith. The magnitude of this tensile stress is lower than that displayed in M. jabalpurensis, M. baghensis, and Subtiliolithus kachchhensis. In M. cylindricus, a shell thickness matching the length of the spheroliths prevents the failure of eggshells, whereas in M. jabalpurensis and M. baghensis, which have thinner shells, the development of additional subspheroliths compensates for the relatively higher magnitude of tensile stresses. Extremely thin eggshell in S. kachchhensis shows a still higher magnitude of tensile stresses, thereby making it prone to cracking, but the propagation of cracks is apparently checked and stability reinforced by wider spacing of pore canals.

Because teeth are the most easily preserved part of the vertebrate skeleton and are particularly morphologically variable in mammals, studies of fossil mammals rely heavily on dental morphology. Dental morphology is used both for systematics and phylogeny as well as for inferences about paleoecology, diet in particular. We analyze the influence of evolutionary history on our ability to reconstruct diet from dental morphology in the mammalian order Carnivora, and we find that much of our understanding of diet in carnivorans is dependent on the phylogenetic constraints on diet in this clade. Substantial error in estimating diet from dental morphology is present regardless of the morphological data used to make the inference, although more extensive morphological datasets are more accurate in predicting diet than more limited character sets. Unfortunately, including phylogeny in making dietary inferences actually decreases the accuracy of these predictions, showing that dietary predictions from morphology are substantially dependent on the evolutionary constraints on carnivore diet and tooth shape. The “evolutionary ratchet” that drives lineages of carnivorans to evolve greater degrees of hypercarnivory through time actually plays a role in allowing dietary inference from tooth shape, but consequently requires caution in interpreting dietary inference from the teeth fossil carnivores. These difficulties are another reminder of the differences in evolutionary tempo and mode between morphology and ecology.

Understanding how time averaging changes during burial is essential for using Holocene and Anthropocene cores to analyze ecosystem change, given the many ways in which time averaging affects biodiversity measures. Here, we use transition-rate matrices to explore how the extent of time averaging changes downcore as shells transit through a taphonomically complex mixed layer into permanently buried historical layers: this is a null model, without any temporal changes in rates of sedimentation or bioturbation, to contrast with downcore patterns that might be produced by human activity. Assuming stochastic burial and exhumation movements of shells between increments within the mixed layer and stochastic disintegration within increments, we find that almost all combinations of net sedimentation, mixing, and disintegration produce a downcore increase in time averaging (interquartile range [IQR] of shell ages), this trend is typically associated with a decrease in kurtosis and skewness and by a shift from right-skewed to symmetrical age distributions. A downcore increase in time averaging is thus the null expectation wherever bioturbation generates an internally structured mixed layer (i.e., a surface, well-mixed layer is underlain by an incompletely mixed layer): under these conditions, shells are mixed throughout the entire mixed layer at a slower rate than they are buried below it by sedimentation. This downcore trend created by mixing is further amplified by the downcore decline in disintegration rate. We find that transition-rate matrices accurately reproduce the downcore changes in IQR, skewness, and kurtosis observed in bivalve assemblages from the southern California shelf. The right-skewed shell age-frequency distributions typical of surface death assemblages—the focus of most actualistic research—might be fossilized under exceptional conditions of episodic anoxia or sudden burial. However, such right-skewed assemblages will typically not survive transit through the surface mixed layer into subsurface historical layers: they are geologically transient. The deep-time fossil record will be dominated instead by the more time-averaged assemblages with weakly skewed age distributions that form in the lower parts of the mixed layer.

The complex morphological evolution of the bivalve Ptychomya throughout the well-studied Agrio Formation in the Neuquén Basin (west-central Argentina, lower/upper Valanginian–lowest Barremian) constitutes an ideal opportunity to study evolutionary patterns and processes occurring at geological timescales. Ptychomya is represented in this unit by four species, the morphological variation of which needs to be temporally assessed to obtain a thorough picture of the evolution of the group. Here we use geometric morphometrics to measure variation in shell outline, ribbing pattern, and shell size in these species. We bracket the ages of our samples using a combination of ammonoid biostratigraphy and absolute ages and study the anagenetic pattern of evolution of each trait by means of paleontological time-series analysis and change tracking. We find that evolution in Ptychomya is mostly speciational, as the majority of traits show stasis, with the exceptions of shell size in P. coihuicoensis and shell outline in P. windhauseni, which seem to evolve directionally toward larger and higher shells, respectively. Ptychomya displays changes in its average morphology and disparity, which are the result of a mixture of taxonomic turnover and mosaic evolution of traits. Pulses of speciation would have been triggered by ecological opportunity, as they occur during the recovery of shallow-burrowing bivalve faunas after dysoxic events affecting the basin. On the other hand, the presence of directional patterns of evolution in P. coihuicoensis and P. windhauseni seems to be the result of a general shallowing-upward trend observed in the basin during the upper Hauterivian–lowest Barremian, as opposed to the cyclical paleoenvironmental stability inferred for the early/late Valanginian–early Hauterivian, which would have prompted stasis in P. koeneni and P. esbelta.

Theoretical and experimental biomechanical approaches are used to test the effect regular archaeocyathan central cavity diameter has on the generation of passive flow through the skeleton. These results are then used to predict a correspondence between gross morphology and paleoenvironmental occurrence. Previous work has demonstrated that regular archaeocyathan morphology generates passive flow, via Bernoulli and viscous entrainment effects, through its porous walls for suspension feeding, a phenomenon that occurs in modern sponges. Efficacy of entrainment depends upon the area of the excurrent pore (i.e., central cavity) over which the ambient flow is moving. Consequently, archaeocyaths should have maximized their central cavity diameters.

Five-centimeter-long, conical and cylindrical acrylic pipes with varying end diameters were tested in a flume to document the relative effects of Bernoulli and viscous entrainment. Each pipe was oriented perpendicular to the flow direction in a uniform flow field, and fluorescein dye was injected at the pipe's mid-length for flow visualization. Models with different-sized apertures consistently exhibit dye movement to the larger opening and greater dye entrainment speeds than models with identically sized apertures, thereby suggesting that viscous entrainment effects are significant and operating in concert with Bernoulli effects. To test for similar effects in archaeocyaths, four brass models were constructed with varying central cavity diameters. Both volume flux and excurrent flow speed of the exiting water increased as the central cavity diameter increased. An analysis of the morphologies that occur in nature confirm these results. Regular archaeocyaths most commonly have central cavity diameters close to their outer wall diameter, thereby maximizing the excurrent pore area.

These results have implications for archaeocyathan paleoecology. Environments with low-magnitude currents should support individuals with larger central cavity diameters than higher energy settings. Data on the occurrence of morphotypes within bioherms of varying flow energies from South Australia support this prediction.

Functional analysis of fossils is and should remain a key component of paleobiological research. Despite recently expressed doubts, conceptual and methodological developments over the past 25 years indicate that robust and testable claims about function can be produced. Functional statements can be made in at least three different hierarchical contexts, corresponding to the degree of structural information available, the position in the phylogenetic hierarchy, and the degree of anatomical specificity. The paradigm approach, which dominated thinking about function in the 1960s and 1970s, has been supplanted with a methodology based on biomechanics. Paleobiomechanics does not assume optimality in organismal design, but determines whether structures were capable of carrying out a given function. The paradigm approach can best be viewed as a way of generating, rather than testing, functional hypotheses. Hypotheses about function can also be developed and supported by well-corroborated phylogenetic arguments. Additional functional evidence can be derived from studies of trace fossils and of taphonomy. New computer techniques, including “Artificial Life” studies, have the potential for producing far more detailed ideas about function and mode of life than have been previously possible. Functional analysis remains the basis for studies of the history of adaptation. It is also an essential component of many paleoecological and paleoenvironmental studies.

Accurately recognizing analogues between fossil and modern ecosystems allows paleoecologists to more fully interpret fossil assemblages and modern ecologists to leverage the fossil record to address long-term ecological and environmental changes. However, this becomes increasingly difficult as taxonomic turnover increases the dissimilarity between ecosystems. Here we use a guild-based approach to compare the ecological similarity of Cretaceous cold-seep assemblages preserved in the Pierre Shale surrounding the Black Hills and modern cold-seep assemblages from five previously recognized biofacies. We modify modern assemblage data to include only those taxa with fossilizable hard parts greater than 5 mm in length to make these modern data sets more comparable to potential fossil analogues. We find that while the Black Hills assemblages are more similar in ecological guild composition to the modern thyasirid biofacies, subsets share similarities in ecological structure to the lucinid and mussel-bed biofacies. The fossil seep assemblages are also more similar to one another than are modern assemblages belonging to the same biofacies, despite greater geographic and temporal dissimilarity among the fossil samples. Furthermore, guild-level ordination analyses show a secondary faunal gradient that reflects community succession in the hard substrate–dominated modern assemblages and reveals a parallel faunal gradient in the soft sediment–dominated Cretaceous assemblages, consistent with a gradient in the influence of seep fluids on the faunas. Thus, while the Black Hills assemblages are quite homogeneous in their composition, they capture ecological variation similar to successional patterns in modern seep systems.

The evolution of novel morphologies can signify expansion of a clade into new niches. This can be studied in the fossil record by investigating the morphospace occupancy of organisms, with small morphospaces signifying low morphological disparity and more diffuse morphospaces suggesting a broader range of morphologies adapted to different environments. Morphological disparity of many taxa (arthropods, crinoids, etc.) from the Cambrian to modern intervals have been studied in this manner. However, no study has investigated this in archaeocyaths, which, as reef builders, can have a disproportionate effect on early Cambrian biodiversity relative to their frequency. Here, we collect morphological data on archaeocyathan sponges, mostly from Laurentia. More than 600 museum specimens and 400 field samples were measured for traditional morphometric characters and discrete gross morphological characteristics. We find that archaeocyaths have an average cup/individual (body) diameter of 10.6 mm. This is significantly smaller than a selected group of modern demosponges and lithistid sponges that measure 94.1 mm and 66.8 mm in diameter, respectively, and each has a larger size variance. Archaeocyathan gross morphologies are also highly constrained to a few simple morphologies (three to six categories), while modern demosponges and lithistids are more diverse (nine categories each). These data indicate that Laurentian archaeocyaths were restricted in their morphological disparity, potentially due to limitations imposed by having a robust calcareous skeleton while still maintaining a large intervallum cavity space to facilitate passive entrainment. The fact that these Cambrian reef builders were restricted in their morphological complexity may have had a strong influence on the biodiversity of early Phanerozoic ecosystems. Furthermore, a clade limited to only a few specific morphologies is at an increased risk of extinction.

Vertebrate microfossil assemblages in a stratigraphic sequence often yield similar assortments of taxa but at different relative abundances, potentially indicative of marginal paleocommunity changes driven by paleoenvironmental change over time. For example, stratigraphically younger assemblages in the Dinosaur Park Formation (DPF) yield proportionally more aquatic taxa, consistent with marine transgression. However, individual deposits may have received specimens from multiple source paleocommunities over time, limiting our ability to confidently identify ecologically significant, paleocommunity differences through direct assemblage comparisons. We adapted a three-source, two-tracer Bayesian mixing model to quantify proportional contributions from different source habitats to DPF microfossil assemblages. Prior information about the compositions of separate, relatively unmixed terrestrial, freshwater, and marine assemblages from the Belly River Group allowed us to define expected taxon percent abundances for the end-member habitats likely contributing specimens to the mixed deposits. We compared the mixed assemblage and end-member distributions using 21 different combinations of vertebrate taxa. Chondrichthyan, dinosaur, and amphibian occurrence patterns ultimately allowed us to parse the contributions from the potential sources to 14 of the 15 mixed assemblages. The results confirmed a significant decline in terrestrial contributions at younger DPF sites, driven primarily by increased freshwater specimen inputs—not incursions from the adjacent marine paleocommunity. A rising base level likely increased lateral channel migration and the prevalence of freshwater habitats on the landscape, factors that contributed to increased paleocommunity mixing at younger channel deposit sites. Bayesian methods can account for source-mixing bias, which may be common in assemblages associated with major paleoenvironmental changes.