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A new compsognathid theropod dinosaur from the oldest assemblage of the Jehol Biota in the Lower Cretaceous Huajiying Formation, northeastern China

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... During the last three decades, newly discovered theropods have dethroned Compsognathus from the iconic status of the "smallest dinosaur" (Xu et al., 2000). Furthermore, other taxa have been included in the compsognathid lineage or have been suggested to be members of the same coelurosaurian grade: Sinosauropteryx (Chen et al., 1998;Chen & Currie, 2001); Scipionyx (see Dal Sasso & Maganuco, 2011); Huaxiagnathus (Hwang et al., 2004); Mirischia (Naish et al., 2004); Juravenator (Göhlich & Chiappe, 2006); Sinocalliopteryx (Ji et al., 2007;Xing et al., 2012); and Xunmenglong (Xing et al., 2019). A specimen referred to Sinosauropteryx by Currie & Chen (2001), NGMC 2124, differs in several features from the former and represents a distinct taxon (Longrich, 2002). ...
... body size range of the compsognathids overlaps with that inferred for immature (hatchling and juvenile) individuals of large-bodied theropods (e.g., Allosaurus; Rauhut & Fechner, 2005;Carpenter, 2010). Several lines of evidence indicate that the holotypes of Juravenator, Scipionyx, Sciurumimus and Xunmenglong are very immature individuals (Göhlich & Chiappe, 2006;Dal Sasso & Maganuco, 2011;Rauhut et al., 2012;Xing et al., 2019). Both specimens of Compsognathus show proportions in the skull and orbit (i.e., round orbit with rostrocaudal diameter about 1/4 of skull length, skull subequal to or longer than femur) and incomplete fusion among the sacral centra which support an immature stage of development (Ostrom, 1978;Peyer, 2006). ...
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Known since the 19 th Century, the compsognathids are among the smallest predatory dinosaurs, and include the first feathered non-avian species found. Traditionally, compsognathids have been considered small and unspecialized coelurosaurs, closer to birds than large-bodied forms like allosauroids and megalosaurids. Yet, all known compsognathids are based on skeletally-immature specimens, and this challenges the accuracy of their traditional phyletic placement. Despite the role of heterochrony in dinosaur evolution is widely recognized, the impact of ontogenetic-biased miscodings in shaping theropod phylogenetics is mostly underestimated. Herein, I show that the standard framework of theropod macroevolution is biased by a series of coding artifacts which violate semaphoront equality prescribed by phylogenetic systematics. I introduce "Ontogenetic State Partitioning" (OSP), a novel coding protocol which integrates ontogenetic and morphological variation under a total evidence approach, and apply it to a densely sampled data set focusing on Mesozoic theropods. The phylogenetic analysis dismissed "Compsognathidae" from being a natural group: its members are identified as juvenile morphs nested among several non-maniraptoriform tetanuran lineages. Conservatism in the immature body plan and greater disparity among large-sized adults differentiate the predatory communities dominated by non-coelurosaurian species (e.g., the so called "triumvirates") from the maniraptoriform-tyrannosaurid faunas (herein named "tyrannies"). This clade-specific differentiation among the communities is confirmed by an analysis of the predatory guild structures including all growth stages: triumvirates and tyrannies result as particular cases along a continuum of communities regulated mainly by alternative contributions of the small-and medium-sized classes. The oldest tyrannies (early Late Cretaceous in age) cluster among non-tyranny communities, supporting the hypothesis that tyrannosaurid-dominated faunas acquired their peculiar structure only after the extinction of the non-coelurosaurian components. The macroevolutionary trajectory that led the maniraptoriforms to realize the avian-like biology may have precluded them from occupying hypercarnivorous large-bodied niches: this bauplan constraint would have favored the tyrannosauroids in opportunistically assuming the apex predatory roles in Late Cretaceous Asiamerica but not elsewhere. The large-scale structure of the Cenozoic radiation of birds is coherent with the framework introduced herein.
... Abundant, mostly well-preserved plant, invertebrate, and vertebrate specimens in these lacustrine deposits imply short transport distances of organisms into large lake environments facilitated by low-energy currents and slack levels of fluvial and deltaic sedimentation (Ding et al., 2014), occasionally interrupted by storm events that create disorganized bedding Li et al., 2007). Stratigraphically, the DW locality is considered part of the lower Yixian Fm that consists of 100-150 m of thick shale and intercalated tuff (Chang et al., 2017;Xing et al., 2020;Yang et al., 2020;Zhang et al., 2020) (Appendix S2). The age of the DW deposit is ca. ...
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The Early Cretaceous terrestrial revolution involved global shifts from gymnosperm to angiosperm dominated floras. However, responses of insect herbivores to these changes remain unexamined. We evaluated 2176 highly sampled plant specimens representing 62 species/morphotypes from the 126 Ma Dawangzhangzi plant assemblage of Northeastern China. Our study consisted of horsetails, ferns, ginkgoaleans, czekanowskialeans, conifers, and an angiosperm. Their herbivory was evaluated by the functional feeding groups of hole feeding, margin feeding, and surface feeding (ectophytic feeders); piercer and suckers, and ovipositing insects (ectoendophytic feeders); mining, galling, and borings (endophytic feeders); and pathogens, collectively constituting 65 damage types (DTs). The plant assemblage was assessed for herbivory richness by DT richness, component community structure, and DT specialization on plant hosts; for herbivory intensity, it was evaluated for DT frequency, herbivorized surface area, and feeding event occurrences. Using feeding event occurrences, the data supported seven species/morphotypes as most intensely herbivorized: Liaoningocladus boii (76.6%), Czekanowskia sp. 1 (8.4%), Czekanowskia rigida (4.10%), Lindleycladus lanceolatus (3.5%), Ginkgoites sp. 2 (2.0%), Podozamites sp. 1 (1.1%), and Solenites sp. 1 (0.9%). The most herbivorized taxa were pinaleans (conifers), then czekanowskialeans, and lastly ginkgoaleans; the monodominant component community was the conifer Liaoningocladus. DT host specialization levels were low. The plant assemblage had an overall low 0.86% of foliage removed by herbivores, explained by physical and chemical antiherbivore defenses, and parasitoid attack. Although Paleozoic, gymnosperm-dominated assemblages had greater herbivory, component community structure of the three most herbivorized taxa are more similar to modern bracken fern and willow than modern gymnosperm taxa. This article is protected by copyright. All rights reserved
... Conservation of the dt2 embryonic cartilage in both birds and crocodilians implies this cartilage has likely remained present since early archosaurs, including the entire dinosaur-bird transition, despite the fact it did not ossify: only dt3 and dt4 were present as adult bones (Figure 5a-c). A small putative dt2 bone has been reported in some coelurosaurian dinosaurs (Xing et al., 2020;Supporting Information). This would be consistent with the inferred presence of a dt2 cartilage, that could ossify occasionally. ...
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The adult ankle of early reptiles had five distal tarsal (dt) bones, but in Dinosauria, these were reduced to only two: dt3 and dt4, articulated to metatarsals (mt) mt3 and mt4. Birds have a single distal tarsal ossification center that fuses to the proximal metatarsals to form a new adult skeletal structure: the composite tarsometatarsus. This ossification center develops within a single large embryonic cartilage, but it is unclear if this cartilage results from fusion of earlier cartilages. We studied embryos in species from four different bird orders, an alligatorid, and an iguanid. In all embryos, cartilages dt2, dt3, and dt4 are formed. In the alligatorid and the iguanid, dt2 failed to ossify: only dt3 and dt4 develop into adult bones. In birds, dt2, dt3, and dt4 fuse to form the large distal tarsal cartilage; the ossification center then develops above mt3, in cartilage presumably derived from dt3. During the entire dinosaur-bird transition, a dt2 embryonic cartilage was always formed, as inferred from the embryology of extant birds and crocodilians. We propose that in the evolution of the avian ankle, fusion of cartilages dt3 and dt2 allowed ossification from dt3 to progress into dt2, which began to contribute bone medially, while fusion of dt3 to dt4 enabled the evolutionary loss of the dt4 ossification center. As a result, a single ossification center expands into a plate-like unit covering the proximal ends of the metatarsals, that is key to the development of an integrated tarsometatarsus.
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The idea that birds are maniraptoran theropod dinosaurs is now considered an evolutionary consensus. An “open” (i.e., completely or substantially perforate) acetabulum is considered an important synapomorphy verifying the bird–dinosaur nexus. Here, I present anatomical evidence from the acetabulum and its important appurtenances, the supracetabular crest and the antitrochanter, that hip anatomy differs substantially between dinosaurs and birds. Given the thin bone of the acetabular walls and the varied tissue, both hard and soft, in the acetabular region and especially the lower part of the basin, it is apparent that many avian skeletons exhibit some anatomical loss of soft tissue and thin bone, some perhaps related to changes in gait, but also in part related to the dramatic trend in bone reduction associated with flight, especially in more advanced crown taxa. Many basal birds and early diverging neornithines tend to have a nearly closed or partially closed acetabula, thus rendering the current terms “open” or “closed” acetabula inaccurate; they should be modified or replaced. Given new evidence presented here, the relationship of “dinosaurs” and birds must be re-evaluated.
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The bird fossil-bearing deposits at the Jiecaigou section, correlative to the Dabeigou Formation, in Fengning, Hebei Province, northern China, is well known for yielding a fossil assemblage representing the earliest evolutionary stage of the Jehol Biota. The precise age of the fossil-bearing deposits, however, is unknown. The 40Ar/39Ar age spectrum obtained on bulk K-feldspars from the tuff layer about 2 m below the bird fossil-bearing layer gave a plateau age of 129.0 +/- 1.3 Ma (2sigma, full external error) and an isochron age of 132.3 +/- 4.5 Ma (2sigma, full external error). Seventeen total-fusion 40Ar/39Ar ages on K-feldspars from the interbedded tuff about 6 m below the fossil-bearing layer resulted in a weighted mean of 130.7 +/- 1.4 Ma (2sigma, full external error). These dates suggest an age of ~131 Ma for the early Jehol Biota and combined with previous dating indicate that this biota lasted at least from 131 Ma to 120 Ma (Late Hauterivian to Aptian). These dates also represent the earliest absolute age for known enantiornithine birds in the world.
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A new compsognathid dinosaur, Sinocalliopteryx gigas gen. et sp. nov., is erected based on a complete skeleton from the Early Cretaceous Yixian Formation of western Liaoning, northeastern China. It shares the features with Huaxiagnathus orientalis in having a manus as long as the humerus plus radius, very large and subequally long manual claws I and II, and reduced olecranon process on the ulna. But it differs from Huaxiagnathus orientalis in having the much large size, a very long maxillary process of premaxilla not extending the vertical level of the maxillary antorbital fossa, and the proportionally longer ulna and so on. Sinocalliopteryx gigas gen. et sp. nov. represents the largest species among the known compsognathid dinosaurs, suggesting the tendency of the body enlargement in compsognathids to some extent. The long filamentous integuments are attached to the whole body of this compsognathid, confirming that such integuments evolved firstly in the basal coelurosaurs. This new giant compsognathid was a fierce carnivorous theropod, as shown further by an incomplete dromaeosaurid leg inside its abdominal cavity.
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We report on a new enantiornithine Eopengornis martini gen. et sp. nov. from the lowest horizon of the Jehol Biota in Hebei, China; dated at 130.7 Mya, this is the second oldest avian bearing fossil deposit in the world, recording the First Appearance Datum of Enantiornithes. The new specimen, only the second enantiornithine and third bird reported from this horizon, preserves numerous synapomorphies with the largest Lower Cretaceous enantiornithine Pengornis houi from the Jiufotang Formation dated at 120 Mya. Together, they form a new avian lineage that lasted over 10 Myr, which is longer than any known clade of Lower Cretaceous enantiornithine. Eopengornis reveals new information about basal enantiornithine morphology such as the presence of a metatarsal V, helping to clarify the early evolution of these dominant Cretaceous avians. Furthermore, Eopengornis preserves a previously unrecognized tail morphology: a pair of elongate fully pennaceous rachis dominated feathers. This discovery confirms hypotheses proposing that the rachis dominated racket-plumes in basal birds represent modified pennaceous feathers. We suggest that the ornamental racket-plumes in enantiornithines and Confuciusornis evolved independently from the basal pygostylian condition, which we infer was a tail formed of normal flight feathers. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 805–819.
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The Early Cretaceous Jehol Biota of northeastern China has become famous over the last two decades as a source of feathered avialan and non-avialan theropods, preserved alongside an array of other fossil vertebrates, invertebrates, and plants. Still more recently, a rich assemblage referred to in this paper as the Daohugou Biota has begun to emerge from Jurassic strata in the same region. Like their counterparts from the Jehol Biota, Daohugou Biota vertebrate specimens are typically preserved in fine-grained lacustrine beds and often retain feathers and other soft-tissue features. At present, 30 vertebrate taxa (five salamanders, one anuran, two lizards, 13 pterosaurs, five dinosaurs, and four mammals) are known from the Daohugou Biota, which was first recognized at the Daohugou locality in Inner Mongolia. The presence of the salamander Chunerpeton tianyiensis, proposed in this paper as an index fossil for the Daohugou Biota, links the Daohugou locality to five other fossil-producing areas in the provinces of Hebei and Liaoning. The strata containing the Daohugou Biota are close to the Middle–Upper Jurassic boundary and belong at least partly to the regionally widespread Tiaojishan Formation. In general, the vertebrate fauna of the Daohugou Biota is strikingly different from that of the Jehol Biota, although paravian dinosaurs, anurognathid pterosaurs, and salamanders with cryptobranchid and hynobiid affinities occur in both. Nevertheless, the Daohugou Biota and the Jehol Biota are two successive Lagerstätte assemblages that collectively offer a taphonomically consistent window into the Mesozoic life of northeast Asia over a significant span of geologic time.
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We describe the anatomy of a new coelurosaurian theropod Aorun zhaoi gen. et sp. nov., from the Middle–Late Jurassic of Xinjiang, China. Histological analysis of the holotype and only known specimen shows that the new taxon is represented by the skeleton of a juvenile individual aged no more than one year. A phylogenetic analysis of theropod relationships places Aorun as a basal member of the Coelurosauria. Although the sole use of a sub-adult ontogenetic exemplar is potentially problematic for phylogenetic reconstruction, we show that the phylogenetic position of Aorun as a member of Coelurosauria is robust to the exclusion of characters known to change during theropod ontogeny. Aorun is the seventh theropod taxon, and temporally oldest coelurosaur, known from the Shishugou Formation, which has one of the most taxonomically diverse Jurassic coelurosaurian theropod faunas in the world.http://zoobank.org/urn:lsid:zoobank.org:pub:5CC73577-9EB3-47AB-9983-1677B278EFFD
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This paper describes a new enantiornithine fossil bird, Vescornis hebeiensis, nov. sp. from the Early Cretaceous of China. We refer Vescornis to the crown clade Euenantiornithes based on several characteristics observed in the thoracic girdle and wing. Vescornis also exhibits characteristics that separate it from other enantiornithine birds, such as the short alular phalanx, the vestigial manual claws, and the well-developed and long foot claws. These features suggest an adaptation towards an improved flight capability, while the ability of Vescornis to climb is reduced compared with many other enantiornithine birds. Résumé : Cet article décrit un nouvel oiseau fossile, Vescornis hebeiensis, sp. nov. (groupe des Enantiornithes), du Crétacé précoce en Chine. Nous référons Vescornis au clade maître Euenantiornithes d'après plusieurs caractéristiques observées dans la ceinture thoracique et les ailes. Vescornis démontre aussi des caractéristiques qui le distinguent des autres oiseaux du groupe des Enantiornithes : la courte phalange de l'alula, les griffes manuelles atrophiées et les griffes longues et bien développées des pieds. Ces caractéristiques suggèrent une adaptation à une meilleure capacité de vol alors que l'habilité de Vescornis à grimper est réduite si on la compare à de nombreux autres oiseaux du groupe des Enantiornithes. (Traduit par la Rédaction) Zhang et al. 1107
Article
We describe a new coelurosaurian theropod, Zuolong salleei, gen. et sp. nov., from exposures of the upper part of the Shishugou Formation at the Wucaiwan locality, Xinjiang Autonomous Region, People's Republic of China. Zuolong has a large, inclined quadrate foramen that extends onto the medial surface of the quadratojugal, an unusually large fovea capitis on the femoral head, and an apomorphically large distal condyle of metatarsal III with a medially projecting flange on the extensor surface. Radiometric dating of the Shishugou Formation constrains the age of the specimen to the beginning of the Late Jurassic (Oxfordian). A cladistic analysis of Zuolong salleei in a broadly sampled theropod data matrix recovers it as a basal coelurosaur. These data make Zuolong one of the oldest coelurosaur fossils yet known that preserves both cranial and postcranial bones.
Article
The recent discovery of small paravian theropod dinosaurs with well-preserved feathers in the Middle-Late Jurassic Tiaojishan Formation of Liaoning Province (northeastern China) has challenged the pivotal position of Archaeopteryx, regarded from its discovery to be the most basal bird. Removing Archaeopteryx from the base of Avialae to nest within Deinonychosauria implies that typical bird flight, powered by the forelimbs only, either evolved at least twice, or was subsequently lost or modified in some deinonychosaurians. Here we describe the complete skeleton of a new paravian from the Tiaojishan Formation of Liaoning Province, China. Including this new taxon in a comprehensive phylogenetic analysis for basal Paraves does the following: (1) it recovers it as the basal-most avialan; (2) it confirms the avialan status of Archaeopteryx; (3) it places Troodontidae as the sister-group to Avialae; (4) it supports a single origin of powered flight within Paraves; and (5) it implies that the early diversification of Paraves and Avialae took place in the Middle-Late Jurassic period.
Article
A study of the distribution of dinosaurian body masses in the Dinosaur Park Formation (DPF; Campanian; southern Alberta), reveals a prominent negative skew; a pattern distinct from those of modern terrestrial faunas. We find a direct and robust correlation between taxon size (estimated live body mass) and known completeness. There is a clear dichotomy between large and small-bodied taxa at around 60 kg, in which taxa less than 60 kg are significantly less complete (mean completeness = 7.6%) than those with an estimated mass of 60 kg or greater (mean = 78.2%). Along with completeness, there is also a strong association of body size and taphonomic mode, with small taxa known largely from isolated and occasionally associated remains, and large taxa known from articulated skeletons. In addition, there is a significant correlation between taxon body mass and both date of discovery and of description, with taxa < 60 kg taking an average of 65.9 and 75.6 years to discover and describe, respectively, compared to 33.6 and 34.1 years for taxa > 60 kg. The rates of both cumulative discovery and description for large taxa are best described by a logarithmic curve nearing an asymptote, whereas small taxa show either a linear or power increase through time. This suggests that our current knowledge of the large-bodied dinosaur assemblage is reasonably representative of the true biological fauna with few discoveries likely to be made in the future. However, small taxa are greatly underestimated in both their diversity and abundance, with many more potential discoveries to be made. Given that (1) the sedimentary deposits and fossil assemblages in the DPF together represent one of the best studied examples of a Mesozoic alluvial‐paralic (terrestrial) ‘palaeoecosystem,’ and (2) similar patterns have been suggested (but not documented) for other Mesozoic terrestrial ecosystems in the Western Interior of North America, we suggest that this pattern of size bias may typify vertebrate fossil assemblages in terrestrial Mesozoic systems. If so, such biases must be considered before patterns of diversity in dinosaur communities through time can be considered accurate, or used to compare and interpret Mesozoic palaeoecosystems.
Article
A reexamination of the French Compsognathus corallestris, from the Portlandian lithographic limestones of the Tithonian of southern France, provides new cranial and postcranial information crucial for a better understanding of the taxon Compsognathus. The French Compsognathus is almost completely preserved either as actual bony elements or as impressions, lacking only the distal portion of its tail, and some of the manual phalanges. It is preserved in two blocks, one containing the skull and postcranial skeleton up to the seventh caudal vertebra, the other caudal vertebrae nine through 31. Compsognathids are currently known from Europe, South America, and China. The absence of an external mandibular fenestra, dorsally fan-shaped dorsal neural spines with hook-shaped ligament attachments, and a very short McI and a PhI-1, which is stouter than the radius distinguish compsognathids from other coelurosaurs. Anatomical and morphological characters of the Bavarian specimen of Compsognathus are nearly identical to those of the French specimen. The differences are related to ontogenetic or within-species variation or are caused by preservational factors. Therefore this study proposes that C. corallestris is a subjective junior synonym of Compsognathus longipes from Bavaria.
Article
An incomplete specimen of Sinosauropteryx prima collected from the Early Cretaceous Yixian Formation of the Dawangzhangzi area in Lingyuan, western Liaoning is depicted. It represents the first systematically described material of this feathered compsognathid outside the Sihetun area in Beipiao. This specimen shows some diagnostic features of Sinosauropteryx prima, such as the very short forelimb in relation to hindlimb with the length ratio of humerus plus radius to femur plus tibia just around 30%, and the long and massive first manual ungual subequal in length to radius. The presence of Sinosauropteryx prima only at Sihetun and Dawangzhangzi supports the suggestion that the fossil-bearing beds in the Sihetun and Dawangzhangzi areas are equivalent to each other within the Yixian Formation.
Article
Over the past 10 years, numerous dinosaur specimens covering several major dinosaurian clades have been recovered from the Lower Cretaceous Jehol Group of western Liaoning. Among ornithischians from the Jehol Group, ornithopod fossils shed new light on the evolution of this largest ornithischian group; ankylosaurian discoveries add morphological diversity relevant to the highly specialized ankylosaurian body-plan and ceratopsian occurrences offer a chance to study patterns of morphological change at the base of the Ceratopsia. The most significant discoveries are exceptionally well-preserved theropod specimens covering most major coelurosaurian groups. Most theropod taxa from the Jehol Biota are the earliest, most basal members of coelurosaurian sub-clades and provide substantial new information important for the reconstruction of coelurosaurian phylogeny and understanding the character evolution. The examination of character distributions along the coelurosaurian lineages reveals that the major structural modifications seen in birds were acquired sequentially and hierarchically early in coelurosaurian evolution. Most significantly, the Liaoning theropod discoveries advanced our understanding of two long-debated evolutionary issues: the origin and early evolution of feathers and the origin of avian flight. The known distribution of the feather-like integumentary structures and true feathers along the coelurosaurian lineages suggests that: (1) simple, filamentous integuments represent a primitive morph in feather evolution; (2) pennaceous feathers evolved early in maniraptoran evolution; and (3) feathers with aerodynamic features originated before the origin of birds. The presence of flight feathers on the metatarsus represents a new morph that is not known previously, but it has implications for understanding the origin of avian flight. The discovery of four-winged dinosaurs was suggested to provide strong evidence supporting the ‘tree-down’ hypothesis for the origin of avian flight, though in-depth analysis and more data are needed to confirm this. A brief analysis of the fossil preservation and faunal composition reveals several interesting characteristics: (1) Volcanic activity might have contributed to the exceptional preservation of dinosaurian skeletons and in particular their soft tissues; (2) Different from most other dinosaur faunas, the Jehol dinosaur fauna has a low ornithischian specific diversity relative to a high theropod specific diversity; and (3) the Liaoning theropods show a strong tendency toward secondary herbivory. The faunal composition suggests a complex biogeographic history for this fauna and provides negative evidence for the hypothesis that eastern Asia was isolated from the Middle Jurassic through late Early Cretaceous times. Copyright © 2006 John Wiley & Sons, Ltd.
Article
Jinfengopteryx is a newly uncovered Archaeopteryx-like avialan bird outside Germany, which was found from the Jehol Biota of northern Hebei in northeastern China. It shares many characters only with Archaeopteryx by the possession of three fenestrae in the antorbital cavity, 23 caudal vertebrae and long tail feathers attached to all the caudal vertebrae. But the former differs from the latter in the relatively short and high preorbital region of skull, more and closely packed teeth, much shorter forelimb compared to hindlimb. Such differences indicate Jinfengopteryx is even slightly more primitive than Archaeopteryx, although both birds can be placed at the root position of the avialan tree based on cladistic analysis. Shenzhouraptor is suggested to be slightly more advanced than Jinfengopteryx + Archaeopteryx, supported by some derived features in teeth, shoulder girdles and forelimbs such as the reduction of tooth number, dorsolaterally directed glenoid facet, very long forelimb and comparatively short manus. Meanwhile, the tail of Shenzhouraptor shows more primitive characters than those of Jinfengopteryx and Archaeopteryx, e.g., the strikingly longer tail composed of more caudal vertebrae and the long tail feathers attached only to distal caudal segments. The mixed primitive and advanced characters reveal the evident mosaic evolution among long-tailed avialan birds.
Article
The so-called Jehol Biota, an excellently preserved Early Cretaceous biota consisting of both lacustrine and terrestrial organisms, is one of the most important Mesozoic fossillagerstätten. Although there have been extensive palaeontological studies, little work has been done on the volcanic settings under which the biota was preserved. The Sihetun area is the most famous fossil locality of the Jehol Biota in western Liaoning, and the volcanic succession in that area is the most representative and best studied. We use a case study of the volcanic succession of the Lower Cretaceous Yixian Formation in the Sihetun area to reconstruct the volcanic complexes and their history, to propose a depositional model of the volcanic successions, and to understand the relationship between volcanic activity and fossil preservation in western Liaoning. The volcanic succession comprises four volcanic complexes, each with distinct products; a shield volcano, an intermediate multi-vent center, a volcanic lake (in summit caldera), and finally lava domes. The presence of a caldera is postulated from exposures which suggest the presence of an inner topographic wall, bounding faults, and intra-caldera fill. Frequent volcanic activities and widespread existence of volcanic lakes during the Early Cretaceous are thought to account for the exceptional preservation of invertebrates and vertebrates of the Jehol Biota in western Liaoning.Research highlights►We reconstruct the volcanic complexes and their history of the Yixian Formation. ►We aim to untangle the relationship between volcanism and fossil preservation. ►Four volcanic complexes are recognized. ►A caldera origin is proposed for the Early Cretaceous volcanic lake in the Sihetun. ►Volcanic activities adjacent lakes increase the chances of fossil preservation.