Vertebrate microfossil assemblages in a stratigraphic sequence often yield similar assortments of taxa but at different relative abundances, potentially indicative of marginal paleocommunity changes driven by paleoenvironmental change over time. For example, stratigraphically younger assemblages in the Dinosaur Park Formation (DPF) yield proportionally more aquatic taxa, consistent with marine transgression. However, individual deposits may have received specimens from multiple source paleocommunities over time, limiting our ability to confidently identify ecologically significant, paleocommunity differences through direct assemblage comparisons. We adapted a three-source, two-tracer Bayesian mixing model to quantify proportional contributions from different source habitats to DPF microfossil assemblages. Prior information about the compositions of separate, relatively unmixed terrestrial, freshwater, and marine assemblages from the Belly River Group allowed us to define expected taxon percent abundances for the end-member habitats likely contributing specimens to the mixed deposits. We compared the mixed assemblage and end-member distributions using 21 different combinations of vertebrate taxa. Chondrichthyan, dinosaur, and amphibian occurrence patterns ultimately allowed us to parse the contributions from the potential sources to 14 of the 15 mixed assemblages. The results confirmed a significant decline in terrestrial contributions at younger DPF sites, driven primarily by increased freshwater specimen inputs—not incursions from the adjacent marine paleocommunity. A rising base level likely increased lateral channel migration and the prevalence of freshwater habitats on the landscape, factors that contributed to increased paleocommunity mixing at younger channel deposit sites. Bayesian methods can account for source-mixing bias, which may be common in assemblages associated with major paleoenvironmental changes.

Vertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

Two major ichnotypes of sauropod trackways have been described: “narrow-gauge,” in which both manus and pes prints approach or intersect the trackway midline, and “wide-gauge,” in which these prints are well apart from the midline. This gauge disparity could be the result of differences in behavior, body size, or morphology between the respective trackmakers. However, the biomechanics of locomotion in large terrestrial vertebrates suggest that sauropods were probably restricted in locomotor behavior, and the lack of systematic size differences between footprint gauges argues against body-size-related influences. We argue that skeletal morphology is responsible for gauge differences and integrate data from locomotor biomechanics and systematics with the track record to predict the hindlimb morphology of wide-gauge trackmakers. Broader foot stances in large, graviportal animals entail predictable mechanical consequences and hindlimb modifications. These could include outwardly angled femora, offset knee condyles, and a more eccentric femoral midshaft cross-section. A survey of sauropod hindlimb morphology reveals that these features are synapomorphies of titanosaurs, suggesting that they were the makers of wide-gauge trackways. The temporal and geographic distribution of titanosaurs is consistent with this hypothesis because wide-gauge trackways predominate during the Cretaceous and are found worldwide. Additional appendicular synapomorphies of titanosaurs are interpreted in light of identifying these animals as wide-gauge trackmakers. We suggest that titanosaurs may have used a bipedal stance more frequently than did other sauropods. These correlations between ichnology, biomechanics, and systematics imply that titanosaurs were unique among sauropods in having a more varied repertoire of locomotor habits.

Vertebrate tracks are a unique, abundant source of fossil data that supplements the skeletal record in many ways. However, the utility of ichnofossil data depends on how specifically the authors of tracks can be identified. Despite this fact, there is little consensus about how to identify potential trackmakers, and existing methods differ in their bases, assumptions, and corresponding implications.

In this paper we support the proposal that trackmakers should be identified primarily by skeletal structures that are both preserved in the ichnofossils and synapomorphies of some body-fossil clade. This synapomorphy-based technique enables certain taxa to be positively identified as candidate trackmakers and others to be excluded from consideration. In addition, the diagnostic level of the synapomorphy (i.e., to a higher or lower level) corresponds to that of the trackmaker. Additional features, such as body size and provenance, can be used in association with synapomorphies as additional differentiae of trackmaker identity.

Trackway analyses are dependent on the level of trackmaker diagnosis, but not all analyses require the same diagnostic specificity. Palichnostratigraphic correlations to the stage level are shown to require at least a genus-level identification of a trackmaker, whereas studies of vertebrate distributions (i.e., origins, extinctions, ranges) accommodate much coarser designations. Anachronistic occurrences of trace and body fossils result in range extensions for either the skeletal taxon or the feature in question. For example, the temporal distribution of theropods can be extended on the basis of the footprint record, resulting in an earlier estimated divergence time for Dinosauria.

This paper investigates trends in the evolution of body size and shape in the Plesiosauria, a diverse clade of Mesozoic marine reptiles. Using measures from well-preserved plesiosaur specimens, we document and interpret evolutionary patterns in relative head size, body size, and locomotor variables. Size increase is a significant trend in the clade as a whole, and in constituent clades. The trend in relative head size is of variance increase; observed head sizes are both smaller and larger than ancestral values. In the locomotor system, changes in propodial and girdle proportions appear concomitant with body size increase and are interpreted as allometric responses to the physical constraints of large body size. Other trends in the locomotor system are significantly correlated with both body size and relative head size. These locomotor trends evolved convergently in several clades of plesiosaurs, and may have had an ecomorphological basis, although data are lacking to constrain speculation on this point. The evolution of the locomotor system in plesiosaurs sheds new light on the response of aquatic tetrapods to the physical constraints of foraging at large body size.

In this paper, I survey hindlimb and pelvic anatomy across non-avian dinosaurs and analyze these within a cladistic framework to quantify patterns of change within the locomotor apparatus. Specifically, I attempt to identify where homoplasy constitutes parallelism and may thereby be used to infer similar selective pressures on hindlimb function. Traditional methods of discrete character optimization are used along with two methods for evaluating changes in continuous characters in a phylogenetic context (squared-change parsimony and clade rank correlation). Resultant patterns are evaluated in light of the biomechanics of locomotion and the relationship between form and function in extant terrestrial vertebrates.

Although non-avian dinosaurian locomotor morphology is strikingly uniform, these analyses reveal the repeated derivations of several morphological features that have potential relevance for hindlimb locomotor function. Anterior and posterior iliac expansion, a medially oriented femoral head, and an elevated femoral lesser trochanter each evolved independently multiple times within Dinosauria. These changes probably reflect enlargement of several hindlimb muscles as well as a general switch in their predominant function from abduction-adduction (characteristic of “sprawling” limb postures) to protraction-retraction (characteristic of parasagittal, or “erect,” limb postures). Several “avian” characteristics are shared with more basal theropods, and many were acquired convergently in other dinosaurian lineages. The evolution of the avian hindlimb therefore represents a cumulative acquisition of characters, many of which were quite far removed in time and function from the origin of flight.

Analyses of non-avian dinosaur locomotion have been hampered by the lack of an appropriate locomotor analog among extant taxa. Birds, though members of the clade Dinosauria, have undergone significant modifications in hindlimb osteology and musculature. These changes have resulted in a uniquely developed system of limb kinematics (involving a more horizontal femoral posture and knee-dominated limb motion), which precludes the direct use of extant birds as models for non-avian dinosaur locomotion. Analyses of locomotor data from extant birds and mammals suggest a causal link between general hindlimb kinematics, bone strains, and limb bone morphology among these taxa. A model is proposed that relates the amount of torsional loading in femora to bone orientation, such that torsion is maximal in horizontal femora and minimal in vertical femora. Since bone safety factors are lower for torsional shear strains than for longitudinal axial strains, an increase in torsion can potentially affect bone morphology dramatically over evolutionary time. Interpreting the nearly identical limb bone dimensions and limb element proportions of non-avian dinosaurs and mammals in the light of this relationship supports the prediction of similar vertical femoral postures and hip-driven limb kinematics in these two groups.

This information can be used to interpret patterns of locomotor evolution within Dinosauria. The evolution of quadrupedalism with large body size and the acquisition of cursorial or graviportal limb morphologies occurred repeatedly but did not affect the underlying uniformity of dinosaur locomotor morphology. Only derived coelurosaurian theropods (paravians) developed significant modifications of the basic dinosaurian patterns of limb use. Changes in theropod hindlimb kinematics and posture apparently began shortly prior to the origin of flight, but did not acquire a characteristically modern avian aspect until after the later acquisition of derived flight characteristics.

In this chapter we discuss methods for analyzing continuous traits, with an emphasis on those approaches that rely on explicit statistical models of evolution and incorporate genealogical information (ancestor–descendant or phylogenetic relationships). After discussing the roles of models and genealogy in evolutionary inference, we summarize the properties of commonly used models including random walks (Brownian motion), directional evolution, and stasis. These models can be used to devise null-hypothesis tests about evolutionary patterns, but it is often better to fit and compare models equally using information criteria and related approaches. We apply these methods to a published data set of dental measurements in a sequence of ancestor–descendant populations in the early primate Cantius, with the particular goal of determining the best-supported mode of evolutionary change in this lineage. We also assess a series of questions about the evolution of femoral dimensions in several clades of dinosaurs, including testing for a trend of increasing body size (Cope's Rule), testing for correlations among characters, and reconstructing ancestral states. Finally, we list briefly some additional models, approaches, and issues that arise in genealogically informed analyses of phenotypic evolution.

Current theories of locomotor biomechanics are based largely on observations of extant terrestrial mammals. However, extant mammals are limited with respect to certain aspects of terrestrial locomotion, and this constraint has confounded interpretations of limb design in this group. Dinosaurs include a wide array of large and small bipeds, record several transitions between bipedalism and quadrupedalism, and show a unique covariation of cursoriality and body size. Thus, the wider applications of biomechanical theories may be tested by applying them to the limb bones of dinosaurs. A broad examination of hindlimb and forelimb bone scaling patterns in dinosaurs and mammals reveals several general similarities that provide insight into the general constraints acting on terrestrial locomotion, particularly in animals with parasagittally oriented limbs. Most limb bones scale with negative allometry in these two groups, and larger taxa tend to scale more negatively than smaller forms. However, the strongly negative scaling of large mammals is mostly restricted to ungulates, whose unusually short femora may be the result of constraints of cursoriality at large body sizes. Bipedal and quadrupedal dinosaurs scale very similarly, with most differences apparently resulting from size rather than posture. Bone curvature tends to decrease with increasing body size, while femoral midshaft eccentricity tends to increase. Femoral midshaft eccentricity is explained as a general adaptation to mediolateral bending on parasagittal limb bones. These trends are more pronounced in dinosaurs than mammals; additional morphological constraints present in the dinosaurian hindlimb may contribute to this distinction.