Primitive Birds Research Articles

Rapid preservation of Jehol Biota in Northeast China from high precision 40Ar/39Ar geochronology

In Liaoning Province, Northeastern China, the Early Cretaceous Jehol Biota records significant evolution and radiation of fauna in terms of diversity, abundance and complexity. The alluvial-to-fluvial Lujiatun and lacustrine Jianshangou beds of the lower Yixian Formation yield exceptionally well-preserved three-dimensional and articulated dinosaur and mammal fossils, and two-dimensional primitive birds/feathered dinosaurs, respectively. Published 40Ar/39Ar ages for the two fossil beds have uncertainties of ± 0.4 to 1.0 Ma (± 2σ analytical uncertainty), and these reflect the measurement of large, and potentially heterogeneous, populations of feldspar crystals. More precise constraints on the timing and duration of biological radiation recorded by this sequence can further quantify evolutionary patterns and rates of diversification of important Early Cretaceous animals and plants. Single crystal 40Ar/39Ar fusion experiments on sanidine from intercalated ash beds yield dates that constrain the deposition of the Jianshangou and Lujiatun fossil beds to between 125.374 ± 0.085 and 125.572 ± 0.120 Ma, and 125.541 ± 0.099 and 125.793 ± 0.127 Ma, respectively. These ages indicate that the lower part of Jianshangou fossil bed was deposited nearly contemporaneously with the Lujiatun fossil bed. Thus, mass mortality events reflected by dinosaur fossil concentrations in the Lujiatun fossil bed and feathered dinosaur/primitive bird fossils in the Jianshangou fossil bed were nearly coeval and short-lived. These 40Ar/39Ar ages, combined with astrochronologic and paleomagnetic results from the lacustrine sediments in the Jianshangou fossil bed, not only refine the duration and rapid radiation of primitive birds and feathered dinosaurs in the deposit, but also suggest that the distribution of magnetic polarity chron boundaries within the Barremian stage in the current geologic time scale (GTS 2020) requires a revision.

About this title - Mesozoic Biological Events and Ecosystems in East Asia

Mesozoic Biological Events and Ecosystems in East Asia covers a wide range of topics, encompassing palaeoenvironments, palaeoecosystems and important vertebrate, invertebrate and plant fossils, some found in amber with excellent preservation of delicate morphological features. Fifty-three authors from a number of different disciplines – geochronology, palaeontology, stratigraphy, sedimentology, tectonics and geochemistry – contribute to the 18 articles in the volume. Well-preserved fossils and rocks continue to be found from marine and terrestrial sediments across East Asia. Over some years, the palaeontological and geological evidence discovered from this region has significantly improved our understanding of Mesozoic environments. In discussing feathered dinosaurs, primitive birds, early mammals, diverse insects, amber inclusions, the oldest-known flowers and research utilizing new, advanced methods, this volume explores Earth's history in even greater detail. What other exciting discoveries are waiting to be unveiled in the future?

The first specimen of Archaeopteryx from the Upper Jurassic Mörnsheim Formation of Germany

ABSTRACTFrom an initial isolated position as the oldest evolutionary prototype of a bird, Archaeopteryx has, as a result of recent fossil discoveries, become embedded in a rich phylogenetic context of both more and less crownward stem-group birds. This has prompted debate over whether Archaeopteryx is simply a convergently bird-like non-avialan theropod. Here we show, using the first synchrotron microtomographic examination of the genus, that the eighth or Daiting specimen of Archaeopteryx possesses a character suite that robustly constrains it as a basal avialan (primitive bird). The specimen, which comes from the Mörnsheim Formation and is thus younger than the other specimens from the underlying Solnhofen Formation, is distinctive enough to merit designation as a new species, Archaeopteryx albersdoerferi sp. nov., but is recovered in close phylogenetic proximity to Archaeopteryx lithographica. Skeletal innovations of the Daiting specimen, such as fusion and pneumatization of the cranial bones, well vascularized pectoral girdle and wing elements, and a reinforced configuration of carpals and metacarpals, suggest that it may have had more characters seen in flying birds than the older Archaeopteryx lithographica. These innovations appear to be convergent on those of more crownward avialans, suggesting that Bavarian archaeopterygids independently acquired increasingly bird-like traits over time. Such mosaic evolution and iterative exploration of adaptive space may be typical for major functional transitions like the origin of flight.

The first dinosaur egg from the Lower Cretaceous of Western Siberia, Russia

The Lower Cretaceous Ilek Formation in Western Siberia (Russia) has yielded various vertebrate fossils, including skeletal remains of dinosaurs. Here we report on a fragmentary theropod egg from the vertebrate locality Shestakovo 3 of the Ilek Formation in Kemerovo Province. We assign the specimen to the oogenus Prismatoolithus (oofamily Prismatoolithidae) as Prismatoolithus ilekensis oosp. nov., on the basis of the following unique combination of characters: ovoid-shaped egg; thin eggshell 300–330 μm thick; angustiprismatic morphotype; eggshell with three different layers; gradual transition between mammillary layer and prismatic layer; abrupt contact between prismatic layer and external layer; mammillary layer to prismatic layer to external layer thickness ratio is 1:3:0.6; prismatic layer with ill-defined squamatic texture; angusticanaliculate pore system; and smooth outer surface. Like other Early Creataceous Prismatoolithus, the egg of Prismatoolithus ilekensis oosp. nov. was laid by a small bodied theropod dinosaur (troodontid or primitive bird) and this taxonomic attribution is supported by results of our phylogenetic analysis. Prismatoolithus ilekensis oosp. nov. is the first Early Cretaceous ootaxon from Russia.urn:lsid:zoobank.org:act:734EAD40-86C3-488B-A61E-B5FF7378BC0E

Insight into the growth pattern and bone fusion of basal birds from an Early Cretaceous enantiornithine bird

Bird skeletons exhibit remarkable modifications that allow for flight. The most distinguishable features are the fusion of the bones in the hand, feet, and pelvis into composite rigid and bony structures. However, the historical origins of these avian bone fusions remain elusive because of the rarity of transitional fossils and developmental studies on modern birds. Here, we describe an Early Cretaceous bird (120 Mya) that has fully fused alular-major metacarpals and pelvis. We discuss the manus and pelvis fusions across Paravian phylogeny and demonstrate that these features evolved independently across nonavian theropods, Enantiornithes, and Ornithuromorpha. The fusions of these bones are rare in known nonavian theropods and Early Cretaceous birds but are well established among Late Cretaceous and modern birds, revealing a complicated evolution pattern unrecognized previously. We posit that the developments of bone fusion were polymorphic close to the origin of birds, resulting in the varying degrees of fusion in Paraves. However, that development polymorphism appears to be fundamentally restricted along the line to modern birds by the Late Cretaceous, where all birds have a completely fused manus and pelvis. Such changes likely correspond to a refinement of flight capability. Alternatively, the degree of bone fusion in this primitive bird may have been related to modifications in genes or developmental paths. Future studies and fossil discoveries are required to clarify these hypotheses and pinpoint the developmental pathways involving the bone fusions in early avian evolution through to their modern pattern.

New chronostratigraphic constraints on the Yixian Formation with implications for the Jehol Biota

The fossils of the Cretaceous Jehol Biota exhibit excellent preservation and extraordinary diversity. Terrestrial fossils, including plants, insects, dinosaurs, birds, mammals and freshwater invertebrates have been discovered from the Dabeigou, Yixian and Jiufotang Formations (and correlative strata) in Central and East Asia. Significant specimens have been recovered from the Yixian Formation of Inner Mongolia, Hebei Province, western Liaoning Province of NE China. The Yixian Formation is generally divided (from bottom to top) into the Lujiatun Unit, Lower Lava Unit, Jianshangou Unit, Upper Lava Unit, Dawangzhangzi Unit and Jingangshan Unit. However, previously reported age data obtained through a range of methods and applied to different units of the Yixian Formation do not consistently integrate with the Yixian's commonly accepted stratigraphic interpretation. Here we summarize previous age data for the Yixian Formation and recalibrate previously reported 40Ar/39Ar ages by using new age interpretations for the same standard (i.e. FCs=28.294). We also present new high-precision 40Ar/39Ar ages of 125.8±1.0Ma and 126.0±0.8Ma for two basaltic samples from the Lujiatun Unit, a unit of previously uncertain age. The new age data and re-calibrated published data indicate that the Lujiatun Unit was deposited contemporaneously with the Jianshangou Unit. The widely accepted stratigraphic column for the Yixian Formation therefore requires reinterpretation. Our study provides significant clues for reconstructing sedimentary environment for the fossil-rich Yixian deposits and allows to constrain evolutionary rates for early mammals, primitive birds and feathered dinosaurs.

The Hypermethylated Regions in Avian Chromosomes

Chromosomal locations and amounts of 5-methylcytosine-rich chromosome regions were detected in the karyotypes of 13 bird species by indirect immunofluorescence using a monoclonal anti-5-methylcytosine antibody. These species belong to 7 orders and 10 families of modern (Neognathae) and primitive (Palaeognathae) birds and are characterized by macro- and microchromosomes as well as ZW sex chromosomes. In all 13 species, the hypermethylated chromosome segments are confined to constitutive heterochromatin. The chromosomal locations of hypermethylated DNA regions in the karyotypes are constant and species-specific. There is no general rule with regard to the distribution of these hypermethylated chromosome regions in the genomes of birds. In most instances, hypermethylated segments are located in the centromeric regions of chromosomes, but in the sex chromosomes, these can also be found in telomeric and interstitial postitions. In most of the species studied, the centromeric heterochromatin in many, if not all, of the microchromosomes is hypermethylated. However, in one species, the only detectable hypermethylated heterochromatic regions are located in one pair of macroautosomes and in the Z sex chromosome, but none of the microchromosomes contains visible quantities of 5-methylcytosine. The analysis of 5-methylcytosine-rich chromosome regions can be very helpful for the comparative cytogenetics of closely related species or subspecies. It also reflects the dynamic evolutionary process operating in the highly repetitive DNA of eukaryotic chromosomes.

Soft-tissue and dermal arrangement in the wing of an Early Cretaceous bird: Implications for the evolution of avian flight.

Despite a wealth of fossils of Mesozoic birds revealing evidence of plumage and other soft-tissue structures, the epidermal and dermal anatomy of their wing’s patagia remain largely unknown. We describe a distal forelimb of an enantiornithine bird from the Lower Cretaceous limestones of Las Hoyas, Spain, which reveals the overall morphology of the integument of the wing and other connective structures associated with the insertion of flight feathers. The integumentary anatomy, and myological and arthrological organization of the new fossil is remarkably similar to that of modern birds, in which a system of small muscles, tendons and ligaments attaches to the follicles of the remigial feathers and maintains the functional integrity of the wing during flight. The new fossil documents the oldest known occurrence of connective tissues in association with the flight feathers of birds. Furthermore, the presence of an essentially modern connective arrangement in the wing of enantiornithines supports the interpretation of these primitive birds as competent fliers.

Mesozoic basins and associated palaeogeographic evolution in North China

In North China, the Mesozoic terrestrial basins, sedimentary palaeogeography and tectonic settings involved five evolutionary stages: (1) the Early‒Middle Triassic, (2) the Late Triassic to Early‒Middle Jurassic, (3) the Late Jurassic to early Early Cretaceous, (4) the middle‒late Early Cretaceous and (5) the Late Cretaceous. The regional punctuated tectonic events occurred during these evolutionary stages.During the Early‒Middle Triassic (stage 1), the Xingmeng Orogenic Belt (XMOB, i.e., eastern part of Central Asia Orogenic Belt, CAOB) of the northern North China was settled in the transition of tectonic environment from syn‒orogenic compression to post‒orogenic extension with intensive uplifting. It is a main provenance in the unified Ordos‒North China Basin.The united continental plate of China and the Qinling‒Dabie‒Sulu Orogenic Belt formed due to convergence and collision between the North China Plate and the Yangtze Plate along two suture zones of the Mianlue and the Shangdan in the terminal Middle Triassic.During the Late Triassic to the Early‒Middle Jurassic (stage 2), the Late Triassic mafic or alkaline rocks and intrusions occurred on the northern and southern margins of North China Craton (NCC) and XMOB, implying that intensified extension happened all over the North China (early phase of stage 2). Additionally, in the late phase of stage 2, the basic volcanicfilling faulted basins were widely distributed in the northeastern North China during the Early–Middle Jurassic, including a series of small- to medium-sized basins with coal-bearing strata and some volcanic rocks in other areas of North China, which was the result of subduction of the Palaeo-Pacific Plate during the Early–Middle Jurassic. An active continental margin with accretionary complex developed in the eastern Heilongjiang of China, Japan and the Far East of Russia at that time. However, in the end of the Early‒Middle Jurassic, because of the Yanshanian orogeny characterized by complicated thrust and fold, the previous unified Ordos–North China Basin was separated by the northeast-oriented Great Xing’an Range and Taihang Mountain uplifted linearment. The differential evolution of basins and sedimentary palaeogeography between eastern and western North China was initiated, and was interpreted to result in the closure of Okhotsk Ocean and the subduction of Palaeo-Pacific Plate (late stage 2).During the Late Jurassic (the early phase of stage 3), a variety of faulted basins occurred in the Yanshan and Yinshan areas in the northeastern North China. In Yanshan area, basins were filled with thickened intermediate volcanic rocks and purple-red coarse-grained clastic rocks. In contrast, only thick layered sedimentary rocks with rare volcanic rocks developed in the Yinshan faulted basins, the Ordos Basin and basins in sourthern North China. XMOB was the main provenance of the Early Mesozoic basins in the North China, while the Ordos Basin and the Hefei Basin were partly supplied by the northern Qinling Orogenic Belt.During the Late Jurassic–early Early Cretaceous (the late phase of stage 3), the northern and northeastern North China experienced extensional movement after the subduction of the Palaeo-Pacific Plate, the closure of the Mongolia–Okhotsk Ocean and the subsequent Yanshanian orogeny. At the same time, a NE-oriented, giant rift basin system (NE Asia Rift) extended from the Yanshan to the western Great Xing’an Range, where rift basins were filled with the regional, NE-oriented, thick coarse-grained clastic rocks and a belt of volcanic rocks. In the meantime, the eastern and northeastern China and most areas of NCC were presented as highland terrains.During the middle‒late Early Cretaceous (stage 4), rift basins developed and accumulated alluvial sediments and interbedded alkaline volcanic rocks in the western and northern North China, including Yingen, Ejinaqi and Erlian regions. Basins were formed on both sides of the Tan-Lu Fault Zone under a striking-slipping force. Furthermore, faulted basins developed in the Yishu Fault Zone of Shandong (central Tan-Lu Fault Zone) as well, where dinosaur fauna flourished. Basic volcanic rocks and fluvial‒lacustrine sediments were deposited in small- or medium-sized rift basins in the northeastern China. The Songliao Basin was a typical giant basin that was mainly filled with late Early Cretaceous lacustrine sediments. A group of rift basins occurred in the Sanjiang area, central Heilongjiang Province, northeastern China.From the middle‒late Early Cretaceous to the Late Cretaceous (stage 5), depositional and subsiding center of the basins constantly shifted southeastwards in Heilongjiang Province. The tectonic setting changed into the Palaeo-Pacific continental margin in north and northeastern China.Besides, during the Late Mesozoic, a huge terrestrial biota, mainly dinosaur fauna, dominated in North China. The Yanliao biota of the Middle–Late Jurassic and the Jehol biota of the Early Cretaceous are characterized by feathered dinosaurs, primitive birds, mammals, pterosaur, insects and plants (angiosperms). In northeastern Asia, this Late Mesozoic tectonic background , palaeogeoraphy and palaeoecology were shared by East China, Korean Peninsula, Japan and the Far East of Russia.

A tale of a ‘middle’ tail

Zhongornis refers to a ‘middle’ or ‘intermediate’ bird because its tail was claimed to be transitional between primitive birds with a long bony tail (such as Archaeopteryx and Jeholornis) and those with a short tail ending in a fused tip called the pygostyle (such as Confuciusornis) [1]. This finding is significant, as it appeared to fill a ‘gap’ at a critical stage in the early evolution of birds. However, after a detailed restudy, O’Connor and Sullivan [2] suggest that this juvenile bird from the Early Cretaceous Jehol fauna of China actually possesses 20, rather than 14, tail vertebrae; further, this tail is very similar to those of Epidexipteryx (a scansoriopterygid) and Caudipteryx (an oviraptorosaur) among the theropods. Based on this and other features, the authors reinterpretZhongornis as the sister taxon of scansoriopterygids, and further suggest that this clade (Zhongornis + Scansoriopterygidae) is the sister group of Oviraptorosauria. Surprisingly, despite the discovery of so many beautifully preserved feathered dinosaurs in China, the relationships among them, especially those close to the origin of birds, are still intriguing. This intrigue applies to Oviraptorosauria, the ‘egg thief lizards’, and Scansoriopterygidae, a recently recognized rare arboreal clade. Consider this: you have four tails, one each from an oviraptorosaur dinosaur, a dromaeosaur dinosaur, a primitive bird (Archaeopteryx), and a true bird (Confuciusornis). Like many others, you may have immediately seen (1) a long bony tail similar in dromaeosaurs and primitive birds, (2) a very short tail with a pygostyle unique in true birds, and (3) a reduced tail, an intermediate condition seen in oviraptorosaurs. However, most recent cladistic analyses reveal Oviraptorosauria as the sister group of Paraves, which includes dromaeosaurs and birds [3]. This forces us to interpret the tail similarities between oviraptorosaurs and birds as having evolved convergently. The robust and flexible oviraptorosaur tails, together with their broad tail-feather fans, were uniquely adapted to serve as dynamic intraspecific display structures [4]. However, the origin of oviraptorosaurs remains a mystery, with no Jurassic record. O’Connor and Sullivan’s study indicates that oviraptorosaurs’ cousins (scansoriopterygids) once lived in the Jurassic trees in the north-eastern China, and their differences might result from adaptation to contrasting ecological niches. Will taking Zhongornis’s tail out of the ‘middle’ bird tail allow us to eventually discover the real ‘middle’ creature someday? Perhaps not! A recent genetic and evolutionary development study shows that a single genetic mutation could have occurred in paravian dinosaurs, which both truncated its tail and fused its distal caudal vertebrae into a pygostyle [5]. Moreover, this potential mutation has pleiotropic effects also leading to fusions inmore anterior vertebrae, ribs, and even digits. These fusions have been observed in mice and modern birds, as well as in Confuciusornis and more advanced birds, but not in Jeholornis and Archaeopteryx [5]. The co-occurrence of Confuciusornis and Jeholornis about125millionyears ago also supports this sudden appearance of short-tailed birds. Therefore, the search for the fantastical middle bird may prove to be futile.

From dinosaurs to birds: a tail of evolution.

A particularly critical event in avian evolution was the transition from long- to short-tailed birds. Primitive bird tails underwent significant alteration, most notably reduction of the number of caudal vertebrae and fusion of the distal caudal vertebrae into an ossified pygostyle. These changes, among others, occurred over a very short evolutionary interval, which brings into focus the underlying mechanisms behind those changes. Despite the wealth of studies delving into avian evolution, virtually nothing is understood about the genetic and developmental events responsible for the emergence of short, fused tails. In this review, we summarize the current understanding of the signaling pathways and morphological events that contribute to tail extension and termination and examine how mutations affecting the genes that control these pathways might influence the evolution of the avian tail. To generate a list of candidate genes that may have been modulated in the transition to short-tailed birds, we analyzed a comprehensive set of mouse mutants. Interestingly, a prevalent pleiotropic effect of mutations that cause fused caudal vertebral bodies (as in the pygostyles of birds) is tail truncation. We identified 23 mutations in this class, and these were primarily restricted to genes involved in axial extension. At least half of the mutations that cause short, fused tails lie in the Notch/Wnt pathway of somite boundary formation or differentiation, leading to changes in somite number or size. Several of the mutations also cause additional bone fusions in the trunk skeleton, reminiscent of those observed in primitive and modern birds. All of our findings were correlated to the fossil record. An open question is whether the relatively sudden appearance of short-tailed birds in the fossil record could be accounted for, at least in part, by the pleiotropic effects generated by a relatively small number of mutational events.

Unique caudal plumage of Jeholornis and complex tail evolution in early birds

The Early Cretaceous bird Jeholornis was previously only known to have a distally restricted ornamental frond of tail feathers. We describe a previously unrecognized fan-shaped tract of feathers situated dorsal to the proximal caudal vertebrae. The position and morphology of these feathers is reminiscent of the specialized upper tail coverts observed in males of some sexually dimorphic neornithines. As in the neornithine tail, the unique "two-tail" plumage in Jeholornis probably evolved as the result of complex interactions between natural and sexual selective pressures and served both aerodynamic and ornamental functions. We suggest that the proximal fan would have helped to streamline the body and reduce drag whereas the distal frond was primarily ornamental. Jeholornis reveals that tail evolution was complex and not a simple progression from frond to fan.

Astrochronology for the Early Cretaceous Jehol Biota in northeastern China

The Early Cretaceous Jehol Biota in northeastern China provides an evolutionary window for ‘feathered’ dinosaurs, primitive birds, insects and early flowering plants. It also provides critical information for the biodiversity changes of the Early Cretaceous terrestrial ecosystem. Here we report a time series analysis for the 11.2-m-thick, fossil-bearing lacustrine deposits at the Sihetun section in western Liaoning, northeastern China on the basis of high-resolution magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) measurements. A hierarchy of sedimentary cycle bands of 120–260cm, 50–67cm and 18–42cm was recorded in the MS and ARM series. With available radioisotope age constraints from the same section, sedimentary cycles of 120–260cm, 50–67cm and 18–42cm were interpreted as Milankovitch cycles of short eccentricity (130 and 95kyr), obliquity (36.6 and 46kyr), and precession (22.1, 20.9 and 18kyr), respectively. The 100kyr-tuned ‘floating’ astronomical time scale indicates that the duration of the 11.2-m-thick section is ~0.67Myr and the average depositional rate is ~1.70cm/kyr. The duration of the 1.8-m-thick, main fossil-bearing interval that contains 8 beds of ‘feathered’ dinosaur/primitive bird fossils can be estimated as short as 150kyr. The results suggest that climate fluctuations manifested in paleobotanical, sedimentological and geochemical records of the Yixian Formation may have been controlled by orbital forcing during Early Cretaceous.

Analysis of Immunoglobulin Transcripts in the Ostrich Struthio camelus, a Primitive Avian Species

Previous studies on the immunoglobulin (Ig) genes in avian species are limited (mainly to galliformes and anseriformes) but have revealed several interesting features, including the absence of the IgD and Igκ encoding genes, inversion of the IgA encoding gene and the use of gene conversion as the primary mechanism to generate an antibody repertoire. To better understand the Ig genes and their evolutionary development in birds, we analyzed the Ig genes in the ostrich (Struthio camelus), which is one of the most primitive birds. Similar to the chicken and duck, the ostrich expressed only three IgH chain isotypes (IgM, IgA and IgY) and λ light chains. The IgM and IgY constant domains are similar to their counterparts described in other vertebrates. Although conventional IgM, IgA and IgY cDNAs were identified in the ostrich, we also detected a transcript encoding a short membrane-bound form of IgA (lacking the last two CH exons) that was undetectable at the protein level. No IgD or κ encoding genes were identified. The presence of a single leader peptide in the expressed heavy chain and light chain V regions indicates that gene conversion also plays a major role in the generation of antibody diversity in the ostrich. Because the ostrich is one of the most primitive living aves, this study suggests that the distinct features of the bird Ig genes appeared very early during the divergence of the avian species and are thus shared by most, if not all, avian species.

Morfologia e topografia do fígado e pâncreas de emas Rhea americana

As emas são aves ratitas nativas do continente sul americano, são consideradas aves primitivas do ponto de vista filogenético que constituem um grupo altamente especializado. Este estudo buscou caracterizar macro e microscopicamente o fígado e pâncreas de emas. O material foi coletado no Centro de Multiplicação de Animais Silvestres (CEMAS), na cidade de Mossoró-RN, Brasil, (Registro IBAMA n° 14.78912). Utilizaram-se 20 animais jovens com idade entre dois e seis meses independente do sexo. Em emas, o fígado se relacionava cranialmente com o ápice do coração, dorsalmente com os pulmões, esôfago e o proventrículo gástrico, caudalmente, com o ventrículo gástrico, o baço, o duodeno e parte do jejuno. Apresentava coloração vermelha escura e possuía apenas dois lobos, sendo o direito ligeiramente menor que o esquerdo. Histologicamente, era revestido por uma cápsula de tecido conjuntivo delgada e cada lóbulo hepático pôde ser identificado pela presença evidente de veias centrais, com muitos sinusoides comunicando-se com elas. O pâncreas, ventralmente, apresentava-se como uma fita fina, formado por um lobo dorsal e um lobo ventral. Longitudinalmente o pâncreas em emas localiza-se no mesentério dorsal desde o fígado até a flexura cranial do duodeno, mantendo-se preso às alças duodenais por ligamentos. Histologicamente, era composto por uma cápsula delgada de tecido conjuntivo denso, com discretos lóbulos separados por tecido conjuntivo capsular, compostos por estruturas tubuloalveolares e ductos. O fígado e pâncreas de emas apresentam padrão morfológico similar ao descrito para aves domésticas.

Likelihood reinstates Archaeopteryx as a primitive bird.

The widespread view that Archaeopteryx was a primitive (basal) bird has been recently challenged by a comprehensive phylogenetic analysis that placed Archaeopteryx with deinonychosaurian theropods. The new phylogeny suggested that typical bird flight (powered by the front limbs only) either evolved at least twice, or was lost/modified in some deinonychosaurs. However, this parsimony-based result was acknowledged to be weakly supported. Maximum-likelihood and related Bayesian methods applied to the same dataset yield a different and more orthodox result: Archaeopteryx is restored as a basal bird with bootstrap frequency of 73 per cent and posterior probability of 1. These results are consistent with a single origin of typical (forelimb-powered) bird flight. The Archaeopteryx-deinonychosaur clade retrieved by parsimony is supported by more characters (which are on average more homoplasious), whereas the Archaeopteryx-bird clade retrieved by likelihood-based methods is supported by fewer characters (but on average less homoplasious). Both positions for Archaeopteryx remain plausible, highlighting the hazy boundary between birds and advanced theropods. These results also suggest that likelihood-based methods (in addition to parsimony) can be useful in morphological phylogenetics.

Synsacrum of a primitive bird from the Upper Cretaceous of Uzbekistan

A partial synsacrum of a primitive bird from the Zenge Kurgan 3 locality in the Kyzyl Kum Desert (Uzbekistan) is described. The vertebrate fauna from this locality is similar to that of the Bissekty Formation of the Dzharakuduk locality (Central Kyzyl Kum, Uzbekistan); however, this synsacrum differs considerably from all other synsacra from Dzharakuduk. The taxonomic position of this bird remains uncertain; it is most similar to some Enantiornithes, although it could have belonged to a primitive ornithuromorph bird. The functional significance of structural differences in the synsacrum of ornithurine and enantiornithine birds is discussed.

Description and ecologic analysis of Hollanda luceria, a Late Cretaceous bird from the Gobi Desert (Mongolia)

Avian fossils from the Upper Cretaceous of Mongolia provide significant scientific insight into the evolution of early birds, primarily due to the scarcity of continental interiors with a well-documented avifauna in the Cretaceous record. This paper describes in detail the anatomy and histology of a new taxon of early ornithuromorph bird, Hollanda luceria, from the Barun Goyot Formation at Khermeen Tsav in the Gobi Desert of Mongolia. The new taxon is represented exclusively by hindlimb elements, and is characterized by having elongated hindlimbs with an extremely reduced metatarsal IV and an unusual tibiotarsal-femoral articulation centered on a highly peaked lateral articular facet of the tibiotarsus. Cladistic and ecospace analyses were also carried out in order to infer evolutionary relationships and ecology of this primitive bird. These analyses indicate that the new taxon is a previously undescribed lineage of basal ornithuromorph and an outgroup of Ornithurae ( sensu Chiappe, 2002), which may have had a cursorial lifestyle similar to that of the modern roadrunner, Geococcyx californianus.

Olfactory acuity in theropods: palaeobiological and evolutionary implications

This research presents the first quantitative evaluation of the olfactory acuity in extinct theropod dinosaurs. Olfactory ratios (i.e. the ratio of the greatest diameter of the olfactory bulb to the greatest diameter of the cerebral hemisphere) are analysed in order to infer the olfactory acuity and behavioural traits in theropods, as well as to identify phylogenetic trends in olfaction within Theropoda. A phylogenetically corrected regression of olfactory ratio to body mass reveals that, relative to predicted values, the olfactory bulbs of (i) tyrannosaurids and dromaeosaurids are significantly larger, (ii) ornithomimosaurs and oviraptorids are significantly smaller, and (iii) ceratosaurians, allosauroids, basal tyrannosauroids, troodontids and basal birds are within the 95% CI. Relative to other theropods, olfactory acuity was high in tyrannosaurids and dromaeosaurids and therefore olfaction would have played an important role in their ecology, possibly for activities in low-light conditions, locating food, or for navigation within large home ranges. Olfactory acuity was the lowest in ornithomimosaurs and oviraptorids, suggesting a reduced reliance on olfaction and perhaps an omnivorous diet in these theropods. Phylogenetic trends in olfaction among theropods reveal that olfactory acuity did not decrease in the ancestry of birds, as troodontids, dromaeosaurids and primitive birds possessed typical or high olfactory acuity. Thus, the sense of smell must have remained important in primitive birds and its presumed decrease associated with the increased importance of sight did not occur until later among more derived birds.

A NEW BASAL LINEAGE OF EARLY CRETACEOUS BIRDS FROM CHINA AND ITS IMPLICATIONS ON THE EVOLUTION OF THE AVIAN TAIL

Abstract: We report on a new Early Cretaceous bird from China that sheds significant light on the evolutionary transition between primitive birds with a long bony tail and those with a short tail ending in a pygostyle. A cladistic analysis of basal birds supports the placement of the new fossil as the sister‐taxon of all pygostylians. Possessing a unique hand morphology with a phalangeal formula of 2‐3‐3‐x‐x and a reduced number of caudal vertebrae lacking a pygostyle, the new specimen reveals anatomical information previously unknown and increases the taxonomic diversity of primitive, non‐pygostylian birds. We infer from the specimen that during the evolution of the avian tail, a decrease in relative caudal length and number of vertebrae preceded the distal fusion of caudals into a pygostyle.