A new specimen of large-bodied basal Enantiornithine Bohaiornis from the Early Cretaceous of China and the inference of feeding ecology in Mesozoic birds

The lacustrine deposits of the Yixian and Jiufotang Formations in the Early Cretaceous Jehol Group in the western Liaoning area of northeast China are well known for preserving feathered dinosaurs, primitive birds and mammals. Here we report a large basal bird, Jeholornis prima gen. et sp. nov., from the Jiufotang Formation. This bird is distinctively different from other known birds of the Early Cretaceous period in retaining a long skeletal tail with unexpected elongated prezygopophyses and chevrons, resembling that of dromaeosaurids, providing a further link between birds and non-avian theropods. Despite its basal position in early avian evolution, the advanced features of the pectoral girdle and the carpal trochlea of the carpometacarpus of Jeholornis indicate the capability of powerful flight. The dozens of beautifully preserved ovules of unknown plant taxa in the stomach represents direct evidence for seed-eating adaptation in birds of the Mesozoic era.

Enantionithine birds are the most blooming branch of early birds and have distinct diversities. A large number of enantionithine birds have been reported from the Early Cretaceous Jiufotang Formation in western Liaoning, China. Recently, we discovered a new eoenantiornithid bird from the Jiufotang Formation in Dapingfang Town, western Liaoning. A new eoenantiornithid bird, Dapingfangornis sentisorhinus gen. et sp. nov., is erected based on this complete skeleton with a skull. The new bird is distinguished from other known Mesozoic birds in a medium to small size, a distinct thorn-like process on the nasals, a sternum with a long and a short lateral processes. The thorn-like process on the nasal has not been discovered among known fossil birds, thus the discovery also provides new materials on the diversities of early birds.

Fossils of juvenile Mesozoic birds provide insight into the early evolution of avian development, however such fossils are rare. The analysis of the ossification sequence in these early-branching birds has the potential to address important questions about their comparative developmental biology and to help understand their morphological evolution and ecological differentiation. Here we report on an early juvenile enantiornithine specimen from the Early Cretaceous of Europe, which sheds new light on the osteogenesis in this most species-rich clade of Mesozoic birds. Consisting of a nearly complete skeleton, it is amongst the smallest known Mesozoic avian fossils representing post-hatching stages of development. Comparisons between this new specimen and other known early juvenile enantiornithines support a clade-wide asynchronous pattern of osteogenesis in the sternum and the vertebral column, and strongly indicate that the hatchlings of these phylogenetically basal birds varied greatly in size and tempo of skeletal maturation.

Extensive research on avian adaptive radiations has led to a presumption that beak morphology predicts feeding ecology in birds. However, this ecomorphological relationship has only been quantified in a handful of avian lineages, where associations are of variable strength, and never at a broad macroevolutionary scale. Here, we used shape analysis and phylogenetic comparative methods to quantify the relationships among beak shape, mechanical advantage, and two measures of feeding ecology (feeding behavior and semiquantitative dietary preferences) in a broad sample of modern birds, comprising most living orders. We found a complex relationship, with most variables showing a significant relationship with feeding ecology but little explanatory power. For example, diet accounts for less than 12% of beak shape variation. Similar beak shapes are associated with disparate dietary regimes, even when accounting for diet-feeding behavior relationships and phylogeny. Very few lineages optimize for stronger bite forces, with most birds exhibiting relatively fast, weak bites, even in large predatory taxa. The extreme morphological and behavioral flexibility of the beak in birds suggests that, far from being an exemplary feeding adaptation, avian beak diversification may have been largely contingent on trade-offs and constraints.

Ornithuromorpha is the most derived avian group in the Early Cretaceous, advanced members of which encompass all living birds (Neornithes). Here we report on a new basal ornithuromorph bird, Bellulia rectusunguis gen. et sp. nov., represented by a nearly complete skeleton from the Early Cretaceous Jehol Biota in northeastern China. A comprehensive phylogenetic analysis resolved the new taxon in a basal position that is only more derived than Archaeorhynchus and Jianchangornis among ornithuromorphs, increasing the morphological diversity of basal ornithuromorphs. The new specimen has a V-shaped furcula with a short hypocleidium, a feature otherwise known only in Schizooura among Cretaceous ornithuromorphs. We discuss the implications of the new taxon on the evolution of morphology of primitive ornithuromorphs, particularly of pectoral girdle, sternum and limb proportion pertaining to powered flight. The preserved gastroliths and pedal morphology indicate herbivory and lakeshore adaption for this new species. © 2015 The Linnean Society of London

A fish-eating enantiornithine bird with a gastric pellet composed of fish bones has recently been reported from the Lower Cretaceous Jiufotang Formation of Liaoning Province, northeastern China. Along with other discoveries, this specimen reveals that distinct features of modern avian digestive system were well established in those early birds. On the basis of a detailed anatomical study presented here, we show that this fish-eating enantiornithine bird represents a new taxon, Piscivorenantiornis inusitatus, gen. et sp. nov. The well-preserved elements of the skull, neck, sternum, and pelvis further enrich our understanding of the morphological diversity in early enantiornithines. Most notably, the cranial articular facet of the caudal cervical vertebra is dorsoventrally concave and mediolaterally convex, a feature otherwise unknown among other birds and with unclear functional significance. http://zoobank.org/urn:lsid:zoobank.org:pub:C87B5BE9-B378-414E-81F3-7FD4162795C4 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Wang, M., and Z. Zhou. 2017. A morphological study of the first known piscivorous enantiornithine bird from the Early Cretaceous of China. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1278702.

New geochronological constraints for the Lower Cretaceous Jiufotang Formation in Jianchang Basin, NE China, and their implications for the late Jehol Biota

Mesozoic remains of embryonic and early juvenile birds are rare. To date, a handful of in ovo embryos and early juveniles of enantiornithines from the Early Cretaceous of China and Spain and the Late Cretaceous of Mongolia and Argentina have comprised the entire published record of perinatal ontogenetic stages of Mesozoic birds. We report on the skeletal morphology of three nearly complete early juvenile avians from the renowned Early Cretaceous Yixian Formation of Liaoning Province in northeastern China. Evidence of the immaturity of these specimens is expressed in the intense grooving and pitting of the periosteal surfaces, the disproportionately small size of the sterna, and the relative size of the skull and orbits. Size notwithstanding, anatomical differences between these three specimens are minimal, leaving no basis for discriminating them into separate taxa. Numerous osteological synapomorphies indicate that they are euenantiornithine birds, the most diverse clade of Enantiornithes, but their identification as members of a particular euenantiornithine taxon remains unclear. Their early ontogenetic stage, however, provides important information about the postnatal development of this specious clade of Cretaceous birds. The presence of pennaceous wing feathers suggests that fledging occurred very early in ontogeny, thus supporting a precocial or highly precocial strategy for enantiornithine hatchlings. The morphology of these new early-stage juveniles is also significant in that they allow a better understanding of the homologies of several avian compound bones because the components of these skeletal compounds are preserved prior to their coossification. The general morphology of the wrist and ankle of these juveniles highlights once again the striking similarity between nonavian theropods and early birds.

In birds, parents adjust their feeding behaviour according to breeding duties, which ulti- mately may lead to seasonal adjustments in nutritional physiology and hematology over the breeding season. Although avian physiology has been widely investigated in captivity, few studies have inte- grated individual changes in feeding and physiological ecology throughout the breeding season in wild birds. To study relationships between feeding ecology and nutritional ecophysiology in Cory's shearwater Calonectris diomedea, we weighed and took blood samples from 28 males and 19 females during the pre-laying, egg-laying, incubation, hatching and chick-rearing periods of the breeding season. In addition, we fitted 6 birds with geolocators to track their foraging movements throughout the reproductive period. Thus, we examined individual changes in (1) nutritional condition (bio- chemistry metabolites); (2) oxygen carrying capacity (hematology); and (3) feeding areas and forag- ing effort (stable isotopes and foraging movements). Geolocators revealed a latitudinal shift in main feeding areas towards more southern and more neritic waters throughout the breeding season, which is consistent with the steady increase in δ 13 C signatures in the blood. Geolocators also showed a decrease in foraging effort from egg-laying to hatching, reflecting the activity decrease associated with incubation duties. Plasma metabolites, body mass and oxygen carrying capacity were associated with temporal changes in nutritional state and foraging effort in relation to recovery after migration, egg formation, fasting shifts during incubation and chick provisioning. This study shows that com- bining physiological and ecological approaches can help us understand the influence of breeding duties on feeding ecology and nutritional physiology in wild birds.

Paleozoic chondrichthyans had a large gape, numerous spike-like teeth, limited cranial kinesis, and a non-suspensory hyoid, suggesting a feeding mechanism dominated by bite and ram. Modern sharks are characterized by a mobile upper jaw braced by a suspensory hyoid arch that is highly kinetic. In batoids, the upper jaw is dissociated from the cranium permitting extensive protrusion of the jaws. Similar to actinopterygians, the evolution of highly mobile mandibular and hyoid elements has been correlated with extensive radiation of feeding modes in elasmobranchs, particularly that of suction. Modern elasmobranchs possess a remarkable variety of feeding modes for a group containing so few species. Biting, suction or filter-feeding may be used in conjunction with ram to capture prey, with most species able to use a combination of behaviors during a strike. Suction-feeding has repeatedly arisen within all recent major elasmobranch clades and is associated with a suite of morphological and behavioral specializations. Prey capture in a diverse assemblage of purported suction-feeding elasmobranchs is investigated in this study. Drop in water pressure measured in the mouth and at the location of the prey shows that suction inflow drops off rapidly with distance from the predator's mouth. Elasmobranchs specializing in suction-feeding may be limited to bottom associated prey and because of their small gape may have a diet restricted to relatively small prey. Behavior can affect performance and overcome constraints imposed by the fluid medium. Suction performance can be enhanced by proximity to a substrate or by decreasing distance from predator to prey using various morphological and/or behavioral characteristics. Benthic suction-feeders benefit by the increased strike radius due to deflection of water flow when feeding close to a substrate, and perhaps require less accuracy when capturing prey. Suction and ram-suction-feeding elasmobranchs can also use suction inflow to draw prey to them from a short distance, while ram-feeding sharks must accelerate and overtake the prey. The relationship between feeding strategy and ecology may depend in part on ecological, mechanistic or evolutionary specialization. Mechanistic suction-feeding specialist elasmobranchs are primarily benthic, while most epibenthic and pelagic elasmobranchs are generalists and use ram, suction, and biting to catch a diversity of prey in various habitats. Some shark species are considered to be ecological specialists in choosing certain kinds of prey over others. Batoids are evolutionary specialists in having a flattened morphology and most are generalist feeders. Filter-feeding elasmobranchs are ecological, mechanistic, and evolutionary specialists.

Mesozoic birds display considerable diversity in size, flight adaptations and feather organization1-4, but exhibit relatively conserved patterns of beak shape and development5-7. Although Neornithine (that is, crown group) birds also exhibit constraint on facial development8,9, they have comparatively diverse beak morphologies associated with a range of feeding and behavioural ecologies, in contrast to Mesozoic birds. Here we describe a crow-sized stem bird, Falcatakely forsterae gen. et sp. nov., from the Late Cretaceous epoch of Madagascar that possesses a long and deep rostrum, an expression of beak morphology that was previously unknown among Mesozoic birds and is superficially similar to that of a variety of crown-group birds (for example, toucans). The rostrum of Falcatakely is composed of an expansive edentulous maxilla and a small tooth-bearing premaxilla. Morphometric analyses of individual bony elements and three-dimensional rostrum shape reveal the development of a neornithine-like facial anatomy despite the retention of a maxilla-premaxilla organization that is similar to that of nonavialan theropods. The patterning and increased height of the rostrum in Falcatakely reveals a degree of developmental lability and increased morphological disparity that was previously unknown in early branching avialans. Expression of this phenotype (and presumed ecology) in a stem bird underscores that consolidation to the neornithine-like, premaxilla-dominated rostrum was not an evolutionary prerequisite for beak enlargement.

Ecological specialization is an important engine of evolutionary change and adaptive radiation, but empirical evidence of local adaptation in marine environments is rare, a pattern that has been attributed to the high dispersal ability of marine taxa and limited geographic barriers to gene flow. The broad-nosed pipefish, Syngnathus typhle, is one of the most broadly distributed syngnathid species and shows pronounced variation in cranial morphology across its range, a factor that may contribute to its success in colonizing new environments. We quantified variation in cranial morphology across the species range using geometric morphometrics, and tested for evidence of trophic specialization by comparing individual-level dietary composition with the community of prey available at each site. Although the diets of juvenile pipefish from each site were qualitatively similar, ontogenetic shifts in dietary composition resulted in adult populations with distinctive diets consistent with their divergent cranial morphology. Morphological differences found in nature are maintained under common garden conditions, indicating that trophic specialization in S. typhle is a heritable trait subject to selection. Our data highlight the potential for ecological specialization in response to spatially variable selection pressures in broadly distributed marine species.

Summary “Protorosaurs” are a group of early archosauromorph reptiles (i.e. stem-archosaurs, the reptile clade containing modern birds and crocodylians). They are characterized by their long necks, which are comprised of elongate cervical vertebrae with low neural spines and long and thin cervical ribs. The group exhibits a high degree of morphological and ecological diversity, and is represented by terrestrial, fully marine, and possibly gliding taxa. As such they represent an important group for understanding the earliest evolution of the archosaur lineage as well as the composition of Triassic ecosystems in the aftermath of the Permo-Triassic mass extinction event. Well-known “protorosaurs” include the Permian Protorosaurus speneri, the Early Triassic Prolacerta broomi, and the Tanystropheidae. The most striking “protorosaurs” are the extremely long-necked Tanystropheus spp. and Dinocephalosaurus orientalis. Recent phylogenetic studies indicate that “Protorosauria” make up several lineages of non-archosauriform archosauromorphs, implying it is a polyphyletic group. This thesis is aimed at improving our understanding of this remarkable group of reptiles by investigating their morphology, taxonomy, biogeographic distribution patterns, palaeobiology, and phylogeny. A new specimen of Prolacerta broomi from the Antarctic Fremouw Formation provides new insights into its morphology and confirms that specimens of this taxon from Antarctica and South Africa belong to the same species, indicating the close faunal ties between these continents during the Early Triassic. The taxonomy of the genus Tanystropheus is reviewed and extensively revised. The number of Tanystropheus species is reduced from six to three. One species, Tanystropheus fossai, differs distinctly from other Tanystropheus species and is therefore reassigned to a separate genus, Sclerostropheus. Two other species, Tanystropheus longobardicus and the newly identified Tanystropheus hydroides are known from the famous Besano Formation of the UNESCO World Heritage Site of Monte San Giorgio. They were previously considered to represent juveniles and adults of the same species, respectively. However, distinct differences in their cranial morphology, supported by osteohistological evidence that the specimens of the smaller species T. longobardicus are skeletally mature, convincingly show that they represent separate species. The species have distinctly contrasting dentitions and thus exploited different food sources. Their co-occurrence in the Besano Formation therefore represents a convincing example of niche partitioning and reveals a surprisingly multifunctional role for the extremely long and stiff neck of Tanystropheus. The cranial morphology of both T. hydroides and Macrocnemus bassanii are studied in detail using high-resolution synchrotron radiation microtomography. This has allowed for the first comprehensive skull reconstructions of these taxa. They reveal much information on skull regions that were previously obscured such as the braincase and in the case of T. hydroides even the endocast and endosseous labyrinth. The skull of M. bassanii shows many plesiomorphic features, whereas the skull of T. hydroides is highly derived and clearly specialized for an aquatic lifestyle. The holotype of Macrocnemus fuyuanensis is redescribed and reveals additional characters that distinguish it from M. bassanii. This reveals that M. fuyuanensis occurred on both the eastern and western margins of the Tethys Ocean, since a specimen from the Besano Formation of Monte San Giorgio can be referred to this species, which is otherwise exclusively known from China. Finally, a new phylogenetic analysis comprising the most comprehensive sample of “protorosaur” taxa to date has been performed considering the new findings presented in this thesis. It confirms both the polyphyly of “Protorosauria” and the monophyly of Tanystropheidae. The position of the putative gliding reptile Ozimek volans within Tanystropheidae is corroborated. The analysis reveals that Prolacerta broomi is more distantly related to Archosauriformes (i.e. stem-archosaurs more closely related to the crown than non-archosauriform archosauromorphs) than previously considered. Additionally, a new clade of long-necked archosauromorphs, Dinocephalosauridae, is recognized, which is at least comprised of the Chinese taxa Dinocephalosaurus orientalis and Pectodens zhenyuensis.

Discovery of the choristodere Hyphalosaurus baitaigouensis from the Lower Cretaceous Jiufotang Formation of western Liaoning, China and its paleobiogeographic significance

A new pterosaur (Pterodactyloidea, Tapejaridae) from the Early Cretaceous Jiufotang Formation of western Liaoning, China and its implications for biostratigraphy