A new juvenile sauropod specimen from the Middle Jurassic Dongdaqiao Formation of East Tibet.

Jurassic strata are widely distributed in the eastern part of Tibet Autonomous Region, and have yielded many dinosaur bones. However, none of these specimens has been studied extensively, and some remain unprepared. Here we provide a detailed description of some new sauropod material, including several cervical vertebrae and a nearly complete scapula, recovered from the Middle Jurassic of Chaya County, East Tibet. The cervical vertebrae have short centra that bear ventral midline keels, as in many non-neosauropod sauropods such as Shunosaurus. Moreover, the cervical centra display deep lateral excavations, partitioned by a septum. The scapula has proximal and distal ends that are both expanded as in mamenchisaurids and neosauropods. However, relatively small body size and lack of fusion of neurocentral sutures in the cervical vertebrae suggest that the available material is from a juvenile, and the length of the cervical centra may have increased relative to the size of the rest of the skeleton in later ontogenetic stages. Phylogenetic analysis provides limited evidence that the new Tibetan sauropod specimen belongs to Eusauropoda, being more derived than Shunosaurus, but is basal to Mamenchisauridae. The new material provides important information on the morphological transition between Shunosaurus and mamenchisaurids, and extends the known biogeographic range of early-diverging sauropods in the Middle Jurassic of East Asia.

Deep reptilian evolutionary roots of a major avian respiratory adaptation.

Vertebral ribs of the anterior thorax in extant birds bear bony prongs called uncinate processes, which improve the mechanical advantage of mm. appendicocostales to move air through the immobile lung and pneumatic air sacs. Among non-avian archosaurs, broad, cartilaginous uncinate processes are present in extant crocodylians, and likely have a ventilatory function. Preserved ossified or calcified uncinate processes are known in several non-avian dinosaurs. However, whether other fossil archosaurs possessed cartilaginous uncinate processes has been unclear. Here, we establish osteological correlates for uncinate attachment to vertebral ribs in extant archosaurs, with which we inferred the presence of uncinate processes in at least 19 fossil archosaur taxa. An ancestral state reconstruction based on the infer distribution suggests that cartilaginous uncinate processes were plesiomorphically present in Dinosauria and arguably in Archosauria, indicating that uncinate processes, and presumably their ventilatory function, have a deep evolutionary history extending back well beyond the origin of birds.

A new confuciusornithid bird with a secondary epiphyseal ossification reveals phylogenetic changes in confuciusornithid flight mode.

The confuciusornithids are the earliest known beaked birds, and constitute the only species-rich clade of Early Cretaceous pygostylian birds that existed prior to the cladogenesis of Ornithothoraces. Here, we report a new confuciusornithid species from the Lower Cretaceous of western Liaoning, northeastern China. Compared to other confuciusornithids, this new species and the recently reported Yangavis confucii both show evidence of stronger flight capability, although the wings of the two taxa differ from one another in many respects. Our aerodynamic analyses under phylogeny indicate that varying modes of flight adaptation emerged across the diversity of confuciusornithids, and to a lesser degree over the course of their ontogeny, and specifically suggest that both a trend towards improved flight capability and a change in flight strategy occurred in confuciusornithid evolution. The new confuciusornithid differs most saliently from other Mesozoic birds in having an extra cushion-like bone in the first digit of the wing, a highly unusual feature that may have helped to meet the functional demands of flight at a stage when skeletal growth was still incomplete. The new find strikingly exemplifies the morphological, developmental and functional diversity of the first beaked birds.

A new basal ichthyosauromorph from the Lower Triassic (Olenekian) of Zhebao, Guangxi Autonomous Region, South China.

Here we describe a newly discovered basal ichthyosauromorph from the Lower Triassic of South China, Baisesaurus robustus gen. et sp. nov. The only known specimen of this new species was collected from the Lower Triassic (Olenekian) Luolou Formation in the Zhebao region of Baise City, on the northwest margin of the Nanpanjiang Basin, and comprises a partial skeleton including the ribs, the gastralia, a limb element, 12 centra, and seven neural arches. Comparisons to a wide variety of Early Triassic marine reptiles show Baisesaurus robustus to be a basal ichthyosauromorph based on the following features: neural arches lack transverse processes; dorsal ribs are slender, and not pachyostotic even proximally; and median gastral elements have long, sharp anterior processes. The limb element is long and robust, and is most likely to be a radius. Baisesaurus robustus is large (estimated length more than 3 m) relative to early ichthyosauromorphs previously discovered in China, and shares noteworthy morphological similarities with Utatsusaurus hataii, particularly with regard to body size and the morphology of the probable radius. Baisesaurus robustus also represents the first record of an Early Triassic ichthyosauromorph from Guangxi Autonomous Region, extending the known geographic distribution of ichthyosauromorphs in South China.

Digital restoration of the pectoral girdles of two Early Cretaceous birds and implications for early-flight evolution.

The morphology of the pectoral girdle, the skeletal structure connecting the wing to the body, is a key determinant of flight capability, but in some respects is poorly known among stem birds. Here, the pectoral girdles of the Early Cretaceous birds Sapeornis and Piscivorenantiornis are reconstructed for the first time based on computed tomography and three-dimensional visualization, revealing key morphological details that are important for our understanding of early-flight evolution. Sapeornis exhibits a double articulation system (widely present in non-enantiornithine pennaraptoran theropods including crown birds), which involves, alongside the main scapula-coracoid joint, a small subsidiary joint, though variation exists with respect to the shape and size of the main and subsidiary articular contacts in non-enantiornithine pennaraptorans. This double articulation system contrasts with Piscivorenantiornis in which a spatially restricted scapula-coracoid joint is formed by a single set of opposing articular surfaces, a feature also present in other members of Enantiornithines, a major clade of stem birds known only from the Cretaceous. The unique single articulation system may reflect correspondingly unique flight behavior in enantiornithine birds, but this hypothesis requires further investigation from a functional perspective. Our renderings indicate that both Sapeornis and Piscivorenantiornis had a partially closed triosseal canal (a passage for muscle tendon that plays a key role in raising the wing), and our study suggests that this type of triosseal canal occurred in all known non-euornithine birds except Archaeopteryx, representing a transitional stage in flight apparatus evolution before the appearance of a fully closed bony triosseal canal as in modern birds. Our study reveals additional lineage-specific variations in pectoral girdle anatomy, as well as significant modification of the pectoral girdle along the line to crown birds. These modifications produced diverse pectoral girdle morphologies among Mesozoic birds, which allowed a commensurate range of capability levels and styles to emerge during the early evolution of flight.

The dinosaur tracks of Tyrants Aisle: An Upper Cretaceous ichnofauna from Unit 4 of the Wapiti Formation (upper Campanian), Alberta, Canada.

The Wapiti Formation of northwest Alberta and northeast British Columbia, Canada, preserves an Upper Cretaceous terrestrial vertebrate fauna that is latitudinally situated between those documented further north in Alaska and those from southern Alberta and the contiguous U.S.A. Therefore, the Wapiti Formation is important for identifying broad patterns in vertebrate ecology, diversity, and distribution across Laramidia during the latest Cretaceous. Tracksites are especially useful as they provide a range of palaeoecological, palaeoenvironmental, and behavioural data that are complementary to the skeletal record. Here, we describe the Tyrants Aisle locality, the largest in-situ tracksite known from the Wapiti Formation. The site occurs in the lower part of Unit 4 of the formation (~72.5 Ma, upper Campanian), exposed along the southern bank of the Redwillow River. More than 100 tracks are documented across at least three distinct track-bearing layers, which were deposited on an alluvial floodplain. Hadrosaurid tracks are most abundant, and are referable to Hadrosauropodus based on track width exceeding track length, broad digits, and rounded or bilobed heel margins. We suggest the hadrosaurid trackmaker was Edmontosaurus regalis based on stratigraphic context. Tyrannosaurids, probable troodontids, possible ornithomimids, and possible azhdarchid pterosaurs represent minor but notable elements of the ichnofauna, as the latter is unknown from skeletal remains within the Wapiti Formation, and all others are poorly represented. Possible social behaviour is inferred for some of the hadrosaurid and small theropod-like trackmakers based on trackway alignment, suitable spacing and consistent preservation. On a broad taxonomic level (i.e., family or above), ichnofaunal compositions indicate that hadrosaurids were palaeoecologically dominant across Laramidia during the late Campanian within both high-and low-latitude deposits, although the role of depositional environment requires further testing.

Taphonomy and taxonomy of a juvenile lambeosaurine (Ornithischia: Hadrosauridae) bonebed from the late Campanian Wapiti Formation of northwestern Alberta, Canada.

Hadrosaurid (duck-billed) dinosaur bonebeds are exceedingly prevalent in upper Cretaceous (Campanian-Maastrichtian) strata from the Midwest of North America (especially Alberta, Canada, and Montana, U.S.A) but are less frequently documented from more northern regions. The Wapiti Formation (Campanian-Maastrichtian) of northwestern Alberta is a largely untapped resource of terrestrial palaeontological information missing from southern Alberta due to the deposition of the marine Bearpaw Formation. In 2018, the Boreal Alberta Dinosaur Project rediscovered the Spring Creek Bonebed, which had been lost since 2002, along the northern bank of the Wapiti River, southwest of Grande Prairie. Earlier excavations and observations of the Spring Creek Bonebed suggested that the site yielded young hadrosaurines. Continued work in 2018 and 2019 recovered ~300 specimens that included a minimum of eight individuals, based on the number of right humeri. The morphology of several recovered cranial elements unequivocally supports lambeosaurine affinities, making the Spring Creek sample the first documented occurrence of lambeosaurines in the Wapiti Formation. The overall size range and histology of the bones found at the site indicate that these animals were uniformly late juveniles, suggesting that age segregation was a life history strategy among hadrosaurids. Given the considerable size attained by the Spring Creek lambeosaurines, they were probably segregated from the breeding population during nesting or caring for young, rather than due to different diet and locomotory requirements. Dynamic aspects of life history, such as age segregation, may well have contributed to the highly diverse and cosmopolitan nature of Late Cretaceous hadrosaurids.

A new two-fingered dinosaur sheds light on the radiation of Oviraptorosauria.

Late Cretaceous trends in Asian dinosaur diversity are poorly understood, but recent discoveries have documented a radiation of oviraptorosaur theropods in China and Mongolia. However, little work has addressed the factors that facilitated this diversification. A new oviraptorid from the Late Cretaceous of Mongolia sheds light on the evolution of the forelimb, which appears to have played a role in the radiation of oviraptorosaurs. Surprisingly, the reduced arm has only two functional digits, highlighting a previously unrecognized occurrence of digit loss in theropods. Phylogenetic analysis shows that the onset of this reduction coincides with the radiation of heyuannine oviraptorids, following dispersal from southern China into the Gobi region. This suggests expansion into a new niche in the Gobi region, which relied less on the elongate, grasping forelimbs inherited by oviraptorosaurs. Variation in forelimb length and manus morphology provides another example of niche partitioning in oviraptorosaurs, which may have made possible their incredible diversity in the latest Cretaceous of Asia.

New titanosauriform (Dinosauria: Sauropoda) specimens from the Upper Cretaceous Daijiaping Formation of southern China.

Titanosauriform sauropod dinosaurs were once considered rare in the Upper Cretaceous of Asia, but a number of titanosauriforms from this stratigraphic interval have been discovered in China in recent years. In fact, all adequately known Cretaceous Asian sauropods are titanosauriforms, but only a few have been well studied, lending significance to any new anatomical information that can be extracted from Asia's Cretaceous sauropod record. Here we give a detailed description of some titanosauriform bones recovered recently from the Upper Cretaceous Daijiaping Formation of Tianyuan County, Zhuzhou City, Hunan Province, southern China. The occurrence of this material in Hunan increases the known geographic range of titanosauriforms in eastern Asia. Although all of the specimens discussed in this paper can be assigned to Titanosauriformes at least tentatively, some bones display a limited number of features that are more typical of basal sauropods and/or derived diplodocoids, suggesting complex patterns of character evolution within Neosauropoda.

A new transitional therizinosaurian theropod from the Early Cretaceous Jehol Biota of China.

Therizinosaurian theropods evolved many highly specialized osteological features in association with their bulky proportions, which were unusual in the context of the generally gracile Theropoda. Here we report a new therizinosaur, Lingyuanosaurus sihedangensis gen. et sp. nov., based on a specimen recovered from the Lower Cretaceous Jehol Group of Lingyuan, Liaoning Province, China, which displays a combination of plesiomorphic and derived features. Most notably, the specimen is characterized by posterior dorsal vertebrae with a complex and unusual laminar structure; an ilium with a highly dorsoventrally expanded preacetabular process showing only slight lateral flaring of the ventral margin, a strongly anterodorsally inclined iliac blade, a small postacetabular process with a strongly concave dorsal margin, and a relatively robust pubic peduncle with a posteroventrally facing distal articular surface; a straight and robust femur with a small lesser trochanter; and a tibia that is longer than the femur. Phylogenetic analysis places Lingyuanosaurus in an intermediate position within Therizinosauria, i.e., between the early-branching therizinosaurs such as Falcarius, Jianchangosaurus, and Beipiaosaurus and the late-branching ones such as Alxasaurus and Therizinosaurus. This new therizinosaur sheds additional light on the evolution of major therizinosaurian characteristics, including particularly the distinctive pelvic girdle and hindlimb morphology seen in this group.

The anatomy and phylogenetic position of the erythrosuchid archosauriform Guchengosuchus shiguaiensis from the earliest Middle Triassic of China.

Erythrosuchidae is a clade of early archosauriform reptiles, which were apex predators in many late Early and Middle Triassic ecosystems, following the Permo-Triassic mass extinction. Erythrosuchids had a worldwide distribution, with well-preserved fossil material known from South Africa, European Russia, and China. We here redescribe the anatomy and revise the taxonomy of Guchengosuchus shiguaiensis, which is one of the stratigraphically oldest erythrosuchids and is known from a single partial skeleton from the lowermost Middle Triassic (lower Anisian) lower Ermaying Formation of Shaanxi Province, China. We provide a new differential diagnosis for Guchengosuchus shiguaiensis, and identify a series of autapomorphies relating to the morphologies of the skull roof and vertebrae. Incorporating updated anatomical information for Guchengosuchus into the most comprehensive morphological phylogenetic analysis available for early archosauromorphs recovers it as an early branching member of Erythrosuchidae, outside of the clade formed by Garjainia, Erythrosuchus, Chalishevia, and Shansisuchus. Fugusuchus hejiapanensis, from the uppermost Lower Triassic to lower Middle Triassic Heshanggou Formation of China, is recovered as the earliest branching member of Erythrosuchidae.

Winged forelimbs of the small theropod dinosaur Caudipteryx could have generated small aerodynamic forces during rapid terrestrial locomotion.

Pennaceous feathers capable of forming aerodynamic surfaces are characteristic of Pennaraptora, the group comprising birds and their closest relatives among non-avian dinosaurs. However, members of the basal pennaraptoran lineage Oviraptorosauria were clearly flightless, and the function of pennaceous feathers on the forelimb in oviraptorosaurs is still uncertain. In the basal oviraptorosaur Caudipteryx both the skeleton and the plumage, which includes pennaceous feathers forming wing-like arrangements on the forelimbs, are well known. We used mathematical analyses, computer simulations and experiments on a robot Caudipteryx with realistic wing proportions to test whether the wings of Caudipteryx could have generated aerodynamic forces useful in rapid terrestrial locomotion. These various approaches show that, if both wings were held in a fixed and laterally extended position, they would have produced only small amounts of lift and drag. A partial simulation of flapping while running showed similarly limited aerodynamic force production. These results are consistent with the possibility that pennaceous feathers first evolved for a non-locomotor function such as display, but the effects of flapping and the possible contribution of the wings during manoeuvres such as braking and turning remain to be more fully investigated.

Exceptional dinosaur fossils reveal early origin of avian-style digestion.

Birds have a highly specialized and efficient digestive system, but when this system originated remains uncertain. Here we report six gastric pellets attributable to the recently discovered 160-million-year-old troodontid dinosaur Anchiornis, which is among the key taxa for understanding the transition to birds. The gastric pellets contain lightly acid-etched lizard bones or fish scales, and some are associated with Anchiornis skeletons or even situated within the oesophagus. Anchiornis is the earliest and most basal theropod known to have produced gastric pellets. In combination with other lines of evidence, the pellets suggest that a digestive system resembling that of modern birds was already present in basal members of the Paraves, a clade including troodontids, dromaeosaurids, and birds, and that the evolution of modern avian digestion may have been related to the appearance of aerial locomotion in this lineage.

Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution.

Highly specialized animals are often difficult to place phylogenetically. The Late Cretaceous members of Alvarezsauria represent such an example, having been posited as members of various theropod lineages, including birds [1-11]. A 70-million-year ghost lineage exists between them and the Late Jurassic putative alvarezsaurian Haplocheirus [12], which preserves so few derived features that its membership in Alvarezsauria has recently been questioned [13]. If Haplocheirus is indeed an alvarezsaurian, then the 70-million-year gap between Haplocheirus and other alvarezsaurians represents the longest temporal hiatus within the fossil record of any theropod subgroup [14]. Here we report two new alvarezsaurians from the Early Cretaceous of Western China that document successive, transitional stages in alvarezsaurian evolution. They provide further support for Haplocheirus as an alvarezsaurian and for alvarezsaurians as basal maniraptorans. Furthermore, they suggest that the early biogeographic history of the Alvarezsauria involved dispersals from Asia to other continents. The new specimens are temporally, morphologically, and functionally intermediate between Haplocheirus and other known alvarezsaurians and provide a striking example of the evolutionary transition from a typical theropod forelimb configuration (i.e., the relatively long arm and three-digit grasping hand of typical tetanuran form in early-branching alvarezsaurians) to a highly specialized one (i.e., the highly modified and shortened arm and one-digit digging hand of Late Cretaceous parvicursorines such as Linhenykus [1, 15]). Comprehensive analyses incorporating data from these new finds show that the specialized alvarezsaurian forelimb morphology evolved slowly and in a mosaic fashion during the Cretaceous.

A new caenagnathid dinosaur from the Upper Cretaceous Wangshi Group of Shandong, China, with comments on size variation among oviraptorosaurs.

The bone-beds of the Upper Cretaceous Wangshi Group in Zhucheng, Shandong, China are rich in fossil remains of the gigantic hadrosaurid Shantungosaurus. Here we report a new oviraptorosaur, Anomalipes zhaoi gen. et sp. nov., based on a recently collected specimen comprising a partial left hindlimb from the Kugou Locality in Zhucheng. This specimen's systematic position was assessed by three numerical cladistic analyses based on recently published theropod phylogenetic datasets, with the inclusion of several new characters. Anomalipes zhaoi differs from other known caenagnathids in having a unique combination of features: femoral head anteroposteriorly narrow and with significant posterior orientation; accessory trochanter low and confluent with lesser trochanter; lateral ridge present on femoral lateral surface; weak fourth trochanter present; metatarsal III with triangular proximal articular surface, prominent anterior flange near proximal end, highly asymmetrical hemicondyles, and longitudinal groove on distal articular surface; and ungual of pedal digit II with lateral collateral groove deeper and more dorsally located than medial groove. The holotype of Anomalipes zhaoi is smaller than is typical for Caenagnathidae but larger than is typical for the other major oviraptorosaurian subclade, Oviraptoridae. Size comparisons among oviraptorisaurians show that the Caenagnathidae vary much more widely in size than the Oviraptoridae.

Genomic evidence reveals a radiation of placental mammals uninterrupted by the KPg boundary.

The timing of the diversification of placental mammals relative to the Cretaceous-Paleogene (KPg) boundary mass extinction remains highly controversial. In particular, there have been seemingly irreconcilable differences in the dating of the early placental radiation not only between fossil-based and molecular datasets but also among molecular datasets. To help resolve this discrepancy, we performed genome-scale analyses using 4,388 loci from 90 taxa, including representatives of all extant placental orders and transcriptome data from flying lemurs (Dermoptera) and pangolins (Pholidota). Depending on the gene partitioning scheme, molecular clock model, and genic deviation from molecular clock assumptions, extensive sensitivity analyses recovered widely varying diversification scenarios for placental mammals from a given gene set, ranging from a deep Cretaceous origin and diversification to a scenario spanning the KPg boundary, suggesting that the use of suboptimal molecular clock markers and methodologies is a major cause of controversies regarding placental diversification timing. We demonstrate that reconciliation between molecular and paleontological estimates of placental divergence times can be achieved using the appropriate clock model and gene partitioning scheme while accounting for the degree to which individual genes violate molecular clock assumptions. A birth-death-shift analysis suggests that placental mammals underwent a continuous radiation across the KPg boundary without apparent interruption by the mass extinction, paralleling a genus-level radiation of multituberculates and ecomorphological diversification of both multituberculates and therians. These findings suggest that the KPg catastrophe evidently played a limited role in placental diversification, which, instead, was likely a delayed response to the slightly earlier radiation of angiosperms.

Morphological Diversity and Evolution of the Jugal in Dinosaurs.

In dinosaurs, as in other reptiles, the homologue of the mammalian zygomatic bone is the jugal. The dinosaurian jugal was primitively triradiate, with posterior, dorsal and anterior processes that respectively contacted the quadratojugal, the postorbital, and the maxilla and lacrimal. However, the jugal evolved along different lines in the three major dinosaurian clades. In theropods this cranial element remained relatively conservative in morphology, apart from being reduced to a rod-like structure in most birds and a few non-avians. In sauropodomorphs the jugal eventually became small, plate-like and nearly restricted to the area below the orbit, even being excluded from the ventral margin of the skull in many derived taxa. Among ornithischians the jugal was highly variable, but in many cases became large and/or adorned with ornamental features such as horns, flanges, and rugosities. The jugal does not appear to have been a site of muscle attachment in most non-avian dinosaurs, but represented an important structural element in the akinetic dinosaurian skull. The conspicuous jugal ornaments seen in many ornithischian dinosaurs, like the less striking ones documented in some saurischians, may have played an important role in the social behavior of the species that possessed them. In many cases they have a weapon-like aspect suggesting use in aggressive displays, if not actual combat, adding to the evidence that agonistic behavior was likely widespread among ornithischians in particular. Anat Rec, 300:30-48, 2017. © 2016 Wiley Periodicals, Inc.

A revision of Sanpasaurus yaoi Young, 1944 from the Early Jurassic of China, and its relevance to the early evolution of Sauropoda (Dinosauria).

The Early Jurassic of China has long been recognized for its diverse array of sauropodomorph dinosaurs. However, the contribution of this record to our understanding of early sauropod evolution is complicated by a dearth of information on important transitional taxa. We present a revision of the poorly known taxon Sanpasaurus yaoi Young, 1944 from the late Early Jurassic Ziliujing Formation of Sichuan Province, southwest China. Initially described as the remains of an ornithopod ornithischian, we demonstrate that the material catalogued as IVPP V156 is unambiguously referable to Sauropoda. Although represented by multiple individuals of equivocal association, Sanpasaurus is nonetheless diagnosable with respect to an autapomorphic feature of the holotypic dorsal vertebral series. Additional material thought to be collected from the type locality is tentatively referred to Sanpasaurus. If correctly attributed, a second autapomorphy is present in a referred humerus. The presence of a dorsoventrally compressed pedal ungual in Sanpasaurus is of particular interest, with taxa possessing this typically 'vulcanodontid' character exhibiting a much broader geographic distribution than previously thought. Furthermore, the association of this trait with other features of Sanpasaurus that are broadly characteristic of basal eusauropods underscores the mosaic nature of the early sauropod-eusauropod transition. Our revision of Sanpasaurus has palaeobiogeographic implications for Early Jurassic sauropods, with evidence that the group maintained a cosmopolitan Pangaean distribution.