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The anatomy of the avian lower respiratory system includes a complex interaction between air-filled pulmonary tissues, pulmonary air sacs, and much of the postcranial skeleton. Hypotheses related to the function and phylogenetic provenance of these respiratory structures have been posed based on extensive interspecific descriptions for an array of taxa. By contrast, intraspecific descriptions of anatomical variation for these features are much more limited, particularly for skeletal pneumatization, and are essential to establish a baseline for evaluating interspecific variation. To address this issue, we collected micro-computed tomography (μCT) scans of live and deceased African grey parrots (Psittacus erithacus) to assess variation in the arrangement of the lungs, the air sacs, and their respective invasion of the postcranial skeleton via pneumatic foramina. Analysis reveals that the two pairs of caudalmost air sacs vary in size and arrangement, often exhibiting an asymmetric morphology. Further, locations of the pneumatic foramina are more variable for midline, non-costal skeletal elements when compared to other pneumatized bones. These findings indicate a need to better understand contributing factors to variation in avian postcranial respiratory anatomy that can inform future intraspecific and interspecific comparisons., (© 2024 The Author(s). Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

Bats and birds are defined by their convergent evolution of flight, hypothesized to require the modular decoupling of wing and leg evolution. Although a wealth of evidence supports this interpretation in birds, there has been no systematic attempt to identify modular organization in the bat limb skeleton. Here we present a phylogenetically representative and ecologically diverse collection of limb skeletal measurements from 111 extant bat species. We compare this dataset with a compendium of 149 bird species, known to exhibit modular evolution and anatomically regionalized skeletal adaptation. We demonstrate that, in contrast to birds, morphological diversification across crown bats is associated with strong trait integration both within and between the forelimb and hindlimb. Different regions of the bat limb skeleton adapt to accommodate variation in distinct ecological activities, with flight-style variety accommodated by adaptation of the distal wing, while the thumb and hindlimb play an important role facilitating adaptive responses to variation in roosting habits. We suggest that the wing membrane enforces evolutionary integration across the bat skeleton, highlighting that the evolution of the bat thumb is less correlated with the evolution of other limb bone proportions. We propose that strong limb integration inhibits bat adaptive responses, explaining their lower rates of phenotypic evolution and relatively homogeneous evolutionary dynamics in contrast to birds. Powered flight, enabled by the membranous wing, is therefore not only a key bat innovation but their defining inhibition., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The subpectoral diverticulum (SPD) is an extension of the respiratory system in birds that is located between the primary muscles responsible for flapping the wing 1,2 . Here we survey the pulmonary apparatus in 68 avian species, and show that the SPD was present in virtually all of the soaring taxa investigated but absent in non-soarers. We find that this structure evolved independently with soaring flight at least seven times, which indicates that the diverticulum might have a functional and adaptive relationship with this flight style. Using the soaring hawks Buteo jamaicensis and Buteo swainsoni as models, we show that the SPD is not integral for ventilation, that an inflated SPD can increase the moment arm of cranial parts of the pectoralis, and that pectoralis muscle fascicles are significantly shorter in soaring hawks than in non-soaring birds. This coupling of an SPD-mediated increase in pectoralis leverage with force-specialized muscle architecture produces a pneumatic system that is adapted for the isometric contractile conditions expected in soaring flight. The discovery of a mechanical role for the respiratory system in avian locomotion underscores the functional complexity and heterogeneity of this organ system, and suggests that pulmonary diverticula are likely to have other undiscovered secondary functions. These data provide a mechanistic explanation for the repeated appearance of the SPD in soaring lineages and show that the respiratory system can be co-opted to provide biomechanical solutions to the challenges of flight and thereby influence the evolution of avian volancy., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Birds are represented by 11,000 species and a great variety of body masses. Modular organisation of trait evolution across birds has facilitated simultaneous adaptation of different body regions to divergent ecological requirements. However, the role modularity has played in avian body size evolution, especially small-bodied, rapidly evolving and diverse avian subclades, such as hummingbirds and songbirds, is unknown. Modularity is influenced by the intersection of biomechanical restrictions, adaptation, and developmental controls, making it difficult to uncover the contributions of single factors such as body mass to skeletal organisation. We develop a novel framework to decompose this complexity, assessing factors underlying the modularity of skeletal proportions in fore-limb propelled birds distributed across a range of body masses. We demonstrate that differences in body size across birds triggers a modular reorganisation of flight apparatus proportions consistent with biomechanical expectations. We suggest weakened integration within the wing facilitates radiation in small birds. Our framework is generalisable to other groups and has the capacity to untangle the multi-layered complexity intrinsic to modular evolution., (© 2024. The Author(s).)

Geometric morphometrics has had a profound impact on our understanding of morphological evolution. However, factors such as sample size and the views and elements selected for two-dimensional geometric morphometric (2DGM) analyses, which are often dictated by specimen availability and time rather than study design, may affect the outcomes of those analyses. Leveraging large intraspecific sample sizes ( n  > 70) for two bat species, Lasiurus borealis and Nycticeius humeralis , we evaluate the impact of sample size on calculations of mean shape, shape variance, and centroid size. Additionally, we assessed the concordance of multiple skull 2D views with one another and characterized morphological variation in skull shape in L. borealis and N. humeralis , as well as a closely related species, Lasiurus seminolus . Given that L. seminolus is a morphologically cryptic species with L. borealis , we assessed whether differences in skull shape and in 2DGM approach would allow species discrimination. We found that reducing sample size impacted mean shape and increased shape variance, that shape differences were not consistent across views or skull elements, and that trends shown by the views and elements were not all strongly associated with one another. Further, we found that L. borealis and L. seminolus were statistically different in shape using 2DGM in all views and elements. These results underscore the importance of selecting appropriate sample sizes, 2D views, and elements based on the hypothesis being tested. While there is likely not a generalizable sample size or 2D view that can be employed given the wide variety of research questions and systems evaluated using 2DGM, a generalizable solution to issues with 2DGM presented here is to run preliminary analyses using multiple views, elements, and sample sizes, thus ensuring robust conclusions., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Unlike the majority of sauropsids, which breathe primarily through costal and abdominal muscle contractions, extant crocodilians have evolved the hepatic piston pump, a unique additional ventilatory mechanism powered by the diaphragmaticus muscle. This muscle originates from the bony pelvis, wrapping around the abdominal viscera, extending cranially to the liver. The liver then attaches to the caudal margin of the lungs, resulting in a sub-fusiform morphology for the entire "pulmo-hepatic-diaphragmatic" structure. When the diaphragmaticus muscle contracts during inspiration, the liver is pulled caudally, lowering pressure in the thoracolumbar cavity, and inflating the lungs. It has been established that the hepatic piston pump requires the liver to be displaced to ventilate the lungs, but it has not been determined if the lungs are freely mobile or if the pleural tissues stretch ventrally. It has been hypothesized that the lungs are able to slide craniocaudally with the liver due to the smooth internal ceiling of the thoracolumbar cavity. We assess this through ultrasound video and demonstrate quantitatively and qualitatively that the pulmonary tissues are sliding craniocaudally across the interior thoracolumbar ceiling in actively ventilating live juvenile, sub-adult, and adult individuals ( n  = 7) of the American alligator ( Alligator mississippiensis ) during both natural and induced ventilation. The hepatic piston is a novel ventilatory mechanism with a relatively unknown evolutionary history. Questions related to when and under what conditions the hepatic piston first evolved have previously been left unanswered due to a lack fossilized evidence for its presence or absence. By functionally correlating specific characters in the axial skeleton to the hepatic piston, these osteological correlates can be applied to fossil taxa to reconstruct the evolution of the hepatic piston in extinct crocodylomorph archosaurs., Competing Interests: Brandon P Hedrick is an Academic Editor for PeerJ. William Thielicke is employed by OPTOLUTION Messtechnik GmbH., (©2023 Grand Pré et al.)

Sensory organs must develop alongside the skull within which they are largely encased, and this relationship can manifest as the skull constraining the organs, organs constraining the skull, or organs constraining one another in relative size. How this interplay between sensory organs and the developing skull plays out during the evolution of sensory diversity; however, remains unknown. Here, we examine the developmental sequence of the cochlea, the organ responsible for hearing and echolocation, in species with distinct diet and echolocation types within the ecologically diverse bat super-family Noctilionoidea. We found the size and shape of the cochlea largely correlates with skull size, with exceptions of Pteronotus parnellii, whose high duty cycle echolocation (nearly constant emission of sound pulses during their echolocation process allowing for detailed information gathering, also called constant frequency echolocation) corresponds to a larger cochlear and basal turn, and Monophyllus redmani, a small-bodied nectarivorous bat, for which interactions with other sensory organs restrict cochlea size. Our findings support the existence of developmental constraints, suggesting that both developmental and anatomical factors may act synergistically during the development of sensory systems in noctilionoid bats., (© 2023 American Association for Anatomy.)

The vertebrate respiratory system is challenging to study. The complex relationship between the lungs and adjacent tissues, the vast structural diversity of the respiratory system both within individuals and between taxa, its mobility (or immobility) and distensibility, and the difficulty of quantifying and visualizing functionally important internal negative spaces have all impeded descriptive, functional, and comparative research. As a result, there is a relative paucity of three-dimensional anatomical information on this organ system in all vertebrate groups (including humans) relative to other regions of the body. We present some of the challenges associated with evaluating and visualizing the vertebrate respiratory system using computed and micro-computed tomography and its subsequent digital segmentation. We discuss common mistakes to avoid when imaging deceased and live specimens and various methods for merging manual and threshold-based segmentation approaches to visualize pulmonary tissues across a broad range of vertebrate taxa, with a particular focus on sauropsids (reptiles and birds). We also address some of the recent work in comparative evolutionary morphology and medicine that have used these techniques to visualize respiratory tissues. Finally, we provide a clinical study on COVID-19 in humans in which we apply modeling methods to visualize and quantify pulmonary infection in the lungs of human patients., (© 2023 American Association for Anatomy.)

AbstractWith diverse mechanical and sensory functions, the vertebrate cranium is a complex anatomical structure whose shifts between modularity and integration, especially in mechanical function, have been implicated in adaptive diversification. Yet how mechanical and sensory systems and their functions coevolve, as well as how their interrelationship contributes to phenotypic disparity, remain largely unexplored. To examine the modularity, integration, and evolutionary rates of sensory and mechanical structures within the head, we analyzed hard and soft tissue scans from ecologically diverse bats in the superfamily Noctilionoidea, a clade that ranges from insectivores and carnivores to frugivores and nectarivores. We identified eight regions that evolved in a coordinated fashion, thus recognizable as evolutionary modules: five associated with bite force and three linked to olfactory, visual, and auditory systems. Interrelationships among these modules differ between Neotropical leaf-nosed bats (family Phyllostomidae) and other noctilionoids. Consistent with the hypothesis that dietary transitions begin with changes in the capacity to detect novel food items followed by adaptations to process them, peak rates of sensory module evolution predate those of some mechanical modules. We propose that the coevolution of structures influencing bite force, olfaction, vision, and hearing constituted a structural opportunity that allowed the phyllostomid ancestor to take advantage of existing ecological opportunities and contributed to the clade's remarkable radiation.

Using morphometrics to study nonavian dinosaur fossils is a practice that predates the origin of the word "dinosaur." By the 1970s, linear morphometrics had become established as a valuable tool for analyzing intra- and interspecific variation in nonavian dinosaurs. With the advent of more recent techniques such as geometric morphometrics and more advanced statistical approaches, morphometric analyses of nonavian dinosaurs have proliferated, granting unprecedented insight into many aspects of their biology and evolution. I outline the past, present, and future of morphometrics as applied to the study of nonavian dinosaurs zeroing in on five aspects of nonavian dinosaur paleobiology where morphometrics has been widely utilized to advance our knowledge: systematics, sexual dimorphism, locomotion, macroevolution, and trackways. Morphometric methods are especially susceptible to taphonomic distortion. As such, the impact of taphonomic distortion on original fossil shape is discussed as are current and future methods for quantifying and accounting for distortion with the goal of reducing the taphonomic noise to biological signal ratio. Finally, the future of morphometrics in nonavian dinosaur paleobiology is discussed as paleobiologists move into a "virtual paleobiology" framework, whereby digital renditions of fossils are captured via methods such as photogrammetry and computed tomography. These primary data form the basis for three-dimensional (3D) geometric morphometric analyses along with a slew of other forms of analyses. These 3D specimen data form part of the extended specimen and help to democratize paleobiology, unlocking the specimen from the physical museum and making the specimen available to researchers across the world., (© 2023 American Association for Anatomy.)

Many species' distributions are being impacted by the acceleration of climate change. Amphibians in particular serve numerous ecosystem functions and are useful indicators of environmental change. Understanding how their distributions have been impacted by climate change and will continue to be impacted is thus important to overall ecosystem health. Plethodon cinereus (Eastern Red-Backed Salamander) is a widespread species of lungless salamander (Plethodontidae) that ranges across northeastern North America. To better understand future potential lungless salamander range shifts, we quantify environmental favorability, the likelihood of membership in a set of sites where environmental conditions are favorable for a species, for P. cinereus in multiple time periods, and examine shifts in the species' distribution. First, utilizing a large data set of georeferenced records, we assessed which bioclimatic variables were associated with environmental favorability in P. cinereus . We then used species distribution modeling for two time periods (1961-1980 and 2001-2020) to determine whether there was a regional shift in environmental favorability in the past 60 years. Models were then used to project future distributions under eight climate change scenarios to quantify potential range shifts. Shifts were assessed using fuzzy logic, avoiding thresholds that oversimplify model predictions into artificial binary outputs. We found that P. cinereus presence is strongly associated with environmental stability. There has been a substantial northward shift in environmental favorability for P. cinereus between 1961-1980 and 2001-2020. This shift is predicted to continue by 2070, with larger shifts under higher greenhouse gas emission scenarios. As climate change accelerates, it is differentially impacting species but has especially strong impacts on dispersal-limited species. Our results show substantial northward shifts in climatic favorability in the last 60 years for P. cinereus , which are likely to be exacerbated by ongoing climate change. Since P. cinereus is dispersal-limited, these models may imply local extirpations along the southern modern range with limited northward dispersal. Continued monitoring of amphibians in the field will reveal microclimatic effects associated with climate change and the accuracy of the model predictions presented here., Competing Interests: The authors declare that they have no conflict of interest., (© 2023 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

The increased use of imaging technology in biological research has drastically altered morphological studies in recent decades and allowed for the preservation of important collection specimens alongside detailed visualization of bony and soft-tissue structures. Despite the benefits associated with these newer imaging techniques, there remains a need for more "traditional" methods of morphological examination in many comparative studies. In this paper, we describe the costs and benefits of the various methods of visualizing, examining, and comparing morphological structures. There are significant differences not only in the costs associated with these different methods (monetary, time, equipment, and software), but also in the degree to which specimens are destroyed. We argue not for any one particular method over another in morphological studies, but instead suggest a combination of methods is useful not only for breadth of visualization, but also for the financial and time constraints often imposed on early-career research scientists., Competing Interests: The authors have no conflicts of interests to declare., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

The secondary evolution of quadrupedality from bipedal ancestry is a rare evolutionary transition in tetrapods yet occurred convergently at least three times within ornithischian dinosaurs. Despite convergently evolving quadrupedal gait, ornithischians exhibited variable anatomy, particularly in the forelimbs, which underwent a major functional change from assisting in foraging and feeding in bipeds to becoming principal weight-bearing components of the locomotor system in quadrupeds. Here, we use three-dimensional multi-body dynamics models to demonstrate quantitatively that different quadrupedal ornithischian clades evolved distinct forelimb musculature, particularly around the shoulder. We find that major differences in glenohumeral abduction-adduction and long axis rotation muscle leverages were key drivers of mechanical disparity, thereby refuting previous hypotheses about functional convergence in major clades. Elbow muscle leverages were also disparate across the major ornithischian lineages, although high elbow extension muscle leverages were convergent between most quadrupeds. Unlike in ornithischian hind limbs, where differences are more closely tied to functional similarity than phylogenetic relatedness, mechanical disparity in ornithischian forelimbs appears to have been shaped primarily by phylogenetic constraints. Differences in ancestral bipedal taxa within each clade may have resulted in disparate ecomorphological constraints on the evolutionary pathways driving divergence in their quadrupedal descendants.

We imaged the lungs of five Cuvier's dwarf caiman (Paleosuchus palpebrosus) via computed tomography (CT) and micro-computed tomography (μCT) and compared these data to the lungs of the American alligator (Alligator mississippiensis). These data demonstrate anatomical commonalities between the lungs of P. palpebrosus and A. mississippiensis, and a few notable differences. The structural similarities are (a) a proximally narrow, distally widened, hook-shaped primary bronchus; (b) a cervical ventral bronchus that branches of the primary bronchus and immediately makes a hairpin turn toward the apex of the lung; (c) a sequential series of dorsobronchi arising from the primary bronchus caudal to the cervical ventral bronchus; (d) intraspecifically highly variable medial sequence of secondary airways; (e) sac-like laterobronchi; and (f) grossly dead-ended caudal group bronchi in the caudal and ventral aspects of the lung. The primary differences between the two taxa are in the overall number of large bronchi (fewer in P. palpebrosus), and the number of branches that contribute to the cardiac regions. Imaging data of both a live and deceased specimen under varying states (postprandial, fasting, total lung capacity, open to atmosphere) indicate that the caudal margin and position of the lungs shift craniocaudally relative to the vertebral column. These imaging data suggest that the smooth thoracic ceiling may be correlated to visceral movement during ventilation, but this hypothesis warrants validation. These results provide the scaffolding for future comparisons between crocodilians, for generating preliminary reconstructions of the ancestral crocodilian bronchial tree, and establishing new hypotheses of bronchial homology across Archosauria., (© 2022 American Association for Anatomy.)

A variety of species undergo ontogenetic niche shifts in either diet, habitat, or both. As a result, multiple ontogenetic stages are able to take advantage of different resources and live in sympatry without competing with one another. The American alligator (Alligator mississippiensis) begins to undergo an ontogenetic niche shift in both diet and habitat at a length of 1.2 m. They transition from a terrestrial wetland environment to a riverine environment and take advantage of different dietary resources. At 1.8 m, A. mississippiensis reaches sexual maturity. Ontogenetic shifts in habitat have the capacity to alter morphology, especially limb morphology, as different age classes traverse different ecological systems. We evaluated shape trends in the scapulae, humeri, ilia, and femora using geometric morphometrics to test whether there were punctuated changes in limb shape, shape disparity, and integration corresponding to either the ontogenetic habitat shift or onset of sexual maturity. We found size to strongly correlate with limb shape but found a continuous size gradient rather than punctuated changes in size. Furthermore, we found that adults (total length > 1.8 m) had significantly higher limb shape disparity than juveniles or subadults, likely related to ontogenetic decreases in limb use and a reduction in limb constraints. Finally, we found that the forelimb and hindlimb acted as a single integrated unit and that neither the forelimb nor hindlimb was significantly more integrated than the other. Therefore, the ontogenetic niche shift itself did not impact limb morphology in A. mississippiensis., (© 2021 American Association for Anatomy.)

Although evolvability of genes and traits may promote specialization during species diversification, how ecology subsequently restricts such variation remains unclear. Chemosensation requires animals to decipher a complex chemical background to locate fitness-related resources, and thus the underlying genomic architecture and morphology must cope with constant exposure to a changing odorant landscape; detecting adaptation amidst extensive chemosensory diversity is an open challenge. In phyllostomid bats, an ecologically diverse clade that evolved plant visiting from a presumed insectivorous ancestor, the evolution of novel food detection mechanisms is suggested to be a key innovation, as plant-visiting species rely strongly on olfaction, supplementarily using echolocation. If this is true, exceptional variation in underlying olfactory genes and phenotypes may have preceded dietary diversification. We compared olfactory receptor (OR) genes sequenced from olfactory epithelium transcriptomes and olfactory epithelium surface area of bats with differing diets. Surprisingly, although OR evolution rates were quite variable and generally high, they are largely independent of diet. Olfactory epithelial surface area, however, is relatively larger in plant-visiting bats and there is an inverse relationship between OR evolution rates and surface area. Relatively larger surface areas suggest greater reliance on olfactory detection and stronger constraint on maintaining an already diverse OR repertoire. Instead of the typical case in which specialization and elaboration are coupled with rapid diversification of associated genes, here the relevant genes are already evolving so quickly that increased reliance on smell has led to stabilizing selection, presumably to maintain the ability to consistently discriminate among specific odorants-a potential ecological constraint on sensory evolution., (© 2022 The Authors. Evolution published by Wiley Periodicals LLC on behalf of The Society for the Study of Evolution.)

The avian pelvis plays a critical role in the hindlimb function of birds, connecting the hindlimb and axial skeleton and serving as the major attachment site for proximal hindlimb musculature. To assess how diversification of locomotor modes in birds has impacted the evolution of avian pelvic morphology, we conducted a two-dimensional geometric morphometric analysis of bird pelves in dorsal and lateral views from 163 species (n = 261) across Aves. We investigated the relationships among pelvic shape and ecology, phylogeny, and allometry, and conducted disparity analyses to understand how pelvic morphospace has been explored through the diversification of Aves. We found that while phylogeny was correlated with shape, locomotor categories were significantly discriminated in morphospace in phylogenetically corrected analyses, as was pelvic size. Major shape trends across Aves distinguishing locomotor categories included the relative area of the preacetabular versus postacetabular ilium, how squat or narrow the pelvis is, and the extent of the caudal pelvic border. Birds adapted for hind limb-propelled swimming had particularly distinctive pelves, with narrow, elongated ilia likely useful for holding the hindlimbs close to the body midline and reducing drag. However, ecology and allometry only account for a small proportion of morphological variation, and in general locomotor groups overlapped substantially in morphospace. These results, alongside disparity through time analyses showing widespread convergence in pelvic morphology throughout the Cenozoic, suggest that avian lineages and ecotypes have extensively explored pelvic morphospace, perhaps aided by a loosening of evolutionary constraints following the evolution of forelimb-powered flight., (© 2022 Wiley Periodicals LLC.)

Genital evolution can be driven by diverse selective pressures. Across taxa we see evidence of covariation between males and females, as well as divergent genital morphologies between closely related species. Quantitative analyses of morphological changes in coevolving male and female genitalia have not yet been shown in vertebrates. This study uses 2D and 3D geometric morphometrics to quantitatively compare the complex shapes of vaginal pouches and hemipenes across three species of watersnakes (the sister taxa Nerodia fasciata, N. sipedon, and a close relative N. rhombifer) to address the relationship between genital morphology and divergence time in a system where sexual conflict may have driven sexually antagonistic coevolution of genital traits. Our pairwise comparisons of shape differences across species show that the sister species have male and female genitalia that are significantly different from each other, but more similar to each other than to N. rhombifer. We also determine that the main axes of shape variation are the same for males and females, with changes that relate to deeper bilobation of the vaginal pouch and hemipenes. In males, the protrusion of the region of spines at the base of the hemipene trades off with the degree of bilobation, suggesting amelioration of sexual conflict, perhaps driven by changes in the relative size of the entrance of the vaginal pouch that could have made spines less effective., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

The role of mechanical morphologies in the exploitation of novel niche space is well characterized; however, the role of sensory structures in unlocking new niches is less clear. Here, we investigate the relationship between the evolution of sensory structures and diet during the radiation of noctilionoid bats. With a broad range of foraging ecologies and a well-supported phylogeny, noctilionoids constitute an ideal group for studying this relationship. We used diffusible iodine-based contrast enhanced computed tomography scans of 44 noctilionoid species to analyze relationships between the relative volumes of three sensory structures (olfactory bulbs, orbits, and cochleae) and diet. We found a positive relationship between frugivory and both olfactory and orbit size. However, we also found a negative relationship between nectarivory and cochlea size. Ancestral state estimates suggest that larger orbits and olfactory bulbs were present in the common ancestor of family Phyllostomidae, but not in other noctilionoid. This constellation of traits indicates a shift toward omnivory at the base of Phyllostomidae, predating their radiation into an exceptionally broad range of dietary niches. This is consistent with a scenario in which changes in sensory systems associated with foraging and feeding set the stage for subsequent morphological modification and diversification., (© 2021 The Authors. Evolution © 2021 The Society for the Study of Evolution.)

Neotropical leaf-nosed bats (family Phyllostomidae) are one of the most diverse mammalian families and Artibeus spp. is one of the most speciose phyllostomid genera. In spite of their species diversity, previous work on Artibeus crania using linear morphometrics has uncovered limited interspecific variation. This dearth of shape variation suggests that differences in cranial morphology are not contributing to niche partitioning across species, many of which are often found in sympatry. Using two-dimensional geometric morphometric methods on crania from eleven species from the Artibeus species complex, the current study demonstrates substantial cranial interspecific variation, sexual size and shape dimorphism, and intraspecific geographic variation. The majority of species were shown to have a unique size and shape, which suggests that each species may be taking advantage of slightly different ecological resources. Further, both sexual size and shape dimorphism were significant in the Artibeus species complex. Male and female Artibeus are known to have sex specific foraging strategies, with males eating near their roosts and females feeding further from their roosts. The presence of cranial sexual dimorphism in the Artibeus species complex, combined with previous work showing that different fruit size and hardness is correlated with different cranial shapes in phyllostomids, indicates that the males and females may be utilizing different food resources, leading to divergent cranial morphotypes. Additional field studies will be required to confirm this emergent hypothesis. Finally, significant geographical shape variation was found in a large intraspecific sample of Artibeus lituratus crania . However, this variation was not correlated with latitude and instead may be linked to local environmental factors. Additional work on ecology and behavior in the Artibeus species complex underlying the morphological variation uncovered in this study will allow for a better understanding of how the group has reached its present diversity., Competing Interests: Brandon P. Hedrick is an Academic Editor for PeerJ., (©2021 Hedrick.)

The avian bronchial tree has a unique and elaborate architecture for the maintenance of unidirectional airflow. Gross descriptions of this bronchial arrangement have traditionally relied upon dissection and casts of the negative (air-filled) spaces. In this study, the bronchial trees of five deceased African grey parrots (Psittacus erithacus) were segmented from micro-computed tomography (μCT) scans into three-dimensional (3D) surface models, and then compared. Select metrics of the primary bronchi and major secondary branches in the μCT scans of 11 specimens were taken to assess left-right asymmetry and quantify gross lung structure. Analysis of the 3D surface models demonstrates variation in the number and distribution of secondary bronchi with consistent direct connections to specific respiratory air sacs. A single model of the parabronchi further reveals indirect connections to all but two of the nine total air sacs. Statistical analysis of the metrics show significant left-right asymmetry between the primary bronchi and the origins of the first four secondary bronchi (the ventrobronchi), consistently greater mean values for all right primary bronchus length metrics, and relatively high coefficients of variation for cross-sectional area metrics of the primary bronchi and secondary bronchi ostia. These findings suggest that the lengths of the primary bronchi distal to the ventrobronchi do not preserve lung symmetry, and that aerodynamic valving can functionally accommodate a wide range of bronchial proportions., (© 2021 Wiley Periodicals LLC.)

The avian lung is highly specialized and is both functionally and morphologically distinct from that of their closest extant relatives, the crocodilians. It is highly partitioned, with a unidirectionally ventilated and immobilized gas-exchanging lung, and functionally decoupled, compliant, poorly vascularized ventilatory air-sacs. To understand the evolutionary history of the archosaurian respiratory system, it is essential to determine which anatomical characteristics are shared between birds and crocodilians and the role these shared traits play in their respective respiratory biology. To begin to address this larger question, we examined the anatomy of the lung and bronchial tree of 10 American alligators (Alligator mississippiensis) and 11 ostriches (Struthio camelus) across an ontogenetic series using traditional and micro-computed tomography (µCT), three-dimensional (3D) digital models, and morphometry. Intraspecific variation and left to right asymmetry were present in certain aspects of the bronchial tree of both taxa but was particularly evident in the cardiac (medial) region of the lungs of alligators and the caudal aspect of the bronchial tree in both species. The cross-sectional area of the primary bronchus at the level of the major secondary airways and cross-sectional area of ostia scaled either isometrically or negatively allometrically in alligators and isometrically or positively allometrically in ostriches with respect to body mass. Of 15 lung metrics, five were significantly different between the alligator and ostrich, suggesting that these aspects of the lung are more interspecifically plastic in archosaurs. One metric, the distances between the carina and each of the major secondary airways, had minimal intraspecific or ontogenetic variation in both alligators and ostriches, and thus may be a conserved trait in both taxa. In contrast to previous descriptions, the 3D digital models and CT scan data demonstrate that the pulmonary diverticula pneumatize the axial skeleton of the ostrich directly from the gas-exchanging pulmonary tissues instead of the air sacs. Global and specific comparisons between the bronchial topography of the alligator and ostrich reveal multiple possible homologies, suggesting that certain structural aspects of the bronchial tree are likely conserved across Archosauria, and may have been present in the ancestral archosaurian lung., (© 2020 Anatomical Society.)

Erythrosuchidae were large-bodied, quadrupedal, predatory archosauriforms that dominated the hypercarnivorous niche in the aftermath of the Permo-Triassic mass extinction. Garjainia , one of the oldest members of the clade, is known from the late Olenekian of European Russia. The holotype of Garjainia prima comprises a well-preserved skull, but highly incomplete postcranium. Recent taxonomic reappraisal demonstrates that material from a bone bed found close to the type locality, previously referred to as ' Vjushkovia triplicostata ', is referable to G. prima. At least, seven individuals comprising cranial remains and virtually the entire postcranium are represented, and we describe this material in detail for the first time. An updated phylogenetic analysis confirms previous results that a monophyletic Garjainia is the sister taxon to a clade containing Erythrosuchus, Shansisuchus and Chalishevia . Muscle scars on many limb elements are clear, allowing reconstruction of the proximal locomotor musculature. We calculate the body mass of G. prima to have been 147-248 kg, similar to that of an adult male lion. Large body size in erythrosuchids may have been attained as part of a trend of increasing body size after the Permo-Triassic mass extinction and allowed erythrosuchids to become the dominant carnivores of the Early and Middle Triassic., Competing Interests: We declare we have no competing interests., (© 2020 The Authors.)

The diversity of research performed by vertebrate paleobiologists is immense, including primary descriptions of newly discovered taxa, biomechanical analyses of extant animals, large-scale macroevolutionary analyses with hundreds of taxa, and many others. This special issue of The Anatomical Record highlights the scope of the research done by paleobiologists, with an emphasis on dinosaurs and their relatives, and is structured into three broad categories of research: (1) anatomical descriptions, (2) the biology of the dinosaurs and their relatives, and (3) macroevolutionary trends. Although these topics all fall within the purview of contemporary paleobiology, many of these topics have been studied in one form or another since the beginning of dinosaur paleobiology as a field. Rather than the topics themselves, what characterizes the modern renaissance of paleobiology is the employment of newly developed quantitative techniques to analyze the relationships between taxa and their evolutionary history. While primary anatomical descriptions remain the central pillar of dinosaur paleobiology, researchers now have a suitable baseline understanding of dinosaurian anatomy and their major evolutionary relationships. Using this baseline, they are able to ask more complex questions and refine their understanding of dinosaurian evolution. The aim of this issue is to exemplify the range of topics examined within dinosaur paleobiology and to look forward to the future of paleobiology. Anat Rec, 303:645-648, 2020. © 2020 American Association for Anatomy., (© 2020 American Association for Anatomy.)

Bone histology grants substantial insight into the growth and biology of fossil vertebrates. Many of the major non-avian dinosaurian clades have been extensively sampled for bone histologic data allowing reconstruction of their growth as well as the assessment of the evolution of growth changes along phylogenies. However, horned ceratopsians are poorly represented in paleohistologic studies. Further, the ceratopsian taxa that have been examined are unevenly sampled phylogenetically with very basal forms and highly derived forms making up the majority of studied taxa. In order to rectify this, we have histologically sampled Avaceratops from Montana and Yehuecauhceratops from northern Mexico to assess how mid-sized basal centrosaurines grew relative to more basal and derived forms. Based on results from these taxa, basal centrosaurines present a mosaic of growth characters intermediate between those seen in basal ceratopsians and more derived centrosaurines. Further, Yehuecauhceratops has many lines of arrested growth preserved, suggesting that the large number of lines of arrested growth found in a high-latitude Pachyrhinosaurus specimen may be a result of phylogeny rather than geography. Since lines of arrested growth are not preserved in long bones of many ceratopsians, especially chasmosaurines, we also histologically sampled ribs of Avaceratops and Pachyrhinosaurus. However, the largest ribs were highly remodeled obscuring lines of arrested growth, making it unlikely that rib histology will clarify growth trends in ceratopsians. These centrosaurines add to the growing ceratopsian histological database and demonstrate that basal centrosaurines grew in a manner intermediate between non-ceratopsid taxa and derived centrosaurines. Anat Rec, 303:935-948, 2020. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)

Asymmetric genitalia and lateralized mating behaviors occur in several taxa, yet whether asymmetric morphology in one sex correlates or coevolves with lateralized mating behavior in the other sex remains largely unexplored. While lateralized mating behaviors are taxonomically widespread, among mammals they are only known in the harbor porpoise (Phocoena phocoena). Males attempt copulation by approaching a female exclusively on her left side. To understand if this unusual lateralized behavior may have coevolved with genital morphology, we quantified the shape of female and male harbor porpoise reproductive tracts using 2D geometric morphometrics and 3D models of the vaginal lumen and inflated distal penis. We found that the vaginas varied individually in shape and that the vaginas demonstrated both significant directional and fluctuating asymmetry. This asymmetry resulted from complex 3D spirals and vaginal folds with deep recesses, which may curtail the depth or direction of penile penetration and/or semen movement. The asymmetric shapes of the vaginal lumen and penis tip were both left-canted with similar angular bends that mirrored one another and correspond with the left lateral mating approach. We suggest that the reproductive anatomy of both sexes and their lateral mating behavior coevolved.

Rodents are the most species-rich order within Mammalia and have evolved disparate morphologies to accommodate numerous locomotor niches, providing an excellent opportunity to understand how locomotor innovation can drive speciation. To evaluate the connection between the evolutionary success of rodents and the diversity of rodent locomotor ecologies, we used a large dataset of proximal limb CT scans from across Myomorpha and Geomyoidea to examine internal and external limb shape. Only fossorial rodents displayed a major reworking of their proximal limbs in either internal or external morphology, with other locomotor modes plotting within a generalist morphospace. Fossorial rodents were also the only locomotor mode to consistently show increased rates of humerus/femur morphological evolution. We propose that these rodent clades were successful at spreading into ecological niches due to high behavioral plasticity and small body sizes, allowing them to modify their locomotor mode without requiring major changes to their proximal limb morphology.

Erythrosuchidae are a globally distributed and important group of apex predators that occupied Early and Middle Triassic terrestrial ecosystems following the Permo-Triassic mass extinction. The stratigraphically oldest known genus of Erythrosuchidae is Garjainia Ochev, 1958, which is known from the late Early Triassic (late Olenekian) of European Russia and South Africa. Two species of Garjainia have been reported from Russia: the type species, Garjainia prima Ochev, 1958, and ' Vjushkovia triplicostata ' von Huene, 1960, which has been referred to Garjainia as either congeneric ( Garjainia triplicostata ) or conspecific ( G. prima ). The holotype of G. prima has received relatively extensive study, but little work has been conducted on type or referred material attributed to ' V. triplicostata '. However, this material includes well-preserved fossils representing all parts of the skeleton and comprises seven individuals. Here, we provide a comprehensive description and review of the cranial anatomy of material attributed to ' V. triplicostata ', and draw comparisons with G. prima . We conclude that the two Russian taxa are indeed conspecific, and that minor differences between them result from a combination of preservation or intraspecific variation. Our reassessment therefore provides additional information on the cranial anatomy of G. prima . Moreover, we quantify relative head size in erythrosuchids and other early archosauromorphs in an explicit phylogenetic context for the first time. Our results show that erythrosuchids do indeed appear to have disproportionately large skulls, but that this is also true for other early archosauriforms (i.e. proterosuchids), and may reflect the invasion of hypercarnivorous niches by these groups following the Permo-Triassic extinction., Competing Interests: We declare we have no competing interests., (© 2019 The Authors.)

Terrestrial tetrapods use their claws to interact with their environments in a plethora of ways. Birds in particular have developed a diversity of claw shapes since they are often not bound to terrestrial locomotion and have heterogeneous body masses ranging several orders of magnitude. Numerous previous studies have hypothesized a connection between pedal claw shape and ecological mode in birds, yet have generated conflicting results, spanning from clear ecological groupings based on claw shape to a complete overlap of ecological modes. The majority of these studies have relied on traditional morphometric arc measurements of keratinous sheaths and have variably accounted for likely confounding factors such as body mass and phylogenetic relatedness. To better address the hypothesized relationship between ecology and claw shape in birds, we collected 580 radiographs allowing visualization of the bony core and keratinous sheath shape in 21 avian orders. Geometric morphometrics was used to quantify bony core and keratinous sheath shape and was compared to results using traditional arc measurements. Neither approach significantly separates bird claws into coarse ecological categories after integrating body size and phylogenetic relatedness; however, some separation between ecological groups is evident and we find a gradual shift from the claw shape of ground-dwelling birds to those of predatory birds. Further, the bony claw core and keratinous sheath are significantly correlated, and the degree of functional integration does not differ across ecological groups. Therefore, it is likely possible to compare fossil bony cores with extant keratinous sheaths after applying corrections. Finally, traditional metrics and geometric morphometric shape are significantly, yet loosely correlated. Based on these results, future workers are encouraged to use geometric morphometric approaches to study claw geometry and account for confounding factors such as body size, phylogeny, and individual variation prior to predicting ecology in fossil taxa., Competing Interests: The authors declare no conflict of interest., (© 2019 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

The loss of previously adaptive traits is typically linked to relaxation in selection, yet the molecular steps leading to such repeated losses are rarely known. Molecular studies of loss have tended to focus on gene sequences alone, but overlooking other aspects of protein expression might underestimate phenotypic diversity. Insights based almost solely on opsin gene evolution, for instance, have made mammalian color vision a textbook example of phenotypic loss. We address this gap by investigating retention and loss of opsin genes, transcripts, and proteins across ecologically diverse noctilionoid bats. We find multiple, independent losses of short-wave-sensitive opsins. Mismatches between putatively functional DNA sequences, mRNA transcripts, and proteins implicate transcriptional and post-transcriptional processes in the ongoing loss of S-opsins in some noctilionoid bats. Our results provide a snapshot of evolution in progress during phenotypic trait loss, and suggest vertebrate visual phenotypes cannot always be predicted from genotypes alone., Competing Interests: AS, KD, LY, KY, PD, BH, ED, LD, SR, KS No competing interests declared, (© 2018, Sadier et al.)

The increased accessibility of soft-tissue data through diffusible iodine-based contrast-enhanced computed tomography (diceCT) enables comparative biologists to increase the taxonomic breadth of their studies with museum specimens. However, it is still unclear how soft-tissue measurements from preserved specimens reflect values from freshly collected specimens and whether diceCT preparation may affect these measurements. Here, we document and evaluate the accuracy of diceCT in museum specimens based on the soft-tissue reconstructions of brains and eyes of five bats. Based on proxies, both brains and eyes were roughly 60% of the estimated original sizes when first imaged. However, these structures did not further shrink significantly over a 4-week staining interval, and 1 week in 2.5% iodine-based solution yielded sufficient contrast for differentiating among soft-tissues. Compared to six "fresh" bat specimens imaged shortly after field collection (not fixed in ethanol), the museum specimens had significantly lower relative volumes of the eyes and brains. Variation in field preparation techniques and conditions, and long-term storage in ethanol may be the primary causes of shrinkage in museum specimens rather than diceCT staining methodology. Identifying reliable tissue-specific correction factors to adjust for the shrinkage now documented in museum specimens requires future work with larger samples.

Breast cancer most frequently metastasizes to the skeleton. Bone metastatic cancer is incurable and induces wide-spread bone osteolysis, resulting in significant patient morbidity and mortality. Mechanical cues in the skeleton are an important microenvironmental parameter that modulate tumor formation, osteolysis, and tumor cell-bone cell signaling, but which mechanical signals are the most beneficial and the corresponding molecular mechanisms are unknown. We focused on interstitial fluid flow based on its well-known role in bone remodeling and in primary breast cancer. We created a full-scale, microCT-based computational model of a 3D model of bone metastasis undergoing applied perfusion to predict the internal mechanical environment during in vitro experimentation. Applied perfusion resulted in uniformly dispersed, heterogeneous fluid velocities, and wall shear stresses throughout the scaffold's interior. The distributions of fluid velocity and wall shear stress did not change within model sub-domains of varying diameter and location. Additionally, the magnitude of these stimuli is within the range of anabolic mechanical signals in the skeleton, verifying that our 3D model reflects previous in vivo studies using anabolic mechanical loading in the context of bone metastasis. Our results indicate that local populations of cells throughout the scaffold would experience similar mechanical microenvironments., (© 2017 Wiley Periodicals, Inc.)

Identification and interpretation of pathologies in the fossil record allows for unique insights into the life histories of extinct organisms. However, the rarity of such finds limits not only the sample size for palaeopathologic studies, but also the types of analyses that may be performed. In this study, we present the first occurrence of a palaeopathology in a vertebrate from the Mesozoic of the East Coast of North America (Appalachia), a pathologic ulna and radius of an indeterminate hadrosaur from the Navesink Formation (New Jersey). X-ray microtomography allowed for both detailed and more accurate diagnosis of the pathologic condition as well as virtual conservation of the specimen. Based on extant archosaurian comparisons, the hadrosaur was diagnosed with severe septic arthritis affecting the proximal ulna and radius. Diagnosis was based on erosion of the joint and highly reactive periosteal bone growth and fusion of the elements. To the best of our knowledge, this is the first recorded account of septic arthritis in dinosaurs. The severity of the pathology suggests the animal suffered with this condition for some time before death. Unfortunately, only the ulna and radius were found. Thus, the extent to which the condition spread to other parts of the body is unknown.

We describe a Psittacosaurus specimen from the Lujiatun beds of the Yixian Formation in Liaoning, China with an abnormality on its left fibula. Although a large number of Psittacosaurus specimens are known, only a single example of a pathologic Psittacosaurus has been previously noted. The specific pathology in the current specimen is believed to be a healed fibular fracture as assessed through a combination of gross morphology, microcomputed tomography (microCT), and histology data. The fracture can be identified using microCT, but the degree of remodeling and the stage of fracture repair are best determined histologically. The fracture callus is made up of radially oriented spokes of woven bone in a cartilage matrix and the original cortical bone prior to the fracture has been largely eroded. A transverse histologic section taken at the level of the fracture shows the displacement of the proximal and distal parts of the fibula. The Psittacosaurus appears to have survived the break considering the deposition of circumferential non-pathologic bone at the periosteal surface outside of the callus. The combination of gross morphological description, microCT data, and histologic data allowed for a full diagnosis of the abnormality. While some previous authors have preferred gross morphological description above other methods for assessing paleopathologies, it is evident based on this specimen that an amalgam of techniques provides greater clarity to paleopathology diagnoses. Although this Psittacosaurus lived in an environment with many predators, it was able to survive with a fracture on its hindlimb, which undoubtedly would have impacted its locomotion. Anat Rec, 299:897-906, 2016. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Psittacosaurus is one of the most abundant dinosaurs known, which allows for extensive study of its growth and form. Previous studies have evaluated growth trajectories of Psittacosaurus using bone histology. However, we present the first study of Psittacosaurus comparative juvenile histology and describe the histology of Psittacosaurus within its first year of life based on multiple sections taken from an exquisite monospecific assemblage of juveniles from the Yixian Formation in Liaoning, China. Specimens studied had femur lengths ranging from 30 to 36 mm. The five juveniles examined all have similar histologic patterns in the midshaft and epiphyseal regions showing that there is limited plasticity in bone development in juvenile Psittacosaurus and that all of the specimens in the assemblage were likely the same age. The microstructure patterns are compatible with the hypothesis that Psittacosaurus was precocial and that these juveniles were neonates. Based on comparisons with other juvenile ornithischians, juvenile Psittacosaurus had a growth rate similar to Orodromeus, slower than that of Maiasaura, Dysalotosaurus, or hadrosaurs consistent with small body size. Our results support previous studies that demonstrated that the orientation of vascular canals is likely not solely reflective of growth rate, but is also affected by underlying biomechanical, structural processes. The number of studies done on theropod and sauropodomorph histology dwarfs those of ornithischians. More studies of ornithischian histology are necessary in order to better establish phylogenetic trends in microstructure and to learn more about growth in this important clade., (© 2016 Wiley Periodicals, Inc.)

While centrosaurines and ceratopsids in general are abundant in the Late Campanian of northern Laramidia, they are much less commonly found in southern Laramidia. This has supported hypotheses of dinosaur provinciality and endemism in the Late Cretaceous with the delineation of at least two separate faunal zones, north and south Laramidia. There have been 12 genera of centrosaurines recognized from northern Laramidia while two genera, Diabloceratops and Nasutoceratops, have been named from southern Laramidia. We present an osteological description and taphonomic outline for a new centrosaurine ceratopsid from the Aguja Formation of northern Coahuila, Mexico that is not currently diagnosable to the generic level, but likely represents a new taxon. Further, we have included three-dimensional surface scans of all material attributed to this animal. Considering the large number of centrosaurines from northern Laramidia, it is likely that cladistic analyses are biased towards this faunal zone. New findings of southern centrosaurines are needed to correct this bias. This discovery expands the range of centrosaurines south to Coahuila, Mexico and adds new information to better characterize the morphology and taxonomy of centrosaurines from southern Laramidia and their evolution in comparison to their northern counterparts.

Non-avian saurischian skulls underwent at least 165 million years of evolution and shapes varied from elongated skulls, such as in the theropod Coelophysis, to short and box-shaped skulls, such as in the sauropod Camarasaurus. A number of factors have long been considered to drive skull shape, including phylogeny, dietary preferences and functional constraints. However, heterochrony is increasingly being recognized as an important factor in dinosaur evolution. In order to quantitatively analyse the impact of heterochrony on saurischian skull shape, we analysed five ontogenetic trajectories using two-dimensional geometric morphometrics in a phylogenetic framework. This allowed for the comparative investigation of main ontogenetic shape changes and the evaluation of how heterochrony affected skull shape through both ontogenetic and phylogenetic trajectories. Using principal component analyses and multivariate regressions, it was possible to quantify different ontogenetic trajectories and evaluate them for evidence of heterochronic events allowing testing of previous hypotheses on cranial heterochrony in saurischians. We found that the skull shape of the hypothetical ancestor of Saurischia likely led to basal Sauropodomorpha through paedomorphosis, and to basal Theropoda mainly through peramorphosis. Paedomorphosis then led from Orionides to Avetheropoda, indicating that the paedomorphic trend found by previous authors in advanced coelurosaurs may extend back into the early evolution of Avetheropoda. Not only are changes in saurischian skull shape complex due to the large number of factors that affected it, but heterochrony itself is complex, with a number of possible reversals throughout non-avian saurischian evolution. In general, the sampling of complete ontogenetic trajectories including early juveniles is considerably lower than the sampling of single adult or subadult individuals, which is a major impediment to the study of heterochrony on non-avian dinosaurs. Thus, the current work represents an exploratory analysis. To better understand the cranial ontogeny and the impact of heterochrony on skull evolution in saurischians, the data set that we present here must be expanded and complemented with further sampling from future fossil discoveries, especially of juvenile individuals.

Nothronychus was the first definitive therizinosaurian discovered in North America and currently represents the most specialized North American therizinosaurian genus. It is known from two species, No. mckinleyi from the Moreno Hill Formation (middle Turonian) in west-central New Mexico, and No. graffami from the Tropic Shale (early Turonian) in south-central Utah. Both species are represented by partial to nearly complete skeletons that have helped elucidate evolutionary trends in Therizinosauria. In spite of the biogeographical and evolutionary importance of these two taxa, neither has received a detailed description. Here, we present comprehensive descriptions of No. mckinleyi and No. graffami, the latter of which represents the most complete therizinosaurid skeleton known to date. We amend previous preliminary descriptions of No. mckinleyi and No. graffami based on these new data and modify previous character states based on an in-depth morphological analysis. Additionally, we review the depositional history of both specimens of Nothronychus and compare their taphonomic modes. We demonstrate that the species were not only separated geographically, but also temporally. Based on ammonoid biozones, the species appear to have been separated by at least 1.5 million years and up to 3 million years. We then discuss the impacts of diagenetic deformation on morphology and reevaluate potentially diagnostic characters in light of these new data. For example, the ulna of No. mckinleyi is curved whereas the ulna of No. graffami was considered straight, a character originally separating the two species. However, here we present the difference as much more likely related to diagenetic compression in No. graffami rather than as a true biologic difference. Finally, we include copies of three-dimensional surface scans of all major bones for both taxa for reference.

Theropoda was one of the most successful dinosaurian clades during the Mesozoic and has remained a dominant component of faunas throughout the Cenozoic, with nearly 10,000 extant representatives. The discovery of Archaeopteryx provides evidence that avian theropods evolved at least 155 million years ago and that more than half of the tenure of avian theropods on Earth was during the Mesozoic. Considering the major changes in niche occupation for theropods resulting from the evolution of arboreal and flight capabilities, we have analyzed forelimb and hindlimb proportions among nonmaniraptoriform theropods, nonavian maniraptoriforms, and basal avialans using reduced major axis regressions, principal components analysis, canonical variates analysis, and discriminant function analysis. Our study is the first analysis on theropod limb proportions to apply phylogenetic independent contrasts and size corrections to the data to ensure that all the data are statistically independent and amenable to statistical analyses. The three ordination analyses we performed did not show any significant groupings or deviations between nonavian theropods and Mesozoic avian forms when including all limb elements. However, the bivariate regression analyses did show some significant trends between individual elements that suggested evolutionary trends of increased forelimb length relative to hindlimb length from nonmaniraptoriform theropods to nonavian maniraptoriforms to basal avialans. The increase in disparity and divergence away from the nonavian theropod body plan is well documented within Cenozoic forms. The lack of significant groupings among Mesozoic forms when examining the entire theropod body plan concurrently suggests that nonavian theropods and avian theropods did not substantially diverge in limb proportions until the Cenozoic., (© 2014 Wiley Periodicals, Inc.)

Psittacosaurus is one of the most abundant and speciose genera in the Dinosauria, with fifteen named species. The genus is geographically and temporally widespread with large sample sizes of several of the nominal species allowing detailed analysis of intra- and interspecific variation. We present a reanalysis of three separate, coeval species within the Psittacosauridae; P. lujiatunensis, P. major, and Hongshanosaurus houi from the Lujiatun beds of the Yixian Formation, northeastern China, using three-dimensional geometric morphometrics on a sample set of thirty skulls in combination with a reevaluation of the proposed character states for each species. Using these complementary methods, we show that individual and taphonomic variation are the joint causes of a large range of variation among the skulls when they are plotted in a morphospace. Our results demonstrate that there is only one species of Psittacosaurus within the Lujiatun beds and that the three nominal species represent different taphomorphotypes of P. lujiatunensis. The wide range of geometric morphometric variation in a single species of Psittacosaurus implies that the range of variation found in other dinosaurian groups may also be related to taphonomic distortion rather than interspecific variation. As the morphospace is driven primarily by variation resulting from taphonomic distortion, this study demonstrates that the geometric morphometric approach can only be used with great caution to delineate interspecific variation in Psittacosaurus and likely other dinosaur groups without a complementary evaluation of character states. This study presents the first application of 3D geometric morphometrics to the dinosaurian morphospace and the first attempt to quantify taphonomic variation in dinosaur skulls.