Analyses of ancient food webs reveal important paleoecological processes and responses to a range of perturbations throughout Earth's history, such as climate change. These responses can inform our forecasts of future biotic responses to similar perturbations. However, previous analyses of ancient food webs rarely accounted for key differences between modern and ancient community data, particularly selective loss of soft-bodied taxa during fossilization. To consider how fossilization impacts inferences of ancient community structure, we (1) analyzed node-level attributes to identify correlations between ecological roles and fossilization potential and (2) applied selective information loss procedures to food web data for extant systems. We found that selective loss of soft-bodied organisms has predictable effects on the trophic structure of “artificially fossilized” food webs because these organisms occupy unique, consistent food web positions. Fossilized food webs misleadingly appear less stable (i.e., more prone to trophic cascades), with less predation and an overrepresentation of generalist consumers. We also found that ecological differences between soft- and hard-bodied taxa—indicated by distinct positions in modern food webs—are recorded in an early Eocene web, but not in Cambrian webs. This suggests that ecological differences between the groups have existed for ≥48 Myr. Our results indicate that accounting for soft-bodied taxa is vital for accurate depictions of ancient food webs. However, the consistency of information loss trends across the analyzed food webs means it is possible to predict how the selective loss of soft-bodied taxa affects food web metrics, which can permit better modeling of ancient communities.

The field of sclerochronology has long been known to paleobiologists. Yet, despite the central role of growth rate, age, and body size in questions related to macroevolution and evolutionary ecology, these types of studies and the data they produce have received only episodic attention from paleobiologists since the field's inception in the 1960s. It is time to reconsider their potential. Not only can sclerochronological data help to address long-standing questions in paleobiology, but they can also bring to light new questions that would otherwise have been impossible to address. For example, growth rate and life-span data, the very data afforded by chronological growth increments, are essential to answer questions related not only to heterochrony and hence evolutionary mechanisms, but also to body size and organism energetics across the Phanerozoic. While numerous fossil organisms have accretionary skeletons, bivalves offer perhaps one of the most tangible and intriguing pathways forward, because they exhibit clear, typically annual, growth increments and they include some of the longest-lived, non-colonial animals on the planet. In addition to their longevity, modern bivalves also show a latitudinal gradient of increasing life span and decreasing growth rate with latitude that might be related to the latitudinal diversity gradient. Is this a recently developed phenomenon or has it characterized much of the group's history? When and how did extreme longevity evolve in the Bivalvia? What insights can the growth increments of fossil bivalves provide about hypotheses for energetics through time? In spite of the relative ease with which the tools of sclerochronology can be applied to these questions, paleobiologists have been slow to adopt sclerochronological approaches. Here, we lay out an argument and the methods for a path forward in paleobiology that uses sclerochronology to answer some of our most pressing questions.

The burgeoning field of phylogenetic paleoecology (Lamsdell et al. 2017) represents a synthesis of the related but differently focused fields of macroecology (Brown 1995) and macroevolution (Stanley 1975). Through a combination of the data and methods of both disciplines, phylogenetic paleoecology leverages phylogenetic theory and quantitative paleoecology to explain the temporal and spatial variation in species diversity, distribution, and disparity. Phylogenetic paleoecology is ideally situated to elucidate many fundamental issues in evolutionary biology, including the generation of new phenotypes and occupation of previously unexploited environments; the nature of relationships among character change, ecology, and evolutionary rates; determinants of the geographic distribution of species and clades; and the underlying phylogenetic signal of ecological selectivity in extinctions and radiations. This is because phylogenetic paleoecology explicitly recognizes and incorporates the quasi-independent nature of evolutionary and ecological data as expressed in the dual biological hierarchies (Eldredge and Salthe 1984; Congreve et al. 2018; Fig. 1), incorporating both as covarying factors rather than focusing on one and treating the other as error within the dataset.

The intersection of paleontology and biomechanics can be reciprocally illuminating, helping to improve paleobiological knowledge of extinct species and furthering our understanding of the generality of biomechanical principles derived from study of extant species. However, working with data gleaned primarily from the fossil record has its challenges. Building on decades of prior research, we outline and critically discuss a complete workflow for biomechanical analysis of extinct species, using locomotor biomechanics in the Triassic theropod dinosaur Coelophysis as a case study. We progress from the digital capture of fossil bone morphology to creating rigged skeletal models, to reconstructing musculature and soft tissue volumes, to the development of computational musculoskeletal models, and finally to the execution of biomechanical simulations. Using a three-dimensional musculoskeletal model comprising 33 muscles, a static inverse simulation of the mid-stance of running shows that Coelophysis probably used more upright (extended) hindlimb postures and was likely capable of withstanding a vertical ground reaction force of magnitude more than 2.5 times body weight. We identify muscle force-generating capacity as a key source of uncertainty in the simulations, highlighting the need for more refined methods of estimating intrinsic muscle parameters such as fiber length. Our approach emphasizes the explicit application of quantitative techniques and physics-based principles, which helps maximize results robustness and reproducibility. Although we focus on one specific taxon and question, many of the techniques and philosophies explored here have much generality to them, so they can be applied in biomechanical investigation of other extinct organisms.

Beta diversity quantifies the spatial structuring of ecological communities and is a fundamental partition of biodiversity, central to understanding many macroecological phenomena in modern biology and paleobiology. Despite its common application in ecology, studies of beta diversity in the fossil record are relatively limited at regional spatial scales that are important for understanding macroevolutionary processes. The spatial scaling of beta diversity in the fossil record is poorly understood, but has significant implications due to temporal variation in the spatial distribution of fossil collections and the large spatiotemporal scales typically employed. Here we test the spatial scaling of several common measures of beta diversity using the Cenozoic shallow-marine molluscan fossil record of New Zealand and derive a spatially standardized time series of beta diversity. To measure spatial scaling, we use and compare grid-cell occupancy based on an equal-area grid and summed minimum spanning tree length, both based on reconstructed paleocoordinates of fossil collections. We find that beta diversity is spatially dependent at local to regional scales, regardless of the metric or spatial scaling utilized, and that spatial standardization significantly changes apparent temporal trends of beta diversity and, therefore, inferences about processes driving diversity change.

Sharks have a long and rich fossil record that consists predominantly of isolated teeth due to the poorly mineralized cartilaginous skeleton. Tiger sharks (Galeocerdo), which represent apex predators in modern oceans, have a known fossil record extending back into the early Eocene (ca. 56 Ma) and comprise 22 recognized extinct and one extant species to date. However, many of the fossil species remain dubious, resulting in a still unresolved evolutionary history of the tiger shark genus. Here, we present a revision of the fossil record of Galeocerdo by examining the morphological diversity and disparity of teeth in deep time. We use landmark-based geometric morphometrics to quantify tooth shapes and qualitative morphological characters for species discrimination. Employing this combined approach on fossil and extant tiger shark teeth, our results only support six species to represent valid taxa. Furthermore, the disparity analysis revealed that diversity and disparity are not implicitly correlated and that Galeocerdo retained a relatively high dental disparity since the Miocene despite its decrease from four to one species. With this study, we demonstrate that the combined approach of quantitative geometric morphometric techniques and qualitative morphological comparisons on isolated shark teeth provides a useful tool to distinguish between species with highly similar tooth morphologies.

An increasing number of unexpectedly diverse benthic communities are being reported from microbially precipitated carbonate facies in shallow-marine platform settings after the end-Permian mass extinction. Ostracoda, which was one of the most diverse and abundant metazoan groups during this interval, recorded its greatest diversity and abundance associated with these facies. Previous studies, however, focused mainly on taxonomic diversity and, therefore, left room for discussion of paleoecological significance. Here, we apply a morphometric method (semilandmarks) to investigate morphological variance through time to better understand the ecological consequences of the end-Permian mass extinction and to examine the hypothesis that microbial mats played a key role in ostracod survival. Our results show that taxonomic diversity and morphological disparity were decoupled during the end-Permian extinction and that morphological disparity declined rapidly at the onset of the end-Permian extinction, even though the high diversity of ostracods initially survived in some places. The decoupled changes in taxonomic diversity and morphological disparity suggest that the latter is a more robust proxy for understanding the ecological impact of the extinction event, and the low morphological disparity of ostracod faunas is a consequence of sustained environmental stress or a delayed post-Permian radiation. Furthermore, the similar morphological disparity of ostracods between microbialite and non-microbialite facies indicates that microbial mats most likely represent a taphonomic window rather than a biological refuge during the end-Permian extinction interval.

Deeper knowledge about how species and communities respond to climate change and environmental gradients should be supported by evidence from the past, especially as modern responses are influenced by anthropogenic pressures, including human population growth, habitat destruction and fragmentation, and intensifying land use. There have been great advances in modeling species’ geographic distributions over shallow time, where consideration of evolutionary change is likely less important due to shorter time for evolution and speciation to occur. Over these shallow time periods, we have more resources for paleoclimate interpretation across large geographic landscapes. We can also gain insight into species and community changes by studying deep records of temporal changes. However, modeling species geographic distributions in deep time remains challenging, because for many species there is sparse coverage of spatial and temporal occurrences and there are fewer paleoclimate general circulation models (GCMs) to help interpret the geographic distribution of climate availability. In addition, at deeper time periods, it is essential to consider evolutionary change within lineages of species. I will discuss a framework that integrates evolutionary information in the form of phylogenetic relatedness from clades of extant closely related species, where and when there are associated fossil occurrences, and the geographic distribution of paleoclimate in deep time to infer species past geographic response to climate change and to estimate where and when there were hotspots of ancient diversification. More work is needed to better understand the evolution of physiological tolerances and how physiological tolerances relate to the climate space in which species occur.

Geographic range size and abundance are important determinants of extinction risk in fossil and extant taxa. However, the relationship between these variables and extinction risk has not been tested extensively during evolutionarily “quiescent” times of low extinction and speciation in the fossil record. Here we examine the influence of geographic range size and abundance on extinction risk during the late Paleozoic (Mississippian–Permian), a time of “sluggish” evolution when global rates of origination and extinction were roughly half those of other Paleozoic intervals. Analyses used spatiotemporal occurrences for 164 brachiopod species from the North American midcontinent. We found abundance to be a better predictor of extinction risk than measures of geographic range size. Moreover, species exhibited reductions in abundance before their extinction but did not display contractions in geographic range size. The weak relationship between geographic range size and extinction in this time and place may reflect the relative preponderance of larger-ranged taxa combined with the physiographic conditions of the region that allowed for easy habitat tracking that dampened both extinction and speciation. These conditions led to a prolonged period (19–25 Myr) during which standard macroevolutionary rules did not apply.

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.

The inner ear of the two higher clades of modern cetaceans (Neoceti) is highly adapted for hearing infrasonic (mysticetes) or ultrasonic (odontocetes) frequencies. Within odontocetes, Platanistoidea comprises a single extant riverine representative, Platanista gangetica, and a diversity of mainly extinct marine species from the late Oligocene onward. Recent studies drawing on features including the disparate tympanoperiotic have not yet provided a consensus phylogenetic hypothesis for platanistoids. Further, cochlear morphology and evolutionary patterns have never been reported. Here, we describe for the first time the inner ear morphology of late Oligocene–early Miocene extinct marine platanistoids and their evolutionary patterns. We initially hypothesized that extinct marine platanistoids lacked a specialized inner ear like P. gangetica and thus, their morphology and inferred hearing abilities were more similar to those of pelagic odontocetes. Our results reveal there is no “typical” platanistoid cochlear type, as the group displays a disparate range of cochlear anatomies, but all are consistent with high-frequency hearing. Stem odontocete Prosqualodon australis and platanistoid Otekaikea huata present a tympanal recess in their cochlea, of yet uncertain function in the hearing mechanism in cetaceans. The more basal morphology of Aondelphis talen indicates it had lower high-frequency hearing than other platanistoids. Finally, Platanista has the most derived cochlear morphology, adding to evidence that it is an outlier within the group and consistent with a >9-Myr-long separation from its sister genus Zarhachis. The evolution of a singular sound production morphology within Platanistidae may have facilitated the survival of Platanista to the present day.

Echinoderms make up a substantial component of Ordovician marine invertebrates, yet their speciation and dispersal history as inferred within a rigorous phylogenetic and statistical framework is lacking. We use biogeographic stochastic mapping (BSM; implemented in the R package BioGeoBEARS) to infer ancestral area relationships and the number and type of dispersal events through the Ordovician for diploporan blastozoans and related species. The BSM analysis was divided into three time slices to analyze how dispersal paths changed before and during the great Ordovician biodiversification event (GOBE) and within the Late Ordovician mass extinction intervals. The best-fit biogeographic model incorporated jump dispersal, indicating this was an important speciation strategy. Reconstructed areas within the phylogeny indicate the first diploporan blastozoans likely originated within Baltica or Gondwana. Dispersal, jump dispersal, and sympatry dominated the BSM inference through the Ordovician, while dispersal paths varied in time. Long-distance dispersal events in the Early Ordovician indicate distance was not a significant predictor of dispersal, whereas increased dispersal events between Baltica and Laurentia are apparent during the GOBE, indicating these areas were important to blastozoan speciation. During the Late Ordovician, there is an increase in dispersal events among all paleocontinents. The drivers of dispersal are attributed to oceanic and epicontinental currents. Speciation events plotted against geochemical data indicate that blastozoans may not have responded to climate cooling events and other geochemical perturbations, but additional data will continue to shed light on the drivers of early Paleozoic blastozoan speciation and dispersal patterns.

The morphological and ecological diversity of lemurs and lorisiformes once rivaled that of the rest of the primate order. Here, we assemble a dataset of 3D models representing the second mandibular molars of a wide range of extant and fossil strepsirrhines encompassing this diversity. We use these models to distill quantitative descriptors of tooth form and then analyze these data using new analytical methods. We employ a recently developed dental topography metric (ariaDNE), which is less sensitive to details of random error in 3D model quality than previously used metrics (e.g., DNE); Bayesian multinomial modeling with metrics designed to measure overfitting risk; and a tooth segmentation algorithm that allows the shapes of disaggregated tooth surface features to be quantified using dental topography metrics. This approach is successful at reclassifying extant strepsirrhine primates to known dietary ecology and indicates that the averaging of morphological information across the tooth surface does not interfere with the ability of dental topography metrics to predict dietary adaptation. When the most informative combination of dental topography metrics is applied to extinct species, many subfossil lemurs and the most basal fossil strepsirrhines are predicted to have been primarily frugivorous or gummivorous. This supports an ecological contraction among the extant lemurs and the importance of frugivory in the origins of crown Strepsirrhini, potentially to avoid competition with more insectivorous and folivorous members of Paleogene Afro-Arabian primate faunas.

Recent studies have acknowledged the many benefits of including fossils in phylogenetic inference (e.g., reducing long-branch attraction). However, unstable taxa are known to be problematic, as they can reduce either the resolution of the strict consensus or branch support. In this study, we evaluate whether unstable taxa that reduce consensus resolution affect support values, and the extent of such impact, under equal and extended implied weighting. Two sets of analyses were conducted across 30 morphological datasets to evaluate complementary aspects. The first focused on the analytical conditions incrementing the terminal instability, while the second assessed whether pruning wildcards improves support. Changes in support were compared with the “number of nodes collapsed by unstable terminals,” their “distance to the root,” the “proportion of missing data in a dataset,” and the “proportion of sampled characters.” Our results indicate that the proportion of missing entries distributed among closely related taxa (for a given character) might be as detrimental for stability as those distributed among characters (for a given terminal). Unstable terminals that (1) collapse few nodes or (2) are closely located to the root node have more influence on the estimated support values. Weighting characters according to their extra steps while assuming that missing entries contribute to their homoplasy reduced the instability of wildcards. Our results suggest that increasing character sampling and using extended implied weighting decreases the impact of wildcard terminals. This study provides insights for designing future research dealing with unstable terminals, a typical problem of paleontological data.

Understanding the distribution of taxa in space and time is key to understanding diversity dynamics. The fossil record provides an avenue to assess these patterns on vast timescales and through major global changes. The Eublastoidea were a conservatively plated Paleozoic echinoderm clade that range from the middle Silurian to the end-Permian. The geographic distribution of the eublastoids, as a whole, has been qualitatively assessed but has historically lacked a quantitative analysis. This is the first examination of the Eublastoidea using probabilistic methods within the R package BioGeoBEARS to assess macroevolutionary trends. Results provide an updated understanding of eublastoid diversity with new peaks and troughs in diversity through their evolutionary history. Lithology is examined in an evolutionary framework and does not have clear evolutionary trends, and there is much work to be done regarding environmental preferences. Biogeographic patterns do not recover precise group origins but do support the previous work that outlines Eublastoidea as a Laurentian clade. Sympatric speciation events dominant the clade's history but are likely exaggerated due to the highly combined areas. Vicariance events are rare and restricted to the Silurian and Devonian, and dispersal events are more common throughout the evolutionary history. Pathways allowing for lineage migrations are noted between southern Laurussia and China in the Devonian and Carboniferous and southern Laurussia and eastern Gondwana in the Carboniferous. Future work will include the addition of more non-Laurentian species into the estimated phylogeny to better estimate these global patterns.

A key question in paleoecology and macroevolution is whether assemblages of species (paleocommunities) are persistent entities that endure over millions of years. While community turnover in the face of abiotic change is the presumed norm, paleocommunities have been shown to persist for long time periods and regardless of environmental disruption. It remains an open question, however, as to what processes allow for this. We investigate these questions by analyzing the Carboniferous brachiopod paleocommunities from the Midcontinent of North America. These diverse communities were subjected to repeated and geologically rapid changes in sea level. Using a suite of statistical techniques, we characterize the nature and scope of changes in these paleocommunities over time. We find that, at the paleocommunity scale, there is no evidence for obdurate ecological stasis, with fluctuations in both taxonomic composition and the associated abundance of taxa. However, at a higher ecological scale, stability is manifest, as diversity patterns remain stable across time, with a consistent number of species that can exist in any given paleocommunity. This suggests ecological rules such as taxon packing are in effect, resulting in a form of ecological stability even in the face of constant disequilibrium, and parallels ecological patterns of disruption and recovery previously observed for invertebrate communities from modern marine systems. Based on these results, we advocate for consideration of different hierarchical entities and scales when interpreting the ecological dynamics of fossil assemblages, as focusing exclusively on changes in taxon identity/abundance or diversity levels can lead to very different results.

Under stress, corals and foraminifera may eject or consume their algal symbionts (“bleach”), which can increase mortality. How bleaching relates to species viability over warming events is of great interest given current global warming. We use size-specific isotope analyses and abundance counts to examine photosymbiosis and population dynamics of planktonic foraminifera across the Paleocene–Eocene thermal maximum (PETM, ~56 Ma), the most severe Cenozoic global warming event. We find variable responses of photosymbiotic associations across localities and species. In the NE Atlantic (DSDP Site 401) PETM, photosymbiotic clades (acarininids and morozovellids) exhibit collapsed size-δ13C gradients indicative of reduced photosymbiosis, as also observed in Central Pacific (ODP Site 1209) and Southern Ocean (ODP Site 690) acarininids. In contrast, we find no significant loss of size-δ13C gradients on the New Jersey shelf (Millville) or in Central Pacific morozovellids. Unlike modern bleaching-induced mass mortality, populations of photosymbiont-bearing planktonic foraminifera increased in relative abundance during the PETM. Multigenerational adaptive responses, including flexibility in photosymbiont associations and excursion taxon evolution, may have allowed some photosymbiotic foraminifera to thrive. We conclude that deconvolving the effects of biology on isotope composition on a site-by-site basis is vital for environmental reconstructions.

Rates of speciation and extinction are often linked to many ecological factors, traits (emergent and nonemergent) such as environmental tolerance, body size, feeding type, and geographic range. Marine gastropods in particular have been used to examine the role of larval dispersal in speciation. However, relatively few studies have been conducted placing larval modes in species-level phylogenetic context. Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades have not considered both phylogenetic context and net speciation (speciation–extinction) rates. This study utilizes Eocene volutid Volutospina species from the U.S. Gulf Coastal Plain and the Hampshire Basin, U.K., to explore the relationships among larval mode, geographic range, and duration. Based on the phylogeny of these Volutospina, we calculated speciation and extinction rates in order to compare the macroevolutionary effects of larval mode. Species with planktotrophic larvae had a median duration of 9.7 Myr, which compared significantly to 4.7 Myr for those with non-planktotrophic larvae. Larval mode did not significantly factor into geographic-range size, but U.S. and U.K. species do differ, indicating a locality-specific component to maximum geographic-range size. Non-planktotrophs (NPTs)were absent among the Volutospina species during the Paleocene–early Eocene. The relative proportions of NPTs increased in the early middle Eocene, and the late Eocene was characterized by disappearance of planktotrophs (PTs). The pattern of observed lineage diversity shows an increasing preponderance of NPTs; however, this is clearly driven by a dramatic extinction of PTs, rather than higher NPT speciation rates during the late Eocene. This study adds nuance to paleontology's understanding of the macroevolutionary consequences of larval mode.

Brachiopods dominated the seafloor as a primary member of the Paleozoic fauna. Despite the devastating effects of the end-Permian extinction, the group recovered during the early Mesozoic only to gradually decline from the Jurassic to today. This decline likely had multiple causes, including increased predation and bioturbation-driven substrate disruption, but the role of changing substrate is not well understood. Given the importance of substrate for extant brachiopod habitat, we documented Mesozoic–Cenozoic lithologic preferences and morphological changes to assess how decreasing firm-substrate habitat may have contributed to the brachiopod decline. Compared with bivalves, Mesozoic brachiopods occurred more frequently and were disproportionately abundant in carbonate lithologies. Although patterns in glauconitic or ferruginous sediments are equivocal, brachiopods became more abundant in coarser-grained carbonates and less abundant in fine-grained siliciclastics. During the Jurassic, brachiopod species rarely had abraded beaks but tended to be more convex with a high beak, potentially consistent with a non-analogue lifestyle resting on the seafloor. However, those highly convex morphotypes largely disappeared by the Cenozoic, when more terebratulides had abraded beaks, suggesting closer attachment to hard substrates. Rhynchonellides disproportionately declined to become a minor component of Cenozoic faunas, perhaps because of less pronounced morphological shifts. Trends in lithologic preferences and morphology are consistent with bioturbation-driven substrate disruption, with brachiopods initially using firmer carbonate sediments as refugia before adapting to live primarily attached to hard surfaces. This progressive habitat restriction likely played a role in the final brachiopod decline, as bioturbating ecosystem engineers transformed benthic habitats in the Mesozoic and Cenozoic.

Lanternfishes currently represent one of the dominant groups of mesopelagic fishes in terms of abundance, biomass, and diversity. Their otolith record dominates pelagic sediments below 200 m in dredges, especially during the entire Neogene. Here we provide an analysis of their diversity and rise to dominance primarily based on their otolith record. The earliest unambiguous fossil myctophids are known based on otoliths from the late Paleocene and early Eocene. During their early evolutionary history, myctophids were likely not adapted to a high oceanic lifestyle but occurred over shelf and upper-slope regions, where they were locally abundant during the middle Eocene. A distinct upscaling in otolith size is observed in the early Oligocene, which also marks their earliest occurrence in bathyal sediments. We interpret this transition to be related to the change from a halothermal deep-ocean circulation to a thermohaline regime and the associated cooling of the deep ocean and rearrangement of nutrient and silica supply. The early Oligocene myctophid size acme shows a remarkable congruence with diatom abundance, the main food resource for the zooplankton and thus for myctophids and whales. The warmer late Oligocene to early middle Miocene period was characterized by an increase in disparity of myctophids but with a reduction in their otolith sizes. A second and persisting secular pulse in myctophid diversity (particularly within the genus Diaphus) and increase in size begins with the “biogenic bloom” in the late Miocene, paralleled with diatom abundance and mysticete gigantism.