Postcranial Morphology Research Articles

Gliding toward an understanding of the origin of flight in bats.

Bats are the only mammals capable of powered flight and have correspondingly specialized body plans, particularly in their limb morphology. The origin of bat flight is still not fully understood due to an uninformative fossil record but, from the perspective of a functional transition, it is widely hypothesized that bats evolved from gliding ancestors. Here, we test predictions of the gliding-to-flying hypothesis of the origin of bat flight by using phylogenetic comparative methods to model the evolution of forelimb and hindlimb traits on a dataset spanning four extinct bats and 231 extant mammals with diverse locomotor modes. Our results reveal that gliders exhibit adaptive trait optima (1) toward relatively elongate forelimbs that are intermediate between those of bats and non-gliding arborealists, and (2) toward relatively narrower but not longer hindlimbs that are intermediate between those of non-gliders and bats. We propose an adaptive landscape based on limb length and width optimal trends derived from our modeling analyses. Our results support a hypothetical evolutionary pathway wherein glider-like postcranial morphology precedes a bat-like morphology adapted to powered-flight, setting a foundation for future developmental, biomechanical, and evolutionary research to test this idea.

Oldest record of a crown anomaluroid rodent from sub-Saharan Africa: a new genus and species from the early Oligocene Topernawi formation of northern Kenya

ABSTRACT Anomaluroid rodents (i.e. Anomaluridae + Zenkerellidae) have a long evolutionary history in Africa dating back to at least the middle Eocene, but Palaeogene fossil members of the anomaluroid crown group have never been found south of the Sahara. Here, we describe the oldest crown anomaluroid from sub-Saharan Africa, Eliwourus topernawiensis (new genus and species) from the early Oligocene Topernawi Formation of northern Kenya. Bayesian phylogenetic tip-dating analysis of a combined molecular-morphological dataset places ~29.5 Ma Eliwourus as an advanced stem anomalurid, and suggests that crown Anomaluridae originated ~28.2 Ma. The gliding behaviour seen in all crown anomalurids had, therefore, likely evolved before the close of the early Oligocene. Bayesian geocoordinates analysis places the origin of crown Anomaluroidea (~47.2 Ma) in northern Africa, and identifies a stem anomalurid dispersal into equatorial eastern Africa in the latest Eocene or earliest Oligocene. We present the first quantitative analysis of the pace of anomaluroid dental evolution and confirm a remarkably slow or bradytelic rate of phenotypic change, despite significant transformations in postcranial morphology related to the evolution of gliding behaviour during the same interval. The Topernawi area was evidently sufficiently forested during the early Oligocene to support both arboreal rodents and primates.

The postcranial anatomy and osteohistology of Terrestrisuchus gracilis (Archosauria, Crocodylomorpha) from the Late Triassic of Wales

AbstractThe earliest crocodylomorphs, known as non‐crocodyliform crocodylomorphs, first appeared during the Late Triassic. In contrast to extant crocodylians, which are all semi‐aquatic, early crocodylomorphs represent terrestrial taxa with a fully erect posture and in most cases a small body size. Their gracile skeletons suggest an active mode of life, possibly similar to contemporaneous, bipedal theropod dinosaurs. Despite this remarkable body plan, the postcranial morphology of early crocodylomorphs has rarely been documented in detail, restricting our ability to infer aspects of their functional morphology and evolution. Here, we provide a detailed description of the postcranium of Terrestrisuchus gracilis, a small‐bodied crocodylomorph from the Late Triassic of Pant‐y‐Ffynnon Quarry (southern Wales, UK), including a description of long bone tissues based on histological thin sections. Almost all elements of the postcranial skeleton have been preserved. The skeleton of Terrestrisuchus gracilis is highly gracile, even for a non‐crocodyliform crocodylomorph. Osteological correlates of the appendicular skeleton suggest that Terrestrisuchus gracilis had a digitigrade, quadrupedal posture. A quantitative analysis of limb robustness corroborates that Terrestrisuchus gracilis was a quadruped. Histological analysis suggests that all sampled specimens were skeletally immature and had fast growth at the time of death, as indicated by the lack of an external fundamental system and the predominance of fibrolamellar bone. The bone tissue is similar to that recently described for Saltoposuchus connectens and certain non‐crocodylomorph pseudosuchians, but differs from Hesperosuchus agilis and crocodyliforms, in which parallel‐fibred bone is more prevalent.

The cranial and postcranial morphology of Hutchemys rememdium and its impact on the phylogenetic relationships of Plastomenidae (Testudinata, Trionychidae)

Hutchemys rememdium is a poorly understood softshell turtle (Trionychidae) from the mid Paleocene of the Williston Basin of North America previously known only from postcranial remains. A particularly rich collection of previously undescribed material from the Tiffanian 4 North American Land Mammal Age (NALMA) of North Dakota is here presented consisting of numerous shells that document new variation, some non-shell postcrania, and cranial remains, which are described based on 3D models extracted from micro-CT data. Although the observed shell variation weakens previously noted differences with the younger species Hutchemys arctochelys from the Clarkforkian NALMA, the two taxa are still recognized as distinct. Parsimony and Bayesian phylogenetic analyses reaffirm the previously challenged placement of Hutchemys rememdium within the clade Plastomenidae, mostly based on novel observations of cranial characters made possible by the new material and the micro-CT data. The new topology supports the notion that the well-ossified plastron of plastomenids originated twice in parallel near the Cretaceous/Paleogene boundary, once in the Hutchemys lineage and once in the Gilmoremys/Plastomenus lineage. Hutchemys rememdium is notable for being the only documented species of trionychid in the mid Paleocene of the Williston Basin. The presence of multiple individuals in a carbonaceous claystone indicates this taxon lived in swamps and lakes and its expanded triturating surface suggests it had a durophagous diet.

The postcranial variability of Quaternary European rhinoceroses: the case study of Stephanorhinus hundsheimensis from the Middle Pleistocene site of Contrada Monticelli (Apulia, southern Italy)

ABSTRACT Five rhinoceros species, mainly distinguishable through cranial, mandibular and dental morphology, were recognized during the Quaternary across Europe. The postcranial morphology of these taxa is quite variable, with strong superposition among species, especially between Stephanorhinus etruscus and Stephanorhinus hundsheimensis. Here, the complete sample including 25 postcranial bones from the early Middle Pleistocene site of Contrada Monticelli (Apulia, southern Italy) is described and compared through morphological and biometric analyses. A few bones, in addition to cranial and mandibular remains from this site, have been previously referred to Stephanorhinus hundsheimensis. We explored the morphological variability of Stephanorhinus hundsheimensis from Contrada Monticelli against the diagnostic characters described in the literature. The size variation of the Contrada Monticelli sample is also investigated, through a comparison with other Quaternary European rhinoceros samples. Our results indicate a wide morphological variability with several distinct characters and a strong morphological affinity between Stephanorhinus etruscus and S. hundsheimensis. Our results suggest that Stephanorhinus hundsheimensis from Contrada Monticelli is a species with a high degree of intraspecific variability, possibly a hybrid population or a population including two morphotypes of the same species.

A review of Palaeogiraffa (Giraffidae, Mammalia) from the Vallesian of the Eastern Mediterranean

Palaeogiraffa is a poorly understood giraffid genus from the Vallesian of Axios Valley (Northern Greece), Turkish Thrace and Central Turkey. The Axios Valley remains come from three non-contemporaneous Vallesian faunas from the localities: Pentalophos, Ravin de la Pluie, and Xirochori, whereas the Turkish remains come from the Vallesian faunas of Middle Sinap, Yulafli, and Küçükçekmece. Remains from Pentalophos and Ravin de la Pluie were described as congeneric with the Iberian Deccenatherium, although they were later attributed to a new, distinct genus known by three different species: Palaeogiraffa macedoniae, Palaeogiraffa pamiri, and Palaeogiraffa major. The type species of the genus, Pg. macedoniae, was based on the most abundant Pentalophos material, while the rest of the species was established mainly on size difference criteria. Here we provide a review of the Palaeogiraffa material in order to (i) test its validity, (ii) re-discuss hypotheses about the genus phylogenetic relationships with other Late Miocene giraffids, and (iii) re-explore intrageneric diversity and number of recognized species based on the available Eastern Mediterranean samples. We confirm Palaeogiraffa as a distinct genus from other Late Miocene giraffids based on its unique proportions, as well as its dental and postcranial morphology. Furthermore, we endorse the likelihood of Palaeogiraffa being phylogenetically linked to the sivatherine lineage, based mainly on its dental and metatarsal morphological features. The generic attribution of specimens from Xirochori, Ravin de la Pluie, Middle Sinap, Yulafli and Küçükçekmece to Palaeogiraffa is adequately supported by the present data. Nevertheless, the recognition of three species is more open to discussion, though they should be retained until more material is available.

The postcranial skeleton of Teyujagua paradoxa (Reptilia: Archosauromorpha) from the early Triassic of South America.

Teyujagua paradoxa is a remarkable early archosauromorph from the Lower Triassic Sanga do Cabral Formation, Brazil. The species was originally described from an almost complete skull and a few associated cervical vertebrae, and no further postcranial elements were known at that time. Additional fieldwork in the Sanga do Cabral Formation, however, was successful in recovering a fairly complete postcranial skeleton attributable to the holotype. Here, we describe this new postcranial material, which is composed of cervical, dorsal, sacral and caudal vertebrae, limbs, pectoral and pelvic girdles, ribs, and gastralia. The description of its postcranial skeleton makes T. paradoxa one of the best-known early-diverging archosauromorphs. The cladistic analysis performed after the scoring of postcranial data recovered T. paradoxa in the same position initially described, close to the node that defines the Archosauriformes. Teyujagua paradoxa shares morphological features with representatives of early-diverging archosauromorphs and archosauriforms, with certain traits demonstrating a mosaic of plesiomorphic and apomorphic character states. We also performed partitioned morphospace and disparity analysis to elucidate the morphological disparity and evolutionary patterns among archosauromorphs. Teyujagua paradoxa occupies a notable position, suggesting an intermediate morphology between early archosauromorphs and proterosuchids. Disparity estimates highlighted Pseudosuchia and Avemetatarsalia as having the highest median disparity, reflecting their diverse cranial and postcranial morphologies, respectively. These findings offer valuable insights into archosauromorph macroevolution and adaptation.

The morphology and histology of a juvenile Sinokannemeyeria from the Middle Triassic Ermaying Formation of Shanxi, North China

Kannemeyeriiformes were dominated tetrapods in the Middle Triassic terrestrial faunae of China. Although abundant materials of Sinokannemeyeria have been collected, their postcranial morphology information is not well studied, especially the juveniles. This paper presents a description of an articulated Sinokannemeyeria skeleton from the Middle Triassic Ermaying Formation and reports the histological microstructure of its femur. This specimen represents a late-stage juvenile based on the histological information. For the first time, this specimen offers insights into the postcrania information of juvenile Sinokannemeyeria.©2023 China Geology Editorial Office.

Limited convergence in the postcranium of aquatic Crocodylomorpha

AbstractThalattosuchia (Early Jurassic to Early Cretaceous) and Dyrosauridea (Late Cretaceous to Early Eocene) are crocodylomorph archosaurs which diversified in fluvial and marine environments and endured extinction events (i.e. Jurassic–Cretaceous boundary for Thalattosuchia; Cretaceous–Palaeogene for Dyrosauridea). Their postcrania remain globally undervalued in anatomical descriptions and diagnoses, shrouding the locomotive adaptations that possibly underpinned their radiations and longevity. We thoroughly surveyed the postcranial morphology of Dyrosauridea and Thalattosuchia, recreated their girdles in three‐dimensions using tens of high‐precisions 3D scans, and analysed their shape using geometric morphometrics. Dyrosauridea and Thalattosuchia have clearly distinct postcrania, even when found within similar environments, suggesting the existence of clade‐specific features limiting the strength of evolutionary convergence. Moreover, the range of postcranial morphologies evolved by dyrosaurids and thalattosuchians is large compared to extant crocodylians, making the latter unsatisfactory functional analogues for every group of extinct crocodylomorphs. Our work reveals the previously unsuspected potential of postcranial anatomy as an abundant source of phylogenetic and taxonomic characters to assess the relationships within Crocodylomorpha. Incorporation of postcranial anatomy therefore appears crucial to fully assess the ecology, disparity, and relationships of crocodylomorphs.

Tree-climbing in search of fruit: an ancient arboreal marsupial megafrugivore from the Miocene of Australia

Diprotodontids, a group of large-bodied wombat-like marsupial herbivores, were broadly distributed in Australasian Cenozoic deposits. While most diprotodontids were terrestrial quadrupeds and are often compared to placental herbivores like rhinoceros and hippopotamuses, the zygomaturine diprotodontid Nimbadon lavarackorum, based on its post-cranial morphology, is thought to have occupied the treetops. Understanding the dietary ecology of N. lavarackorum during the Miocene can help clarify potential motivations for an arboreal lifestyle. Here, we conducted dental microwear texture analysis (DMTA) and stable isotope analysis (SIA) of N. lavarackorum specimens from the Riversleigh World Heritage Area and compared them to analogous extant mammals to assess the likelihood that these tree-dwelling marsupials occupied a unique ecological niche during the Miocene in Australia—arboreal megafrugivores. The DMTA of N. lavarackorum (i.e., low anisotropy and high complexity) is most similar to extant mammals that include a high proportion of fruit in their diet and is inconsistent with and statistically distinct from obligate folivores. Stable carbon isotopes of N. lavarackorum also indicate the consumption of C3 food sources, consistent with the consumption of 13C enriched fruit in a C3 forest environment. Fruits may have been a motivation for this ca 70 kg marsupial moving into or staying in the treetops—an ecological niche that is currently unoccupied in Australia today.Larisa DeSantis [larisa.desantis@vanderbilt.edu], Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA; Michael Archer [m.archer@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia; Karen Black [k.black@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia; Suzanne Hand [s.hand@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia; Vera Korasidis [vera.korasidis@unimelb.edu.au], Department of Geography, Earth and Atmospheric Sciences, University of Melbourne, Parkville, VIC, 3010, Australia.

Migratory behavior in the enigmatic Late Pleistocene bovid Rusingoryx atopocranion

For many animals, migration is an important strategy for navigating seasonal bottlenecks in resource availability. In the savannas of eastern Africa, herds of grazing animals, including blue wildebeest (Connochaetes taurinus), Thomson's gazelle (Eudorcas thomsonii), and plains zebra (Equus quagga), travel hundreds of kilometers annually tracking suitable forage and water. However, we know nearly nothing about migration among the extinct species that often dominated Late Pleistocene communities. Using serially sampled 87Sr/86Sr and δ13C, we characterize the prehistoric movement and diet of the enigmatic wildebeest Rusingoryx atopocranion from two localities (Karungu and Rusinga Island) in the Lake Victoria Basin of western Kenya. We find clear evidence for migration in all four individuals studied, with three 87Sr/86Sr series demonstrating high-amplitude fluctuations and all falling outside the modeled isoscape 87Sr/86Sr ranges of the fossil localities from which they were recovered. This suggests that R. atopocranion exhibited migratory behavior comparable to that of its closest living relatives in the genus Connochaetes. Additionally, individuals show seasonally-variable δ13C, with a higher browse intake than modern and fossil eastern African alcelaphins indicating behavioral differences among extinct taxa otherwise unrecognized by comparison with extant related species. That this species was highly migratory aligns with its morphology matching that of an open grassland migrant: it had open-adapted postcranial morphology along with a unique cranial structure convergent with lambeosaurine dinosaurs for calling long distances. We further hypothesize that its migratory behavior may be linked to its extinction, as R. atopocranion disappears from the Lake Victoria Basin fossil sequence coincident with the refilling of Lake Victoria sometime after 36 ka, potentially impeding its past migratory routes. This study characterizes migration in an extinct eastern African species for the first time and shapes our ecological understanding of this unique bovid and the ecosystems in which Middle Stone Age humans lived.

New postcranial remains of ground sloths (Xenarthra, Folivora, Mylodontidae) from Southern Brazil

Diagnoses of Mylodontidae species are generally based on skull, mandibular, and tooth characteristics, and rarely on postcranial morphology, due to the lack of postcranial material associated with the cranial material. The studies of postcranial anatomy have generally a biomechanical focus and reflect a set of functions of skeletal structures, but their interpretation in phylogenetic analysis is still limited. In Pleistocene deposits of Rio Grande do Sul State, Brazil, an important set of postcranial specimens was collected, belonging to Mylodontidae. They were morphologically and morphometrically analyzed, allowing us to observe some diagnostic characters such as the humeral entepicondylar foramen and crests, shape of the radial shaft, angle of distal articulation of the tibia, as well as the angle of proximal articulation of the astragalus. The material was also compared with specimens from other South American localities. Most of the remains were assigned to Glossotherium robustum and Lestodon armatus. In addition, a new Scelidotheriinae was recorded for Rio Grande do Sul State. The study indicated significant differences in the postcranial morphology, which allowed the recognition of some specific diagnostic characters. Keywords: Mylodontinae, Scelidotheriinae, hindlimb, forelimb, Pleistocene, Rio Grande do Sul.

Some aspects of the postcranial morphology of the Ural-Mugodzhar population in the Late Bronze Age

The paper reports on the osteometric data of skeletons from the burials of the Kozhumberdy group of the Late Bronze Age Alakul Culture (Southern Ural). The research is aimed to reveal the character of the variability of osteometric features of the sample group and its comparison with synchronous groups of the steppe zone of Eurasia. Twenty-four male and seventeen female skeletons were investigated. Taking into account the poor preser-vation of the material, a new method of identification of sex, developed by I.M. Sineva, was applied. The results of the study of the series by statistical methods (principal component analysis, nonparametric Mann — Whitney cri-terion) are presented. A high degree of morphological diversity of the variants of the skeletal development under the dominance of a rather gracile osteological complex within the Bronze Age of the steppe Eurasia is observed. Several individuals, characterized by the increased size of the skeleton, are distinguished. The similarity of the main part of the studied sample group with the synchronous population of the steppe-forest-steppe zone of the Cis-Urals and Upper Ob Basin is revealed. At the same time, the Kozhumberdy group morphologically differs from the agricultural population of the Bronze Age in Central Asia. These results indicate the main direction of the mor-phological links of the Kozhumberdy group of the Alakul Culture with the sample groups of the Sintashta Culture of the Cis-Urals and Andronovo Culture of Western Siberia. There is also present an insignificant component as-sociated with the Early Bronze Age population of the steppe Volga-Ural region (the Yamnaya Culture). The as-sumption made previously on the basis of the study of craniological materials about a single morphological basis for the formation of the population of the Alakul and Srubnaya Cultures of the Bronze Age is not confirmed. The main component in the formation of the physical appearance of the Srubnaya population is the local Volga-Ural population. As the morphological basis for the formation of the Alakul Ural-Mugodzhar group we consider the Sintashta population of the Cis-Urals.

Main anatomical characteristics of the hominin fossil humeri from the Sima de los Huesos Middle Pleistocene site, Sierra de Atapuerca, Burgos, Spain: An update.

Some of the Sima de los Huesos (SH) humeri have been previously studied and described elsewhere. Here we present an updated inventory and a review of the specimens recovered to the present day. The morphological key traits of the adult and subadult specimens are described, discussed, and illustrated. The SH humeri share with Neandertals many traits usually considered to be Neandertal specializations, thus, most of this morphological pattern is not exclusive to them. The variation found within fossil samples stresses the frequential nature of all these traits and in the specific case of the SH humeri, most of the traits considered as phylogenetically relevant are retained by their descendants, the Neandertals. Some traits are plesiomorphic for the entire genus Homo or are present in European hominins since the early Pleistocene. Finally, some other traits display high variability within the SH sample or different hominin samples and are of uncertain phylogenetic value. Altogether, this evidence is consistent with the hypothesis based on the overall cranial and postcranial morphology that the SH hominins are a sister group to the later Neandertals.

New Fossil Giant Panda Relatives (Ailuropodinae, Ursidae): A Basal Lineage of Gigantic Mio-Pliocene Cursorial Carnivores

Among the fossil members of the giant panda subfamily of ursid carnivorans, Ailuropodinae, one group of species is of giant size, those of Indarctos. Indarctos species have some dental resemblances to and may be closely related to Agriotherium, although there are other clear differences between these taxa, and no known species has definitive shared derived traits that could link these two genera. Here we describe a rich suite of fossil material from both North America and eastern Asia, all belonging to a new genus, Huracan, which possesses characters shared with both Agriotherium and Indarctos but also has diagnostic autapomorphies. The new taxon was distributed widely in the Holarctic during the latest Miocene, including at least four species: the type species Huracan schneideri (previously Agriotherium schneideri) from the latest Hemphillian (Hh4) and possibly early Blancan North American Land Mammal “Ages” (NALMAs), North America; H. coffeyi from the early Late Hemphillian (Hh3) NALMA, North America; H. qiui, sp. nov., from the Baodean Asian Land Mammal “Age” (ALMA), northern China; and H. roblesi from the MN13 zone (latest Miocene–earliest Pliocene) of Spain. Huracan is the nearest sister taxon to Agriotherium, the latter herein considered to be an ailuropodine (in the tribe Agriotheriini) rather than a hemicyonid, and the common ancestor of both genera evolved from Indarctos (with resultant paraphyly of that taxon) or another Indarctos-like ailuropodine bear, likely in eastern Asia. The dentitions of Huracan and Agriotherium both are more specialised for carnivory than most Indarctos species, indicating a radiation of diverse ecological carnivores earlier in the history of the later-diverging, highly specialized herbivores in the giant panda lineage. Their postcranial morphology suggests that species in both genera (Huracan and Agriotherium) were more cursorial than species assigned to Indarctos, and thus well adapted to more open habitats. These derived traits may explain the worldwide replacement of Indarctos species by Huracan and Agriotherium species during the latest Miocene, in response to significant global cooling and expansion of C4 grasslands that occurred at that time.

Interspecific competition in ictitheres (Carnivora: Hyaenidae) from the Late Miocene of Eurasia

The present paper deals with the ecomorphological characteristics of two sympatric species of ictitheres: Ictitherium viverrinum Roth & Wagner, 1854 and Hyaenictitherium wongii (Zdansky, 1924) from the Late Miocene of the Eastern Mediterranean. These two species represent different taxonomic groups with allegedly distinct ecological roles. The values of 11 ecomorphological proxies were calculated using cranial and dental elements, in order to make an extensive comparison between them (body mass, bite force, canines’ and incisors’ bending strength, endocranial volume, relative rostral width, dental mesowear, intercuspid notches and carnassial vs grinding surfaces). The proxies show similar results for both species, pointing out that they had a similar ecological niche in the Late Miocene ecosystems. Carnivorans are usually in the top of the food chain, so the existence of two ecologically similar species in the same spatiotemporal range results in interspecific competition. This explains the geographical distinction of the two species with several localities being dominated by only one of the two (e.g. Samos for Hyaenictitherium Kretzoi, 1938 and Pikermi for Ictitherium Wagner, 1848). The reason for the prevalence of each genus can be associated with their postcranial morphology, as Hyaenictitherium has been proposed to be better adapted to chase hunting, because of its longer limbs, while Ictitherium is characterized by shorter and stouter limbs.

Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds.

Ichthyornis has long been recognized as a pivotally important fossil taxon for understanding the latest stages of the dinosaur-bird transition, but little significant new postcranial material has been brought to light since initial descriptions of partial skeletons in the 19th Century. Here, we present new information on the postcranial morphology of Ichthyornis from 40 previously undescribed specimens, providing the most complete morphological assessment of the postcranial skeleton of Ichthyornis to date. The new material includes four partially complete skeletons and numerous well-preserved isolated elements, enabling new anatomical observations such as muscle attachments previously undescribed for Mesozoic euornitheans. Among the elements that were previously unknown or poorly represented for Ichthyornis, the new specimens include an almost-complete axial series, a hypocleideum-bearing furcula, radial carpal bones, fibulae, a complete tarsometatarsus bearing a rudimentary hypotarsus, and one of the first-known nearly complete three-dimensional sterna from a Mesozoic avialan. Several pedal phalanges are preserved, revealing a remarkably enlarged pes presumably related to foot-propelled swimming. Although diagnosable as Ichthyornis, the new specimens exhibit a substantial degree of morphological variation, some of which may relate to ontogenetic changes. Phylogenetic analyses incorporating our new data and employing alternative morphological datasets recover Ichthyornis stemward of Hesperornithes and Iaceornis, in line with some recent hypotheses regarding the topology of the crownward-most portion of the avian stem group, and we establish phylogenetically-defined clade names for relevant avialan subclades to help facilitate consistent discourse in future work. The new information provided by these specimens improves our understanding of morphological evolution among the crownward-most non-neornithine avialans immediately preceding the origin of crown group birds.

Halibee fossil assemblages reveal later Pleistocene cercopithecins (Cercopithecidae: Primates) in the Middle Awash of Ethiopia

AbstractObjectivesThe goals of this study were to describe and interpret two new fossil assemblages of cercopithecin monkeys (n = 328), one from the Faro Daba beds (ca. 100,000 years) and the other one from the Chai Baro beds (>158,000 years old), in the Afar Rift of Ethiopia.Materials and MethodsWe describe the two assemblages and compare them to extant cercopithecin species and the smaller fossil assemblage from Asbole, Ethiopia (ca. 600 ka). We use a population‐based approach to the taxonomy given the unusually large number of specimens. Craniodental and postcranial anatomy are presented. Evidence of locomotor habitus is described and evaluated in a framework of hybridization and postcranial plasticity.ResultsWe attribute all cercopithecin specimens from both beds to cf. Chlorocebus and conclude that the Faro Daba and Chai Baro assemblages likely sample single species at each time horizon. Subtle differences between the two assemblages, mostly in postcranial morphology, are insufficient to justify separation at the species level.DiscussionThe large sample sizes and unique preservational aspects of these two assemblages open a new window into the recent evolution of guenons. Our data indicate that these fossil populations may be ancestral to the cercopithecins currently living in the Afar region of Ethiopia.

Royal knifefish generate powerful suction feeding through large neurocranial elevation and high epaxial muscle power.

Suction feeding in ray-finned fishes involves powerful buccal cavity expansion to accelerate water and food into the mouth. Previous XROMM studies in largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus) and channel catfish (Ictalurus punctatus) have shown that more than 90% of suction power in high performance strikes comes from the axial musculature. Thus, the shape of the axial muscles and skeleton may affect suction feeding mechanics. Royal knifefish (Chitala blanci) have an unusual postcranial morphology, with a ventrally flexed vertebral column and relatively large mass of epaxial muscle. Based on their body shape, we hypothesized that royal knifefish would generate high power strikes by utilizing large neurocranial elevation, vertebral column extension and epaxial shortening. As predicted, C. blanci generated high suction expansion power compared with the other three species studied to date (up to 160 W), which was achieved by increasing both the rate of volume change and the intraoral subambient pressure. The large epaxial muscle (25% of body mass) shortened at high velocities to produce large neurocranial elevation and vertebral extension (up to 41deg, combined), as well as high muscle mass-specific power (up to 800 W kg-1). For the highest power strikes, axial muscles generated 95% of the power, and 64% of the axial muscle mass consisted of the epaxial muscles. The epaxial-dominated suction expansion of royal knifefish supports our hypothesis that postcranial morphology may be a strong predictor of suction feeding biomechanics.

New data on the postcranial skeleton of the tapejarid Sinopterus from the Early Cretaceous Jehol Biota

ABSTRACT We reported a new skeleton of the tapejarid Sinopterus from the Jehol Biota, providing more additional information of the postcranial morphology, especially the anatomy of the tail, the pectoral and the pelvic girdles. The reduced tail is composed of nine caudal vertebrae, as a new evidence of the tail reduction of the azhdarchoids. An eminence is present on the posterior surface above the coracoidal crest, as the first record in the Jehol tapejarids, comparable with the modest coracoidal tubercle of the Brazilian tapejarids Caiuajara, Keresdrakon, and Tupandactylus, which implies a coexistence of the coracoidal crest and the coracoidal tubercle in the tapejarids. The pelvic girdle has an elongate pre-acetabular process, a hatchet-like postacetabular process, a medium-sized obturator foramen, and a kidney-shaped prepubic blade. The postacetabular process is unconstricted in the mid-shaft, and its terminus is subequal to the acetabulum in length, distinct from the more derived condition in the Brazilian tapejarids. This discovery sheds a new light on the evolution of the postcranial morphology in tapejarids and azhdarchoids.