The choice of measures used to estimate the richness of species, genera, or higher taxa is a crucial matter in paleobiology and ecology. This paper evaluates four methods called shareholder quorum subsampling, true richness estimated using a Poisson sampling model (TRiPS), squares, and the corrected first-order jackknife (cJ1). Quorum subsampling interpolates to produce a relative richness estimate, while the other three extrapolate to the size of the overall species pool. Here I use routine ecological data to show that squares and cJ1 pass several basic validation tests, but TRiPS does not. First, TRiPS estimates are insensitive to the shape of abundance distributions, being entirely predicted by total counts of species and of individuals regardless of the details. Furthermore, TRiPS tends not to extrapolate at all when sampling is moderate or intense. Second, all three extrapolators yield lower values when they work with small uniform subsamples of large raw inventories. The third test is a split-analyze-and-sum analysis: each inventory is divided between the most common and least common halves of the abundance distribution, the methods are applied to the half-inventories, and the estimates are summed. Squares and cJ1 perform well here, but TRiPS does not extrapolate as long as the full inventories are reasonably well-sampled. It is otherwise not particularly accurate. The extrapolators are largely insensitive to the influence of abundance distribution evenness, as quantified using Pielou's J and a new index called the ratio of means. Quorum subsampling generally performs well, but it stumbles on the split-analyze-and-sum test and is confounded somewhat by evenness.

Sutural perimeters of 301 Late Jurassic ammonites scale as the 3/8 power of phragmocone volume. This implies that septal surface grows as the ¾ power of body mass, the exponent of Kleiber's law (1932), one of the best-established empirical laws in biology, which is well known to be the scaling exponent of basal metabolic rate. Sutural complexity, as measured by fractal dimensions, emerges from the relationship between sutural perimeter and phragmocone volume, thus supporting the interpretations of septal folding as a mechanism for the increase in septal surface and as demanded by metabolic and physiologic processes (e.g., respiration or body chamber transport). The implications of these results strongly suggest that ammonite septa were involved in more than a simple structural support.

Although we do not know the cause of death of most fossil animals, mortality is often associated with ecological stress due to seasonality and other stochastic events (droughts, storms, volcanism) that may have caused shifts in feeding ecology preceding death. In these instances, dental microwear, which reflects feeding ecology in a narrow window of time, may provide a biased view of diet. Mesowear, another dental-wear proxy based on the morphology of worn cusps, requires macroscopic amounts of dental wear and reflects diet for a longer interval and may be less prone to bias from near-death ecological stress. We compared congruence between microwear and mesowear of North American, fossil rhinocerotid mass-death assemblages and collections of hunted modern rhinocerotids to test the hypothesis that fossil assemblages yield more incongruous microwear and mesowear data as a result of near-death ecological disturbances. In extant rhinos, both mesowear and microwear are associated with diet and height of the feeding environment. Mesowear and microwear in the modern rhinocerotid collections are statistically correlated, with strong relationships between average mesowear scores and labially distributed dental microwear. In contrast, a relationship between mesowear and microwear was not observed among the fossil rhinocerotid assemblages. Mesowear suggests that the fossil rhinos had low-abrasion diets, suggesting that they fed from clean, possibly tall vegetation. Some, but not all, mass-death assemblages produce microwear data with excessive scratches and/or pits compared with expectations based on mesowear results, suggesting that dental microwear was altered shortly before death in some but not all of the fossil assemblages. The dental-wear proxies available to paleoecologists provide a mosaic of dietary evidence reflecting diet over long (mesowear) and more abbreviated (microwear) periods of time that, together, provide a richer understanding of feeding ecology and its relationship to environment, seasonal change, and other ecological disturbances.

Torticonic (helically-coiled) ammonoids have been most commonly interpreted as vagile, benthonic forms. Their mode of coiling, however, places the siphuncle in a functionally dorsolateral, rather than ventral position on the shell whorl due to: 1) their probable apex-upward shell orientation during life, and 2) size asymmetry of the lateral sutural saddles due to helical coiling, associated with upward siphuncle displacement. The resultant positioning of the siphuncle produces cameral liquid de-coupling soon after initiation of cameral liquid removal (emptying of liquid from a newly formed chamber within the phragmocone). Since in Recent chambered cephalopods cameral liquid de-coupling increases efficiency of vertical migration, a similar mode of life was indicated for the torticonic ammonites.

We assessed selective extinction patterns in bivalves during a late Neogene mass extinction event observed along the temperate Pacific coast of South America. The analysis of 99 late Neogene and Quaternary fossil sites (recorded from 7°S to 55°S), yielding ∼2800 occurrences and 118 species, revealed an abrupt decline in Lyellian percentages during the late Neogene–Pleistocene, suggesting the existence of a mass extinction that decimated ∼66% of the original assemblage. Using the late Neogene data set (n = 59 species, 1346 occurrences), we tested whether the extinction was nonrandom according to taxonomic structure, life habit, geographic range, and body size. Our results showed that the number of higher taxa that went extinct was not different than expected by random. At first sight, extinction was selective only according to life habit and geographic range. Nevertheless, when phylogenetic effects were accounted for, body size also showed significant selectivity. In general, epifaunal, small-sized (after phylogenetic correction), and short-ranged species tended to have increased probability of extinction. This is verified by strong interactions between the variables herein analyzed, suggesting the existence of nonlinear effects on extinction chances. In the heavily decimated epifaunal forms, survival was not enhanced by widespread ranges or larger body sizes. Conversely, the widespread and large-sized infaunal forms tended to have lower probability of extinction. Overall, the ultimate extinction of late Neogene bivalve species along the Pacific coast of South America seems to have been determined by a complex interplay of ecological and historical (phylogenetic) effects.

Lysorophus, a serpentiform, nearly limbless, aquatic Paleozoic amphibian was described in detail by Sollas in 1920. Although Sollas did not discuss cranial kinesis, his original reconstructions suggest that Lysorophus had an unusually kinetic skull for an amphibian. We have reexamined the skull of Lysorophus and find that kinesis, if present, was slight. The maxillae, premaxillae, and vomers might have moved in limited protraction and retraction, with the premaxillae rotating about their contacts with the nasals. There is a possibility of small medio-lateral movements of the lacrimal and maxilla as a unit at the lacrimal-prefrontal joint. The skull of Lysorophus shows many features convergent with the skulls of burrowing reptiles, such as amphisbaenians. Modifications in the skull of Lysorophus from a more primitive tetrapod condition seem associated with burrowng in a soft substratum rather than with kinesis per se.

Within a ∼60-Myr interval in the Late Triassic to Early Jurassic, a major mass extinction took place at the end of Triassic, and several biotic and environmental events of lesser magnitude have been recognized. Climate warming, ocean acidification, and a biocalcification crisis figure prominently in scenarios for the end-Triassic event and have been also suggested for the early Toarcian. Radiolarians, as the most abundant silica-secreting marine microfossils of the time, provide a control group against marine calcareous taxa in testing selectivity and responses to changing environmental parameters. We analyzed the origination and extinction rates of radiolarians, using data from the Paleobiology Database and employing sampling standardization, the recently developed gap-filler equations and an improved stratigraphic resolution at the substage level. The major end-Triassic event is well-supported by a late Rhaetian peak in extinction rates. Because calcifying and siliceous organisms appear similarly affected, we consider global warming a more likely proximate trigger of the extinctions than ocean acidification. The previously reported smaller events of radiolarian turnover fail to register above background levels in our analyses. The apparent early Norian extinction peak is not significant compared to the long-term trajectory, and is probably a sampling artifact. The Toarcian Oceanic Anoxic Event, previously also thought to have caused a significant radiolarian turnover, did not significantly affect the group. Radiolarian diversity history appears unique and complexly forced, as its trajectory parallels major calcareous fossil groups at some events and deviates at others.

Determining which biological traits affect taxonomic durations is critical for explaining macroevolutionary patterns. Two approaches are commonly used to investigate the associations between traits and durations and/or extinction and origination rates: analyses of taxonomic occurrence patterns in the fossil record and comparative phylogenetic analyses, predominantly of extant taxa. By capitalizing upon the empirical record of past extinctions, paleontological data avoid some of the limitations of existing methods for inferring extinction and origination rates from molecular phylogenies. However, most paleontological studies of extinction selectivity have ignored phylogenetic relationships because there is a dearth of phylogenetic hypotheses for diverse non-vertebrate higher taxa in the fossil record. This omission inflates the degrees of freedom in statistical analyses and leaves open the possibility that observed associations are indirect, reflecting shared evolutionary history rather than the direct influence of particular traits on durations. Here we investigate global patterns of extinction selectivity in Devonian terebratulide brachiopods and compare the results of taxonomic vs. phylogenetic approaches. Regression models that assume independence among taxa provide support for a positive association between geographic range size and genus duration but do not indicate an association between body size and genus duration. Brownian motion models of trait evolution identify significant similarities in body size, range size, and duration among closely related terebratulide genera. We use phylogenetic regression to account for shared evolutionary history and find support for a significant positive association between range size and duration among terebratulides that is also phylogenetically structured. The estimated range size–duration relationship is moderately weaker in the phylogenetic analysis due to the down-weighting of closely related genera that were both broadly distributed and long lived; however, this change in slope is not statistically significant. These results provide evidence for the phylogenetic conservatism of organismal and emergent traits, yet also the general phylogenetic independence of the relationship between range size and duration.

The miniaturization of shells, often observed in Mesozoic brachiopods, is analyzed in two species of the well-known genus Homoeorhynchia. We investigated shell development in the context of recent works that consider growth as a function of size, shape, and age. The miniaturization results from heterochronic disturbances during development. Although these shells exhibit a large morphological plasticity, architectural constraints limit their morphogenesis, so that small adult specimens are not exactly reduced replicas of large ones. Adult morphology depends largely on the pattern of rib formation, with miniaturization arising by two different processes affecting this pattern: predisplacement of the appearance of ribs in H. meridionalis and acceleration in H. cynocephala. The first case seems to be a reversible process without evolutionary consequences, but the second occurs within an evolutionary trend. In both cases, the miniaturization seems to be related to environmental influences. Study of the growth pathway of these species allows recognition of basic characters in the morphological variation of populations.

The Ordovician was a time of drastic biological and geological change. Previous work has suggested that there was a dramatic increase in global diversity during this time, but also has indicated that regional dynamics and dynamics in specific environments might have been different. Here, we contrast two paleocontinents that have different geological histories through the Ordovician, namely Laurentia and Baltica. The first was situated close to the equator throughout the whole Ordovician, while the latter has traversed tens of latitudes during the same time. We predict that Baltica, which was under long-term environmental change, would show greater average and interval-to-interval origination and extinction rates than Laurentia. In addition, we are interested in the role of the environment in which taxa originated, specifically, the patterns of onshore–offshore dynamics of diversification, where onshore and offshore areas represent high-energy and low-energy environments, respectively. Here, we predict that high-energy environments might be more conducive for originations.

Our new analyses show that the global Ordovician spike in genus richness from the Dapingian to the Darriwilian Stage resulted from a very high origination rate at the Dapingian/Darriwilian boundary, while the extinction rate remained low. We found substantial interval-to-interval variation in the origination and extinction rates in Baltica and Laurentia, but the probabilities of origination and extinction are somewhat higher in Baltica than Laurentia. Onshore and offshore areas have largely indistinguishable origination and extinction rates, in contradiction to our predictions. The global spike in origination rates at the Dapingian/Darriwilian boundary is apparent in Baltica, Laurentia, and onshore and offshore areas, and abundant variability in diversification rates is apparent over other time intervals for these paleocontinents and paleoenvironments. This observation hints at global mechanisms for the spike in origination rates at the Dapingian/Darriwilian boundary but a domination of more regional and local mechanisms over other time intervals in the Ordovician.

We have produced computer simulations of multiramous graptoloids with the intention of defining the rules governing branching strategies and colony form. Close matches between such simulations and real graptolites show that complex rhabdosomes may be produced by the permutation of relatively simple sets of rules. Those designs found in nature produce an efficient and regular distribution of zooids through the area included by an essentially planar rhabdosome. Strikingly geometrical arrays of stipes, such as the Goniograptus and yin/yang patterns, closely approach paradigmatic harvesting arrays. For dichotomously branching anisograptids the evolutionary trend in reduction of “primary stipes” can be explained by the production of larger spreading colonies. Multiramous graptoloids fed during vertical movement through the water column. Changes in a single branching decision may produce considerable changes in rhabdosome morphology, but these are not necessarily of high taxonomic importance; this is proved by a specimen which is a morphological combination of two “genera.” Although primarily under genetic control, certain modifications to colony form were probably the result of inhibitory interaction between adjacent stipes.

Recent excavations of Ediacaran assemblages have revealed striking bed-to-bed variation in diversity–abundance structure, offering potential insight into the ecology and taphonomy of these poorly understood early Metazoan ecosystems. Here we compare faunal variability in Ediacaran assemblages to that of younger benthic assemblages, both fossil and modern. We decompose the diversity of local assemblages into within-collection (α) and among-collection (β) components and show that β diversity in Ediacaran assemblages is unusually high relative to younger assemblages. Average between-bed ecological dissimilarities in the Phanerozoic fossil record are comparable to within-habitat dissimilarities typically observed over meter to kilometer scales in modern benthic marine habitats, but dissimilarities in Ediacaran assemblages are comparable to those typically observed over 10–100 km scales in modern habitats. We suggest that the unusually variable diversity–abundance structure of Ediacaran assemblages is due both to their preservation as near snapshots of benthic communities and to original ecological differences, in particular the paucity of motile taxa and the near lack of predation and infaunalization.

Nonmammalian cynodonts represent a speciose and ecologically diverse group with a fossil record stretching from the late Permian until the Cretaceous. Because of their role as major components of Triassic terrestrial ecosystems and as the direct ancestors of mammals, cynodonts are an important group for understanding Mesozoic tetrapod diversity. We examine patterns of nonmammalian cynodont species richness and the quality of their fossil record. A supertree of cynodonts is constructed from recently published trees and time calibrated using a Bayesian approach. While this approach pushes the root of Cynodontia back to the earliest Guadalupian, the origins of Cynognathia and Probainognathia are close to their first appearance in the fossil record. Taxic, subsampled, and phylogenetic diversity estimates support a major cynodont radiation following the end-Permian mass extinction, but conflicting signals are observed at the end of the Triassic. The taxic diversity estimate shows high diversity in the Rhaetian and a drop across the Triassic/Jurassic boundary, while the phylogenetic diversity indicates an earlier extinction between the Norian and Rhaetian. The difference is attributed to the prevalence of taxa based solely on teeth in the Rhaetian, which are not included in the phylogenetic diversity estimate. Examining the completeness of cynodont specimens through geological time does not support a decrease in preservation potential; although the median completeness score decreases in the Late Triassic, the range of values remains consistent. Instead, the poor completeness scores are attributed to a shift in sampling and taxonomic practices: an increased prevalence in microvertebrate sampling and the naming of fragmentary material.

Understanding temporal patterns in biodiversity is an enduring question in paleontology. Compared with studies of taxonomic diversity, long-term perspectives on ecological diversity are rare, particularly in terrestrial systems. Yet ecological diversity is critical for the maintenance of biodiversity, especially during times of major perturbations. Here, we explore the ecological diversity of Cretaceous herbivorous dinosaurs leading up to the K-Pg extinction, using dental and jaw morphological disparity as a proxy. We test the hypothesis that a decline in ecological diversity could have facilitated their rapid extinction 66 Ma. We apply three disparity metrics that together capture different aspects of morphospace occupation and show how this approach is key to understanding patterns of morphological evolution. We find no evidence of declining disparity in herbivorous dinosaurs as a whole—suggesting that dinosaur ecological diversity remained high during the last 10 Myr of their existence. Clades show different disparity trends through the Cretaceous, but none except sauropods exhibits a long-term decline. Herbivorous dinosaurs show two disparity peaks characterized by different processes; in the Early Cretaceous by expansion in morphospace and in the Campanian by morphospace packing. These trends were only revealed by using a combination of disparity metrics, demonstrating how this approach can offer novel insights into macroevolutionary processes underlying patterns of disparity and ecological diversity.

A new method of data analysis offers a potentially powerful tool for statistically evaluating hypotheses of rate in temporally-ordered evolutionary phenomena. We present a method for bootstrapping time-ordered data sets to test hypotheses of the equality of rate. This method is applicable to both nonrandom and random generative processes. The method is applied to the data of Malmgren et al. (1983) for the Globorotalia plesiotumida–G. tumida planktonic foraminiferan lineage and the data of Reyment (1982) for the benthonic foraminiferan Afrobolivina afar. G. plesiotumida is recognizable on the basis of independent data as a species distinct from G. tumida, its descendant. Evolutionary change rate during the evolution of G. tumida from G. plesiotumida is shown to be faster than rates within either species. The pattern of variation exhibited by A. afar includes a time interval of more rapid change; this more rapid change is observed post hoc. A bootstrapping model based on post hoc observations reveals the rate in this time interval to be not significantly faster than expected in such post hoc intervals.

Recent ideas about the role of competition in the ecology and evolution of acorn barnacles are based partly on relationships between morphology and the outcome of competition for space. One hypothesis is that present distributions and patterns of evolutionary diversification and decline among acorn barnacles reflect the competitive exclusion and replacement of solid-walled forms by those with tubiferous skeletal structure. An alternate view is that large barnacles generally outcompete smaller ones, independent of differences in skeletal structure, with predation and disturbance favoring the ecological and evolutionary success of small barnacles. Field experiments and observations in the Gulf of California suggested that the small, solid-walled species, Chthamalus anisopoma, competitively exlcudes the larger, tubiferous Tetraclita stalactifera confinis on the lower part of the shore. Greater tolerance to aerial exposure appears to allow Tetraclita to occupy a high intertidal refuge above Chthamalus. A common denominator among several cases of competitive exclusion in acorn barnacles is the greater settlement density of the competitive dominant, not its morphology. Morphological considerations alone are insufficient to predict or explain the outcome of competition between barnacle species.

The hadrosaurids were a successful group of herbivorous dinosaurs. During the Late Cretaceous, 100 to 66 million years ago, hadrosaurids had high diversity, rapid speciation rates, and wide geographic distribution. Most hadrosaurids were large bodied and had similar postcranial skeletons. However, they show important innovations in the skull, including disparate crests that functioned as socio-sexual display structures, and a complex feeding apparatus, with specialized jaws bearing dental batteries. Little is known about the macroevolutionary processes that produced these evolutionary novelties. Here we provide novel perspectives using evolutionary rate and disparity analyses. Our results show that hadrosaurid cranial evolution was complex and dynamic, but their postcranial skeleton and body size were conservative. High cranial disparity was achieved through multiple bursts of phenotypic innovation. We highlight contrasting evolutionary trends within hadrosaurids between the disparate facial skeleton and crests, which both showed multiple high-rate shifts, and the feeding apparatus, which had low variance and high rates on a single phylogenetic branch leading to the diverse Saurolophidae. We reveal that rapid evolutionary rates were important for producing the high disparity of exaggerated crests and present novel evidence that the hadrosaurid diversification was linked to both a key adaptive innovation in the feeding apparatus and multiple bursts of innovation in socio-sexual displays.

The environmental transformations that occurred during the Neogene had profound effects on spatiotemporal biodiversity patterns, yet the modulating role of traits (i.e., physiological, ecological, and life-history traits) remains little understood. We tested this idea using the Neogene fossil record of chondrichthyans along the temperate Pacific coast of South America (TPSA). Information for georeferenced occurrences and ecological and life-history information of 38 chondrichthyan fossil genera in 42 Neogene sites was collected. Global georeferenced records were used to estimate present-day biogeographic distributions of the genera and to characterize the range of oceanographic conditions in which each genus lives as a proxy of their realized niche. Biogeographic range shifts (Neogene–present) were evaluated at regional and local scales. The role of traits as drivers of different range dynamics was evaluated using random forest models. The magnitude and direction of biogeographic range shifts were different at both spatial scales. At a regional scale, 34% of genera contracted their ranges, disappearing from the TPSA. At a local scale, a similar proportion of genera expanded and contracted their southern endpoints of distribution. The models showed a high precision at both spatial scales of analyses, but the relative importance of predictor variables differed. At a regional scale, disappearing genera tended to have a higher tolerance to salinity, lower sea surface temperature (SST) range, and smaller body sizes. At a local scale, genera contracting their ranges tended to live at greater depths, tolerate lower levels of primary productivity, and show a reduced tolerance to higher and lower SST ranges. The magnitude and direction of the changes in the range distribution were scale dependent and variable across the genera. Hence, multiple environmental exogenous factors interacted with taxon traits during the Neogene, creating a mosaic of biogeographic dynamics.

Previous attempts to quantify the test-flattening trend in Heterostegina depressa with water depth have been rather unsuccessful. Due to its broad depth distribution, H. depressa is a perfect model species to calibrate test flattening as a bathymetric signal for fossil assemblages. This might enable us to better reconstruct paleoenvironments of fossil communities of larger foraminifera or even provide clues to the degree of transport in allochthonous deposits. In this study, we used growth-independent functions to describe the change of test thickness throughout ontogeny. Four growth-invariant characters, deriving from these functions, clearly quantify a transition of individuals with thicker to thinner central parts along the water-depth gradient. This transition is probably controlled by light intensity, because the photosymbionts of H. depressa (diatoms) are most effective at low irradiation levels. Thus, specimens at shallower depths grow thicker to reduce light penetration, whereas specimens living deeper than the light optimum increase their surface by flattening to obtain better exposure to light.