PHYLOGENY AND FORELIMB DISPARITY IN WATERBIRDS

Previous work has shown that the relative proportions of wing components (i.e., humerus, ulna, carpometacarpus) in birds are related to function and ecology, but these have rarely been investigated in a phylogenetic context. Waterbirds including “Pelecaniformes,” Ciconiiformes, Procellariiformes, Sphenisciformes, and Gaviiformes form a highly supported clade and developed a great diversity of wing forms and foraging ecologies. In this study, forelimb disparity in the waterbird clade was assessed in a phylogenetic context. Phylogenetic signal was assessed via Pagel's lambda, Blomberg's K, and permutation tests. We find that different waterbird clades are clearly separated based on forelimb component proportions, which are significantly correlated with phylogeny but not with flight style. Most of the traditional contents of “Pelecaniformes” (e.g., pelicans, cormorants, and boobies) cluster with Ciconiiformes (herons and storks) and occupy a reduced morphospace. These taxa are closely related phylogenetically but exhibit a wide range of ecologies and flight styles. Procellariiformes (e.g., petrels, albatross, and shearwaters) occupy a wide range of morphospace, characterized primarily by variation in the relative length of carpometacarpus and ulna. Gaviiformes (loons) surprisingly occupy a wing morphospace closest to diving petrels and penguins. Whether this result may reflect wing proportions plesiomorphic for the waterbird clade or a functional signal is unclear. A Bayesian approach detecting significant rate shifts across phylogeny recovered two such shifts. At the base of the two sister clades Sphenisciformes + Procellariiformes, a shift to an increase evolutionary rate of change is inferred for the ulna and carpometacarpus. Thus, changes in wing shape begin prior to the loss of flight in the wing‐propelled diving clade. Several shifts to slower rate of change are recovered within stem penguins.     

The effects of locomotion on the structural characteristics of avian limb bones

Despite the wide range of locomotor adaptations in birds, little detailed attention has been given to the relationships between the quantitative structural characteristics of avian limb bones and bird behaviour. Possible differences in forelimb relative to hindlimb strength across species have been especially neglected. We generated cross‐sectional, geometric data from peripheral quantitative computed tomography scans of the humerus and femur of 127 avian skeletons, representing 15 species of extant birds in 13 families. The sample includes terrestrial runners, arboreal perchers, hindlimb‐propelled divers, forelimb‐propelled divers and dynamic soarers. The hindlimb‐propelled diving class includes a recently flightless island form. Our results demonstrate that locomotor dynamics can be differentiated in most cases based on cross‐sectional properties, and that structural proportions are often more informative than bone length proportions for determining behaviour and locomotion. Recently flightless forms, for example, are more easily distinguished using structural ratios than using length ratios. A proper phylogenetic context is important for correctly interpreting structural characteristics, especially for recently flightless forms. Some of the most extreme adaptations to mechanical loading are seen in aquatic forms. Penguins have forelimbs adapted to very high loads. Aquatic species differ from non‐aquatic species on the basis of relative cortical thickness. The combination of bone structural strength and relative cortical area of the humerus successfully differentiates all of our locomotor groups. The methods used in this study are highly applicable to fossil taxa, for which morphology is known but behaviour is not. The use of bone structural characteristics is particularly useful in palaeontology not only because it generates strong signals for many locomotor guilds, but also because analysing such traits does not require knowledge of body mass, which can be difficult to estimate reliably for fossil taxa. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 153 , 601–624.     

Relationship between osteology and aquatic locomotion in birds: determining modes of locomotion in extinct Ornithurae

The evolutionary history of aquatic invasion in birds would be incomplete without incorporation of extinct species. We show that aquatic affinities in fossil birds can be inferred by multivariate analysis of skeletal features and locomotion of 245 species of extant birds. Regularized discriminant analyses revealed that measurements of appendicular skeletons successfully separated diving birds from surface swimmers and flyers, while also discriminating among different underwater modes of swimming. The high accuracy of this method allows detection of skeletal characteristics that are indicative of aquatic locomotion and inference of such locomotion in bird species with insufficient behavioural information. Statistical predictions based on the analyses confirm qualitative assessments for both foot‐propelled (Hesperornithiformes) and wing‐propelled (Copepteryx) underwater locomotion in fossil birds. This is the first quantitative inference of underwater modes of swimming in fossil birds, enabling future studies of locomotion in extinct birds and evolutionary transitions among locomotor modes in avian lineage.     

Forelimb Kinematics of Rats Using XROMM,with Implications for Small Eutherians and Their Fossil Relatives

The earliest eutherian mammals were small-bodied locomotor generalists with a forelimb morphology that strongly resembles that of extant rats. Understanding the kinematics of the humerus, radius, and ulna of extant rats can inform and constrain hypotheses concerning typical posture and mobility in early eutherian forelimbs. The locomotion of Rattus norvegicus has been extensively studied, but the three-dimensional kinematics of the bones themselves remains under-explored. Here, for the first time, we use markerless XROMM (Scientific Rotoscoping) to explore the three-dimensional long bone movements in Rattus norvegicus during a normal, symmetrical gait (walking). Our data show a basic kinematic profile that agrees with previous studies on rats and other small therians: rats maintain a crouched forelimb posture throughout the step cycle, and the ulna is confined to flexion/extension in a parasagittal plane. However, our three-dimensional data illuminate long-axis rotation (LAR) movements for both the humerus and the radius for the first time. Medial LAR of the humerus throughout stance maintains an adducted elbow with a caudally-facing olecranon process, which in turn maintains a cranially-directed manus orientation (pronation). The radius also shows significant LAR correlated with manus pronation and supination. Moreover, we report that elbow flexion and manus orientation are correlated in R. norvegicus: as the elbow angle becomes more acute, manus supination increases. Our data also suggest that manus pronation and orientation in R. norvegicus rely on a divided system of labor between the ulna and radius. Given that the radius follows the flexion and extension trajectory of the ulna, it must rotate at the elbow (on the capitulum) so that during the stance phase its distal end lies medial to ulna, ensuring that the manus remains pronated while the forelimb is supporting the body. We suggest that forelimb posture and kinematics in Juramaia, Eomaia, and other basal eutherians were grossly similar to those of rats, and that humerus and radius LAR may have always played a significant role in forelimb and manus posture in small eutherian mammals.     

Fossil grebes from the Truckee Formation (Miocene) of Nevada and a new phylogenetic analysis of Podicipediformes (Aves)

Podicipediformes is a cosmopolitan clade of foot‐propelled diving birds that, despite inhabiting marine and lacustrine environments, have a poor fossil record. In this contribution, we describe three new grebe fossils from the diatomite beds of the Late Miocene Truckee Formation (10.2 ± 0.2 Ma) of Nevada (USA). Two postcranial skeletons and an associated set of wing elements indicate that at least two distinct grebe species occupied the large, shallow Lake Truckee during the Miocene. Phylogenetic analysis of morphological data supports a basal divergence between a clade uniting the dabchicks (Tachybaptus, Limnodytes, Poliocephalus) and a clade uniting Podilymbus, Rollandia, Podiceps and Aechmophorus. Missing data, combined with a paucity of informative skeletal characters, make it difficult to place the Truckee grebes within either of these major clades. Given the weak projection of the cnemial crests compared with extant grebes, it also remains plausible that these specimens represent stem lineage grebes. Although more material is needed to resolve the phylogenetic position of the Truckee grebes, our analysis offers insight into the tempo of grebe evolution by placing the Miocene taxon Thiornis sociata within the dabchick clade. Thiornis sociata provides a minimum age calibration of 8.7 Ma for the basal divergence among dabchicks. Based on the recovery of a nonmonophyletic Tachybaptus and placement of the Western Hemisphere ‘Tachybaptus’ dominicus as the basal member of the otherwise exclusively Eastern Hemisphere dabchick clade, we resurrect the genus Limnodytes for this extant species (Limnodytes dominicus). Our results also nest the large, long‐necked Aechmophorus grebes within the genus Podiceps, as the sister taxon to Podiceps major.     

Flightlessness in the Galápagos cormorant (Compsohalieus [Nannopterum] harrisi): heterochrony, giantism and specialization

A study of flightlessness in the Galápagos cormorant (Compsohalieus [Nannopterum] harrisi) was undertaken using study skins and skeletons of C. harrisi and eight flighted confamilials; in addition, four skin specimens and disassociated skeletal elements of the extinct spectacled cormorant (C. perspicillatus) of Beringia, reputed by some to have been flightless, were studied. Anatomical specimens of C. penicillatus and C. harrisi were dissected for myological comparisons. Flightless C. harrisi is 1.6 to 2.2 times as heavy as its extant flighted congeners; males averaged 3958 g and females averaged 2715 g in total body weight. Estimates of body weight for C. perspicillatus based on femur length approximated 3900 g. Wing lengths of C. harrisi were smaller than those of any other cormorant, averaging 190 mm and 170 mm for males and females, respectively. Wing-loadings (g body mass.cm^-2 wing area) of flighted cormorants ranged from 1.0 to 1.7. Estimated wing-loadings, incorporating approximate wing areas, were 2.0 and 5.1 g.cm^-2 for C. perspicillatus and C. harrisi, respectively; the former suggests that C. perspicillatus was probably capable of laboured flight. The small wings of C. harrisi result from an c. 50% shortening of remiges, accompanied by reduced asymmetry of vane widths and increased rounding of the tips, and significant reductions in lengths of wing bones, particularly the radius and ulna. Numbers of primary and secondary remiges in C. harrisi remain unchanged. Multivariate morphometries revealed that sexual dimorphism in external and skeletal dimensions is significantly greater in C. harrisi than in flighted cormorants. Canonical analysis of six external measurements indicated that C. harrisi is distinguished primarily by its relatively short wings. Skeletal peculiarities of C. harrisi were diverse, including conformational changes in the sternum, furcula, coracoid, humerus, ulna, radius, carpometacarpus and patella. Mensural comparisons confirmed substantial reductions in elements of the pectoral girdle of C. harrisi, particularly the sternal carina, as well as the alar skeleton, especially the radius and ulna. Differential shortening of the wing elements resulted in significant differences in proportions within the wing skeleton. These unique skeletal proportions of C. harrisi, in addition to its great overall size, combine to produce an immense multivariate skeletal distance between C. harrisi and all confamilials. Sexual dimorphism in skeletal dimensions, in both total and size-corrected data, was 2–3 times greater in C. harrisi than in other phalacrocoracids sampled. Most pectoral muscles of C. harrisi were absolutely or relatively smaller than those of C. penicillatus, in spite of its larger body size. No muscles or parts thereof were lacking in the pectoral limb of C. harrisi, but a number of qualitative differences distinguished the musculature of the flightless species, including: an exceptionally tough skin involving a well-developed M. pectoralis pars abdominalis and M. latissimus dorsi interscapularis; a thin, medially obsolete and laterally extensive M. pectoralis pars thoracica; a weakly developed M. rhomboideus profundus consisting of a variably tendinous fascia invested with three fasciculi of muscle fibres; an extraordinarily thick, extensive M. obliquus externus abdominis, which, together with a unique cnemio-costal slip of smooth muscle, restricts the metapatagium through an anchoring of M. serratus superficialis metapatagialis; and the presence of a unique alular muscle named here as M. levator alulae. Fusions of the tendons of origin and insertion, respectively, of M. flexor digiti superficialis and M. flexor digiti profundus in C. harrisi, muscles derived from a common muscle primordium, and the retention of a carpometacarpal tendon of M. flexor carpi ulnaris cranialis constitute strong evidence of pectoral paedomorphosis in C. harrisi. Mensural comparisons quantified the reduction of pectoral muscles in C. harrisi and indicated that these reductions were especially pronounced in the distal musculature. Morphological characteristics of Phalacrocoracidae, together with the exploitation of localized marine food resources and weakly developed seasonal movements of Compsohalieus, may have predisposed the founding population of C. harrisi to flightlessness. Anatomical changes in C. harrisi are exceeded in degree among foot-propelled diving birds by those of only a few fossil flightless birds (e.g. Hesperomis, Chendytes). Many of the morphological peculiarities of C. harrisi are paedomorphic, although several are not attributable to developmental heterochrony. These morphological characters of flightless C. harrisi are considered with respect to locomotion, feeding ecology, reproduction and demography of the species, and are compared with those of other flightless carinates.     

The automating skeletal and muscular mechanisms of the avian wing (Aves)

The avian wing possesses the ability to synchronize flexion or extension of the elbow and wrist joints automatically. Skeletal and muscular mechanisms are involved in generating this phenomenon. The drawing-parallels action of the radius and ulna coordinates the movements of the forearm with the carpus. Movement of the radius along the length of the forearm isnot dependent on the shape disparity between the dorsal and ventral condyles of the humerus, nor is it generated by the shape of the dorsal condyle itself. Instead, shifting of the radius toward the wrist occurs during humeroulnar flexion when the radius, being pushed by muscles toward the ulna, is deflected off theIncisura radialis toward the wrist. Movement of the radius toward the elbow occurs during the latter stages of humeroulnar extension when, as the dorsal condyle of the humerus and the articular surface of the ulna's dorsal cup roll apart, the radius gets pulled by the humerus and its ligaments away from the wrist. Synchronization of the forearm with the manus is accomplished by twojoint muscles and tendons.M. extensor metacarpi radialis and the propatagial tendons act to extend the manus in unison with the forearm, whileM. extensor metacarpi ulnaris helps these limb segments flex simultaneously.M. flexor carpi ulnaris, in collaboration with the drawing-parallels mechanisms, flexes the carpus automatically when the elbow is flexed, thereby circumducting the manus from the plane of the wing toward the body. In a living bird, these skeletal and muscular coordinating mechanisms may function to automate the internal kinematics of the wing during flapping flight. A mechanized wing may also greatly facilitate the initial flight of fledgling birds. The coordinating mechanisms of the wing can be detected in a bird's osteology, thereby providing researchers with a new avenue by which to gauge the flight capabilities of avian fossil taxa.     

Postcranial morphology of the extinct caviine rodent Microcavia criolloensis (late Pleistocene,South America)

A comparative study of the appendicular skeletal morphology, with a particular emphasis on the autopodial elements (manus and pes), of the extinct caviine rodent Microcavia criolloensis (Late Pleistocene, Uruguay), together with that of living species of Microcavia and some allied caviines is performed. Burrow‐digging and above‐ground behaviour by M. criolloensis could have evolved in the Late Pleistocene, as with its relative M. australis in the Recent. This is suggested based on the morphology of preserved articulated skeletons along with fossil burrow‐like structures. The most remarkable features are: in its forelimb, where the humerus has a structure that would have allowed it to perform similar activities to M. australis, based on humeral width across the epicondiles relative to total humerus length index and a good resistance as indicated by high values relating the diameter of the diaphysis to its total length. Qualitative comparison shows that M. criolloensis had a stout, wide manus with relatively short digits including short, wide phalanges, despite its large size. In its hind limb there is a stout hind‐foot with relatively short and wide metatarsals and phalanges, as compared with those of the recent species, that could arguably be considered a useful tool for shovelling out displaced soil. The generalized morphology suggests above‐ground behaviour together with digging ability. The environmental adaptations of M. criolloensis are also briefly discussed, which seem to differ from those of its extant relatives. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 795–806.     

Bony‐toothed birds (Aves: Pelagornithidae) from the Middle Eocene of Belgium

Abstract: We describe well‐preserved remains of the Pelagornithidae (bony‐toothed birds) from the middle Eocene of Belgium, including a sternum, pectoral girdle bones and humeri of a single individual. The specimens are tentatively assigned to Macrodontopteryx oweni Harrison and Walker, 1976 , which has so far only been known from the holotype skull and a referred proximal ulna. Another species, about two times larger, is represented by an incomplete humerus and tentatively identified as Dasornis emuinus ( Bowerbank, 1854 ). The fossils provide critical new data on the osteology of the pectoral girdle of bony‐toothed birds. For the first time, the sternum of one of the smaller species is preserved, and this bone exhibits a more plesiomorphic morphology than the recently described sternum of the giant Miocene taxon Pelagornis. The coracoid resembles that of the Diomedeidae (albatrosses) in overall morphology, but because bony‐toothed birds lack apomorphies of the Procellariiformes, the similarities are almost certainly owing to convergence. Bony‐toothed birds were often compared with the ‘Pelecaniformes’ by previous authors, who especially made comparisons with the Sulidae (gannets and boobies). However, the coracoid distinctly differs from that of extant ‘pelecaniform’ birds, and the plesiomorphic presence of a foramen nervi supracoracoidei as well as the absence of a well‐delimited articulation facet for the furcula supports a position outside the Suloidea, the clade to which the Sulidae belong.     

Cross sectional geometry of the forelimb skeleton and flight mode in pelecaniform birds

Avian wing elements have been shown to experience both dorsoventral bending and torsional loads during flapping flight. However, not all birds use continuous flapping as a primary flight strategy. The pelecaniforms exhibit extraordinary diversity in flight mode, utilizing flapping, flap‐gliding, and soaring. Here we (1) characterize the cross‐sectional geometry of the three main wing bone (humerus, ulna, carpometacarpus), (2) use elements of beam theory to estimate resistance to loading, and (3) examine patterns of variation in hypothesized loading resistance relative to flight and diving mode in 16 species of pelecaniform birds. Patterns emerge that are common to all species, as well as some characteristics that are flight‐ and diving‐mode specific. In all birds examined, the distal most wing segment (carpometacarpus) is the most elliptical (relatively high I_max/I_min) at mid‐shaft, suggesting a shape optimized to resist bending loads in a dorsoventral direction. As primary flight feathers attach at an oblique angle relative to the long axis of the carpometacarpus, they are likely responsible for inducing bending of this element during flight. Moreover, among flight modes examined the flapping group (cormorants) exhibits more elliptical humeri and carpometacarpi than other flight modes, perhaps pertaining to the higher frequency of bending loads in these elements. The soaring birds (pelicans and gannets) exhibit wing elements with near‐circular cross‐sections and higher polar moments of area than in the flap and flap‐gliding birds, suggesting shapes optimized to offer increased resistance to torsional loads. This analysis of cross‐sectional geometry has enhanced our interpretation of how the wing elements are being loaded and ultimately how they are being used during normal activities. J. Morphol., 2011. © 2011 Wiley‐Liss,Inc.     

Bone microstructure of Vegavis iaai (Aves,Anseriformes) from the Upper Cretaceous of Vega Island,Antarctic Peninsula

Vegavis iaai is a neornithine bird coming from the Late Cretaceous Sandwich Bluff Member of the López de Bertodano Formation (Maastrichtian), Antarctic Peninsula. Vegavis constitutes the only unquestionable Cretaceous neornithine bird, and is known by the holotype and specimen MACN-PV 19.748. The goal of this paper is to present a detailed osteohistological analysis of V. iaai. Vegavis shows a highly vascularized fibrolamellar matrix lacking lines of arrested growths, features widespread among modern birds. This is consistent with previous hypotheses indicating that modern birds were dominant at high latitudes. This is probably related to high-metabolic rates shared by modern birds, whereas archaic taxa as Enantiornithes are absent or form a minority part of High-Latitude bird assemblages. Vegavis was a diver, characterised by a certain degree of limb osteosclerosis, with an increase of bone inner compactness, and inhibition of secondary remodelling, with no effect on the external dimensions of the bone, a combination of characters related to diving lifestyle. Based on Relative Bone Thickness it is possible to infer that Vegavis was a foot-propelled diving bird, similar to some extant anseriforms. Occurrence of osteosclerotic limb bones in Vegavis and Polarornis may constitute a derived shared feature, sustaining the hypothesis that both taxa are phylogenetically related.     

Functional osteology of the avian wrist and the evolution of flapping flight

The avian wrist is extraordinarily adapted for flight. Its intricate osteology is constructed to perform four very different, but extremely important, flight-related functions. (1) Throughout the downstroke, the cuneiform transmits force from the carpometacarpus to the ulna and prevents the manus from hyperpronating. (2) While gliding or maneuvering, the scapholunar interlocks with the carpometacarpus and prevents the manus from supinating. By employing both carpal bones simultaneously birds can lock the manus into place during flight. (3) Throughout the downstroke-upstroke transition, the articular ridge on the distal extremity of the ulna, in conjuction with the cuneiform, guides the manus from the plane of the wing toward the body. (4) During take-off or landing, the upstroke of some heavy birds exhibits a pronounced flick of the manus. The backward component of this flick is produced by reversing the wrist mechanism that enables the manus to rotate toward the body during the early upstroke. The upward component of the flick is generated by mechanical interplay between the ventral ramus of the cuneiform, the ventral ridge of the carpometacarpus, and the ulnocarpo-metacarpal ligament. Without the highly specialized osteology of the wrist it is doubtful that birds would be able to carry out successfully the wing motions associated with flapping flight. Yet in Archaeopteryx, the wrist displays a very different morphology that lacks all the key features found in the modern avian wrist. Therefore, Archaeopteryx was probably incapable of executing the kinematics of modern avian powered flight.     

The locomotion of Babakotia radofilai inferred from epiphyseal and diaphyseal morphology of the humerus and femur

Palaeopropithecids, or “sloth lemurs,” are a diverse clade of large‐bodied Malagasy subfossil primates characterized by their inferred suspensory positional behavior. The most recently discovered genus of the palaeopropithecids is Babakotia, and it has been described as more arboreal than Mesopropithecus, but less than Palaeopropithecus. In this article, the within‐bone and between‐bones articular and cross‐sectional diaphyseal proportions of the humerus and femur of Babakotia were compared to extant lemurs, Mesopropithecus and Palaeopropithecus in order to further understand its arboreal adaptations. Additionally, a sample of apes and sloths (Choloepus and Bradypus) are included as functional outgroups composed of suspensory adapted primates and non‐primates. Results show that Babakotia and Mesopropithecus both have high humeral/femoral shaft strength proportions, similar to extant great apes and sloths and indicative of forelimb suspensory behavior, with Babakotia more extreme in this regard. All three subfossil taxa have relatively large femoral heads, also associated with suspension in modern taxa. However, Babakotia and Mesopropithecus (but not Palaeopropithecus) have relatively small femoral head surface area to shaft strength proportions suggesting that hind‐limb positioning in these taxa during climbing and other behaviors was different than in extant great apes, involving less mobility. Knee and humeral articular dimensions relative to shaft strengths are small in Babakotia and Mesopropithecus, similar to those found in modern sloths and divergent from those in extant great apes and lemurs, suggesting more sloth‐like use of these joints during locomotion. Mesopropithecus and Babakotia are more similar to Choloepus in humerofemoral head and length proportions while Palaeopropithecus is more similar to Bradypus. These results provide further evidence of the suspensory adaptations of Babakotia and further highlight similarities to both extant suspensory primates and non‐primate slow arboreal climbers and hangers. J. Morphol. 277:1199–1218, 2016. © 2016 Wiley Periodicals, Inc.     

Anatomical network analysis of the musculoskeletal system reveals integration loss and parcellation boost during the fins‐to‐limbs transition

Tetrapods evolved from within the lobe‐finned fishes around 370 Ma. The evolution of limbs from lobe‐fins entailed a major reorganization of the skeletal and muscular anatomy of appendages in early tetrapods. Concurrently, a degree of similarity between pectoral and pelvic appendages also evolved. Here, we compared the anatomy of appendages in extant lobe‐finned fishes (Latimeria and Neoceratodus) and anatomically plesiomorphic amphibians (Ambystoma, Salamandra) and amniotes (Sphenodon) to trace and reconstruct the musculoskeletal changes that took place during the fins‐to‐limbs transition. We quantified the anatomy of appendages using network analysis. First, we built network models—in which nodes represent bones and muscles, and links represent their anatomical connections—and then we measured network parameters related to their anatomical integration, heterogeneity, and modularity. Our results reveal an evolutionary transition toward less integrated, more modular appendages. We interpret this transition as a diversification of muscle functions in tetrapods compared to lobe‐finned fishes. Limbs and lobe‐fins show also a greater similarity between their pectoral and pelvic appendages than ray‐fins do. These findings on extant species provide a basis for future quantitative and comprehensive reconstructions of the anatomy of limbs in early tetrapod fossils, and a way to better understand the fins‐to‐limbs transition.     

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.     

Avian wing proportions and flight styles: first step towards predicting the flight modes of mesozoic birds

We investigated the relationship between wing element proportions and flight mode in a dataset of living avian species to provide a framework for making basic estimates of the range of flight styles evolved by Mesozoic birds. Our results show that feather length (f(prim)) and total arm length (ta) (sum of the humerus, ulna and manus length) ratios differ significantly between four flight style groups defined and widely used for living birds and as a result are predictive for fossils. This was confirmed using multivariate ordination analyses, with four wing elements (humerus, ulna/radius, manus, primary feathers), that discriminate the four broad flight styles within living birds. Among the variables tested, manus length is closely correlated with wing size, yet is the poorest predictor for flight style, suggesting that the shape of the bones in the hand wing is most important in determining flight style. Wing bone thickness (shape) must vary with wing beat strength, with weaker forces requiring less bone. Finally, we show that by incorporating data from Mesozoic birds, multivariate ordination analyses can be used to predict the flight styles of fossils.     

FLIGHTLESSNESS IN GREBES (AVES,PODICIPEDIDAE): ITS INDEPENDENT EVOLUTION IN THREE GENERA

The morphological bases of flightlessness in three genera of grebes were studied using 790 study skins, 322 skeletons, myological data from 40 anatomical specimens studied by Sanders (1967), and ancillary data on wing-loadings. Three species, Rollandia microptera, Podilymbus gigas, and Podiceps taczanowskii, are considered to be flightless; each is endemic to a high-altitude, neotropical lake or lake system. Compared to their flighted (capable of flight) sister-species, the three flightless species shared several broadly convergent characters: larger body mass and skeletal dimensions (exclusive of the sternal carina), reductions in relative lengths of wing, tail, and primary remiges, and reduction in the relative size of breast muscles. Rollandia microptera exhibited the greatest morphological differences from its flighted sister-species; these differences were comparable to intergeneric morphometric differences in magnitude and involved a tripling of body mass, a modal loss of one primary remex in each wing, absolute reduction of the sternal carina, flattening of proximal wing elements, a large morphometric shift in skeletal dimensions, an increase in the scapulocoracoid angle, and six qualitative differences in the pectoral musculature. Morphological differences between Podilymbus gigas and its flighted congener were comparatively minor; flightlessness in this species, if genuine, evidently results from an allometric increase in size combined with a large decrease in relative bulk of breast musculature and shift of alar muscle mass. Podiceps taczanowskii was intermediate in degree of anatomical difference from its flighted relatives, but was unique in its slight reduction in absolute length of the wings and decrease in absolute widths of the skeletal wing elements. Multivariate differences in external characters associated with flightlessness were strongly convergent in the three genera, but multivariate differences in skeletal proportions differed substantially among genera in detail. An estimate of wing-loading indicated that Podilymbus gigas and, especially, Podiceps taczanowskii may be only “flight-impaired” rather than flightless. Relative wing lengths and conformation of sterna in Rollandia microptera and Podiceps taczanowskii indicate that morphological changes associated with flightlessness are paedomorphic; intraspecific allometry in Rollandia indicates that the underlying ontogenetic change may involve a delay in the start of pectoral-alar development (postdisplacement). Flightlessness in grebes, a family typified by moderately heavy wing-loadings and relatively small pectoral muscles, is related in all three instances to the year-round residency afforded by large lakes at low latitudes. The primary selective advantages of morphological changes leading to flightlessness probably are related to the thermodynamic advantages of increased body sizes, feeding specialization associated with enlargement of the bill, and reduction of intraspecific niche overlap through increased sexual dimorphism; the changes are also possibly related to economy of pectoral-alar development.     

First record of a tarsometatarsus of Tonsala hildegardae (Plotopteridae) and other avian remains from the late Eocene/early Oligocene of Washington State (USA)

New bird fossils from the late Eocene/early Oligocene Makah Formation and the Oligocene Pysht Formation on the Olympic Peninsula (Washington State, USA) are described. A partial skeleton from the Pysht Formation includes the first reported tarsometatarsus of Tonsala hildegardae Olson, 1980, a wing-propelled diving bird of the taxon Plotopteridae. It shows that Tonsala had a tarsometatarsus that was morphologically intermediate between that of the late Eocene Phocavis and more derived plotopterids. We introduce the new taxon Tonsalinae nov. subfam. for a clade including all named plotopterids except Phocavis, Plotopterum, and the recently described Stemec. We furthermore describe a partial plotopterid pelvis and a sternum from the Makah Formation. The sternum shows a close resemblance to that of extant Phalacrocoracoidea (cormorants and darters) and may be the earliest North American record of this taxon.     

Regional heterothermy and conservation of core temperature in emperor penguins diving under sea ice

Temperatures were recorded at several body sites in emperor penguins (Aptenodytes forsteri) diving at an isolated dive hole in order to document temperature profiles during diving and to evaluate the role of hypothermia in this well-studied model of penguin diving physiology. Grand mean temperatures (+/-S.E.) in central body sites during dives were: stomach: 37.1+/-0.2 degrees C (n=101 dives in five birds), pectoral muscle: 37.8+/-0.1 degrees C (n=71 dives in three birds) and axillary/brachial veins: 37.9+/-0.1 degrees C (n=97 dives in three birds). Mean diving temperature and duration correlated negatively at only one site in one bird (femoral vein, r=-0.59, P<0.05; range <1 degrees C). In contrast, grand mean temperatures in the wing vein, foot vein and lumbar subcutaneous tissue during dives were 7.6+/-0.7 degrees C (n=157 dives in three birds), 20.2+/-1.2 degrees C (n=69 in three birds) and 35.2+/-0.2 degrees C (n=261 in six birds), respectively. Mean limb temperature during dives negatively correlated with diving duration in all six birds (r=-0.29 to -0.60, P<0.05). In two of six birds, mean diving subcutaneous temperature negatively correlated with diving duration (r=-0.49 and -0.78, P<0.05). Sub-feather temperatures decreased from 31 to 35 degrees C during rest periods to a grand mean of 15.0+/-0.7 degrees C during 68 dives of three birds; mean diving temperature and duration correlated negatively in one bird (r=-0.42, P<0.05). In general, pectoral, deep venous and even stomach temperatures during diving reflected previously measured vena caval temperatures of 37-39 degrees C more closely than the anterior abdominal temperatures (19-30 degrees C) recently recorded in diving emperors. Although prey ingestion can result in cooling in the stomach, these findings and the lack of negative correlations between internal temperatures and diving duration do not support a role for hypothermia-induced metabolic suppression of the abdominal organs as a mechanism of extension of aerobic dive time in emperor penguins diving at the isolated dive hole. Such high temperatures within the body and the observed decreases in limb, anterior abdomen, subcutaneous and sub-feather temperatures are consistent with preservation of core temperature and cooling of an outer body shell secondary to peripheral vasoconstriction, decreased insulation of the feather layer, and conductive/convective heat loss to the water environment during the diving of these emperor penguins.