Long bones (femora, humeri) are the most abundant remains of sauropod dinosaurs. Their length is a good proxy for body length and body mass, and their histology is informative about ontogenetic age. Here we provide a comparative assessment of histologic changes in growth series of several sauropod taxa, including diplodocids (Apatosaurus, Diplodocus, indeterminate Diplodocinae from the Tendaguru Beds and from the Morrison Formation), basal macronarians (Camarasaurus, Brachiosaurus, Europasaurus), and titanosaurs (Phuwiangosaurus, Ampelosaurus). A total of 167 long bones, mainly humeri and femora, and 18 limb girdle bones were sampled. Sampling was performed by core drilling at prescribed locations at midshaft, and 13 histologic ontogenetic stages (HOS stages) were recognized. Because growth of all sauropod long bones is quite uniform, with laminar fibrolamellar bone being the dominant tissue, HOS stages could be recognized across taxa, although with minor differences. Histologic ontogenetic stages generally correlate closely with body size and thus provide a means to resolve important issue like the ontogenetic status of questionable specimens. We hypothesize that sexual maturity was attained at HOS-8, well before maximum size was attained, but we did not find sexually differentiated growth trajectories subsequent to HOS-8. On the basis of HOS stages, we detected two morphotypes in the Camarasaurus sample, a small one (type 1) and a larger one (type 2), presumably representing different species or sexual dimorphism.

Taxon discovery underlies many studies in evolutionary biology, including biodiversity and conservation biology. Synonymy has been recognized as an issue, and as many as 30–60% of named species later turn out to be invalid as a result of synonymy or other errors in taxonomic practice. This error level cannot be ignored, because users of taxon lists do not know whether their data sets are clean or riddled with erroneous taxa. A year-by-year study of a large clade, Dinosauria, comprising over 1000 taxa, reveals how systematists have worked. The group has been subject to heavy review and revision over the decades, and the error rate is about 40% at generic level and 50% at species level. The naming of new species and genera of dinosaurs is proportional to the number of people at work in the field. But the number of valid new dinosaurian taxa depends mainly on the discovery of new territory, particularly new sedimentary basins, as well as the number of paleontologists. Error rates are highest (>50%) for dinosaurs from Europe; less well studied continents show lower totals of taxa, exponential discovery curves, and lower synonymy rates. The most prolific author of new dinosaur names was Othniel Marsh, who named 80 species, closely followed by Friedrich von Huene (71) and Edward Cope (64), but the “success rate” (proportion of dinosaurs named that are still regarded as valid) was low (0.14–0.29) for these earlier authors, and it appears to improve through time, partly a reflection of reduction in revision time, but mainly because modern workers base their new taxa on more complete specimens. If only 50% of species are valid, evolutionary biologists and conservationists must exercise care in their use of unrevised taxon lists.

An early Pliocene fossil locality in the Canadian High Arctic preserves the remains of the extinct beaver Dipoides sp. (Castoridae, Rodentia) in association with an assemblage of fossil beaver-cut wood. The wood assemblage presents a first opportunity to investigate woodcutting behavior and ecological performance in an extinct castorid genus. This study compares woodcutting in Dipoides sp. with that of the modern beaver, Castor canadensis, using evidence from small-diameter cut sticks (i.e., sticks transected by parallel series of cut marks) in combination with behavioral observations of Castor woodcutting. During woodcutting both Castor and Dipoides used their incisors unilaterally; the upper incisor was pressed against the stick while the corresponding lower incisor cut. Cut marks were relatively larger for Castor than Dipoides (scaled to incisor size). Compared with Dipoides, Castor more frequently used a cutting strategy that minimized the number of cuts needed to transect a stick (e.g., clipping as opposed to chip removal). Taken together, the behavioral evidence suggests that ecological cutting performance was lower for Dipoides than Castor.

The consensus view that the amount of rock available for sampling does not significantly and systematically bias Phanerozoic marine diversity patterns has broken down. How changes in rock availability and sampling intensity affect our estimates of past biodiversity has been investigated with a variety of new approaches. A number of proxies for the amount of rock available for sampling have been used, but most of these proxies do not rely directly on evidence from large-scale geological maps (maps that cover small areas) and accompanying memoirs. Most previous map-based studies focused on single regions or relied on small-scale synoptic maps. We collected data from published geological maps and memoirs from western Europe, Australia, and Chile, which we combined with COSUNA data from the United States to generate the first multiregional data set for investigating whether the global Phanerozoic marine diversity record is a true global record, or is instead biased toward North America and Western Europe as has long been suspected. Both short and long-term trends in variation in the amount of outcrop display limited correlation among the regions studied. A series of diversification models obtained better matches to observed fossil diversity from the European and U.S. records than for the Chilean and Australian records, further supporting suspicions that the global Phanerozoic diversity curve is disproportionately influenced by European and U.S. fossil data. These results indicate that future research into Phanerozoic marine diversity patterns should not continue to apply global eustatic curves as a proxy for rock at outcrop, but should use regional data on rock occurrence.

Temporal variation in sampling intensity and geologically controlled rates of fossil preservation distort macroevolutionary patterns in the fossil record. Here, we use a comprehensive, list-based compilation of taxonomically and stratigraphically vetted global crinoid genus occurrences to evaluate and correct for the effects of variable and incomplete sampling from the Ordovician through Early Silurian. After standardizing the number of occurrences or the number of biofacies used to estimate the stratigraphic ranges of genera and after adjusting rates of turnover to account for the incomplete preservation of true extinction and origination pulses, we find support for several important revisions to the macroevolutionary history of crinoids. First, in contrast to the uncorrected data, sample-standardized genus richness does not appear to increase by more than 20% after an abrupt Middle Ordovician (Harnagian) diversification. Second, the only significant short-term change in genus richness following the Harnagian increase is a ≥24% decline from the Rawtheyan to the Hirnantian. Third, volatility in rates of genus extinction is increased after adjusting for preservation and there remain significant peaks of extinction in the Rawtheyan, which marks the end-Ordovician extinction, and in the middle of the Early Silurian. Finally, significant increases in origination rates occur in the Early Silurian. These results reaffirm the importance of the end-Ordovician extinction for crinoids, but they also highlight the comparatively poorly sampled Early Silurian as a time of turnover among crinoids.

Crinoid genus extinction rates are positively correlated with area-weighted rates of sedimentary package truncation, suggesting that extinction may have been controlled by physical environmental changes, such as the contraction of unique epicontinental sea habitats. The lack of a correlation between genus origination and sedimentary package initiation reinforces this hypothesis and suggests that other factors, such as evolutionary innovations and biotic interactions during the Ordovician radiation, may have been more important in controlling the diversification of crinoids.

Questions related to dinosaur behavior can be difficult to answer conclusively by using morphological studies alone. As a complement to these approaches, carbon and oxygen isotope ratios of tooth enamel can provide insight into habitat and dietary preferences of herbivorous dinosaurs. This approach is based on the isotopic variability in plant material and in surface waters of the past, which is in turn reflected by carbon and oxygen isotope ratios of animals that ingested the organic matter or drank the water. Thus, it has the potential to identify and characterize dietary and habitat preferences for coexisting taxa.

In this study, stable isotope ratios from coexisting hadrosaurian and ceratopsian dinosaurs of the Hell Creek Formation of North Dakota are compared for four different stratigraphic levels. Isotopic offsets between tooth enamel and tooth dentine, as well as taxonomic differences in means and in patterns of isotopic data among taxa, indicate that primary paleoecological information is preserved. The existence of taxonomic offsets also provides the first direct evidence for dietary niche partitioning among these herbivorous dinosaur taxa. Of particular interest is the observation that the nature of this partitioning changes over time: for some localities ceratopsian dinosaurs have higher carbon and oxygen isotope ratios than hadrosaurs, indicating a preference for plants living in open settings near the coast, whereas for other localities isotope ratios are lower, indicating a preference for plants in the understory of forests. In most cases the isotope ratios among hadrosaurs are similar and are interpreted to represent a dietary preference for plants of the forest canopy. The inferred differences in ceratopsian behavior are suggested to represent a change in vegetation cover and hence habitat availability in response to sea level change or to the position of river distributaries. Given our current lack of taxonomic resolution, it is not possible to determine if dietary and habitat preferences inferred from stable isotope data are associated with single, or multiple, species of hadrosaurian/ceratopsian dinosaurs.

Sauropod dinosaurs were the largest terrestrial animals and their growth rates remain a subject of debate. By counting growth lines in histologic sections and relating bone length to body mass, it has been estimated that Apatosaurus attained its adult body mass of about 25,000 kg in as little as 15 years, with a maximum growth rate over 5000 kg/yr. This rate exceeds that projected for a precocial bird or eutherian mammal of comparable estimated body mass. An alternative method of estimating limb length and body mass for each growth line, and fitting the resulting age/mass data to the von Bertalanffy growth equation, yields a revised growth curve suggesting that Apatosaurus adult mass was reached by 70 years with a maximum growth rate of 520 kg/yr. This alternative method for growth rate determination can also be applied to histological studies of other sauropods. At only about half the mass of Apatosaurus, Janenschia took between 20 and 30 years to attain its adult size (over 14,000 kg). This result is supported by independent evidence of estimated bone apposition rates. Despite having an adult body mass greater than Apatosaurus, the titanosaurid Alamosaurus attained a mass over 32,000 kg within 45 years and a maximum growth rate of 1000 kg/yr. Titanosaurids may have been the fastest growing of all sauropods. Even so, sauropod growth rate estimates produced using the von Bertalanffy equation fall between those projected for reptiles and those for precocial birds of equivalent projected body mass. These results are comparable to those found for smaller dinosaurs, and suggest that sauropods grew at rates similar to other dinosaurs in spite of their great size.

Sabertooths exhibit one of the most extreme feeding adaptations seen in mammals. The functional consequences of accommodating extremely elongate upper canine teeth are severe, resulting in a well-documented suite of cranial modifications. We used geometric morphometric methods to study the evolution of overall shape in the skulls of extant and extinct feline and machairodontine felids, as well as extinct nimravids. Trends in skull evolution were evaluated by using relative warps analysis and tested for association with body size and canine tooth length. Primitive sabertooths from all lineages exhibit cranial shapes more similar to conical-toothed cats, despite the presence of moderately developed saberteeth. More-derived forms in both nimravids and felids diverge in skull morphospace to form two distinct sabertooth types (dirk-toothed and scimitar-toothed) that differ in canine shape. Skull shape in conical-toothed cats is strongly associated with body size, but not canine length. However, within each sabertooth lineage, skull shape is significantly correlated with canine length, suggesting that gape-related demands drove the evolution of sabertooth skull morphology.

Body mass is an important organism-level variable in mammalian biology, correlated with physiology, life history, and ecology. To analyze the dynamics of body size evolution, increases and decreases in body mass were tallied for ancestor-descendant (AD) species pairs for 519 terrestrial caniform taxa. To account for uncertainty phylogeny, a bootstrapping routine shuffled hypothesized AD pairs, and average proportions of increases were binned as a function of ancestral body mass. A set of models relating the rate of body size increase were evaluated with the Akaike Information Criterion (AIC). AIC selected three models of the candidate set as equivalent in support by the observed body mass data. These three models propose body size increase for small AD pairs and body size decrease for large AD pairs, although they differ in their treatment of taxa at intermediate sizes.

These results demonstrate the presence of constraints bounding the caniform distribution at large and small body sizes, stabilizing the distribution through time, which stands in contrast to a broader mammalian pattern. At a finer phylogenetic scale, subclades within intermediate size classes display proportions that are significantly different from unbiased, with several clades previously cited as examples of “Cope's Rule” showing biased increases in size, and basal mustelids (badgers, and allied genera), Mephitidae (skunks), and Vulpini (“foxes”) exhibiting biased decreases. The caniform pattern is therefore the result of superimposed, clade-specific trajectories, demonstrating that the inferred dynamics of body size evolution and even the direction of trends in body size evolution within the Caniformia, and for mammals in general, depend on the hierarchical scale of the analysis.

The three dimensional structure of vegetation is an important component of ecosystems, yet it is difficult to reconstruct from the fossil record. Forests or woodlands prevailed at mid-latitudes in North America during the early Eocene but tree spacing and canopy structure are uncertain. Here we use stable carbon isotope values (δ13C) in early Eocene mammalian faunas to infer canopy structure. We compare δ13C values in two diverse fossil assemblages from the central Bighorn Basin to values predicted for mammals in a variety of open and closed habitats, based on modern floras and faunas. We conclude that these early Eocene faunas occupied an open canopy forest. We also use carbon and oxygen isotopes to infer diet and microhabitat. Three higher level taxa have significantly different mean δ13C values, and values are negatively correlated with body mass. The pattern suggests diets high in leaves for larger mammals, and fruit or other non-foliar plant organs for small ones. A preference in the larger mammals for wetter habitats with high water availability to plants may also have contributed to the pattern.

The Caune de l'Arago Cave (southern France) has yielded one of the best preserved and best documented sedimentary successions of the European Middle Pleistocene (Oxygen Isotopic Stages 14 to 12). Herbivorous ungulates (horse, reindeer, red deer, fallow deer, bison, musk ox, argali, and tahr) are well represented in the three major stratigraphic units CM1, CM2, and CM3. CM1 and CM3 correspond to cold and dry climate and CM2 represents temperate and humid environmental conditions. Dental microwear and mesowear analyses were performed for the ungulates from CM1–3 to test whether these methods of dental wear evaluation were suitable for detecting climate-driven changes in the dietary resources of the Arago ungulate community. We found that both dental mesowear and microwear indicate dietary traits and their relationship to climatic conditions as reflected by vegetation cover and community structure. In all units, even if some species seem to share habitats or resources, it appears that the overlap in their feeding ecology is very low. The CM1 and CM3 units, where pollen analysis indicates that the climate was cold and dry, show the lowest diversity in dietary traits. The CM2, where climate is known to be more temperate and humid, the spectrum of dietary traits is large—grazers, browsers, and mixed feeders are present.

Principal components analysis (PCA) of 21 shell parameters (geometry, sculpture, aperture shape, and suture complexity) in 597 L. Devonian to L. Triassic ammonoid genera (spanning ~166 Myr) shows that eight basic morphotypes appeared within ~20 Myr of the first appearance of ammonoids. With one exception, these morphotypes persisted throughout the Paleozoic, occurring in ~75% of the ~5-Myr time bins used in this study. Morphotypes were not exclusive to particular lineages. Their persistence was not just a product of phylogenetic constraints or longevity, and multiple iterations of the same morphotypes occurred at different times and in different groups. Although mass extinction events severely condensed the range of morphologic variation and taxonomic diversity, the effects were short lived and most extinct morphotypes were usually iterated within 5 Myr. The most important effect of mass extinctions on ammonoid evolutionary history seems to have been their role in large scale taxonomic turnovers; they effectively eliminated previously dominant orders at the Frasnian/Famennian (F/F) (Agoniatitida), the Devonian/Mississippian (D/M) (Clymeniida), and the Permian/Triassic (P/T) (Goniatitida and Prolecanitida) extinctions. Survivors varied from two (P/T) to four (D/M) and five genera (F/F). These events generated sharp reductions in morphologic disparity at the D/M (58%) and at the P/T (59%), but there was a net increase at the F/F (38%). There was no obvious survival bias for particular morphotypes, but 64% are interpreted to have been Nautilus-like nektobenthic. The recurrence of particular combinations of morphology and their strong independence of phylogeny are strong arguments for functional constraint. Intervals between mass extinctions seem to have been relatively static in terms of morphotype numbers, in contrast to numbers of genera. Significant decreases in genus diversity (54%) and morphologic disparity (33%) commenced in the mid-Permian (Wordian/Capitanian boundary), well before the final P/T event.

It has recently been argued that barren intervals of marine sedimentary rock are less common in the Cenozoic than in the Paleozoic, and that this arises as a direct consequence of widespread epeiric seas and the prevalence of dysaerobic conditions at such times. We show, using an independent and more direct measure of rock outcrop through time in western Europe, that barren marine sedimentary rocks do become less frequent toward the present, but that this is not linked to any epeiric-seas effect. The proportion of barren to fossiliferous rock outcrop correlates well with the inferred Phanerozoic marine diversity curve (although more so in the Paleozoic than in the post-Paleozoic), and shows no correlation or only a weak negative correlation with area over which the sediments have been deposited. We therefore concluded that the Phanerozoic trend in fossiliferousness most likely records the degree to which space is occupied in the shallow marine realm.

New manuscripts should be submitted as a single PDF file (text, tables, and figures all in one file) with a separate PDF file for the cover letter to: Paleo-Journal@si.edu. The cover letter should include up to five suggested reviewers and their contact information. The subject of the email should be the lead author's name, e.g., “Simpson.” If the corresponding author differs from the lead author, follow the first name with the corresponding author's name in parentheses, e.g., “Simpson (Magruder).” In all correspondence beyond the initial submission, please put your assigned ms number on the subject line of your email.