Although Phanerozoic increases in the global richness, local richness, and evenness of marine invertebrates are well documented, a common explanation for these patterns has been difficult to identify. Evidence is presented here from marine invertebrate communities that there is a Phanerozoic increase in the fundamental biodiversity number (θ), which describes diversity and relative abundance distributions in neutral ecological theory. If marine ecosystems behave according to the rules of Hubbell’s Neutral Theory of Biodiversity and Biogeography, the Phanerozoic increase in θ suggests three possible mechanisms for the parallel increases in global richness, local richness, and evenness: (1) an increase in the per-individual probability of speciation, (2) an increase in the area occupied by marine metacommunities, and (3) an increase in the density (per-area abundance) of marine organisms. Because speciation rates have declined over time and because there is no clear evidence for an increase in metacommunity area through the Phanerozoic, the most likely of these is an increase in the spatial density of marine invertebrates over the Phanerozoic, an interpretation supported by previous studies of fossil abundance. This, coupled with a Phanerozoic rise in body size, suggests that an increase in primary productivity through time is the primary cause of Phanerozoic increases in θ, global richness, local richness, local evenness, abundance, and body size.

Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of extant plants, the ones of M. talaris are exceptional in that they have variable morphology. They bore two wings that produced a range of wing configurations, from seeds with two equal-sized wings to single-winged specimens, via various stages of underdevelopment of one of the wings. To examine the effects of various seed morphologies on aerodynamics and dispersal potential, we studied the flight performance of paper models of three morphotypes: symmetric double-winged, asymmetric double-winged, and single-winged. Using a high-speed camera we identified the mode of descent (plummeting, gliding, autorotation) and quantified descent speed, autorotation frequency, and other flight characteristics. To validate such modeling as an inferential tool, we compared descent of extant analogues (kauri; Agathis australis) with descent of similarly constructed seed models. All three seed morphotypes exhibited autorotating flight behavior. However, double-winged seeds, especially symmetric ones, failed to initiate slow autorotative descent more frequently than single-winged seeds. Even when autorotating, symmetric double-winged seeds descend faster than asymmetric double-winged ones, and descent is roughly twice as fast compared to single-winged seeds. Moreover, the relative advantage that (effectively) single-winged seeds have in slowing descent during autorotation becomes larger as seed weight increases. Hence, the range in seed wing configurations in M. talaris produced a wide variation in potential dispersal capacity. Overall, our results indicate that the evolutionarily novel autorotating winged seeds must have improved conifer seed dispersal, in a time when animal vectors for dispersion were virtually absent. Because of the range in wing configuration, the early evolution of autorotative flight in conifers was a functionally imperfect one, which provides us insight into the evolutionary developmental biology of autorotative seeds in conifers.

The extent of morphologic innovation during the Ediacaran–Cambrian diversification of animals was unique in the history of metazoan life. This episode was also associated with extensive changes in the redox state of the oceans, in the structure of benthic and pelagic marine ecosystems, in the nature of marine sediments, and in the complexity of developmental interactions in Eumetazoa. But did the phylogenetic and morphologic breadth of this episode simply reflect the unusual outcome of recurrent evolutionary processes, or was it the unique result of circumstances, whether in the physical environment, in developmental mechanisms, or in ecological interactions? To better characterize the uniqueness of the events, I distinguish among these components on the basis of the extent of sensitivity to initial conditions and unpredictability, which generates a matrix of possibilities from fully contingent to fully deterministic. Discriminating between these differences is important for informing debates over determinism versus the contingency in the history of life, for understanding the nature of evolutionary theory, and for interpreting historically unique events.

Fossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological sample of 50 tibiae of the hadrosaurid dinosaur Maiasaura peeblesorum allows predictions of annual growth and ecological interpretations based on more histologic data than any previous large sample study. Tibia length correlates well (R2>0.9) with diaphyseal circumference, cortical area, and bone wall thickness, thereby allowing longitudinal predictions of annual body size increases based on growth mark circumference measurements. With an avian level apposition rate of 86.4 μm/day, Maiasaura achieved over half of asymptotic tibia diaphyseal circumference within its first year. Mortality rate for the first year was 89.9% but a seven year period of peak performance followed, when survivorship (mean mortality rate=12.7%) was highest. During the third year of life, Maiasaura attained 36% (x=1260 kg) of asymptotic body mass, growth rate was decelerating (18.2 μm/day), cortical vascular orientation changed, and mortality rate briefly increased. These transitions may indicate onset of sexual maturity and corresponding reallocation of resources to reproduction. Skeletal maturity and senescence occurred after 8 years, at which point the mean mortality rate increased to 44.4%. Compared with Alligator, an extant relative, Maiasaura exhibits rapid cortical increase early in ontogeny, while Alligator cortical growth is much lower and protracted throughout ontogeny. Our life history synthesis of Maiasaura utilizes the largest histological sample size for any extinct tetrapod species thus far, demonstrating how large sample microanalyses strengthen paleobiological interpretations.

Insect taphonomy is a topic that has drawn interest because of its potential biases on diversity patterns and the ecological information recorded by ancient insect faunas. Other than the onset of common amber fossilization in the Cretaceous, very little is known about long-term trends in the nature and quality of insect preservation and, as a result, the effects of taphonomic biases are poorly constrained. We assembled a database of nearly 7000 Carboniferous–Pliocene insect adpression (compression and impression) species from the primary literature to assess changes in insect taphonomy over time and test biotic and environmental controls on preservation. We grouped the fossils into 10-Myr bins and scored preservation of holotype specimens as either articulated bodies or isolated wings; articulated specimens with a body implied a generally higher quality of preservation. Paleozoic and Triassic insect holotypes are known overwhelmingly from isolated wings (only 12% articulated bodies), but our database shows a significant increase in the percentage preserved as articulated bodies, to more than 70%, beginning about 160 Myr ago in the Late Jurassic. This transition could reflect variations in the robustness of different insect orders and shifts in the taxonomic composition of insect faunas, but all the major orders in the database exhibit significant increases in articulation. Instead, a shift to increased preservation in lacustrine paleoenvironments, which contain a greater proportion of articulated body fossils, explains most of the trend. The pronounced Late Jurassic increase in articulation has implications for evolutionary and ecological reconstructions, for example, suggesting that preserved insect diversity may be biased downward in the earlier part of their history when articulation was poor.

Multivariate methods such as cluster analysis and ordination are basic to paleoecology, but the messy nature of fossil occurrence data often makes it difficult to recover clear patterns. A recently described faunal similarity index based on the Forbes coefficient improves results when its complement is employed as a distance metric. This index involves adding terms to the Forbes equation and ignoring one of the counts it employs (that of species found in neither of the samples under consideration). Analyses of simulated data matrices demonstrate its advantages. These matrices include large and small samples from two partially overlapping species pools. In a cluster analysis, the widely used Dice coefficient and the Euclidean distance metric both create groupings that reflect sample size, the Simpson index suggests large differences that do not exist, and the corrected Forbes index creates groupings based strictly on true faunal overlap. In a principal coordinates analysis (PCoA) the Forbes index almost removes the sample-size signal but other approaches create a second axis strongly dominated by sample size. Meanwhile, species lists of late Pleistocene mammals from the United States capture biogeographic signals that standard ordination methods do recover, but the adjusted Forbes coefficient spaces the points out more sensibly. Finally, when biome-scale lists for living mammals are added to the data set and extinct species are removed, correspondence analysis misleadingly separates out the biome lists, and PCoA based on the Dice coefficient places them to the edge of the cloud of fossil assemblage data points. PCoA based on the Forbes index places them in more reasonable positions. Thus, only the adjusted Forbes index is able to recover true biological patterns. These results suggest that the index may be useful in analyzing not only paleontological data sets but any data set that includes species lists having highly variable lengths.

Ecological niche modeling (ENM) is a quantitative approach to predict species’ abiotic requirements. It is a correlative technique, requiring geographically explicit information on species occurrences and the suites of environmental conditions experienced at each occurrence point. The output of these models is a set of environmental suitability rules that can be projected geographically and through time to test biogeographic, ecologic, and evolutionary hypotheses. Although developed by biologists and used extensively in the modern, ENM is in its early stages of application to the deep-time fossil record (hence PaleoENM). In part its limited use in the fossil record thus far reflects the methodological challenge of constructing paleoenvironmental layers needed for PaleoENM analysis, whereas in the modern these layers are available from large public databases (e.g., WorldClim). This paper provides a contextual and methodological framework for appropriately applying PaleoENM, including best practices for developing species occurrence and paleoenvironmental data sets for PaleoENM analyses.

Research into the relationship between leaf form and climate over the last century has revealed that, in many species, the sizes and shapes of leaf characters exhibit highly structured and predictable patterns of variation in response to the local climate. Several procedures have been developed that quantify covariation between the relative abundance of plant character states and the states of climate variables as a means of estimating paleoclimate parameters. One of the most widely used of these is the Climate Leaf Analysis Multivariate Program (CLAMP). The consistency, accuracy and reliability with which leaf characters can be identified and assigned to CLAMP character-state categories is critical to the accuracy of all CLAMP analyses. Here we report results of a series of performance tests for an image-based, fully automated at the point of use, leaf character scoring system that can be used to generate CLAMP leaf character state data for: leaf bases (acute, cordate and round), leaf apices (acute, attenuate), leaf shapes (ovate, elliptical and obovate), leaf lobing (unlobed, lobed), and leaf aspect ratios (length/width). This image-based system returned jackknifed identification accuracy ratios of between 87% and 100%. These results demonstrate that automated image-based identification systems have the potential to improve paleoenvironmental inferences via the provision of accurate, consistent and rapid CLAMP leaf-character identifications. More generally, our results provide strong support for the feasibility of using fully automated, image-based morphometric procedures to address the general problem of morphological character-state identification.

We use a Gaussian logistic regression model to characterize epoch-to-epoch and stage-tostage changes in the latitudinal response curves of Cenozoic marine bivalve and gastropod genera along the global latitudinal gradient, and analyze these changes to understand the mode and tempo of changes in latitudinal distribution. A ubiquitous ‘‘hollow curve’’ pattern is apparent, wherein smaller changes in response-curve parameters are much more common than larger changes. Curves are strikingly consistent in terms of the average level of change exhibited, despite the many unique environmental and biological changes documented between each of these intervals. This implies that the pace and magnitude of changes in the latitudinal distribution of marine mollusks are not controlled, in aggregate, by time-period-specific conditions. Additionally, we find no evidence for long-term migration from tropical to extratropical latitudes. Our results instead favor a model of either equatorward migration or no general trend. This likely reflects the tendency of genera to maintain their highest concentrations in the tropics even if their ranges become extended out of the tropics over time.

Arthropods are known to display a variable number of eye lenses and this number mostly increases during their development. In trilobites, most species possessing schizochroal eyes exhibit a notable intraspecific variation in the number of dorso ventral files of eye lenses that can be age related (i.e., growth) or not (i.e., living environment). Several previous studies have shown that some trilobite groups (e.g. phacopids) tend to have fewer lenses/files in representatives from the deeper habitats than those from shallower habitats. In this study, we analyzed the pattern of variation in the number of dorso ventral files of eye lenses in two Devonian phacopid trilobites from the Prague Basin of the Czech Republic. We quantified their intraspecific variability. To better understand the patterning, we compared more than 120 individuals. Data first reveal evidence of a bimodal distribution of lens/file number without intermediate forms among each of two studied populations of Prokops prokopi (Chlupáč, 1971) and throughout the ontogeny of Pedinopariops insequens (Chlupáč, 1977). Our results indicate that caution must be taken for taxonomical affiliation and biodiversity analyses of taxa in which the intraspecific variability is unclear. Additionally, we investigated possible relations of these bimodalities to the stratigraphical position of studied populations and to the paleoenvironment. In Prokops prokopi, a slightly different age of both populations, together with supposed differences in the local environments can be responsible for observed variability. In Pedinopariops insequens, stress conditions possibly related to the approaching onset of the Basal Choteč Event can be responsible for surprising intrapopulation variability. We speculate that the stress conditions could cause a bimodal selection and possibly also the change of ontogenetic trajectory within this species. Pedinopariops insequens was the only phacopid in the Prague Basin that crosses the Lower/Middle Devonian boundary and survived also the onset of Basal Choteč Event.

Macroevolutionary and macroecological studies must account for biases in the fossil record, especially when questions concern the relative abundance and diversity of taxa that differ in preservation and sampling potential. Using Cenozoic marine mollusks from a temperate setting (New Zealand), we find that much of the long-term temporal variation in gastropod versus bivalve occurrences is correlated with the stage-level sampling probabilities of aragonitic versus calcitic taxa. Average sampling probabilities are higher for calcitic species, but this contrast is time-varying in a predictable way, being concentrated in stages with widespread carbonate deposition.

To understand these results fully, we link them with analyses at the level of individual point occurrences. Doing so reveals that aragonite bias is effectively absent in terrigenous clastic sediments. In limestones, by contrast, calcitic species have at least twice the odds of sampling as aragonitic species. This result is most pronounced during times of widespread carbonate deposition, where the difference in the per-collection odds of sampling species is a factor of eight. During carbonate-rich intervals, calcitic taxa also have higher odds of sampling in clastics. At first glance this result may suggest simple preservational bias against aragonite. However, comparing relative odds of aragonitic versus calcitic sampling with absolute sampling rates shows that the positive calcite bias during carbonate-rich times reflects higher than average occurrence rates for calcitic taxa (rather than lower rates for aragonitic taxa) and that the negative aragonite bias in limestones reflects lower than average occurrence rates for aragonitic taxa (rather than higher rates for calcitic taxa).

Our results therefore indicate a time-varying interplay of two main factors: (1) taphonomic loss of aragonitic species in carbonate sediments, with no substantial bias in terrigenous clastics; and (2) an ecological preference of calcitic taxa for environments characteristic of periods with pervasive carbonate deposition, irrespective of lithology per se.

—Stable isotope ratios of carbon and nitrogen in archaeological and modern bone samples have been used to reconstruct the dietary changes of the South American sea lion Otaria flavescens from the late Holocene to the present in the southwestern Atlantic. We sampled bones from archaeological sites in northern-central and southern Patagonia, Argentina, and bones housed in modern scientific collections. Additionally, we analyzed the stable isotope ratios in ancient and modern shells of intertidal molluscs to explore changes in the isotope baseline and allow comparison between bone samples from different periods after correction for baseline shifts. Results confirmed the trophic plasticity of the South American sea lion, demonstrated the much larger impact of modern exploitation of marine resources as compared with that of hunter-gatherers, and underscored the dissimilarity between the past and modern niches of exploited species. These conclusions are supported by the rather stable diet of South American sea lions during several millennia of aboriginal exploitation, in both northern-central and southern Patagonia, and the dramatic increase in trophic level observed during the twentieth century. The recent increase in trophic level might be related to the smaller population size resulting from modern sealing and the resulting reduced intraspecific competition. These results demonstrate how much can be learned about the ecology of modern species thanks to retrospective studies beyond the current, anthropogenically modified setting where ecosystem structure is totally different from that in the pristine environments where current species evolved.

The Guadalupian (middle Permian) extinction may have triggered substantial ecological restructuring in level-bottom communities, such as turnover in dominant brachiopod genera or a shift from abundant brachiopods to mollusks, despite comparatively minor taxonomic losses. However, ecological changes in relative abundance have been inferred from limited data; as a result, constraints on important shifts like the brachiopod-mollusk transition are imprecise. Here, I reevaluate the magnitude of ecological shifts during the Guadalupian–Lopingian (G-L) interval by supplementing previous census counts of silicified assemblages with counts from non-silicified assemblages and global occurrence data, both sourced from the Paleobiology Database. Brachiopod occurrences are consistent with more pronounced faunal composition changes from the Guadalupian to Lopingian than among stages within those intervals, but only in Iran and South China, and not in Pakistan or a Tethys-wide data set. In Iran and South China, Bray-Curtis dissimilarity values comparing occurrence frequencies between adjacent stages were elevated across the G-L transition, although other intervals exhibited similarly large shifts. However, genus occurrence frequencies were less strongly correlated or were anti-correlated across the G-L transition, suggesting moderate faunal turnover among dominant brachiopod genera. In contrast to previous inferences from silicified faunas, abundances of brachiopods, bivalves, and gastropods remained consistent from the Guadalupian to Lopingian in non-silicified local counts and global occurrences, implying that the brachiopod-mollusk shift did not occur until the end-Permian extinction. Ecological and taxonomic consequences were both minor in level-bottom settings, suggesting that severe environmental perturbations may not be necessary to explain biotic changes during the Guadalupian-Lopingian transition.

Paleobiologists must propose a priori hypotheses of homology when conducting a phylogenetic analysis of extinct taxa. The distributions of such “primary” homologies among species are fundamental to phylogeny reconstruction because they reflect a prior belief in what constitutes comparable organismal elements and are the principal determinants of the outcome of phylogenetic analysis. Problems arise when fossil morphology presents seemingly equivocal hypotheses of homology, herein referred to as antinomies. In groups where homology recognition has been elusive, such as echinoderms, these problems are commonly accompanied by the presence (and persistence) of poor descriptive terminology in taxonomic literature that confounds an understanding of characters and stymy phylogenetic research. This paper combines fossil morphology, phylogenetic systematics, and insights from evolutionary developmental biology to outline a research program in Phylogenetic Paleo-ontogeny. A “paleo” ontogenetic approach to character analysis provides a logical basis for homology recognition and discerning patterns of character evolution in a phylogenetic context. To illustrate the utility of the paleo-ontogenetic approach, I present a reassessment of historically contentious plate homologies for “pan-cladid” crinoids (Cladida, Flexibilia, Articulata). Developmental patterns in living crinoids were combined with the fossil record of pan-cladid morphologies to investigate primary posterior plate homologies. Results suggest the sequence of morphologic transitions unfolding during the ontogeny of extant crinoids are developmental relics of their Paleozoic precursors. Developmental genetic modules controlling posterior plate development in pan-cladid crinoids have likely experienced considerable constraint for over 250 million years and limited morphologic diversity in the complexity of calyx characters. Future phylogenetic analyses of pan-cladids are recommended to consider the presence of a single plate in the posterior region homologous with the radianal, rather than the anal X, as is commonly assumed.

Scleractinian corals have two fundamentally different life strategies, which can be inferred from morphological criteria in fossil material. In the non-photosymbiotic group nutrition comes exclusively from heterotrophic feeding, whereas the photosymbiotic group achieves a good part of its nutrition from algae hosted in the coral’s tissue. These ecologic differences arose early in the evolutionary history of corals but with repeated evolutionary losses and presumably also gains of symbiosis since then. We assessed the biodiversity dynamics and environmental occupancy of both ecologic groups to identify times when the evolutionary losses of symbiosis as inferred from molecular analyses might have occurred and if these can be linked to environmental change. Two episodes are likely: The first was in the mid-Cretaceous when non-symbiotic corals experienced an origination pulse and started to become more common in deeper, non-reef habitats and on siliciclastic substrates initiating a long-term offshore trend in occupancy. The second was around the Cretaceous/Paleogene boundary with another origination pulse and increased occupancy of deep-water settings in the non-symbiotic group. Environmental factors such as rapid global warming associated with mid-Cretaceous anoxic events and increased nutrient concentrations in Late Cretaceous–Cenozoic deeper waters are plausible mechanisms for the shift. Turnover rates and durations are not significantly different between the two ecologic groups when compared over the entire history of scleractinians. However, the deep-water shift of non-symbiotic corals was accompanied by reduced extinction rates, supporting the view that environmental occupancy is a prominent driver of evolutionary rates.

Both molecular clocks and the first appearances of major groups in the fossil record suggest that most of the range of diatom morphologies observed today had evolved by the end of the Cretaceous Period. Despite this, a canonical reading of the Cenozoic fossil record suggests a dramatic rise in taxonomic diversity that can be interpreted as an explosion of morphological variety. We investigated this apparent discrepancy by using a discrete-character-based, empirical diatom morphospace, resolved by molecular phylogeny and by fossil occurrences through time. The morphospace shows little correspondence to phylogeny and little Cenozoic change in disparity as measured by mean pairwise distance. There is, however, an increase in the total volume of morphospace occupied. Although the increase in occupied volume through time ostensibly supports a conclusion of increasing morphological variety, sampling biases and other data suggest an underlying stationary pattern more consistent with molecular clock data.

Morphospace occupation through time provides a view of diversification distinct from the more familiar taxonomic tabulations. However, this view is subject to the same geological biases long recognized in studies of taxonomic diversification, where techniques for correcting secular bias in sampling have become standard practice. In this study, we apply sampling standardization techniques to a morphospace investigation to test whether observed stratigraphic trends in morphospace occupation are artifacts of trends in sampling. When sampling bias is corrected by randomized subsampling, all disparity metrics show stationary patterns, or at most directional changes of small magnitude. Metrics describing the average dispersion of taxa in morphospace are less subject to sampling bias than those describing the total extent of morphospace occupied. We also investigate a measure of disparity that is insensitive to sampling intensity, introducing a geographic component of morphological disparity. By analogy to α and β components of taxonomic diversity, we suggest the notions of α and β disparity, and find that α disparity remains roughly constant through time. Our analysis also allows us to present the first taxonomic diversity curve of diatoms under shareholder quorum subsampling (SQS), showing similar results to previously published subsampling methods: a roughly twofold rise over the Cenozoic, with peak diversity around the Eocene/Oligocene boundary. Tests for methodological bias from choices in ordination method and data culling during morphospace construction indicate that our results are relatively insensitive to both factors: Cenozoic occupation of planktonic diatom morphospace is largely unchanging. We find a similarly stationary pattern when we directly analyze the morphological data, seeing no change in the prevalence of taxa with different sets of morphological characters. More broadly, our results make clear that a complete view of morphological disparity must consider sampling biases, which can be addressed with wellestablished, quantitative methods in morphospaces populated using occurrence-level data.

The use of sclerobiosis as a tool for paleoenvironmental and paleoecological research is undermined by a lack of comparable methods for sclerobiont data collection and analysis. We present a new method for mapping sclerobiont distributions across any host, and offer an example of how the method may be used to interpret sclerobiont data in relation to host orientation. This approach can also be used to assess the suitability of beds and fossil material for paleoenvironmental reconstruction.

A sample of 150 encrusted dorsibiconvex atrypide brachiopods were selected from six beds in the Waterways Formation (latest Givetian – Early Frasnian; Alberta, Canada). The dorsal and ventral valves of each brachiopod were photographed. Sclerobiont taxa were mapped onto the photographs, and the maps were used to create stacked images with each of the 25 brachiopod specimens from each bed. Based on the life orientation of dorsibiconvex atrypides, three zones were designated on the host: the post mortem zone, (only available to sclerobionts after death and reorientation of the host); the shaded zone (brachial valve, excluding the post mortem zone); and the exposed zone (ventral valve).

Randomization simulation results indicate that all beds likely exhibit non random encrustation patterns, and corroborate the hypotheses that: (1) much of the encrustation occurred while the hosts were alive, and (2) these beds and fossils have experienced little physical reworking or transport and would be suitable for paleoenvironmental analysis. Mapping sclerobionts across hosts can serve as a unifying method to increase the recognition and use of sclerobiosis in paleontological studies.

The latest Aalenian–early Bajocian time interval (ca. 171-169 Ma) is marked by a global reorganization of oceanic plates with the Central Atlantic opening and the formation of the Pacific plate. This time interval is also marked by a global geochemical perturbation of δ13C with a negative excursion at the Aalenian/Bajocian boundary and a positive excursion during the early Bajocian. Evolutionary diversifications of marine invertebrate taxa, namely ammonites, radiolarians, and coccolithophorids, are recorded at that time. Concerning coccolithophorids, this interval witnesses the diversification and expansion of the most successful Mesozoic genus: Watznaueria. In this study, we explore the potential environmental, ecological, and biological forcing at the origin of Watznaueria diversification and its effect on the coccolith assemblages through quantification of the absolute and relative abundances of calcareous nannofossils in two Middle Jurassic key sections: Cabo Mondego (Portugal) and Chaudon-Norante (France). In both sections, we find an increase in nannofossil absolute abundance and flux at the beginning of the lower Bajocian, coeval with an increase in absolute and relative abundances of Watznaueria spp., followed by a plateau in the middle and upper part of the lower Bajocian. The increase of Watznaueria spp. is synchronous with a decrease in relative abundance of other major coccolith taxa, whereas the absolute abundance of these species did not decrease. During the climatically driven early Bajocian eutrophication event, Watznaueria spp. integrated into the calcareous nannoplankton community in two successive evolutionary steps involving first W. contracta and W. colaccicchii, and second W. britannica and W. aff. manivitiae. Step 1 was driven by an increase in niche carrying capacities linked to the early Bajocian eutrophication. Step 2 was driven by specific adaptation of the newly evolved Watznaueria species to bloom in nutrient-rich environments not exploited before. These evolutionary events have initiated the 100-Myr reign of Watznaueria over the calcareous nannoplankton community.

Ecomorphological diversity of Mesozoic mammals was presumably constrained by selective pressures imposed by contemporary vertebrates. In accordance, Mesozoic mammals for a long time had been viewed as generalized, terrestrial, small-bodied forms with limited locomotor specializations. Recent discoveries of Mesozoic mammal skeletons with distinctive postcranial morphologies have challenged this hypothesis. However, ecomorphological analyses of these new postcrania have focused on a single taxon, a limited region of the skeleton, or have been largely qualitative.

For more comprehensive locomotor inference in Mesozoic mammals, we applied multivariate analyses to a morphometric data set of extant small-bodied mammals. We used 30 osteological indices derived from linear measurements of appendicular skeletons of 107 extant taxa that sample 15 orders and eight locomotor modes. Canonical variate analyses show that extant small-bodied mammals of different locomotor modes have detectable and predictable morphologies. The resulting morphospace occupation reveals a morphofunctional continuum that extends from terrestrial to scansorial, arboreal, and gliding modes, reflecting an increasingly slender postcranial skeleton with longer limb output levers adapted for speed and agility, and extends from terrestrial to semiaquatic/semifossorial and fossorial modes, reflecting an increasingly robust postcranial skeleton with shorter limb output levers adapted for powerful, propulsive strokes. We used this morphometric data set to predict locomotor mode in ten Mesozoic mammals within the Docodonta, Multituberculata, Eutriconodonta, “Symmetrodonta,” and Eutheria. Our results indicate that these fossil taxa represent five of eight locomotor modes used to classify extant taxa in this study, in some cases confirming and in other cases differing from prior ecomorphological assessments. Together with previous locomotor inferences of 19 additional taxa, these results show that by the Late Jurassic mammals had diversified into all but the saltatorial and active flight locomotor modes, and that this diversification was greatest in the Eutriconodonta and Multituberculata, although sampling of postcranial skeletons remains uneven across taxa and through time.