Hindlimb Proportions Research Articles

Evolutionary integration of forelimb and hindlimb proportions within the bat wing membrane inhibits ecological adaptation.

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.

The last ceratosaur of Asia: a new noasaurid from the Early Cretaceous Great Siberian Refugium.

The noasaurid ceratosaur Kiyacursor longipes gen. et sp. nov. is described based on a fragmentary skeleton including cervical vertebra, pectoral girdle, humerus and hind limbs from the Lower Cretaceous (Aptian) Ilek Formation at Shestakovo 1 locality in Western Siberia, Russia. This is the first ceratosaur from the Early Cretaceous of Asia, extending the stratigraphic range of Ceratosauria by 40 Myr on that continent. Kiyacursor shares unique hind limb proportions with Elaphrosaurus and Limusaurus, suggesting improved cursorial ability. These taxa show an ostrich-like specialization of the pes, with a large third metatarsal and greatly reduced second metatarsal. By contrast, all other fast running non-avian theropod dinosaurs have an arctometatarsalian pes, with the third metatarsal strongly reduced proximally. The new taxon lived in the Early Cretaceous ecosystem containing a number of other Jurassic relics, such as stem salamanders, protosuchian and shartegosuchid crocodyliforms, tritylodontid synapsids and docodontan mammaliaforms.

Proportional variation and scaling in the hindlimbs of hopping mammals, including convergent evolution in argyrolagids and jerboas

Bipedal hopping is a mode of locomotion seen today in four rodent lineages and one clade of marsupials. The Argyrolagidae, marsupials from the Oligocene to Pliocene of South America, have also been considered to be hoppers. These lineages all convergently evolved similar general morphologies, with elongated hindlimbs, reduced forelimbs, and elongated tails, and their similarities and variations may be informative in understanding the evolution of hopping in mammals. This study uses principal components analysis and log-log regressions to investigate variation in the hindlimb proportions of these hopping mammals and how this relates to body mass. We find that the distribution of hopping mammal masses is bimodal, divided at roughly 500 g. These two domains among hopping mammals may reflect optimisation for different forms of hopping locomotion; species under 500 g tend to have more elongated metatarsals relative to the rest of their hindlimbs, perhaps to facilitate rapid vertical jumps for predator evasion, a behaviour not seen in larger hoppers. Despite this bimodal distribution in body mass, hindlimb proportions cluster more by clade than mass, with some similarities among clades being especially noteworthy. The jerboas (Dipodidae, Rodentia) and Argyrolagidae share a particularly extreme degree of metatarsal elongation. The drivers of this convergence are unclear, but we hypothesise that the elongation may be related to the reduction/fusion of metatarsals in these groups, or a greater reliance on bipedality at slow speeds, as jerboas are known to utilise multiple bipedal gaits in addition to hopping.

New Comparative Data on the Long Bone Microstructure of Large Extant and Extinct Flightless Birds

Here, we investigate whether bone microanatomy can be used to infer the locomotion mode (cursorial vs. graviportal) of large terrestrial birds. We also reexamine, or describe for the first time, the bone histology of several large extant and extinct flightless birds to (i) document the histovariability between skeletal elements of the hindlimb; (ii) improve our knowledge of the histological diversity of large flightless birds; (iii) and reassess previous hypotheses pertaining to the growth strategies of modern palaeognaths. Our results show that large extinct terrestrial birds, inferred as graviportal based on hindlimb proportions, also have thicker diaphyseal cortices and/or more bony trabeculae in the medullary region than cursorial birds. We also report for the first time the occurrence of growth marks (not associated with an outer circumferential layer-OCL) in the cortices of several extant ratites. These observations support earlier hypotheses that flexible growth patterns can be present in birds when selection pressures for rapid growth within a single year are absent. We also document the occurrence of an OCL in several skeletally mature ratites. Here, the high incidence of pathologies among the modern species is attributed to the fact that these individuals were probably long-lived zoo specimens.

New material of Phuwiangvenator yaemniyomi (Dinosauria: Theropoda) from the type locality: Implications for the early evolution of Megaraptora

Phuwiangvenator yaemniyomi is a mid-sized, early branching megaraptoran theropod from the Lower Cretaceous Sao Khua Formation of Phu Wiang Mountain, Khon Kaen Province, northeastern Thailand. The holotype includes dorsal and sacral vertebrae, lower legs, hand and foot elements. Here we describe new skeletal material pertaining to the same individual representing the holotype of Phuwiangvenator based on size, shape, and shared phylogenetic affinities. This material was recovered at the same quarry as the holotype and consists of an incomplete fibula, left and right metatarsals. A new autapomorphy observed from the new material is the presence of a long, deep fossa between the lateral and medial distal condyles of the metatarsal II that extends to the distal articular facet is visible in anterior view. The metatarsal III of Phuwiangvenator is relatively short, more similar to the proportion present in basal carcharodontosaur Concavenator than in the derived megaraptorans, but more gracile than other basal allosauroids. Its hindlimb proportions are similar to the basal carcharodontosaur Neovenator than other more derived megaraptorans and coelurosaurs. Phuwiangvenator shows a combination of features shared with allosauroids and basal coelurosaurs and appears to be “intermediate” between non-megaraptorid and megaraptorid theropods. The present work adds anatomical data on this theropod and provides information on the early evolution of the Megaraptora.

First discovery of a deinonychosaur trackway from the lower Upper Cretaceous of southeastern China

The new deinonychosaur trackway was recovered from the lower Upper Cretaceous Jinhua Formation of Zhejiang Province, southeastern China. This trackway includes nine well-preserved tracks characterized by elongate and didactyl morphology, and thus is assigned to the ichnospecies Velociraptorichnus sichuanensis. This trackway enables more accurate estimations of the speed and gait of the trackmaker for the ichnogenus Velociraptorichnus than the previous studies because the latter is based only on two consecutive tracks. Due to substantial differences in hindlimb proportions between the two clades assignable to the trackmaker of Velociraptorichnus, namely Dromaeosauridae and Troodontidae, we calculated the speed of trackmaker for each pattern. The estimated speeds resulted in 6.1 km/h for dromaeosaurids and 4.6 km/h for troodontids, both of which indicate that this trackway was made by a walking gait. This is the first record of a deinonychosaur trackway from the Cretaceous of southeastern China and extends the known distribution of didactyl theropod ichnotaxa. In combination with previous studies, it also suggests that a diverse ichnoassemblage of non-avian theropods was widely distributed in East Asia during that time.

Increased performance in juvenile baboons is consistent with ontogenetic changes in morphology.

In many primates, the greater proportion of climbing and suspensory behaviors in the juvenile repertoire likely necessitates good grasping capacities. Here, we tested whether very young individuals show near-maximal levels of grasping strength, and whether such an early onset of grasping performance could be explained by ontogenetic variability in the morphology of the limbs in baboons. We quantified a performance trait, hand pull strength, at the juvenile and adult stages in a cross-sectional sample of 15 olive baboons (Papio anubis). We also quantified bone dimensions (i.e., lengths, widths, and heights) of the fore- (n = 25) and hind limb (n = 21) elements based on osteological collections covering the whole development of olive baboons. One-year old individuals demonstrated very high pull strengths (i.e., 200% of the adult performance, relative to body mass), that are consistent with relatively wider phalanges and digit joints in juveniles. The mature proportions and shape of the forelimb elements appeared only at full adulthood (i.e., ≥4.5 years), whereas the mature hind limb proportions and shape were observed much earlier during development. These changes in limb performance and morphology across ontogeny may be explained with regard to behavioral transitions that olive baboons experience during their development. Our findings highlight the effect of infant clinging to mother, an often-neglected feature when discussing the origins of grasping in primates. The differences in growth patterns, we found between the forelimb and the hind limb further illustrate their different functional roles, having likely evolved under different ecological pressures (manipulation and locomotion, respectively).

Intraspecific variation in a lizard from the Central Mexican Plateau: intersexual differences in size and shape explored

AbstractMorphological adaptations of individuals are directly (or indirectly) determined by the environment. Depending on sex, these adaptations may vary in different ways, given that different selective forces may be operating on organisms. Here, we evaluate intraspecific morphological variation (size and shape) in two populations of Sceloporus grammicus that occur in different structural habitats (trees and rocks). No difference in overall body size was found between the two populations. However, strong differences were found in body shape; the tree population was characterized by having shorter hindlimb proportions than the rock population, which agrees with the theory of biomechanical models. Furthermore, our results show that this species is dimorphic in size and shape, both in sex and population effects. A review of the literature suggests that the large overall body size and relatively longer distal segments of males could be an advantage for defending their territory, and the observation that females had relatively longer head length may be related to trophic niche divergence; however, this remains to be tested. Detailed quantification of behaviour, performance and reproductive characteristics must be performed to shed light on the evolution of sexual dimorphism in this widely distributed species in Mexico.

A diminutive species of emu (Casuariidae: Dromaiinae) from the late Miocene of the Northern Territory, Australia

ABSTRACTA new, diminutive species of dromaiine casuariid, Dromaius arleyekweke, is described from dispersed skeletal elements from the late Miocene Waite Formation of the Northern Territory, Australia. Remains of D. arleyekweke, sp. nov., have been found from the Ongeva Local Fauna in the Alcoota Scientific Reserve, but most remains come from the stratigraphically lower Alcoota Local Fauna where they form part of a densely fossiliferous series of mingled bone beds. Previously, remains of the new species had been referred to the basal dromaiine genus, Emuarius, but phylogenetic appraisal of new specimens indicates that the species shared a more recent common ancestor with the extant Dromaius novaehollandiae than it did with the type species of Emuarius, E. gidju. Consequently, the new species is placed in the genus Dromaius as its oldest known member. Derived characters of D. arleyekweke that are shared with D. novaehollandiae to the exclusion of E. gidju include a distally flattened external condyle of the distal end of the tibiotarsus and a more elongate tarsometatarsus, with marked transverse compression of the midshaft and a weakly impressed median sulcus on trochlea metatarsi II. Casuariid evolution shows a trend of increasingly cursorial hind limb proportions on the emu lineage, but D. arleyekweke has a tarsometatarsus that is more elongate than that of D. novaehollandiae. This implies nonlinear evolution of cursoriality in dromaiines and that D. arleyekweke evolved extreme cursorial proportions independently of D. novaehollandiae, or that a high degree of cursoriality evolved early in Dromaius and was reversed in the Pliocene D. ocypus.

An Amphibious Whale from the Middle Eocene of Peru Reveals Early South Pacific Dispersal of Quadrupedal Cetaceans

Cetaceans originated in south Asia more than 50 million years ago (mya), from a small quadrupedal artiodactyl ancestor [1-3]. Amphibious whales gradually dispersed westward along North Africa and arrived in North America before 41.2 mya [4]. However, fossil evidence on when, through which pathway, and under which locomotion abilities these early whales reached the New World is fragmentary and contentious [5-7]. Peregocetus pacificus gen. et sp. nov. is a new protocetid cetacean discovered in middle Eocene (42.6 mya) marine deposits of coastal Peru, which constitutes the first indisputable quadrupedal whale record from the Pacific Ocean and the Southern Hemisphere. Preserving the mandibles and most of the postcranial skeleton, this unique four-limbed whale bore caudal vertebrae with bifurcated and anteroposteriorly expanded transverse processes, like those of beavers and otters, suggesting a significant contribution of the tail during swimming. The fore- and hind-limb proportions roughly similar to geologically older quadrupedal whales from India and Pakistan, the pelvis being firmly attached to the sacrum, an insertion fossa for the round ligament on the femur, and the retention of small hooves with a flat anteroventral tip at fingers and toes indicate that Peregocetus was still capable of standing and even walking on land. This new record from the southeastern Pacific demonstrates that early quadrupedal whales crossed the South Atlantic and nearly attained a circum-equatorial distribution with a combination of terrestrial and aquatic locomotion abilities less than 10 million years after their origin and probably before a northward dispersal toward higher North American latitudes. VIDEO ABSTRACT.

Comparative hindlimb bone morphology in noctilionid fisher bats (Chiroptera: Noctilionidae), with emphasis onNoctilio leporinuspostnatal development

AbstractThe hindlimbs allow bats to attach to the mother from birth, and roost during independent life. Despite the great morphological diversity in Chiroptera, the hindlimbs morphology and its postnatal development have been poorly studied. Postnatal development of hindlimbs inNoctilio leporinusis described, further comparing the morphology of adults with that ofNoctilio albiventrisand previously reported species (Desmodus rotundus,Artibeus lituratus,Molossus molossus). The ossification ending sequence at autopodium elements ofN. leporinusdoes not follow the distal to proximal directional sequence described forD. rotundus, exhibiting a heterochronic delayed ossification ending for the digits ofN. leporinusregarding other hindlimb elements, associated with the bigger relative autopodium size of this fisher bat regarding other bat species. Noctilionid bats share the same adult hindlimb bone morphology, except for differences at hindlimb proportions and calcar ossification degree. There are differences in the number and position of bony processes, slots and sesamoids of adult noctilionid fisher bats regarding previously reported species; most differences are concentrated at the autopodium and are related to an increased surface for muscular insertion and the structural support of claws. These facts seem to be closely associated with functional demands of the feeding strategy of noctilionid fisher bats.

Reinterpretation of a previously described Jehol bird clarifies early trophic evolution in the Ornithuromorpha.

STM35-3 from the Yixian Formation is the only Early Cretaceous ornithuromorph preserving direct evidence of granivory. The crop contains numerous seeds and the preservation of gastroliths presumably within the ventriculus indicates this diet was paired with the presence of a gastric mill as in living granivorous birds. STM35-3 was originally referred to Hongshanornis longicresta, member of a diverse clade of small, basal ornithuromorphs with elongate hindlimbs known as the Hongshanornithidae. Hindlimb proportions suggest that hongshanornithids were wading birds, an ecological inference somewhat in conflict with direct evidence suggesting Hongshanornis fed on seeds. However, close inspection of STM35-3 reveals that the specimen represents a new species not closely related to hongshanornithids, distinguished by large forelimbs that exceed the length of the hindlimbs, robust and narrow coracoids, and a delicate edentulous rostrum. By contrast, all hongshanornithids have hindlimbs that far exceed the length of the forelimbs, coracoids with wide sternal margins, and small teeth throughout the upper and lower jaws. Reinterpretation of this new taxon, Eogranivora edentulata gen. et sp. nov, helps to clarify trophic driven patterns of tooth loss within the Ornithuromorpha. Apparent loss of the hallux may represent the first such occurrence in a Mesozoic bird and suggests a highly terrestrial lifestyle.

The earliest bird-line archosaurs and the assembly of the dinosaur body plan.

The relationship between dinosaurs and other reptiles is well established, but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies. The closest extinct relatives of dinosaurs either have highly derived morphologies or are known from poorly preserved or incomplete material. Here we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch. The anatomy of T. rhadinus provides key information that unites several enigmatic taxa from across Pangaea into a previously unrecognized clade, Aphanosauria. This clade is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia. We demonstrate that several anatomical features long thought to characterize Dinosauria and dinosauriforms evolved much earlier, soon after the bird-crocodylian split, and that the earliest avemetatarsalians retained the crocodylian-like ankle morphology and hindlimb proportions of stem archosaurs and early pseudosuchians. Early avemetatarsalians were substantially more species-rich, widely geographically distributed and morphologically diverse than previously recognized. Moreover, several early dinosauromorphs that were previously used as models to understand dinosaur origins may represent specialized forms rather than the ancestral avemetatarsalian morphology.

The effects of a skeletal muscle titin mutation on walking in mice.

Titin contributes to sarcomere assembly, muscle signaling, and mechanical properties of muscle. The mdm mouse exhibits a small deletion in the titin gene resulting in dystrophic mutants and phenotypically normal heterozygotes. We examined the effects of this mutation on locomotion to assess how, and if, changes to muscle phenotype explain observed locomotor differences. Mutant mice are much smaller in size than their siblings and gait abnormalities may be driven by differences in limb proportions and/or by changes to muscle phenotype caused by the titin mutation. We quantified differences in walking gait among mdm genotypes and also determined whether genotypes vary in limb morphometrics. Mice were filmed walking, and kinematic and morphological variables were measured. Mutant mice had a smaller range of motion at the ankle, shorter stride lengths, and shorter stance duration, but walked at the same relative speeds as the other genotypes. Although phenotypically similar to wildtype mice, heterozygous mice frequently exhibited intermediate gait mechanics. Morphological differences among genotypes in hindlimb proportions were small and do not explain the locomotor differences. We suggest that differences in locomotion among mdm genotypes are due to changes in muscle phenotype caused by the titin mutation.

An approach to scoring cursorial limb proportions in carnivorous dinosaurs and an attempt to account for allometry.

From an initial dataset of 53 theropod species, the general relationship between theropod lower-leg length and body mass is identified. After factoring out this allometric relationship, theropod hindlimb proportions are assessed irrespective of body mass. Cursorial-limb-proportion (CLP) scores derived for each of the considered theropod taxa offer a measure of the extent to which a particular species deviates in favour of higher or lower running speeds. Within the same theropod species, these CLP scores are found to be consistent across multiple adult specimens and across disparate ontogenetic stages. Early theropods are found to have low CLP scores, while the coelurosaurian tyrannosauroids and compsognathids are found to have high CLP scores. Among deinonychosaurs, troodontids have consistently high CLP scores, while many dromaeosaur taxa, including Velociraptor and Deinonychus, have low CLP scores. This indicates that dromaeosaurs were not, overall, a particularly cursorily adapted group. Comparisons between the CLP scores of Tyrannosaurus and specimens referred to the controversial genus Nanotyrannus indicate a strong discrepancy in cursorial adaptations, which supports the legitimacy of Nanotyrannus and the previous suggestions of ecological partitioning between Nanotyrannus and the contemporaneous Tyrannosaurus.

A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada

ABSTRACTAn articulated, 1.5 m long skeleton of a juvenile Chasmosaurus, lacking only the front limbs, pectoral girdles, and terminal caudal vertebrae, was collected from the Dinosaur Park Formation in Dinosaur Provincial Park, Alberta. The short, tall skull has a narrow frill that lacks a posterior embayment. Many of the cranial bones are co-ossified in spite of the small size of the specimen. The nasals form an incipient horncore, and the short, knob-like postorbital horncore lacks sinuses. The palpebral is not fused to the rest of the skull. The frontal fontanelle is keyhole-shaped. The triangular squamosal extends to the back of the parietals. Epiossifications are lacking, although the squamosal margin is thick and scalloped. The parietal has a pronounced midline sagittal crest. Parietal fenestrae, if present, would have been narrow and elongate. There are only 18 maxillary tooth positions. The syncervical comprises three co-ossified, but distinct vertebrae. Anterior caudal vertebrae support unfused caudal ribs. Ossified tendons in the neck, trunk, and sacrum do not extend into the tail. Hind limb proportions are comparable to those of adult ceratopsids. The pedal unguals are distally acute. Skin impressions are similar to those of mature chasmosaurines. Phylogenetic analysis, if all characters are coded as they are seen, suggests that the specimen is a basal chasmosaurine. When size or age dependent characters are recoded as ‘?,’ the specimen groups with other Chasmosaurus. These characters should only be used in phylogenetic analyses when all specimens are mature.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Currie, P. J., R. B. Holmes, M. J. Ryan, and C. Coy. 2016. A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1048348.

Convex-hull mass estimates of the dodo (Raphus cucullatus): application of a CT-based mass estimation technique

The external appearance of the dodo (Raphus cucullatus, Linnaeus, 1758) has been a source of considerable intrigue, as contemporaneous accounts or depictions are rare. The body mass of the dodo has been particularly contentious, with the flightless pigeon alternatively reconstructed as slim or fat depending upon the skeletal metric used as the basis for mass prediction. Resolving this dichotomy and obtaining a reliable estimate for mass is essential before future analyses regarding dodo life history, physiology or biomechanics can be conducted. Previous mass estimates of the dodo have relied upon predictive equations based upon hind limb dimensions of extant pigeons. Yet the hind limb proportions of dodo have been found to differ considerably from those of their modern relatives, particularly with regards to midshaft diameter. Therefore, application of predictive equations to unusually robust fossil skeletal elements may bias mass estimates. We present a whole-body computed tomography (CT) -based mass estimation technique for application to the dodo. We generate 3D volumetric renders of the articulated skeletons of 20 species of extant pigeons, and wrap minimum-fit ‘convex hulls’ around their bony extremities. Convex hull volume is subsequently regressed against mass to generate predictive models based upon whole skeletons. Our best-performing predictive model is characterized by high correlation coefficients and low mean squared error (a = − 2.31, b = 0.90, r2 = 0.97, MSE = 0.0046). When applied to articulated composite skeletons of the dodo (National Museums Scotland, NMS.Z.1993.13; Natural History Museum, NHMUK A.9040 and S/1988.50.1), we estimate eviscerated body masses of 8–10.8 kg. When accounting for missing soft tissues, this may equate to live masses of 10.6–14.3 kg. Mass predictions presented here overlap at the lower end of those previously published, and support recent suggestions of a relatively slim dodo. CT-based reconstructions provide a means of objectively estimating mass and body segment properties of extinct species using whole articulated skeletons.

Morphology and motion: hindlimb proportions and swing phase kinematics in terrestrially locomoting charadriiform birds.

Differing limb proportions in terms of length and mass, as well as differences in mass being concentrated proximally or distally, influence the limb's moment of inertia (MOI), which represents its resistance to being swung. Limb morphology - including limb segment proportions - thus probably has direct relevance for the metabolic cost of swinging the limb during locomotion. However, it remains largely unexplored how differences in limb proportions influence limb kinematics during swing phase. To test whether differences in limb proportions are associated with differences in swing phase kinematics, we collected hindlimb kinematic data from three species of charadriiform birds differing widely in their hindlimb proportions: lapwings, oystercatchers and avocets. Using these three species, we tested for differences in maximum joint flexion, maximum joint extension and range of motion (RoM), in addition to differences in maximum segment angular velocity and excursion. We found that the taxa with greater limb MOI - oystercatchers and avocets - flex their limbs more than lapwings. However, we found no consistent differences in joint extension and RoM among species. Likewise, we found no consistent differences in limb segment angular velocity and excursion, indicating that differences in limb inertia in these three avian species do not necessarily underlie the rate or extent of limb segment movements. The observed increased limb flexion among these taxa with distally heavy limbs resulted in reduced MOI of the limb when compared with a neutral pose. A trade-off between exerting force to actively flex the limb and potential savings by a reduction of MOI is skewed towards reducing the limb's MOI as a result of MOI being in part a function of the radius of gyration squared. Increased limb flexion is a likely means to lower the cost of swinging the limbs.

A new specimen of the Early Cretaceous birdHongshanornis longicresta: insights into the aerodynamics and diet of a basal ornithuromorph

The discovery of Hongshanornis longicresta, a small ornithuromorph bird with unusually long hindlimb proportions, was followed by the discovery of two closely related species, Longicrusavis houi and Parahongshanornis chaoyangensis. Together forming the Hongshanornithidae, these species reveal important information about the early diversity and morphological specialization of ornithuromorphs, the clade that contains all living birds. Here we report on a new specimen (DNHM D2945/6) referable to Hongshanornis longicresta that contributes significant information to better understand the morphology, trophic ecology, and aerodynamics of this species, as well as the taxonomy of the Hongshanornithidae. Most notable are the well-preserved wings and feathered tail of DNHM D2945/6, which afford an accurate reconstruction of aerodynamic parameters indicating that as early as 125 million years ago, basal ornithuromorphs had evolved aerodynamic surfaces comparable in size and design to those of many modern birds, and flight modes alike to those of some small living birds.

Chicken-sized oviraptorid dinosaurs from central China and their ontogenetic implications

Oviraptorids are a group of specialized non-avian theropod dinosaurs that were generally one to 8m in body length. New specimens of baby oviraptorids from the Late Cretaceous of Henan Province are some of the smallest individuals known. They include diagnostic characters such as the relative position of the antorbital fenestra and the external naris, distinct opening in the premaxilla anteroventral to the external naris, antorbital fossa partly bordered by premaxilla posterodorsally, lacrimal process of premaxilla does not contact the anterodorsal process of the lacrimal, parietal almost as long as frontal; in dorsal view, posterior margin forms a straight line between the postzygapophyses in each of the fourth and fifth cervicals; femur longer than ilium. They also elucidate the ontogenetic processes of oviraptorids, including fusion of cranial elements and changes in relative body proportions. Hind limb proportions are constant in oviraptorids, regardless of absolute body size or ontogenetic stage. This suggests a sedentary lifestyle that did not involve the pursuit of similar-sized prey. The functional implications for bite force and therefore dietary preferences are better understood through the study of such small animals. The comparison of the measurements of 115 skeletons indicates that oviraptorids maintain their hind limb proportions regardless of ontogenetic stage or absolute size, which is a pattern seen more commonly in herbivores than in carnivores. This may weakly support the hypothesis that oviraptorids are herbivores rather than active carnivores.