The Mississippi River watershed drains 40% of the continental United States, and the tremendous primary productivity in the adjacent north-central Gulf of Mexico has created one of the most extensive dead zones on Earth. In contrast, smaller watersheds deliver fewer nutrients to the northeastern gulf, and consequently, productivity is limited and hypoxia is uncommon. How has variation in primary productivity, oxygen availability, and sea-surface temperature affected coastal food webs? Here, we investigate environmental controls on the size of molluscan predators and prey in the northern Gulf of Mexico using Holocene death assemblages. Linear mixed models indicate that bivalve size and the frequency of drilling predation are affected by dissolved oxygen concentrations; drilling frequency declines with declining oxygen, whereas bivalve size increases. In contrast, sea-surface temperature is positively associated with the size of molluscan predators and prey. Net primary productivity contributes relatively little to predator or prey size, and predator-to-prey size ratios do not vary consistently with environmental conditions across the northern gulf. Larger bivalves in areas of oxygen limitation may be due to decreased predation pressure and, consequently, greater prey longevity. The larger size of bivalves and predatory gastropods in warmer waters may reflect enhanced growth under these conditions, provided dissolved oxygen concentrations exceed a minimum threshold. Holocene death assemblages can be used to test long-standing hypotheses regarding environmental controls on predator−prey body-size distributions through geologic time and provide baselines for assessing the ongoing effects of anthropogenic eutrophication and warming on coastal food webs.

Conspicuous centers of biodiversity are frequently attributed to local conditions that promote speciation or resistance to extinction, but recent diversification studies indicate this mode of explanation might not be very general, so it may be fruitful to revisit the role of dispersal in concentrating biodiversity. Here we consider the processes underlying the marine diversity hotspot in the Indo-West Pacific among comatulid crinoids, suspension-feeding echinoderms conspicuous on modern tropical reefs. We used ancestral-range reconstruction on a phylogeny of extant crinoids, assembled a new occurrence database of fossil comatulids and interrogated it with probabilistic preservational models, and developed a morphological character matrix to estimate the relationships among living and fossil comatulids. Ancestral-range reconstruction on a phylogeny of extant comatulids recovers an origin outside the Indo-Pacific and elevated dispersal into it. A new occurrence database records the comatulid clade spreading out gradually from origin in the Early Jurassic of the West Tethys. Comatulids do not appear in their modern hotspot until the Oligocene, and taphonomic analyses show these results cannot be explained solely as a result of inadequate sampling in Asia and Oceania. Finally, phylogenetic analyses demonstrate that deeply nested crown-group comatulids had originated before the clade became well established in the East Tethys, implying many independent dispersals into the modern hotspot. These consilient results suggest a biodiversity hotspot that owes its existence to dispersals out of the ancient West Tethys rather than to elevated in situ diversification.

For paleobiologists interested in extinct carnivorous reptiles, publication of Walter Auffenberg's (1981) 13–month field study of the Komodo dragon (Varanus komodoensis), or ora, as he prefers to call it, provides a useful portrait of a reptile as the top predator of a terrestrial community. A great deal of information about the ora's habitat utilization, activity patterns, diet, social behavior, and reproduction is presented.

As the most recent time in Earth history when global temperatures were warmer than at present, the peak of the last interglacial (Marine Isotope Substage [MIS] 5e; ~120,000 years ago) can serve as a pre-anthropogenic baseline for a warmer near-future world. Here we use a new compilation of 22 fossil localities in California that have been reliably dated to MIS 5e to establish baseline expectations for contemporary bivalve species movements by identifying and analyzing bivalve species with “extralimital” ranges, that is, species that occupied the California region during MIS 5e but are now restricted to adjacent regions. We find that 15% of species (n = 142) found in MIS 5e localities have extralimital ranges and currently occupy warmer waters to the south of the California region. The majority of extralimital occurrences occur in paleo-embayments, suggesting that these sheltered habitats were more suitable habitats for warm-water species than exposed coasts during the MIS 5e. We further find that extralimital species now tend to occur in cooler, more seasonally productive coastal waters and to occupy more offshore islands when compared with the broader species pool immediately south of California. These findings suggest that high dispersal potential and preexisting tolerances to environmental conditions similar to California's comparatively cool and seasonally productive environments may have enabled extralimital bivalves to colonize the California region during MIS 5e.

Recent studies have shown that modes of evolution, namely directional trend, random walk, and stasis, vary across morphologic traits and over the geographic range of a taxon. If so, is it possible that our interpretation of evolutionary modes is actually driven by our selection of traits in a study? In an attempt to answer this question, we have restudied the middle Miocene planktonic foraminifera Fohsella lineage, an iconic example of gradual morphologic evolution. In contrast to previous studies that have focused on the gross morphology as embodied by the edge view of tests, we analyze here multiple phenotypic traits chosen because their biologic and ecologic significance is well understood in living populations. We find that traits in the lineage did not evolve in concert. The timing and geographic pattern of changes in shape, coiling direction, size, and ecology were different. The evolution of this lineage is a mosaic combination of different evolutionary modes for different traits. We suggest that overemphasis on the evolution of some single trait, such as the edge-view outline, from narrow geographic ranges has significantly underestimated the dynamic evolutionary history of this group.

Few methods exist that put a posterior probability on the hypothesis that a thing is gone forever given its sighting history. A recently proposed Bayesian method is highly accurate but aggressive, generating many near-zero or near-one probabilities of extinction. Here I explore a Bayesian method called the agnostic equation that makes radically different assumptions and is much more conservative. The method assumes that the overall prior probability of extinction is 50% and that slices of the prior are exponentially distributed across the time series. The conditional probability of the data given survival is based on a simple, long-known combinatorial expression that captures the chance all presences would fall at random before or within the last sighting’s interval (L) given that they could fall anywhere. The same equation is used to compute the conditional probability given extinction at the start of each interval i, that is, the chance that all sightings would fall before or within L given that none could equal or postdate i. The conditional probability is zero for all hypothesized extinction intervals through L. Bayes’s theorem is then used to compute the posterior extinction probability. It is noted that recycling the mean posterior for a population as a prior improves the method’s accuracy. The agnostic equation differs from an earlier, related one, because it explicitly includes a term to represent the hypothesis of survival, and it therefore does not assume that the species has necessarily gone extinct within the sampling window. Simulations demonstrate that the posterior extinction probabilities are highly accurate when considered as a suite but individually indecisive, rarely approaching one. This property is advantageous whenever inferring extinction would have dangerous consequences. The agnostic method is therefore advocated in cases where conservative estimates are desired.

Biological variation fuels evolutionary change. Across longer timescales, however, polymorphisms at both the genomic and phenotypic levels often persist longer than would be expected under standard population genetic models such as positive selection or genetic drift. Explaining the maintenance of this variation within populations across long time spans via balancing selection has been a major triumph of theoretical population genetics and ecology. Although persistent polymorphisms can often be traced in fossil lineages over long periods through the rock record, paleobiology has had little to say about either the long-term maintenance of phenotypic variation or its macroevolutionary consequences. I explore the dynamics that occur when persistent polymorphisms maintained over long lineage durations are filtered into descendant lineages during periods of demographic upheaval that occur at speciation. I evaluate these patterns in two lineages: Ectocion, a genus of Eocene mammals, and botryocrinids, a Mississippian cladid crinoid family. Following origination, descendants are less variable than their ancestors. The patterns by which ancestral variation is sorted cannot be distinguished from drift. Maintained and accumulated polymorphisms in highly variable ancestral lineages such as Barycrinus rhombiferus Owen and Shumard, 1852 may fuel radiations as character states are sorted into multiple descendant lineages. Interrogating the conditions under which trans-specific polymorphism is either maintained or lost during periods of demographic and ecological upheaval can explain how population-level processes contribute to the emergent macroevolutionary dynamics that shape the history of life as preserved in the fossil record.

Certain taxa are noticeably common within collections, widely distributed, and frequently long-lived. We have examined these dominant genera as compared with rarer genera, with a focus on their temporal histories. Using occurrence data from the Paleobiology Database, we determined which genera belonging to six target groups ranked among the most common within each of 49 temporal bins based on occurrences. The turnover among these dominant taxa from bin to bin was then determined for each of these groups, and all six groups when pooled. Although dominant genera are only a small fraction of all genera, the patterns of turnover mimic those seen in much larger compilations of total biodiversity. We also found that differences in patterns of turnover at the top ranks among the higher taxa reflect previously documented comparison of overall turnover among these classes. Both dominant and nondominant genera exhibit, on average, symmetrical patterns of rise and fall between first and last appearances. Dominant genera rarely begin at high ranks, but nevertheless tend to be more common when they first appear than nondominant genera. Moreover, dominant genera rarely are in the top 20 when they last appear, but still typically occupy more localities than nondominant genera occupy in their last interval. The mechanism(s) that produce dominant genera remain unclear. Nearly half of dominant genera are the type genus of a family or subfamily. This is consistent with a simple model of morphological and phylogenetic diversification and sampling.

Fossil bones were once living tissues that demanded internal blood perfusion in proportion to their metabolic requirements. Metabolic rates were primarily associated with bone growth (modeling) in the juvenile stages and with alteration and repair of existing bone affected by weight bearing and locomotion (remodeling) in later stages. This study estimates blood flow rates to the tibia shafts of the Late Cretaceous hadrosaurid Maiasaura peeblesorum, based on the size of the primary nutrient foramina in fossil bones. Foramen size quantitatively reflects arterial size and hence blood flow rate. The results showed that the bone metabolic intensity of juveniles (ca. 1 year old) was greater than fourfold higher than that of 6- to 11-year-old adults. This difference is much greater than expected from standard metabolic scaling and is interpreted as a shift from the high metabolic demands for primary bone modeling in the rapidly growing juveniles to a lower metabolic demand of adults to remodel their bones for repair of microfractures accumulated during locomotion and weight bearing. Large nutrient foramina of adults indicate a high level of cursorial locomotion characteristic of tachymetabolic endotherms. The practical value of these results is that juvenile and adult stages should be treated separately in interspecific analyses of bone perfusion in relation to body mass.

With Jack Sepkoski's sudden death from heart failure on May 1, 1999, paleontology lost one of its most important figures. In his 25–year career, Jack published more than 70 research articles, 15 of them in this journal, and an equal number of reviews, commentaries, and abstracts. He co-edited Paleobiology (1983–86), received the Schuchert Award (1983), and served as President of the Paleontological Society (1995–96). In 1997, he was elected to the Polish Academy of Sciences and in the same year received the Medal of the University of Helsinki. Further recognition would surely have followed but for his untimely death.

Conodont elements have high rates of morphological evolution, but the drivers of this disparity are debated. Positive allometric relationships between dimensions of food-processing surfaces and entire P1 elements have been used to argue that these elements performed mechanical digestion. If involved in food processing, the surface of the element should grow at a rate proportional to the increase in energy requirements of the animal. This inference of function relies on the assumption that the energy requirements of the animal grew faster (≅ mass0.75) than the tooth area (≅ mass0.67). We reevaluate this assumption based on metabolic rates across animals and calculate the allometry in platform-bearing P1 elements of Late Triassic co-occurring taxa, Metapolygnathus communisti and Epigondolella rigoi, using 3D models of ontogenetic series. Positive allometry is found in platform and element dimensions in both species, supporting a grasping-tooth hypothesis, based on the assumption that metabolic rate in conodonts scaled with body mass similarly to that in fish and ectotherms. We also calculate the curvature of the P1 platform surface using the Dirichlet normal energy (DNE) as a proxy for diet. DNE values increase with body mass, supporting the assumption that conodont metabolic rates increased faster than mass0.67. We finally find that adults in both taxa differ in their food bases, which supports trophic diversification as an important driver of the remarkable disparity of conodont elements.

Camelids (Camelidae) were a diverse and widely distributed group in South America during the Pleistocene. According to the fossil record, three species inhabited southern Brazil in the recent past: Hemiauchenia paradoxa, Lama guanicoe, and Vicugna vicugna. The analysis of carbon and oxygen stable isotope ratios in bioapatite provides insight into the paleobiology of nonliving animals and the environment they used to inhabit. We applied this tool to investigate the diet of camelids from two geological localities in southern Brazil: Touro Passo and Santa Vitória Formations (H. paradoxa, n = 7; L. guanicoe, n = 6; V. vicugna, n = 4). Carbon stable isotopes from enamel, dentin, and bone indicated that H. paradoxa and L. guanicoe had diets comprising mostly C3 grasses, but the latter showed a broader diet due to one individual with a mixed diet, whereas V. vicugna had a mixed C3–C4 diet. These different foraging behaviors may have minimized interspecific competition and favored niche partitioning and the coexistence of related species. Combined oxygen and carbon isotope data showed a consistent diet according to climate, probably due to the greater availability in glacial periods of cool-season grasses, which mainly use the C3 photosynthetic pathway. Given their adaptations to grazing, the climate amelioration, followed by the loss of grasslands, likely had a great impact on camelid populations, leading to their extinction in southern Brazil. These results, therefore, contribute to the understanding of the dynamics of paleocommunities in this region.

Melanin pigments are central to colors and patterns in modern vertebrate integuments, which inform upon ecological and behavioral strategies like crypsis, aposematism, and sociosexual selection. Over the last decade, melanin has emerged as a valuable tool for predicting color in exceptionally preserved fossil feathers and subsequent testing of paleobiological hypotheses in long-extinct dinosaurs and birds. Yet much remains to be learned about melanin stability, diagenetic alterations to melanin chemistry, and their implications for “paleocolor reconstruction.” Pressure–temperature maturation experiments with modern feathers offer a way to examine these topics but have mostly been conducted in closed-system capsules or open-system aluminum foil. Both methods have operational limitations and do not consider the filtering effect of porous sediment matrices on thermally labile chemical groups versus stable ones during natural fossilization. We use sediment-encased maturation to resolve this issue and demonstrate replication of organic preservation of melanin highly comparable to compression fossils. Our experiments, coupled with time-of-flight secondary ion mass spectrometry, show predictable volatilization of N/S-bearing molecules and increased melanin cross-linking with elevated temperatures. We also suggest that eumelanin is more stable compared with pheomelanin at higher temperatures, explaining why eumelanic colors (black, dark brown, iridescent) are better preserved in fossils than pheomelanic ones (reddish brown). Furthermore, we propose that proteins preferentially undergo hydrolysis more so than forming N-heterocycles in selectively open systems analogous to natural matrices. Thus, we conclude that melanin pigments and not diagenetically altered protein remnants are the key players in promoting fossilization of soft tissues like feathers.

Ecophenotypic variation in populations is driven by differences in environmental variables. In marine environments, ecophenotypic variation may be caused by differences in hydrodynamic conditions, substrate type, water depth, temperature, salinity, oxygen concentration, and habitat heterogeneity, among others. Instances of ecophenotypic variation in modern and fossil settings are common, but little is known about the influences of time averaging and spatial averaging on their preservation. Here we examine the shell morphology of two adjacent populations, both live collected and death assemblages, of the infaunal, suspension-feeding, intertidal bivalve Leukoma staminea from the well-studied Argyle Creek and Argyle Lagoon locations on San Juan Island, Washington. Individuals in the low-energy lagoon are free to burrow in the fine-grained substrate, while clams in the high-energy creek are precluded from burrowing in the rocky channel. Our results demonstrate variation in size and shape between the adjacent habitats. Lagoon clams are larger, more disk-shaped, and have relatively larger siphons than their creek counterparts, which are smaller, more spherical in shape, and have a relatively shallower pallial sinus. This ecophenotypy is preserved among death assemblages, although with generally greater variation due to time averaging and shell transport. Our interpretation is that ecophenotypic variation, in this case, is induced by differing hydrodynamic regimes and substrate types, cumulatively resulting in physiological trade-offs diverting resources from feeding and respiration to stability and shell strength, all of which have the potential to be preserved in the fossil record.

With 14 species recorded, the Miocene La Venta bat fauna is the most diverse bat paleocommunity in South America. It includes the oldest plant-visiting bat in the New World and some of the earliest representatives of the extant families Phyllostomidae, Thyropteridae, and Noctilionidae. La Venta's Notonycteris magdalenensis is an extinct member of the subfamily Phyllostominae, a group of modern Neotropical animalivorous bats, and is commonly included in studies of the evolution of Neotropical bats, but aspects of its biology remain unclear. In this study, we used multivariate dental topography analysis (DTA) to reconstruct the diet of N. magdalenensis by quantitatively comparing measures of molar complexity with those of 25 modern noctilionoid species representing all major dietary habits in bats. We found clear differences in molar complexity between dietary guilds, indicating that DTA is potentially an informative tool to study bat ecomorphology. Our results suggest N. magdalenensis was probably an omnivore or insectivore, rather than a carnivore like its modern relatives Chrotopterus auritus and Vampyrum spectrum. Also, we reconstructed the body mass of N. magdalenensis to be ~95 g, larger than most insectivorous bats, but smaller than the largest carnivorous bat (V. spectrum). Our results confirm that N. magdalenensis was not a specialized carnivore. It remains to be demonstrated that the specialized carnivory ecological niche was occupied by the same lineage of phyllostomines from at least the middle Miocene. Combining our diet and body-mass reconstructions, we suggest that N. magdalenensis exhibits morphological pre-adaptations crucial for the evolution of specialized carnivory.

The Late Triassic conodont species Mockina ex gr. carinata and Mockina ex gr. englandi were exceptionally prevalent among the marine fauna of the Panthalassan realm from the middle Norian through to the Rhaetian. Leading into the complete extinction of conodonts near the Triassic/Jurassic boundary, a significant turnover event occurred in conodont fauna across the Norian/Rhaetian boundary (NRB), with the pectiniform elements of common Rhaetian genera from Tethys exhibiting minimal or absent platforms. This intergeneric trend of platform reduction is not as evident in Panthalassa, where these genera are very rare, but morphometric analyses of M. ex gr. carinata and M. ex gr. englandi specimens from across the Canadian Cordillera demonstrate that comparable shifts in morphology occurred intraspecifically in Panthalassa across the NRB, confirming the global extent of these trends. Pectiniform elements of M. ex gr. carinata display a sequential reduction of platform width from the middle Norian to late Norian to Rhaetian, whereas pectiniform elements of M. ex gr. englandi display a reduction of platform width only from the late Norian to Rhaetian. Specimens of both species that have a mid-platform length to breadth ratio greater than 3:1 are restricted to the Rhaetian. Specimens from the Kennecott Point section on Haida Gwaii, British Columbia, demonstrate that this morphological shift occurred somewhat later than other biostratigraphic proxies for the NRB. The global trend of platform width reduction in many conodont pectiniform elements may reflect a change in primary diet away from hard food sources, perhaps suggesting some degree of carbonate biomineralization suppression beginning around the NRB. This interpretation would support CO2 outgassing as the causal mechanism of the environmental disturbance at the NRB and identify the NRB as a significant turning point for Late Triassic ecosystems, marking the beginning of a protracted, multiphase end-Triassic mass extinction.

Taxonomic status of several members of the family Naticidae is extremely vague because of its simple shell morphology. Conventional taxonomic classification schemes suggest that most of the morphological characters tend to be homoplastic and exhibit convergence. Such morphological convergence complicates naticid taxonomy and makes it difficult to understand the evolutionary history of this group; several unrelated taxa are often misidentified as naticids, thereby exaggerating the actual diversity of this group. Here, we employ a standard landmark-based approach to understand the pattern of morphological evolution of this family. Ordination methods such as principal components analysis and canonical variate analysis were used to create morphospaces, and disparity was quantified using variance and range. Our results reveal that when naticids are compared with their sister taxon, Ampullinidae, the two families show significant differences in their average shapes, despite their superficial resemblances. Among naticids, although the mean shapes of the individual subfamilies are different, overall, the family Naticidae has displayed extreme morphological conservatism from the Jurassic to the Holocene. Interestingly, this conservatism has been unaffected by taxonomic changes—neither the extinction of the subfamily Gyrodinae nor the appearance of the subfamily Sininae affected this morphological conservatism. Naticids have always shown strong ecological preference toward an infaunal mode of life and strict behavioral selectivity in handling and preying upon infaunal organisms, and this ecological and behavioral conservatism could have enabled them to diversify without undergoing a change in their basic Bauplan.

Paleecological data allow not only the study of trends along deep-time chronological transects but can also be used to reconstruct ecological gradients through time, which can help identify causal factors that may be strongly correlated in modern ecosystems. We have applied such an analysis to Bergmann’s rule, which posits a causal relationship between temperature and body size in mammals. Bergmann’s rule predicts that latitudinal gradients should exist during any interval of time, with larger taxa toward the poles and smaller taxa toward the equator. It also predicts that the strength of these gradients should vary with time, becoming weaker during warmer periods and stronger during colder conditions. We tested these predictions by reconstructing body-mass trends within canid and equid genera at different intervals of the Oligo-Miocene along the West Coast of North America. To allow for comparisons with modern taxa, body mass was reconstructed along the same transect for modern Canis and Odocoileus. Of the 17 fossil genera analyzed, only two showed the expected positive relationship with latitude, nor was there consistent evidence for a relationship between paleotemperature and body mass. Likewise, the strength of body-size gradients does not change predictably with climate through time. The evidence for clear gradients is ambiguous even in the modern genera analyzed. These results suggest that, counter to Bergmann’s rule, temperature alone is not a primary driver of body size and underscore the importance of regional-scale paleoecological analyses in identifying such drivers.

Electron backscatter diffraction (EBSD) has been widely used in recent studies of eggshells for its convenience in collecting in situ crystallographic information. China has a wide variety of dinosaur eggshells, although nearly none have been studied with this technique. Elongatoolithid eggs include many oogenera, although the microstructural differences of some were not highly appreciated, leading to several parataxonomic problems. In this paper, we surveyed seven elongatoolithid oogenera in China using EBSD in order to acquire more information about their microstructural variation. It is shown in this paper that in some elongatoolithid eggshells, scaly calcite grains that form the squamatic ultrastructure are not the only form of calcite in the continuous layer. Large columnar grains separated by high-angled grain boundaries and slender subgrains separated by radially arranged low-angled grain boundaries could exist in certain areas of the eggshells such as Macroolithus and Macroelongatoolithus. This paper discusses the criteria for identifying squamatic ultrastructure and proposes type I (rich in rugged high-angled grain boundaries) and type II (rich in both rugged high- and low-angled grain boundaries) squamatic ultrastructures. A pathological layer is found in Undulatoolithus pengi. An external zone is identified in the eggshell of Heishanoolithus changii, which does not support its position within the oofamily Elongatoolithidae. We argue that Paraelongatoolithus no longer belongs to Elongatoolithidae based on a combination of reticulated ornamentation, columnar continuous layer, and acicular mammillae. The high structural variation in elongatoolithid eggshells also implies that it may be inappropriate to relate all previous elongatoolithid eggshells to oviraptorosaurs and assume they are non-monophyletic.