A morphologically diverse assemblage of organic-walled fossils from the middle Neoproterozoic Svanbergfjellet Formation, Spitsbergen, is identified as a monospecific assemblage representing the Gongrosira-phase of a vaucheriacean xanthophyte alga. As such, it provides a range of additional criteria with which to identify fossil vaucheriaceans and confirms the identification of Palaeovaucheria in the Mesoproterozoic Lakhanda Formation. Pronounced taxonomic inflation, through the practice of form-taxonomy, suggests that overall estimates of eukaryotic diversity in the Proterozoic need to be adjusted downward. Combined with positive evidence for low levels of speciation and extended stasis, pre-Cambrian eukaryotes are seen to evolve at a fundamentally lower rate than their Phanerozoic counterparts. This slower turnover accounts for the “delayed” appearance of animals without appeal to external triggers or constraints. The Cambrian acceleration of evolutionary rates was a direct consequence of newly introduced animals, whereas the much slower overall rates of the Proterozoic imply an absence of earlier metazoans.

Morphometric analyses of sauropod limbs have the potential to illuminate functional aspects of sauropod locomotion and paleobiology. However, analyses of sauropod limb dimensions typically show few discernible morphological trends because of large size differences among the individuals in a sample. For sauropods, combined analyses of both limb dimension and shape may be more desirable. Numerous humeri and femora from Apatosaurus, Diplodocus, and Camarasaurus provide an opportunity to explore and compare limb morphology in contemporaneous, sympatric sauropods. Thin-plate splines were used to analyze landmark-based shape differences in combination with traditional morphometrics. The aims of the analysis were (1) to determine if humerus and femur shape were significantly different among the genera; (2) to determine where shape changes occurred; and (3) to infer the basic functional implications of the shape differences using an Extant Phylogenetic Bracket approach. Few differences were detected among the genera using traditional morphometric analyses, and linear regression revealed a predominantly isometric relationship between most measurement variables and element size. Thin-plate splines revealed significant shape differences among the taxa. Apatosaurus humeri and femora were the most robust, with expanded regions for muscle insertion and more distally placed deltopectoral and caudofemoral landmarks. Diplodocus humeri and femora were gracile, with more proximally located landmarks of muscular insertion. Camarasaurus humeri were surprisingly gracile, with a less extensive deltopectoral crest, but had more robust femora similar to those of Apatosaurus. Few differences distinguished juvenile from adult specimens. These data suggest some locomotor differences were present among the three genera.

The effects of specialization on subsequent morphological evolution are poorly understood. Specialization has been implicated in both adaptive radiations that result from key innovations and evolutionary “dead ends,” where specialized characteristics appear to limit subsequent evolutionary options. Despite much theoretical debate, however, empirical studies remain infrequent. In this paper, we use sister-group comparisons to evaluate the effect of morphological specialization to a particular ecological niche, hypercarnivory, on subsequent taxonomic and morphological diversity. Six sets of sister groups are identified in which one clade exhibits hypercarnivorous characteristics and the sister clade does not. Comparison results are summed across the categories “hypercarnivore” and “sister group.” We also evaluate whether increasing degrees of specialization are correlated with decreasing phenotypic variation. Results presented here indicate that specialization to hypercarnivory has no effect on taxonomic diversity, but a strong effect on subsequent morphological diversity related to the jaws and dentition, and that increasing specialization does not correlate with morphological diversity except in the most specialized sabertoothed taxa, which exhibit higher variance than less specialized morphs, possibly due to selection on other characteristics.

The compactness profile of femoral cross-sections and body size of 105 specimens of 46 species of lissamphibians was studied to assess the effect of lifestyle (aquatic, amphibious, or terrestrial). Several tests that incorporate phylogenetic information (permutational multiple linear regression incorporating phylogenetic distances, logistic regression using phylogenetic weighting, concentrated-changes tests) show that the return to a fully aquatic lifestyle is associated with an increase in the compactness of the femur and an increase in body size. However, amphibious taxa cannot be distinguished from terrestrial ones solely on the basis of size or compactness. Body size and compactness profile parameters of the femur exhibit a phylogenetic signal (i.e., closely related taxa tend to be more similar to each other than to distantly related taxa).

Mathematical equations obtained from our data by using logistic regression with phylogenetic weighting are used to infer the lifestyle of four early stegocephalians. The results are generally congruent with prevailing paleontological interpretations, which suggests that this method could be applied to infer the lifestyle of early taxa whose lifestyle is poorly understood.

Modern histological techniques allow paleontologists to investigate the internal microstructure of bone tissue. We apply high resolution images of histological thin sections from an ontogenetic series (not conspecific) of pachycephalosaurid frontoparietal domes to test the hypothesis that these Late Cretaceous dinosaurs used their heads as battering rams, analogous to the behavior of the bighorn sheep, Ovis canadensis, or as a thermoregulatory device. Our analysis reveals that the internal structure of the pachycephalosaur dome is a dynamic tissue that reflects the changeable expansion and vascularity of the dome throughout ontogeny. The radiating structures within the frontoparietal dome, used previously to support “head-butting” hypotheses, are unexpectedly transitory, diminishing in mature individuals and nearly absent in adult skulls where head-butting behavior is presumed to occur. The unique architecture of the pachycephalosaurid dome is dividable into three distinct Zones. We demonstrate that the relative vascularity, associated tissue structures, and orientation and density of Sharpey's fibers within these Zones are modified during growth. Evidence for an external dome covering in vivo precludes the determination of the final shape of the pachycephalosaur skull. On the basis of these new observations, we propose that cranial display in support of species recognition and communication is a more parsimonious interpretation of the function of the pachycephalosaurid dome. Sexual display behaviors were probably secondary.

Many late Pleistocene fossil localities contain the remains of multiple mammoths. Some of these sites have been interpreted as representing the mass death of an entire herd, or family group, of mammoths. These assemblages have been cited as evidence of intense human predation and used to reconstruct mammoth population dynamics. However, these interpretations remain controversial because the taphonomic settings of many sites are still debated. To reconstruct the taphonomic setting of each site and the movement patterns of mammoths among sites, I used analyses of carbon, oxygen, and strontium isotope ratios in mammoth tooth enamel. The carbon isotopes of fossils vary with diet and local vegetation, oxygen isotopes vary with local climate, and strontium isotopes vary with local soil chemistry. If Pleistocene mammoths traveled together in small family groups, then mammoths from sites that represent family groups should have lower isotopic variability than mammoths from sites containing unrelated individuals. I tested this conjecture by comparing the isotopic variability among mammoths from two sites—one that represents the mass death of a single herd (Waco, Texas) and one representing a time-averaged accumulation (Friesenhahn Cave, Texas)—and then used these analyses to examine mammoths from three Clovis sites: Blackwater Draw, New Mexico; Dent, Colorado; and Miami, Texas. Low levels of carbon isotope variability were found to be the most diagnostic signal of herd/family group association. Although the variability of oxygen and strontium isotope ratios proved less useful for identifying family group assemblages, these signals did provide information about the movement patterns of individuals among different sites. High levels of variability in each of the isotope systems at Clovis sites suggest that all of the sites examined represent time-averaged accumulations of unrelated individuals, rather than the mass deaths of family groups.

In addition, analyses of the mean isotope values of Clovis mammoths show that although most mammoths from Blackwater and Miami had similar values, the values of Dent mammoths were significantly different. This demonstrates that the Dent mammoths belonged to a separate population and suggests that Clovis mammoths did not routinely undertake long distance (≥600 km) migrations.

Distributional patterns of eye lens variation in different morphs of the phacopine trilobite Acuticryphops acuticeps (Kayser 1889) are investigated. The specimens were collected from the latest Frasnian preceding the Upper Kellwasser (UKW) global extinction event in the Frasnian-Famennian (Late Devonian) stratotype section at Coumiac, southern France. In six successive populations a gradual reduction in the mean number of lenses occurs within the short time span of a single conodont Zone. This morphological change cannot be imputed either to the size of individual specimens or to variation in cephalic morphology. Thus morphs with different numbers of eye lenses are considered intraspecific. However, the intrapopulational percentage relation between morphs does not remain constant, as the coefficient of variation in lens number continuously increases from one population to the next. Cases of individuals with asymmetric eyes appear in the two latest assemblages prior to the UKW level. The fact that the total variation of the shape of the cephalon is not affected in these assemblages suggests that the morphological changes observed in the visual complex may account for the relaxation of selective pressures on this trait. Such a change in the regime of selection would have been accompanied by a lessening of the processes that control the development of this trait. As the phenomenon of eye reduction is not restrained by local conditions at Coumiac (Montagne Noire) but occurs contemporaneously to various extents in other crustal blocks such as Rhenish Slate Mountains (Avalonia), Thuringia (Armorica), and Morocco (Northern Gondwana), it is considered as constituting an adaptation to global eustatic deepening that occurred in the terminal Frasnian just before the global extinction event.

The phylogenetic relationships of fossil and extant members of the primate superfamily Hominoidea are reassessed by using both conventional (morphological) cladistic and stratocladistic (incorporating morphological and temporal data) techniques. The cladistic analysis recovers four most parsimonious cladograms that distinguish postcranially primitive (“archaic”) and derived (“modern”) hominoid clades in the earliest Miocene of East Africa and supports distinct hominine and pongine clades. However, the relationships among the pongines and hominine clades and other Eurasian hominoids remain ambiguous and there is weak support (Bremer decay indices, reduced consensus, and bootstrap proportions) for several other parts of the proposed phylogeny.

An examination of the partitioning of homoplasy across the two major hominoid clades recovered in the cladistic analysis indicates that the majority of the observed homoplasy resides in the postcranially derived clade. An examination of the partitioning of homoplasy across anatomical regions indicates that dental characters display a significantly higher level of homoplasy than postcranial characters. A rarefaction analysis demonstrates that the higher homoplasy associated with the dental characters is not the result of sampling biases, indicating that postcranial skeletal characters are likely the more reliable phylogenetic indicators in the hominoids.

The branching order of the most parsimonious cladograms shows better than average congruence with the observed ordering of first appearances in the fossil record, implying that the hominoid fossil record is surprisingly good. As with morphologic parsimony debt, most of the stratigraphic parsimony debt in these cladograms is associated with the “modern” hominoid clade. A stratocladistic analysis of the data recovers a single most parsimonious phylogenetic tree with a different cladistic topology from the morphological cladogram. The most striking difference is the elimination of the postcranially primitive clade of hominoids in the early Miocene in favor of a pectinate succession of taxa. The relative position of the late-appearing taxon Oreopithecus is also altered in the stratocladistic hypothesis. Topological differences between the cladistic and stratocladistic hypotheses highlight two intervals of significant discord between the morphological and temporal data-the early Miocene of eastern Africa and the late Miocene of Eurasia. The first discrepancy is likely the result of poor preservation and morphological homoplasy in Morotopithecus, as the fossil record in the early Miocene of eastern Africa for the ingroup is rather good. The second discrepancy is likely the result of the unusual preservation conditions associated with the late Miocene hominoid Oreopithecus.

To reconstruct the paleodiet and habitat preference of gomphotheres, we measured the carbon and oxygen isotope composition of 68 bone and tooth samples for three species of Gomphotheriidae from 24 different localities (Argentina, Bolivia, Ecuador, Chile, and Brazil). Additionally, we measured the isotopic oxygen in the phosphate of 30 samples to control diagenetic alteration. We calculated the correlation between pairs of δ18Op-δ18Oc values for enamel, dentine, and bone, taken from the same individual in order to verify whether the oxygen of structural apatite carbonate was in equilibrium with body water. Because of the good correlation obtained among pairs of the three skeletal components, we considered the δ13C results of all components to be equally representative of both gomphothere groups, and we used them collectively in the analysis of the data.

To compare the different groups of specimens, we divided the samples into six groups, taking into account their taxonomy as well as their geographic and stratigraphic distribution. Cuvieronius specimens from Chile were exclusively C3 plants eaters, whereas specimens from Bolivia and Ecuador had a mixed C3-C4 diet. Stegomastodon showed a wider range of dietary adaptations. Specimens from Quequén Salado in Buenos Aires Province were entirely C3 feeders, whereas the diet of specimens from La Carolina Peninsula (Ecuador) was exclusively C4. The remaining South American groups analyzed were C3-C4 mixed-feeders. Carbon isotope composition of bone and teeth decreased as latitude increased. We found evidence of an exclusively C3-dominated diet at approximately 35–41°S. This result confirms that ancient feeding ecology cannot always be inferred from dental morphology or extant relatives. Data from middle and late Pleistocene indicated that, over time, there was an adaptive change in paleodiet from predominantly mixed-feeders to more specialized feeders. We propose that this dietary evolution was one of the causes that forced gomphotheres to extinction in South America. In addition, the data presented in this paper suggest that because of the different feeding preferences among mastodons, mammoths, and gomphotheres, only the bunodont gomphotheres reached South America.

Anomodont therapsids were the most diverse and abundant group of terrestrial vertebrate herbivores during the Late Permian and much of the Triassic. Their success has been widely attributed to a complex mastication system that was based on a propalinal sliding of the lower jaw. Traditionally, anomodont phylogeny has been viewed as an essentially linear sequence of taxa, each with more specializations for propaliny, culminating in the radiation of the dicynodont anomodonts. However, recent phylogenetic work has shown that similar specializations for propaliny can be found in members of two distinct anomodont clades, the endemic Russian Venyukovioidea and the unnamed clade consisting of Galeops + Dicynodontia. These specializations have been inferred to be present in the common ancestor of the venyukovioids and dicynodonts, implying a single origin of propaliny in anomodonts. Here a reevaluation of the anomodont feeding system is presented, and the possibility that propaliny evolved twice within the group is specifically addressed. First, I examine current hypotheses regarding anomodont phylogeny, using a modified version of data sets presented by previous authors. Then I consider the evolution of four characters related to propaliny in the context of the resulting phylogeny. The results of this investigation suggest that a dual origin of propaliny within anomodonts is not unlikely, but it depends largely on the interpretation of equivocal or poorly preserved features in some critical taxa, especially Otsheria. Given that the power stroke of mastication in basal synapsids involved the application of a posterodorsally directed force on the lower jaw, the evolution of propaliny in basal synapsids may not have been difficult. Furthermore, the independent evolution of propaliny in several other nonmammalian synapsid clades (e.g., Edaphosauria, Gorgonopsia) suggests that homoplasy may be the rule rather than the exception for this feature. Finally, the possibility of a dual origin of propaliny in anomodonts has important implications for the more general problem of the evolution of herbivory in terrestrial vertebrates. In particular, it suggests that propaliny alone was not enough to guarantee success as a herbivore during the late Paleozoic and early Mesozoic.

The quantification of disparity is an important aspect of recent macroevolutionary studies, and it is usually motivated by theoretical considerations about the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, How sensitive is any given disparity signal to different aspects of sampling and data analysis? Here we explore this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare patterns at the genus and species levels, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometrics, and discrete characters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in temporal resolution, and a general deceleration in morphological diversification is apparent. Different morphometric methods also produce similar signals. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometrics records a much lower value. This difference appears to reflect primarily the measurement of different aspects of overall morphology. Disparity patterns are similar at both the genus and species levels. Moreover, inclusion or exclusion of the sister order Holasteroida and the stem group Disasteroida in the sampled morphospace did not affect proportional changes in spatangoid disparity. Similar results were found for spatangoid subclades vis-à-vis spatangoids as a whole. The relative robustness of these patterns implies that the choice of temporal scale, morphometric scheme, and taxonomic level may not affect broad trends in disparity and the representation of large-scale morphospace structure.

The study of ancient biodiversity trends is confounded by biases of the paleontologic record, but standardizing sampling intensity among time intervals can ameliorate sample-size biases. We show that several existing standardization methods are intimately linked to the spatial components of diversity (alpha, the within-assemblage diversity; and beta, the between-assemblage diversity). The subsampling curves generated by these methods can also be generated by various manipulations of alpha and beta, so that one can predict the responses of the methods to specific changes in alpha or beta diversity. The responses of the subsampling methods to changes in total diversity depend on whether measured alpha or measured beta diversity changed. Like biodiversity, sampling consists of a within-sample component (the number of specimens collected per locality) and a between-sample component (the number of localities). Several subsampling methods (rarefaction, OW, O2W) attempt to standardize sampling effort at both levels, although they use no direct information on the former. Instead, they alter sampling intensity at the beta level to compensate for perceived biases at the alpha level. We show that alpha and beta diversity are not so easily interchangeable and that the accuracy of the subsampling methods depends critically on the spatial characteristics of diversity in a data set. Current methods are calibrated only to the abundance-richness characteristics of individual collections, but the amount of beta diversity and the degree to which the rareness/commonness of taxa correlates among samples also strongly affect the accuracy of the subsampling methods. We offer new calibrations based on empirical data sets that account for these factors. Our findings do not support Alroy et al.'s (2001) tentative claim that the taxonomic radiation in the Cenozoic marine realm is an artifact of biased sampling intensity. Their diversity curves that most strongly contradict Sepkoski's traditional Phanerozoic curve are based on a method that overcorrects for local sample-size biases, whereas the remaining curves are either consistent with the traditional curve or ambiguous because of the limited temporal and taxonomic coverage of the analysis. Other factors may bias Sepkoski's curve, but there is insufficient evidence to claim that variations in sampling intensity are the major determinant of its long-term trajectory.

Cenozoic sediments of Florida contain one of the most highly fossiliferous sequences of extinct sirenians in the world. Sirenians first occur in Florida during the Eocene (ca. 40 Ma), have their peak diversity during the late Oligocene–Miocene (including the widespread dugongid Metaxytherium), and become virtually extinct by the late Miocene (ca. 8 Ma). Thereafter during the Pliocene and Pleistocene, sirenians are represented in Florida by abundant remains of fossil manatees (Trichechus sp.). Stable isotopic analyses were performed on 100 teeth of fossil sirenians and extant Trichechus manatus from Florida in order to reconstruct diets (as determined from δ13C values) and habitat preferences (as determined from δ18O values) and test previous hypotheses based on morphological characters and associated floral and faunal remains. A small sample (n = 6) of extant Dugong dugon from Australia was also analyzed as an extant model to interpret the ecology of fossil dugongs.

A pilot study of captive manatees and their known diet revealed an isotopic enrichment (ɛ∗) in δ13C of 14.0‰, indistinguishable from previously reported ɛ∗ for extant medium to large terrestrial mammalian herbivores with known diets. The variation in δ18OV-SMOW reported here is interpreted to indicate habitat preferences, with depleted tooth enamel values (≈25‰) representing freshwater rivers and springs, whereas enriched values (≈30‰) indicate coastal marine environments. Taken together, the Eocene to late Miocene sirenians (Protosirenidae and Dugongidae) differ significantly in both δ13C and δ18O from Pleistocene and Recent manatees (Trichechidae). In general, Protosiren and the fossil dugongs from Florida have carbon isotopic values that are relatively positive (mean δ13C = −0.9‰) ranging from −4.8‰ to 5.6‰, interpreted to represent a specialized diet of predominantly seagrasses. The oxygen isotopic values (mean δ18O = 29.2‰) are likewise relatively positive, indicating a principally marine habitat preference. These interpretations correlate well with previous hypotheses based on morphology (e.g., degree of rostral deflection) and the known ecology of modern Dugong dugon from the Pacific Ocean. In contrast, the fossil and extant Trichechus teeth from Florida have relatively lower carbon isotopic values (mean δ13C = −7.2‰) that range from −18.2‰ to 1.7‰, interpreted as a more generalized diet ranging from C3 plants to seagrasses. The relatively lower oxygen isotopic values (mean δ18O = 28.1 ‰) are interpreted as a more diverse array of freshwater and marine habitat preferences than that of Protosiren and fossil dugongs. This study of Cenozoic sirenians from Florida further demonstrates that stable isotopes can test hypotheses previously based on morphology and associated floral and faunal remains. All these data sets taken together result in a more insightful approach to reconstructing the paleobiology of this interesting group of ancient aquatic mammalian herbivores.