Cretaceous origins of the vibrotactile bill-tip organ in birds

Some probe-foraging birds locate their buried prey by detecting mechanical vibrations in the substrate using a specialized tactile bill-tip organ comprising mechanoreceptors embedded in densely clustered pits in the bone at the tip of their beak. This remarkable sensory modality is known as ‘remote touch’, and the associated bill-tip organ is found in probe-foraging taxa belonging to both the palaeognathous (in kiwi) and neognathous (in ibises and shorebirds) clades of modern birds. Intriguingly, a structurally similar bill-tip organ is also present in the beaks of extant, non-probing palaeognathous birds (e.g. emu and ostriches) that do not use remote touch. By comparison with our comprehensive sample representing all orders of extant modern birds (Neornithes), we provide evidence that the lithornithids (the most basal known palaeognathous birds which evolved in the Cretaceous period) had the ability to use remote touch. This finding suggests that the occurrence of the vestigial bony bill-tip organ in all modern non-probing palaeognathous birds represents a plesiomorphic condition. Furthermore, our results show that remote-touch probe foraging evolved very early among the Neornithes and it may even have predated the palaeognathous–neognathous divergence. We postulate that the tactile bony bill-tip organ in Neornithes may have originated from other snout tactile specializations of their non-avian theropod ancestors.     

Flightlessness affects cranial morphology in birds

Flightless birds belonging to phylogenetically distant clades share several morphological features in the pectoral and pelvic apparatus. There are indications that skull morphology is also influenced by flightlessness. In this study we used a large number of flightless species to test whether flightlessness in modern birds does indeed affect cranial morphology. Discriminant analyses and variation partitioning show evidence for a relationship between skull morphology and the flightless condition in birds. A possible explanation for the change in cranial morphology can be linked to the reduced selective force for light-weight skulls in flightless birds. This makes an increase in muscle mass, and therefore an enlargement of muscle insertion areas on the skull, possible. We also compared the ontogenetic trajectory of Gallus with the adult morphology of a sample of flightless species to see whether the apomorphic features characterizing the skull of flightless birds share the same developmental basis, which would indicate convergent evolution by parallelism. Skull morphology (expressed as principal component scores) of palaeognathous flightless birds (ratites) is dissimilar (higher scores) to juvenile stages of the chicken and therefore seem peramorphic (overdeveloped). Principal component scores of adult neognathous flightless birds fall within the range of chicken development, so no clear conclusions about the ontogenetic trajectories leading to their sturdier skull morphology could be drawn.     

Analyses of mitochondrial DNA nest ratite birds within the Neognathae: supporting a neotenous origin of ratite morphological characters

It is commonly acknowledged that the basal divergence among extant birds is between Palaeognathae and Neognathae. However, recent analyses of mitochondrial sequences have challenged that notion. In order to investigate this fundamental phylogenetic question, the complete mitochondrial DNA (mtDNA) molecule of the rook Corvus frugilegus (Passeriformes) was sequenced and included in phylogenetic analyses with the previously reported complete mtDNAs of the chicken Gallus gallus (Galliformes) and two ratite species, the ostrich Struthio camelus and the rhea Rhea americana (Struthioniformes). The analyses reconstructed a split between Passeriformes and a branch including Galliformes and Struthioniformes. Thus, the result is inconsistent with the traditional understanding of a basal avian divergence between Palaeognathae and Neognathae. The findings suggest that the morphological characteristics of the ratites are secondarily acquired, probably through neoteny and that the ratites are descendants of flying, neognathous ancestors.     

Microspectrophotometry of the photoreceptors of palaeognathous birds — the emu and the tinamou

Summary With the aid of a microspectrophotometer the visual pigments and oil globules in the retina of the emu (Dromiceius novae-hollandiae), the brushland tinamou (Nothoprocta c. cinerascens) and the Chilean tinamou (Nothoprocta perdicaria sanborni) were characterized. All three of these palaeognathous birds contain in their rods a typical rhodopsin with _max near 500 nm. Each of these birds has cones containing iodopsin-like visual pigments with _max in the 560–570 nm spectral region. No unequivocal evidence was obtained for the presence of cone pigments other than this iodopsin-like pigment, although one cell thought to be a cone, and containing a visual pigment with _max near 498 nm, was observed in the retina of the brushland tinamou. The oil globule systems of the three palaeognathous species are identical to each other and are much simpler than is typical for neognathous birds in that only two different types of globule are present, one with _T50 at 508 nm and another with _T50 at 568 nm. Comparison of the data with observations made on neognathous species indicates (1) that palaeognathous birds probably have poorer color discrimination capabilities than neognathous birds and (2) that the tinamou is more closely related to the ratites than to the galliform species.This study was supported, in part, by NIH Grant No. EY01839 (A.J. Sillman), NIH Grant No. EY00323 (W.N. McFarland) and NSF Grant No. 78-07657 (E.R. Loew). The authors thank E. Clinite, R. Dunford, C. Murphy, R. Riis and D. Weathers for their valuable assistance. Thanks also go to R.E. Burger for his gift of the emus.     

Comparative ossification and development of the skull in palaeognathous birds (Aves: Palaeognathae)

Ratites and tinamous are a morphologically diverse group of flightless and weakly flighted birds. As one of the most basal clades of extant birds, they are frequently used as an outgroup for studies discussing character evolution within other avian orders. Their skeletal development is not well known in spite of their important phylogenetic position, and studies have historically been plagued with small sample sizes and limited anatomical and temporal scope. Here, I describe the ossification of the skull in the emu (Dromaius novaehollandiae), ostrich (Struthio camelus), greater rhea (Rhea americana), and elegant crested‐tinamou (Eudromia elegans). Skeletal development is remarkably consistent within palaeognaths, in spite of large differences in absolute size and incubation period. Adult morphology appears to play a role in interordinal differences in the sequence and timing of ossification of certain bones. Neither the timing of cranial ossification events relative to stage nor the sequence of ossification events provides any evidence in support of a paedomorphic origin of the palaeognathous palate. This study provides an important first look at the timing and sequence of skull development in palaeognathous birds, providing data that can be compared to better‐studied avian systems in order to polarize ontogenetic characters. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 184–200.     

Zur Evolution basicranialer Gelenke bei Vögeln,insbesondere bei Hühner- und Entenvögeln (Galloanseres)

On the evolution of basicranial articulations of birds, especially of fowl and waterfowl (Galloanseres) Basicranial articulations are among the most neglected structures of the avian feeding apparatus. Based on the presented ontogenetic evidence two nonhomologous types of basicranial articulations are distinguished in birds: 1. A basipterygoid articulation developing from an early embryonic quadratopolar comissure, which is homologous to the basipterygoid articulation of other amniotes. This diarthrosis is present in all paleognathous as well as in many juvenile and some adult neognathous birds. 2. A rostropterygoid articulation developing through apposition of the pterygoid on the parasphenoid. This secondary articulation is known from galliform and ansenform birds (Galloanseres). Based on ontogenetic evidence as well as functional analysis following hypothesis explaining the evolution of rostropterygoid articulations in the Galloanseres is proposed: 1. In the groundplan of birds (Aves, sensu Gauthier 1986) a basipterygoid articulation was present continuously during ontogeny. It protected the pterygoid-quadrate articulation against propalineal distortion by controlling the movement of the caudal end of the flexible, but undivided pterygopalatinal bar. This construction is preserved in recent paleognaths. 2. In the groundplan of the Neognathae an intrapterygoid joint subdividing the pterygopalatinal bar was formed in juveniles. Consequently the basipterygoid articulation had lost its function in adults and was therefore developed only in embryonic and juvenile stages. This condition is present in many recent neognaths. 3. In the stemline of the Galloanseres the intrapterygoid joint was already formed in embryos. Since an undivided pterygopalatinal bar is absent in any ontogenetic stage of the Galloanseres, no basipterygoid articulation is being formed. The recent Galloanseres retain this developmental pattern. 4. In the groundplan of the Galloanseres a newly developed rostropterygoid articulation was present providing a support for the pterygopalatinal bar. This articulation could withstand not only pressure but also increasing tension occurring as a consequence of the development of a gliding jaw joint and a firm grip with beak tips, both consequences of increasing herbivory in the Galloanseres. Since the basipterygoid articulation was reduced, a new secondary joint had to be developed.     

THE ONTOGENY OF THE CRANIAL BONES, CRANIAL PERIPHERAL AND CRANIAL PARASYMPATHETIC NERVES, TOGETHER WITH A STUDY OF THE VISCERAL MUSCLES OF STRUTHIO

Abstract The skull of Struthio is typically avian. There are, however, many cranial features that are neotenic in relation to the other Dromaeognathae and Neognathae. The premaxillary-vomer arthrosis is present in the embryo of Struthio but is absent in the adult; it is present in the adults of the other Dromaeognathae; the trabeculo-capsular entity is uninterrupted: therefore, there is no mesokinetic joint; kinesis, as a result, is limited. No orbitosphenoid present; septum ossifies as mesethmoid which appears on the dorsal surface. There are only two circumorbital bones present: the lacrimal and the jugal. The auditory region has only two centres of ossification: the prootic and opisthotic. The quadrate has a single elongated condyle of the processus oticus which articulates with the prootic and squamosal. The cranial base is ossified as the basioccipital and basisphenoid, the latter being of mixed origin. There are five dermal bones in the lower jaw of Struthio ; the gonial is present. The trigeminus musculature is reduced and shows very definite neotenic features. The peripheral cranial nerves are typically avian. The cranial parasympathetic nerves are well developed in the embryo but show definite signs of resorption in the later stages of development. The hyoid apparatus is mainly cartilaginous; the hyoid musculature is reduced.     

Small clades at the periphery of passerine morphological space

Among passerine birds (order Passeriformes), tribe- to family-level clades with five or fewer species are more frequent than one would expect from a homogeneous speciation and extinction process. Previous analyses also suggested that small clades tend to be marginal geographically and/or ecologically. In this study, I use principal component (PC) scores based on eight log-transformed measurements of the wing, tail, leg, and beak to test the hypothesis that small clades (相似文献   

The deep divergences of neornithine birds: a phylogenetic analysis of morphological characters

Consensus is elusive regarding the phylogenetic relationships among neornithine (crown clade) birds. The ongoing debate over their deep divergences is despite recent increases in available molecular sequence data and the publication of several larger morphological data sets. In the present study, the phylogenetic relationships among 43 neornithine higher taxa are addressed using a data set of 148 osteological and soft tissue characters, which is one of the largest to date. The Mesozoic non‐neornithine birds Apsaravis, Hesperornis, and Ichthyornis are used as outgroup taxa for this analysis. Thus, for the first time, a broad array of morphological characters (including both cranial and postcranial characters) are analyzed for an ingroup densely sampling Neornithes, with crown clade outgroups used to polarize these characters. The strict consensus cladogram of two most parsimonious trees resultant from 1000 replicate heuristic searches (random stepwise addition, tree‐bisection‐reconnection) recovered several previously identified clades; the at‐one‐time contentious clades Galloanseres (waterfowl, fowl, and allies) and Palaeognathae were supported. Most notably, our analysis recovered monophyly of Neoaves, i.e., all neognathous birds to the exclusion of the Galloanseres, although this clade was weakly supported. The recently proposed sister taxon relationship between Steatornithidae (oilbird) and Trogonidae (trogons) was recovered. The traditional taxon “Falconiformes” (Cathartidae, Sagittariidae, Accipitridae, and Falconidae) was not found to be monophyletic, as Strigiformes (owls) are placed as the sister taxon of (Falconidae + Accipitridae). Monophyly of the traditional “Gruiformes” (cranes and allies) and ”Ciconiiformes” (storks and allies) was also not recovered. The primary analysis resulted in support for a sister group relationship between Gaviidae (loons) and Podicipedidae (grebes)—foot‐propelled diving birds that share many features of the pelvis and hind limb. Exclusion of Gaviidae and reanalysis of the data set, however, recovered the sister group relationship between Phoenicopteridae (flamingos) and grebes recently proposed from molecular sequence data.     

Evolution of the Spindlin Gene in Birds: Independent Cessation of the Recombination of Sex Chromosomes at the Spindlin Locus in Neognathous Birds and Tinamous, a Palaeognathous Avian Family

Tinamous (Aves, Palaeognathae, Tinamiformes) are primitive birds, generally considered to be the sister group to the ratites. Tinamous possess a W sex-chromosome, intermediate in heterochromatization between the largely euchromatic W chromosome of the ratites and the highly condensed W chromosome of the neognathous birds. Of the four genes which are known to have diverged copies on the neognathous avian W and Z chromosome (ATP5A1, CHD1, PKC and SPIN) only the spindlin gene has W- and Z-chromosomal forms in the tinamiformes. This paper describes experiments which show that the sequences of these forms are more similar to each other and to the homologous undifferentiated spindlin gene sequences in the ratite genome than to the W or Z forms of the spindlin gene in other, neognathous species. This suggests that cessation of recombination at the spindlin locus of the ancestral W and Z chromosomes of the paleognathous tinamiformes and the neognathous avian species were independent events.     

Cranial and appendicular ontogeny of Bactrosaurus johnsoni,a hadrosauroid dinosaur from the Late Cretaceous of northern China

Abstract: The juvenile anatomy of various cranial and appendicular elements of the hadrosauroid dinosaur Bactrosaurus johnsoni is described in detail. Growth changes are documented from juvenile to adult stages for each skeletal element available. In the studied skull, ontogenetic trends consist of: development of features on the ventral surface of the frontal; reduction in the slope of the posteromedial process of the premaxilla; a posterior shift of the dorsal process of the maxilla; development of concavities on the medial surface of the prefrontal; increased robustness and development of the ventral flange of the jugal; decreased curvature of the long axis of the quadrate; increased ventral deflection of the dentary; and changes in the length/width proportions and depth of the anterior surface of the predentary. In the appendicular skeleton, the majority of ontogenetic variation from juvenile to adult occurs in the limb bones, including increased robustness of the deltopectoral crest of the humerus; relative shortening of the ulna; increased development of the fourth trochanter and mediolateral widening of the distal end of the femur; increased expansion of the cnemial crest of the tibia; and the increased prominence of articular protuberances and flanges of the metatarsals. A survey of the phylogenetically informative characters present in B. johnsoni indicates that several characters concerning the frontal, maxilla, jugal, quadrate, predentary, dentary, scapula, humerus and ilium are affected by ontogeny. Nevertheless, the majority of phylogenetic characters are not ontogenetically variable, suggesting that a substantial amount of the information provided by juvenile and subadult specimens for phylogenetic inference is reliable in basal hadrosauroids.     

Comparison of the Z and W sex chromosomal architectures in elegant crested tinamou (<Emphasis Type="Italic">Eudromia elegans</Emphasis>) and ostrich (<Emphasis Type="Italic">Struthio camelus</Emphasis>) and the process of sex chromosome differentiation in palaeognathous birds

To clarify the process of avian sex chromosome differentiation in palaeognathous birds, we performed molecular and cytogenetic characterization of W chromosome-specific repetitive DNA sequences for elegant crested tinamou (Eudromia elegans, Tinamiformes) and constructed comparative cytogenetic maps of the Z and W chromosomes with nine chicken Z-linked gene homologues for E. elegans and ostrich (Struthio camelus, Struthioniformes). A novel family of W-specific repetitive sequences isolated from E. elegans was found to be composed of guanine- and cytosine-rich 293-bp elements that were tandemly arrayed in the genome as satellite DNA. No nucleotide sequence homologies were found for the Struthioniformes and neognathous birds. The comparative cytogenetic maps of the Z and W chromosomes of E. elegans and S. camelus revealed that there are partial deletions in the proximal regions of the W chromosomes in the two species, and the W chromosome is more differentiated in E. elegans than in S. camelus. These results suggest that a deletion firstly occurred in the proximal region close to the centromere of the acrocentric proto-W chromosome and advanced toward the distal region. In E. elegans, the W-specific repeated sequence elements were amplified site-specifically after deletion of a large part of the W chromosome occurred.     

A New Pterosaur from the Jurassic of Cuba

Cacibupteryx caribensis gen. et sp. nov. is a new pterosaur of the family Rhamphorhynchidae found in western Cuba, in rocks of the Jagua Formation (Middle–Upper Oxfordian). The holotype, a skull and part of the left wing, is one of the few Jurassic pterosaurs that is well preserved in three dimensions. The new taxon shares characters with early and late Jurassic pterosaurs, and is one of the few late Jurassic taxa from western Laurasia and Gondwana. Furthermore, Cacibupteryx joins Nesodactylus hesperius Colbert from Cuba, and Sordes pilosus Sharov, from Kazakhstan as the most complete pterosaur recorded from the Middle–Upper Oxfordian. Cacibupteryx caribensis is one of the largest Jurassic pterosaurs known, and its skull possesses several distinct characters, including relatively broad roof elements (mainly frontal and parietal bones), a jugal with a prominent recess, occipital table trapezoidal in shape with the maximum width between the quadrate bones, and a small fenestra located in the posterior part of the pterygoid bones. In the Oxfordian, the Caribbean Corridor separated Laurasia and western Gondwana. The diversity of the marine herpetofauna found in the Jagua Vieja Member (Jagua Formation), and of teleostean fish, confirms that the corridor was an effective seaway over which flew at least Nesodactylus and Cacibupteryx .     

The cranial and cervical osteology of the european oystercatcher Haematopus ostralegus L.

The cranial and cervical osteology of the European oystercatcher, Haematopus ostralegus L. is completely described from both whole skeletons and spirit specimens. Contrary to previous reports, the postorbital ligament shows variability in bifurcation and attachment, with the posterior branch, where present, attaching either to the suprameatic process or the zygomatic process. In addition, the quadrate ligament, which had been described as originating from the suprameatic process, appears instead to attach to the zygomatic process in some specimens. The caudal mandibular fenestra, earlier considered absent in oystercatchers, is present in all specimens examined. The cranium is additionally distinguished by a number of features which may be unique to oystercatchers. A fourth, previously unrecorded, division of the maxillopalatine strut is present, while the palatine process of the premaxilla is reduced to a thickening along the edge of the premaxillary process of the palatine. The distinctiveness of the oystercatcher cranium is particularly evident in the area of the quadratomandibular articulation, which possesses features potentially important for stabilizing the joint. A deep retroarticular notch is present, guiding a large medial jugomandibular ligament along the posterior margin of the articulation. A lateral mandibular tuberosity, which is received dorsally by an emargination of the jugal arch and quadrate, may act as an osteological brace, preventing posterior shifting of the closed mandible. The 15 cervical vertebrae are divided on the basis of structural criteria into three sections.     

The early history of modern birds inferred from DNA sequences of nuclear and mitochondrial ribosomal genes

The traditional view of avian evolution places ratites and tinamous at the base of the phylogenetic tree of modern birds (Neornithes). In contrast, most recent molecular studies suggest that neognathous perching birds (Passeriformes) compose the oldest lineage of modern birds. Here, we report significant molecular support for the traditional view of neognath monophyly based on sequence analyses of nuclear and mitochondrial DNA (4.4 kb) from every modern avian order. Phylogenetic analyses further show that the ducks and gallinaceous birds are each other's closest relatives and together form the basal lineage of neognathous birds. To investigate why other molecular studies sampling fewer orders have reached different conclusions regarding neognath monophyly, we performed jackknife analyses on our mitochondrial data. Those analyses indicated taxon-sampling effects when basal galloanserine birds were included in combination with sparse taxon sampling. Our phylogenetic results suggest that the earliest neornithines were heavy-bodied, ground-dwelling, nonmarine birds. This inference, coupled with a fossil bias toward marine environments, provides a possible explanation for the large gap in the early fossil record of birds.     

Synchrotron microtomography-based osteohistology of Gansus yumenensis: new data on the evolution of uninterrupted bone deposition in basal birds

Many studies of the limb bones from birds of the major clades reveal a mosaic evolution in morphological characters. From this, we assume that uninterrupted compact bone evolved independently multiple times outside of the crown group. We hypothesise that there are key intraskeletal changes in the osteohistological features, such as the organisation of the vascular network. To test these hypotheses, we analysed and described the osteohistological features of five different midshaft samples of Gansus yumenensis, a non-ornithurine Euornithes from China, based on virtual models obtained from synchrotron microtomography scans, a less invasive method that the traditional physical cross section. We performed quantitative analyses with volume, surface area and estimated ratios. The osteohistological features of Gansus yumenensis were compared with those of stem and crown birds. From our analyses, we discuss the pros/cons of using synchrotron microtomography scans compared to traditional physical cross section. Our analyses demonstrate that Gansus yumenensis is the fourth described extinct Euornithes to exhibit uninterrupted bone deposition in all bone samples, providing further support for multiple origins of this feature outside of the bird crown group. Finally, our osteohistological investigation of Gansus yumenensis provides future study avenues regarding the evolution and development of bone tissue in fossil birds.     

Comparative ossification sequence and skeletal development of the postcranium of palaeognathous birds (Aves: Palaeognathae)

Palaeognaths constitute one of the most basal lineages of extant birds, and are also one of the most morphologically diverse avian orders. Their skeletal development is relatively unknown, in spite of their important phylogenetic position. Here, we compare the development of the postcranial skeleton in the emu (Dromaius novaehollandiae), ostrich (Struthio camelus), greater rhea (Rhea americana) and elegant crested‐tinamou (Eudromia elegans), focusing on ossification. All of these taxa are characterized by element loss in the appendicular skeleton, but there are several developmental mechanisms through which this loss occurs, including failure to chondrify, failure to ossify and fusion of cartilages prior to ossification. Further evidence is presented here to support a reduction in size of skeletal elements resulting in a delay in the timing of ossification. This study provides an important first look at the timing and sequence of postcranial ossification in palaeognathous birds, and discusses the influence of changes in the pattern of skeletal development on morphological evolution.     

Functional and evolutionary consequences of cranial fenestration in birds

Ostrich‐like birds (Palaeognathae) show very little taxonomic diversity while their sister taxon (Neognathae) contains roughly 10,000 species. The main anatomical differences between the two taxa are in the crania. Palaeognaths lack an element in the bill called the lateral bar that is present in both ancestral theropods and modern neognaths, and have thin zones in the bones of the bill, and robust bony elements on the ventral surface of their crania. Here we use a combination of modeling and developmental experiments to investigate the processes that might have led to these differences. Engineering‐based finite element analyses indicate that removing the lateral bars from a neognath increases mechanical stress in the upper bill and the ventral elements of the skull, regions that are either more robust or more flexible in palaeognaths. Surgically removing the lateral bar from neognath hatchlings led to similar changes. These results indicate that the lateral bar is load‐bearing and suggest that this function was transferred to other bony elements when it was lost in palaeognaths. It is possible that the loss of the load‐bearing lateral bar might have constrained diversification of skull morphology in palaeognaths and thus limited taxonomic diversity within the group.     

Biomechanics of cranial kinesis in birds: Testing linkage models in the white-throated sparrow (Zonotrichia albicollis)

Cranial kinesis in sparrows refers to the rotation of the upper jaw around its kinetic joint with the braincase. Avian jaw mechanics may involve the coupled motions of upper and lower jaws, in which the postorbital ligament transfers forces from the lower jaw, through the quadrate, pterygoid, and jugal bones, to the upper jaw. Alternatively, jaw motions may be uncoupled, with the upper jaw moving independently of the lower jaw. We tested hypotheses of cranial kinesis through the use of quantitative computer models. We present a biomechanical model of avian jaw kinetics that predicts the motions of the jaws under assumptions of both a coupled and an uncoupled mechanism. In addition, the model predicts jaw motions under conditions of force transfer by either the jugal or the pterygoid bones. Thus four alternative models may be tested using the proposed model (coupled jugal, coupled pterygoid, uncoupled jugal, uncoupled pterygoid). All models are based on the mechanics of four-bar linkages and lever systems and use morphometric data on cranial structure as the basis for predicting cranial movements. Predictions of cranial motions are tested by comparison to kinematics of white-throated sparrows (Zonotrichia albicollis) during singing. The predicted relations between jaw motions for the coupled model are significantly different from video observations. We conclude that the upper and lower jaws are not coupled in white-throated sparrows. The range of jaw motions during song is consistent with a model in which independent contractions of upper and lower jaw muscles control beak motion. © 1996 Wiley-Liss, Inc.