Documenting sexual dimorphism for structures that exhibit indeterminate growth can be more difficult than for structures exhibiting determinate growth. Most proboscidean tusks are ever-growing structures that change size and shape throughout life. Sexual dimorphism is pronounced in tusks of mature individuals, but the external form of tusks offers no clear evidence of maturation, and it is difficult to distinguish a young male's tusk from that of an older female. Thus, with previous approaches, knowledge of age was often required to assess sex from tusk measurements. This study examines sexual dimorphism of American mastodon (Mammut americanum) tusks through principal components analysis to determine which aspects of tusk form contribute most strongly to the variance among measurements and to explore the relationship between tusk form and individual age and sex. Twenty-one mastodon tusks from the Great Lakes region were evaluated in two analyses, the first focusing on geometrically distinct aspects of tusk form and the second adding measurements that reflect ontogenetic changes in a single aspect of morphology (circumference). Both analyses separated mastodons by sex (PC-I) and sorted them by age (PC-II). The distribution of tusks on the PC-II versus PC-I plane provides better discrimination of sex than univariate or bivariate methods because tusks of similar size and opposite sex appear near opposite ends of an age spectrum. The second analysis enhances sorting by age, thereby clarifying assessment of sex. This work contributes to studies of mastodon paleobiology by presenting a reliable method for assessing the sex of an individual from tusk measurements without requiring independent knowledge of age.

The species richness of extant metazoan phyla displays a strong association with the ontogenetic timing of germ-line determination. Taxa with early ontogenetic determination of the germ-line are characterized by low species number relative to taxa with late or variable determination. A test for a similar association in fossil taxa is compromised by the fact that all phyla displaying early determination of the germ-line are small, soft-bodied groups which lack a reliable fossil record. To the extent that this correlation reflects causality, patterns of evolutionary diversification have been decidedly non-random. The fact that ontogenetic timing of germ-line determination defines the extent to which genetic variation arising during the course of ontogeny may be inherited suggests a possible causal foundation for the pattern.

Fitting the generalized inverse Gaussian-Poisson distribution (GIGP) to observed frequency distributions of taxa from the Late Triassic Molteno Formation of South Africa has yielded estimates of the corresponding preserved biodiversities. Three extrapolations have been made on the basis of the uniquely rich megaflora/insect coassemblages from 100 taphocoenoses: insect species—335 observed, 7740 preserved; vegetative species—206 observed, 667 preserved; gymnosperm ovulate orders—16 observed, 84 preserved. The reliability of the results varies according to the abundance and observed diversity of the taxa. These results, with further estimations in a companion paper of existed diversity (regional, continental and global), hint at Late Triassic floral and faunal richness akin to today. This conflicts with the traditionally held model of an increasing cone of biodiversity through time and suggests a phase of explosive evolution in the Triassic hitherto unsuspected. Application of the GIGP to other well-documented collections from other periods might reveal a pattern of diversity trends offering fundamentally new insights into the evolving terrestrial biosphere.

Widespread concern about environmental pollution is putting a new question to the fossil record: How has the biosphere reacted to chemical changes in the past? Monera and Protoctista might be expected to provide valuable clues in this quest since their biomineral remains are generally formed in conditions closely related to the environment. But why do unicells biomineralize at all? It was with such questions in mind that an international symposium of the Systematics Association on “Biomineralization in Lower Plants and Animals” was held at Birmingham on April 15–19, 1985. Monerans, protoctistans, lichens, calcareous algae, and bryozoans were discussed in 36 papers, of which 23 are to be published in a volume by Oxford University Press. This volume, edited by Leadbeater and Riding (1986), will form a natural sequel to the papers in Miller et al. (1984) on mineral phases in biology and in Westbroek and de Jong (1983) on biomineralization and biological metal accumulation.

Muscular articulations on the brachials and pinnules of Paleozoic crinoids have traditionally been inferred by the presence of a transverse ridge. We here provide evidence that the microstructure of the stereom, fine meshed where muscles once inserted and coarse meshed where ligaments were emplaced, provides a reliable microstructural criterion for muscular articulation on well-preserved arm ossicles. Partially pyritized ossicles of Aesiocrinus magnificus Miller & Gurley from the Lane Shale of Pennsylvanian age at Kansas City, Missouri exhibit well-preserved stereom in three dimensions under the scanning electron microscope. These brachial and pinnular plates show clearly the distinctiveness of stereom at sites of muscule and ligament attachment. This criterion should be useful in tracing the evolutionary development of flexible arm articulations in several lineages of Paleozoic crinoids.

We infer the body-size scaling slope of metabolic rate in a trilobite by applying a cell-size model that has been proposed to explain metabolic scaling in living organisms. This application is especially tractable in fossil arthropods with well-preserved compound eyes because the number and size of eye facets appear to be useful proxies for the relative number and size of cells in the body. As a case study, we examined the ontogenetic scaling of facet size and number in a ∼390-Myr-old local assemblage of the trilobite Eldredgeops rana, which has well-preserved compound eyes and a wide body-size range. Growth in total eye lens area resulted from increases in both facet area and number in relatively small (presumably young) specimens, but only from increases in facet area in large (presumably more mature) specimens. These results suggest that early growth in E. rana involved both cell multiplication and enlargement, whereas later growth involved only cell enlargement. If the cell-size model is correct, then metabolic rate scaled allometrically in E. rana, and the scaling slope of log metabolic rate versus log body mass decreased from ∼0.85 to 0.63 as these animals grew. This inferred age-specific change in metabolic scaling is consistent with similar changes frequently observed in living animals. Additional preliminary analyses of literature data on other trilobites also suggest that the metabolic scaling slope was <1 in benthic species, but ∼1 in pelagic species, as has also been observed in living invertebrates. The eye-facet size (EFS) method featured here opens up new possibilities for examining the bioenergetic allometry of extinct arthropods.

Mesozoic tooth marks on bone surfaces directly link consumers to fossil assemblage formation. Striated tooth marks are believed to form by theropod denticle contact, and attempts have been made to identify theropod consumers by comparing these striations with denticle widths of contemporaneous taxa. The purpose of this study is to test whether ziphodont theropod consumer characteristics can be accurately identified from striated tooth marks on fossil surfaces. We had three major objectives (1) to experimentally produce striated tooth marks and explain how they form; (2) to determine whether body size characteristics are reflected in denticle widths; and (3) to determine whether denticle characters are accurately transcribed onto bone surfaces in the form of striated tooth marks. We conducted controlled feeding trials with the dental analogue Varanus komodoensis (the Komodo monitor). Goat (Capra hircus) carcasses were introduced to captive, isolated individuals. Striated tooth marks were then identified, and striation width, number, and degree of convergence were recorded for each. Denticle widths and tooth/body size characters were taken from photographs and published accounts of both theropod and V. komodoensis skeletal material, and regressions were compared among and between the two groups. Striated marks tend to be regularly striated with a variable degree of branching, and may co-occur with scores. Striation morphology directly reflects contact between the mesial carina and bone surfaces during the rostral reorientation when defleshing. Denticle width is influenced primarily by tooth size, and correlates well with body size, displaying negative allometry in both groups regardless of taxon or position. When compared, striation widths fall within or below the range of denticle widths extrapolated for similar-sized V. komodoensis individuals. Striation width is directly influenced by the orientation of the carina during feeding, and may underestimate but cannot overestimate denticle width. Although body size can theoretically be estimated solely by a striated tooth mark under ideal circumstances, many caveats should be considered. These include the influence of negative allometry across taxa and throughout ontogeny, the existence of theropods with extreme denticle widths, and the potential for striations to underestimate denticle widths. This method may be useful under specific circumstances, especially for establishing a lower limit body size for potential consumers.

Gould (1980) claims that a “new and general theory of evolution” is emerging. He examines the modern synthesis and asserts that it is being rejected by present day evolutionary biologists. The purpose of this note is to show that Gould's view of the modern synthesis is distorted. Any rejection of the modern synthesis must rest on a more balanced characterization than that presented by Gould.

As paleobiology continues to address an ever broader array of questions, it becomes increasingly important to interpret confidently the meaning of the pattern of fossil occurrences as found in outcrop. To this end, sequence stratigraphy is an important tool for paleobiologists because it predicts the distribution of unconformities, facies changes, and changes in sedimentation rate, all factors known from numerous previous studies to affect the quality of the fossil record. Computer simulations now make it possible not only to model sequence architecture within sedimentary basins, but also to model the occurrence of fossils within those basins. These models generate predictions regarding the stratigraphic distribution of first and last occurrences, changes in species abundance, changes in species morphology, and the distribution of gaps in fossil ranges. Although confirmation of some of these predictions has been found in field studies, the extent to which these predictions describe the fossil record in general is still unknown. If the predicted patterns of fossil occurrences are found to be widespread, it will suggest that a relatively simple model of fossil occurrences in outcrops could become a new tool for solving a wide array of paleobiologic and biostratigraphic problems. With such models, paleobiologists and biostratigraphers will be able to use model data to test the accuracy of newly developed methods of analysis.

The schizochroal eye of trilobites bears lenses of high optical quality. Cooperation between adjacent lenses, which must have had retinas rather than rhabdomeres, might have allowed the trilobite stereoscopic vision throughout its visual field. We propose a simple neurophysiological model for the schizochroal eye in which neural connections between lenses on vertical “visual strips” could have provided the integration necessary for stereoscopic vision. Simple neural signals could have coded information on the position, size, speed and nature of an object in the field of view. The model of stereoscopic vision is consistent with data on the shape of the eye, the arrangement of lenses on its surface, and with current views on the origin and early evolution of the schizochroal eye. It implies that the lens arrangement, neural network and shape of the eye surface were a coadapted morphological complex, and it is consistent with accepted ideas of the Phacopina as living in benthic habitats in the photic zone.

The rapid and accurate taxonomic identification of fossils is of great significance in paleontology, biostratigraphy, and other fields. However, taxonomic identification is often labor-intensive and tedious, and the requisition of extensive prior knowledge about a taxonomic group also requires long-term training. Moreover, identification results are often inconsistent across researchers and communities. Accordingly, in this study, we used deep learning to support taxonomic identification. We used web crawlers to collect the Fossil Image Dataset (FID) via the Internet, obtaining 415,339 images belonging to 50 fossil clades. Then we trained three powerful convolutional neural networks on a high-performance workstation. The Inception-ResNet-v2 architecture achieved an average accuracy of 0.90 in the test dataset when transfer learning was applied. The clades of microfossils and vertebrate fossils exhibited the highest identification accuracies of 0.95 and 0.90, respectively. In contrast, clades of sponges, bryozoans, and trace fossils with various morphologies or with few samples in the dataset exhibited a performance below 0.80. Visual explanation methods further highlighted the discrepancies among different fossil clades and suggested similarities between the identifications made by machine classifiers and taxonomists. Collecting large paleontological datasets from various sources, such as the literature, digitization of dark data, citizen-science data, and public data from the Internet may further enhance deep learning methods and their adoption. Such developments will also possibly lead to image-based systematic taxonomy to be replaced by machine-aided classification in the future. Pioneering studies can include microfossils and some invertebrate fossils. To contribute to this development, we deployed our model on a server for public access at www.ai-fossil.com.

The modern gorgonocephalid ophiuroid Astrophyton, a basketstar, has feeding habits which may be analogous to those of some Paleozoic crinoids that lack pinnulate arms (Meyer and Lane 1975). Field study has demonstrated the very quick response of Astrophyton when plankton impinge upon its arms. Study of the skeletal microstructure by scanning electron microscopy has shown that the quick response is facilitated by the development of relatively large ventral muscle fossae and articular surfaces whose shape follows a catenary curve. Prey are impaled by spines which articulate with the ventral surface of vertebral ossicles. Stereomic microstructure of vertebral ossicles is galleried where ligaments are present and labyrinthic where muscular tissue is present. The same microstructures are found in muscular articulations of modern crinoids. Future work on the arm structure of Paleozoic taxocrinids and cyathocrinids may demonstrate structural analogies and suggest similarities in food capture between such crinoids and modern baskets tars.

The deep-sea Cenozoic planktonic microfossil record has the unique characteristics of continuously well-preserved populations of most species, with virtually unlimited sample size, and therefore constitutes, in principle, a major resource for macroevolutionary research. Antarctic Neogene radiolarians in particular, are diverse, abundant and consistently well-preserved and evolved rapidly. This fauna is, in theory, a near-perfect testing ground for paleodiversity reconstructions. In this study we determined the diversity history of these faunas from a new quantitative, taxonomically complete data set from Neogene and Quaternary sections at several Antarctic sites. The pattern retrieved by our whole-fauna data set shows a significant, largely extinctionless ecological change in faunal composition and decrease in the evenness of species' abundances during the late Miocene, followed 3 Myr later, at around 5 Ma, by a significant drop in diversity. We tentatively associate this ecological event with a synchronous, regional change in the composition of the primary producers, but as yet cannot identify any environmental changes associated with the later extinction. Further, our whole-fauna diversity history was compared to diversity computed from much less complete, biostratigraphically oriented studies of species' occurrences, compiled in the Neptune database and reconstructed by using subsampling methodologies. Comparison of our whole-fauna and subsampling-reconstructed diversity patterns shows that the first-order trends are the same in both, suggesting that, to some degree, such literature compilations can be used to explore diversity history of plankton. However, our results also highlight substantial errors and distortions in the reconstructed diversity which make it poorly suited to more-detailed studies (e.g., for comparison of diversity history with paleoenvironmental history). We conclude that detailed studies of plankton diversity, and particularly those attempting to understand the relation between diversity and paleoceanographic change, should be based on taxonomically comprehensive, quantitative data.

Plant–insect associations have been a significant component of terrestrial ecology for more than 400 Myr. Exploring these interactions in the fossil record through novel perspectives provides a window into understanding evolutionary and ecological forces that shaped these interactions. For the past several decades, researchers have documented, described, and categorized fossil evidence of these interactions. Drawing on powerful tools from network science, we propose here a bipartite network representation of fossilized plants and their herbivore-induced leaf damage to understand late Paleozoic plant–insect interactions at the local community level. We focus on four assemblages from north-central Texas, but the methods used in this work are general and can be applied to any well-preserved fossil flora. Network analysis can address key questions in the evolution of insect herbivory that often would be difficult to summarize using standard herbivory metrics.

This study uses a comprehensive, revised, and updated global bivalve dataset combining information from two major databases available to study temporal trends in Phanerozoic bivalve richness: the Sepkoski Compendium and the Paleobiology Database. This compilation results in greater taxonomic and stratigraphic coverage than possible with either of the two databases alone. However, there are challenges in directly comparing these two sources due to differences in their taxonomic designations and stratigraphic range information. Moreover, both of these datasets are fraught with a number of taxonomic errors, which can significantly bias the overall richness estimate. Additionally, a substantial number of taxonomic corrections were made before a new Phanerozoic bivalve richness curve was produced. The new generic taxonomic curve is comparable with the trajectory of the Sepkoski’s modern fauna and shows rapid and substantial diversification through the Ordovician, followed by a Paleozoic plateau, a Mesozoic high, and Cenozoic diversification after a small reduction in richness associated with the K/Pg extinction. The steep Cenozoic rise documented in the raw richness curve derived from the new dataset is likely real, and reflects the overall robustness and completeness of the bivalve fossil record.

Paleobiological diversity is often expressed as α (within-sample), β (among-sample), and γ (total) diversities. However, when studying the effects of extinction on diversity patterns, only variations in α and γ diversities are typically addressed. A null model that examines changes in β diversity as a function of percent extinction is presented here.

The model examines diversity in the context of a hierarchical sampling strategy that allows for the additive partitioning of γ diversity into mean α and β diversities at varying scales. Here, the sampling hierarchy has four levels: samples, beds, facies, and region; thus, there are four levels of α diversity (α1, α2, α3, α4) and three levels of β diversity (β1, β2, and β3). Taxa are randomly assigned to samples within the hierarchy according to probability of occurrence, and initial mean α and β values are calculated. A regional extinction is imposed, and the hierarchy is resampled from the remaining extant taxa. Post-extinction mean α and β values are then calculated.

Both non-selective and selective extinctions with respect to taxon abundance yield decreases in α, β, and γ diversities. Non-selective extinction with respect to taxon abundance shows little effect on diversity partitioning except at the highest extinction magnitudes (above 75% extinction), where the contribution of α1 to total γ increases at the expense of β3, with β1 and β2 varying little with increasing extinction magnitude. The pre-extinction contribution of α1 to total diversity increases with increased probabilities of taxon occurrence and the number of shared taxa between facies. Both β1 and β2 contribute equally to total diversity at low occurrence probabilities, but β2 is negligible at high probabilities, because individual samples preserve all the taxonomic variation present within a facies. Selective extinction with respect to rare taxa indicates a constant increase in α1 and constant decrease in β3 with increasing extinction magnitudes, whereas selective extinction with respect to abundant taxa yields the opposite pattern of an initial decrease in α1 and increase in β3. Both β1 and β2 remain constant with increasing extinction for both cases of selectivity. By comparing diversity partitioning before and after an extinction event, it may be possible to determine whether the extinction was selective with respect to taxon abundances, and if so, whether that selectivity was against rare or abundant taxa.

Field data were collected across a Late Ordovician regional extinction in the Nashville Dome of Tennessee, with sampling hierarchy similar to that of the model. These data agree with the abundant-selective model, showing declines in α, β, and γ diversities, and a decrease in α1 and increase in β3, which suggests this extinction may have targeted abundant taxa.

Steneofiber, an early Miocene European beaver, showed evidence of a K-strategy model of reproduction and important morphological modifications for better adaptation to a semiaquatic way of life. At the same time, a North American branch of Castoridae developed not only a parental care system but also a series of cranial and postcranial osteological adaptations to a burrowing way of life. As the North American and the European Castoridae evolved independently from each other for at least fifteen m.y., these behavioral trends seem to have been inherent in the family for a long time and have apparently promoted, up to the present time, the spread of semiaquatic forms on the two continents; on the contrary, the burrowing branch of the Castoridae rapidly vanished.

The phenomenon of selective biotic extinction is commonly explained as the result of the extinction of specialized organisms and the survival of generalized organisms during a time of environmental stress. Using 48 orders of aquatic free-living arthropods, we test the hypothesis that generalized organisms tend to have longer geologic ranges than specialized organisms. The degree of specialization, as expressed through morphological complexity, is measured by the diversity of limb pairs on the arthropod body. The resulting “tagmosis value” reflects the functional differentiation of limb pairs to perform specific tasks and thus may estimate ecological specialization. No statistically significant correlation exists between an order's typical degree of morphological specialization and its geologic range. Degree of specialization is not an important determinant of evolutionary persistence at this taxonomic level. Evolutionary longevity may depend on the adaptive type (e.g., trophic role, relationship to substrate, etc.) represented by the taxon and on the assortment of these adaptive types.

Reconciliation of paleontological and molecular phylogenetic evidence holds great promise for a better understanding of the temporal succession of cladogenesis and character evolution, especially for taxa with a fragmentary fossil record and uncertain classification. In zoology, studies of this kind have largely been restricted to Bilateria. Hexactinellids (glass sponges) readily lend themselves to test such an approach for early-branching (non-bilaterian) animals: they have a long and rich fossil record, but for certain taxa paleontological evidence is still scarce or ambiguous. Furthermore, there is a lack of consensus for taxonomic interpretations, and discrepancies exist between neontological and paleontological classification systems. Using conservative fossil calibration constraints and the largest molecular phylogenetic data set assembled for this group, we infer divergence times of crown-group Hexactinellida in a Bayesian relaxed molecular clock framework. With some notable exceptions, our results are largely congruent with interpretations of the hexactinellid fossil record, but also indicate long periods of undocumented evolution for several groups. This study illustrates the potential of an integrated molecular/paleobiological approach to reconstructing the evolution of challenging groups of organisms.