Recovery of marine biodiversity following the Permo-Triassic extinction is thought to have been delayed relative to other mass extinctions. Terrestrial vertebrate biodiversity is said to have taken as much as 15 Myr longer to recover than the marine. The present study tests, at the scale of an individual fossil community, whether a disparity in biodiversity existed in the American Southwest, between the Moenkopi Formation, containing an early Middle Triassic (Anisian) terrestrial tetrapod fauna, and the Chinle Formation, containing a successor Late Triassic (Norian) tetrapod fauna. Taking Chinle faunal biodiversity to represent full biotic recovery, comparison of taxonomic and guild diversity of faunas from similar depositional and taphonomic environments in these two formations allowed us to assess the possibility of incipient terrestrial recovery of biodiversity in the Anisian.

Comparisons were made between the Holbrook Member fauna of the Moenkopi, a unit best characterized as a low-sinuosity medium- to coarse-grained fluvial deposit, and each of four Chinle stratigraphic units, representing fluvial settings from sandy low-sinuosity to muddy high-sinuosity. Three metrics were applied: generic and familial taxonomic diversity and guild diversity; these were compared by rarefaction. Simpson and Shannon diversity metrics augmented the analysis. Units of extraordinary preservation in the Chinle—the so-called blue layers—were removed from the analysis. In all tests the biodiversity of the Holbrook Member fauna is within the variation seen in Chinle faunas.

If the results of our study represent global conditions, they suggest that by at least early Anisian time (∼6 Myr after the P/T extinction) biodiversity had reached levels comparable to those seen in the Late Triassic. This potentially brings the terrestrial vertebrate recovery in line with the 4–8 Myr it took for recovery in the marine realm.

All erect, branching (ramose) organisms adhere to the same fundamental geometric growth law: the rate of distal growth decreases away from the branch axis. Regardless of the phylogenetic history of an organism, the formation of cylindrical branches requires adherence to this law. In colonial ramose organisms such as trees, corals, and bryozoans, this law poses a problem. How do colonies coordinate the growth rates of the individual modules to produce an integrated branch? This question is addressed in the context of three Ordovician and three Devonian species of ramose trepostome bryozoans. Using remnant growing tips in the endozone as isochronous surfaces, relative rates of skeletal secretion among zooids were measured. Measurements of skeletal and void spaces across a colony branch enabled calculation of the volume of skeletal material secreted by zooids between successive remnant growing tips. Results indicate that rate of skeletal secretion systematically decreases from the branch axis outward into the exozone. This suggests that zooid morphogenesis is controlled to a certain degree by the colony. Colonial control over zooidal growth rates in turn regulates the shape of the colony.

C. M. Yonge's idea that differences in habitat distribution and species diversity between archaeogastropods and caenogastropods are caused by differences in their respective abilities to obtain oxygen in turbid water is tested experimentally for the first time. Of 11 species of marine prosobranchs studied—six archaeogastropods and five caenogastropods—three archaeogastropods and two caenogastropods show significant reductions of respiration in response to turbidity, as shown using one-way analysis of covariance (ANCOVA). Two-way nested ANCOVA, which goes beyond one-way ANCOVA by incorporating all data into a single analysis, was also unable to detect any significant difference between archaeogastropods and caenogastropods in their respiratory responses to turbidity. Though the number of species studied was limited, the data and statistical tests suggest that there may be no biologically important systematic difference between archaeogastropods and caenogastropods in their respiratory responses to turbid conditions. Results of this study cast doubt on the validity of Yonge's hypothesis and suggest the need for new research into the controls of gastropod distribution and species diversity.

Focusing on the question of trends in Homo erectus cranial capacity evolution, Rightmire contends to have reanalyzed the data and demonstrated “a pattern of change … quite different from that described by Wolpoff.” Accepting the procedures used in this earlier analysis (Wolpoff 1984), he does this by changing the composition of the Homo erectus sample.

Life history theory has undergone considerable scrutiny since Stearns (1976) pointed out that neither the deterministic nor the stochastic theories, then current, provided an adequate fit for much of the empirical data he reviewed. Today, opinions on the future of life history studies may vary according to one's view of the mode of operation of evolution itself, the gradualist recommending detailed intraspecific studies and selection experiments, and the punctuationist aiming toward models involving laboratory speciation experiments (Stearns 1980).

In the assessment of Phanerozoic marine global biodiversity, there has been longstanding interest in quantifying compositional similarities among sampling points as a function of their distances from one another (geodisparity). Previous research has demonstrated that faunal similarity between any two locations tends to decrease significantly as the great circle distance (GCD) between the locations increases, but the rate of decrease begins to stabilize at transoceanic distances. The accuracy of these assessments, and comparisons among different temporal intervals, may suffer, however, because of intervening landmasses that are not accounted for when distance is calibrated simply as GCD. Here, we present a new method for determining the shortest overwater distance (WD) between two marine locations, and we use the method to recalibrate for several Phanerozoic intervals previous measures of global geodisparity in the taxonomic compositions of marine biotas. WD was determined by using a cost-distance approach in ArcGIS, modified to work on a spherical, as opposed to a planar, surface. Results demonstrate two notable effects of using WD. First, mean compositional similarity between locations tends to decrease more continuously as a function of distance with WD than with GCD. Second, pairs of locations with WDs that are at least 50% greater than their GCDs tend to have lower compositional similarity to one another than those with more closely matching WDs and GCDs. These differences are expected as WD better represents the “true” distance between locations; they diminish at GCDs of 5000 km or more when clear, transoceanic paths between locations become more common. Despite these effects, using WD does not alter fundamental temporal trends in global geodisparity through the Phanerozoic observed in previous research, but it is likely to have more significant ramifications for more confined paleobiogeographic investigations.

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 unique body plan of frogs (Lissamphibia: Anura) has been largely conserved from at least 200 Myr, and its evolution from a more generalized tetrapod condition is still poorly understood, in part due to the scarce early fossil record of Salientia, the anuran total-group. The origin of the anuran Bauplan has been classically explained as an adaptation to jumping, but recent studies incorporating new data in a phylogenetic context have challenged the popular jumping hypothesis. Here we revisit and test this hypothesis from a paleobiological perspective by integrating limb data from a wide range of extant and fossil frogs. We first explored the evolution of limb proportions from the Jurassic to the Paleogene to understand when the present limb diversity originated and whether, and to what extent, limb proportions have been conserved over the last 200 Myr. We then inferred the locomotor capabilities of extinct species by phylogenetic flexible discriminant analysis, and from these inferences, we studied the locomotor diversity of frogs over geological time and reconstructed the ancestral state for frog-like salientians. The evolution of limb proportions is characterized by an early diversification that was underway in the Jurassic, followed by a repeated convergence over a limited area of the morphospace that was already explored by the Early Cretaceous. In agreement with this early limb diversity, the Jurassic stem species were also locomotory diverse, and their inferred locomotor modes do not support the jumping hypothesis. We propose that the patterns found herein of repeated convergent evolution of both limb proportions and locomotor capabilities over geological time hamper any attempt to confidently infer the ancestral locomotion mode and, it therefore might be time to start focusing on other hypotheses on the origin of the anuran Bauplan that are not related to locomotion.

As of September 2019, the Florida Museum of Natural History (FLMNH) had a curated collection of 117,449 chondrichthyan specimens from Florida, spanning the Eocene through the Pleistocene. Herein, I evaluate the completeness of the chondrichthyan fossil record from Florida based on the FLMNH collection, while analyzing patterns in taxonomic and ecomorphological diversity. At least 70 chondrichthyan taxa were recognized, representing 10 orders, 26 families, and 42 genera; of which, 20 taxa represent first occurrences from Florida. A sample of 107,698 specimens was organized into 12 time bins to analyze taxonomic and ecomorphological diversity, with an expectation that diversity patterns would correspond with global climate events (e.g., the Eocene–Oligocene transition and the middle Miocene climatic optimum). However, diversity patterns were obscured by pervasive sampling bias, attributable to variable collection methods, research prioritizations, and regional lithologic controls. Sampling is particularly poor for smaller specimens and older geologic units (e.g., the Paleogene). Despite incomplete sampling of the Florida chondrichthyan fossil record, there was an apparent turnover along the Atlantic and Gulf Coastal Plains from a lamniform- to carcharhiniform-dominated chondrichthyan fauna that occurred during the Eocene. This turnover corresponded with the extinction of many lamniform taxa with grasping-dominated dentition types (e.g., Brachycarcharias, Jaekelotodus, and Macrorhizodus). Selachian taxa that survived the late Eocene extinctions were predominantly represented by cutting-dominant dentition types. As cutting aids in the dismemberment of prey, this may reflect a macroevolutionary trend toward active predation and scavenging on larger prey, such as marine mammals, teleost fish, and other sharks.

Where did the modern lineages of placental mammals originate? Recent molecular data seemingly have overturned not only schemata of placental relationships based on morphological data, but also hypotheses about the time and place of origin of the modern lineages. The original hypothesis of Northern Hemisphere origin, based on the fossil record, has been replaced by a “Garden of Eden” hypothesis of origins on a southern continent, based on molecular phylogenies. But, do the molecular data really support this new view of placental mammal origins?

Modern paleoanthropology is broadly interdisciplinary, integrating the results of studies in hominid (or more generally primate) paleontology, morphology and systematics with archeology, stratigraphy, chronometry, general paleontology, taphonomy and ecology, among other fields. (I here employ the term “hominid” to include all advanced hominoids of Miocene to Pleistocene age, following Delson and Andrews, 1975; similarly “hominine” (or “human”) refers to members of the subfamily Homininae of this usage, especially Australopithecus and Homo. Many other authors restrict hominine/human to Homo alone, employing hominid where I use hominine.) This integrative approach has been both spectacular and successful in eastern Africa (see Laporte 1980), due to the influence of F. C. Howell, the Leakeys and their colleagues, but it has also been responsible for recent advances in other temporal and spatial intervals in human evolution. In this review, I will concentrate on the morpho-evolutionary aspects of recent paleoanthropological studies, indicating major sources and new developments. Most fossils not otherwise referenced are discussed, albeit often with a different interpretation, in Wolpoff's (1980a) text.

The Rhynchonellida is a major group of brachiopods that survived the “big five” mass extinctions and flourished after the Permian/Triassic (P/Tr) crisis. However, phylogenetic and character evolution in the Rhynchonellida across the P/Tr transition is poorly understood. In view of the widespread homoplasy across this order, we employ a tip-dated Bayesian analysis to reconstruct phylogenetic relationships for late Permian–Triassic rhynchonellides. The same data were also analyzed using three other methods: undated Bayesian, equal-weighting, and implied-weighting parsimony. Compared with trees generated by other methods, those constructed by tip-dating best account for the homoplasy in this group and are closer to previous assumptions on the evolution of this order. Based on the analyses of multiple trees, the major increase in lineage richness occurred in the Early and early Middle Triassic. Also, richness in the Anisian almost reached the highest level seen in the Triassic. According to fossil records, a pronounced reduction in shell size and in the development of ornamentation occurred after the P/Tr extinction, which is largely due to the loss of large and highly sculptured genera and the diversification of small-sized and weakly ornamented genera. Ancestral-state estimation of shell size and development of ornamentation, coupled with comparisons of other characters, indicate that the Early–Middle Triassic mature “small-sized taxa” may have characters displayed by juveniles of their ancestors. This suggests that for these genera, paedomorphosis was possibly a strategy to survive and diversify in the harsh environment after the P/Tr extinction.

A fundamental question in paleobiology is whether ecology is correlated with evolutionary history. By combining time-calibrated phylogenetic trees with genus occurrence data through time, we can understand how environmental preferences are distributed on a tree and evaluate support for models of ecological similarity. Exploring parameters that lend support to each evolutionary model will help address questions that lie at the nexus of the evolutionary and ecological sciences. We calculated ecological difference and phylogenetic distance between species pairs for 83 taxa used in recent phylogenetic revisions of the brachiopod order Strophomenida. Ecological difference was calculated as the pairwise distance along gradients of water depth, carbonate, and latitudinal affinity. Phylogenetic distance was calculated as the pairwise branch length between tips of the tree. Our results show no relationship between ecological affinity and phylogeny. Instead results suggest an ecological burst during the initial radiation of the clade. This pattern likely reflects scaling at the largest macroevolutionary and macroecological scales preserved in the fossil record. Hierarchical scaling of ecological and evolutionary processes is complex, but phylogenetic paleoecology is an avenue for better evaluating these questions.

Gastropods often show signs of unsuccessful attacks by durophagous predators in the form of healed scars in their shells. As such, fossil gastropods can be taken as providing a record of predation through geological time. However, interpreting the number of such scars has proved to be problematic—Would a low number of scars mean a low rate of attack or a high rate of success, for example? Here we develop a model of population dynamics among individuals exposed to predation, including both lethal and nonlethal attacks. Using this model, we calculate the equilibrium distributions of ages and healed scars in the population and among fossilized specimens, based on the assumption that predation is independent of age or scar number. Based on these results, we formally show that the rates of attack and success cannot be disambiguated without further information about population structure. Nevertheless, by making the assumptions that the non-durophagous predatory death rate is both constant and low, we show that it is possible to use relatively small assemblages of gastropods to produce accurate estimates of both attack and success rates, if the overall death rate can be estimated. We consider likely violations of the assumptions in our model and what sort of information would be required to solve this problem in these more general cases. However, it is not easy to extract the relevant information from the fossil record: a variety of important biases are likely to intervene to obscure the data that gastropod assemblages may yield. Nonetheless, the model provides a theoretical framework for interpreting summary data, including for comparison between different assemblages.

Synrhabdosomes, structures made of mostly radially arrayed graptolite rhabdosomes attached by distal regions of their virgulae, have been considered as biological entities by some in the past, but as taphonomic structures by others more recently. Our survey of at least 200 synrhabdosomes, more than 90 of which derive from one locality in northwestern Spain, shows that all synrhabdosomes are most probably entirely monospecific assemblages composed of a more or less finite number of rhabdosomes, all of which are consistently straight or only weakly curved, and all of which bear simple, or relatively simple, thecae. We conclude, therefore, that synrhabdosomes are biological entities, and we suggest that they formed infrequently as, perhaps, temporary structures to increase food-gathering efficiency during times of lower plankton supply in local, relatively restricted water masses.

We use scanning electron microscopy imaging to examine the shell microstructure of fossil and living species in five families of caenogastropods (Strombidae, Volutidae, Olividae, Pseudolividae, and Ancillariidae) to determine whether parallel or convergent evolution is responsible for the development of a unique caenogastropod trait, the extreme parietal callus (EPC). The EPC is defined as a substantial thickening of both the spire callus and the callus on the ventral shell surface such that it covers 50% or more of the surface. Caenogastropods as a whole construct the EPC convergently, using a variety of low-density, poorly organized microstructures that are otherwise uncommon in caenogastropod non-callus shell construction. Within clades, however, we see evidence for parallelism in decreased regulation in both the shell and callus microstructure. Low-density and poorly ordered microstructure—such as used for the EPC—uses less organic scaffolding and is less energetically expensive than normal shell microstructure. This suggests the EPC functions to rapidly and inexpensively increase shell thickness and overall body size. Tests of functional ecology suggest that the EPC might function both to defend against crushing predation through increased body size and dissipation of forces while aiding in shell orientation of highly mobile gastropods. These interpretations hinge on the current phylogenetic placement of caenogastropod families, emphasizing the essential contribution of phylogeny when interpreting homoplasy.

Large body size in Keen’s mouse, Peromyscus keeni, has been regarded as a relictual character that developed in times of geographic separation from P. maniculatus. However, body-size changes in Keen’s mouse have not been studied in detail. To address this problem the present paper compares the size of ancient and modern Peromyscus specimens from Vancouver Island. Results indicate that Late Pleistocene Peromyscus from Arch-2 Cave and early Holocene Peromyscus from Pellucidar Cave are significantly larger than those of modern P. maniculatus and P. keeni. Morphology and linear discriminant analyses support tentative assignment of several ancient specimens to P. keeni. Radiocarbon age estimates of 11,960±45 BP (14,004–13,637 cal BP) on a small mammal bone and 12,370±35 BP (14,695–14,148 cal BP) on Ursus arctos from Arch-2 Cave place these faunas on the island as relative sea level fell from a postglacial highstand, suggesting a local source for faunas with limited over-water dispersal capacities. Results of this study are consistent with insular relictual gigantism in Keen’s mouse, although some modification of the original hypothesis is needed to explain the smaller size of modern than ancient mice.

Taphonomic processes are informative about the magnitude and timing of paleoecological changes but remain poorly understood with respect to freshwater invertebrates in spring-fed rivers and streams. We compared taphonomic alteration among freshwater gastropods in live, dead (surficial shell accumulations), and fossil (late Pleistocene–early Holocene in situ sediments) assemblages from two Florida spring-fed systems, the Wakulla and Silver/Ocklawaha Rivers. We assessed taphonomy of two gastropod species: the native Elimia floridensis (n = 2504) and introduced Melanoides tuberculata (n = 168). We quantified seven taphonomic attributes (aperture condition, color, fragmentation, abrasion, juvenile spire condition, dissolution, and exterior luster) and combined those attributes into a total taphonomic score (TT). Fossil E. floridensis specimens exhibited the greatest degradation (highest TT scores), whereas live specimens of both species were least degraded. Specimens of E. floridensis from death assemblages were less altered than fossil specimens of the same species. Within death assemblages, specimens of M. tuberculata were significantly less altered than specimens of E. floridensis, but highly degraded specimens dominated in both species. Radiocarbon dates on fossils clustered between 9792 and 7087 cal BP, whereas death assemblage ages ranged from 10,692 to 1173 cal BP. Possible explanations for the observed taphonomic patterns include: (1) rapid taphonomic shell alteration, (2) prolonged near-surface exposure to moderate alteration rates, and/or (3) introduction of reworked fossil shells into surficial assemblages. Combined radiocarbon dates and taphonomic analyses suggest that all these processes may have played a role in death assemblage formation. In these fluvial settings, shell accumulations develop as a complex mixture of specimens derived from multiple sources and characterized by multimillennial time-averaging. These findings suggest that, when available, fossil assemblages may be more appropriate than death assemblages for assessing preindustrial faunal associations and recent anthropogenic changes in freshwater ecosystems.