The furcula and the evolution of avian flight

The presence of a short furcula in Archaeopteryx suggests that this bird possessed a small, shortfibered, cranial portion of the pinnate m. pectoralis originating from the furcula and possibly from the aponeurosis between the furcula and the coracoid and cartilaginous sternum, and inserting on the cranial edge of the humerus, and an equally small, short-fibered pinnate caudal part of the same muscle arising from the presumably cartilaginous sternum and inserting on the ventral surface of the deltoid crest of the humerus. In Archaeopteryx, the cranial-most portion of the m. pectoralis protracted the wing and held it in place against the backward pressure, or drag, of the air when the bird flew. There is no basis for postulating that the caudal part of the m. pectoralis in Archaeopteryx was sufficiently large for active flapping flight, although this presumably small muscle probably held the wings in a horizontal position necessary for aerial locomotion. The muscle fibers of all parts of the m. pectoralis were short because the small distance between its origin and insertion. The combination of features in the pectoral system of Archaeopteryx indicates strongly that this bird was a specialized glider, not an active flapping flier. Avian flight started from the trees downward, not from the ground upward.     

The population history of extant and extinct hyenas

We have analyzed partial DNA sequences of the mitochondrialcytochrome b gene from extant striped, brown, and spotted hyenasas well as from Pleistocene cave hyenas. Sequences of the Pleistocenecave hyenas from Eurasia and modern spotted hyenas from Africaare intermixed in phylogenetic analyses, questioning any taxonomicdelineation between the two groups. Contrary to cave hyenasin Eurasia, spotted hyenas in Africa show a phylogeographicpattern with little geographical overlap between two mitochondrialDNA (mtDNA) clades, suggesting two Pleistocene refugia in thenorth and south of Africa. Our results, furthermore, suggestthree waves of migration from Africa to Eurasia for spottedhyenas, around 3, 1, and 0.3 MYA. A recent emigration of stripedhyenas from Africa to Eurasia took place less than 0.1 MYA,resulting in a dramatic expansion of the geographical rangeof striped hyenas. In striped hyenas and within the geographicalrange of mtDNA clades in spotted hyenas, we found identicalsequences several thousand kilometers apart, indicating a highrate of migration during the Pleistocene as well as the Holocene.Both striped and brown hyenas show low amounts of genetic diversity,with the latter ones displaying just a single haplotype.     

Body mass in large extant and extinct carnivores

Body mass in six species of Plio-Pleistocene carnivores was estimated based on the relationship between mass and cross-sectional geometric properties, distal articular surface area, lengths and circumferences of proximal limb bones (femur and humerus) in 28 species of extant carnivores. All measures, except lengths, were found to give congruent body mass estimates. Two of the extinct carnivores ( Smilodon fatalis and Panthera atrox ) are estimated to be as much as one and a half times heavier than previously thought. Based on these results inferences are made concerning possible prey species.     

DNA from extinct giant lemurs links archaeolemurids to extant indriids

Background  

Although today 15% of living primates are endemic to Madagascar, their diversity was even greater in the recent past since dozens of extinct species have been recovered from Holocene excavation sites. Among them were the so-called "giant lemurs" some of which weighed up to 160 kg. Although extensively studied, the phylogenetic relationships between extinct and extant lemurs are still difficult to decipher, mainly due to morphological specializations that reflect ecology more than phylogeny, resulting in rampant homoplasy.     

Morphogenesis of bone ornamentation in extant and extinct crocodilians

Summary Histological study of bone in the skull and osteoscutes of extant and extinct Crocodylia reveals that the skeletal ornamentation of crocodiles is caused by a process of differential, superficial resorption of bone. A partial reconstruction follows the resorption, and several resorption-reconstruction cycles are necessary to suit pit dimensions to overall bone growth. Bone ornamentation is a dynamic structure during ontogeny: the shape and the location of a given pit or groove vary in accordance with the instantaneous regional trends of skeletal growth. This supports the contention that bone oranmentation can be used as a reliable indicator of regional bone growth trends.     

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.     

A wing-assisted running robot and implications for avian flight evolution

DASH+Wings is a small hexapedal winged robot that uses flapping wings to increase its locomotion capabilities. To examine the effects of flapping wings, multiple experimental controls for the same locomotor platform are provided by wing removal, by the use of inertially similar lateral spars, and by passive rather than actively flapping wings. We used accelerometers and high-speed cameras to measure the performance of this hybrid robot in both horizontal running and while ascending inclines. To examine consequences of wing flapping for aerial performance, we measured lift and drag forces on the robot at constant airspeeds and body orientations in a wind tunnel; we also determined equilibrium glide performance in free flight. The addition of flapping wings increased the maximum horizontal running speed from 0.68 to 1.29 m s?1, and also increased the maximum incline angle of ascent from 5.6° to 16.9°. Free flight measurements show a decrease of 10.3° in equilibrium glide slope between the flapping and gliding robot. In air, flapping improved the mean lift:drag ratio of the robot compared to gliding at all measured body orientations and airspeeds. Low-amplitude wing flapping thus provides advantages in both cursorial and aerial locomotion. We note that current support for the diverse theories of avian flight origins derive from limited fossil evidence, the adult behavior of extant flying birds, and developmental stages of already volant taxa. By contrast, addition of wings to a cursorial robot allows direct evaluation of the consequences of wing flapping for locomotor performance in both running and flying.     

The biology of extinct and extant sawfish (Batoidea: Sclerorhynchidae and Pristidae)

Sclerorhynchids (extinct sawfishes, Batoidea), pristids (extant sawfish, Batoidea) and pristiophorids (sawsharks, Squalomorphi) are the three elasmobranch families that possess an elongated rostrum with lateral teeth. Sclerorhynchids are the extinct sawfishes of the Cretaceous period, which reached maximum total lengths of 100 cm. The morphology of their rostral teeth is highly variable. Pristid sawfish occur circumtropically and can reach maximum total lengths of around 700 cm. All pristid species are globally endangered due to their restricted habitat inshore. Pristiophorid sawsharks are small sharks of maximum total lengths below 150 cm, which occur in depths of 70–900 m. Close examination of the morphology of pectoral fin basals and the internal structure of the rostrum reveals that sclerorhynchids and pristids evolved independently from rhinobatids, whereas pristiophorids are squalomorph sharks. The elongation of the rostrum may be an adaptation for feeding, as all marine vertebrate taxa that possess this structure are said to use it in the context of feeding.     

Disentangling ancient interactions: a new extinct passerine provides insights on character displacement among extinct and extant island finches

Background

Evolutionary studies of insular biotas are based mainly on extant taxa, although such biotas represent artificial subsets of original faunas because of human-caused extinctions of indigenous species augmented by introduced exotic taxa. This makes it difficult to obtain a full understanding of the history of ecological interactions between extant sympatric species. Morphological bill variation of Fringilla coelebs and F. teydea (common and blue chaffinches) has been previously studied in the North Atlantic Macaronesian archipelagos. Character displacement between both species has been argued to explain bill sizes in sympatry. However, this explanation is incomplete, as similar patterns of bill size have been recorded in F. coelebs populations from islands with and without F. teydea.

Methodology/Principal Findings

The discovery of a new extinct species in Tenerife (Canary Islands), here named Carduelis aurelioi n. sp. (slender-billed greenfinch), provides the opportunity to study ancient ecological interactions among Macaronesian finches. To help understand the evolutionary histories of forest granivores in space and time, we have performed a multidisciplinary study combining: (1) morphological analyses and radiocarbon dating (11,460±60 yr BP) of the new taxon and, (2) molecular divergence among the extant finch species and populations in order to infer colonization times (1.99 and 1.09 My for F. teydea and F. coelebs respectively).

Conclusion/Significance

C. aurelioi, F. coelebs and F. teydea co-habited in Tenerife for at least one million years. The unique anatomical trends of the new species, namely chaffinch-like beak and modified hind and forelimbs, reveal that there was a process of divergence of resource competition traits among the three sympatric finches. The results of our study, combined with the presence of more extinct greenfinches in other Macaronesian islands with significant variation in their beak sizes, suggests that the character displacement has influenced patterns of divergence in bill size and shape on other Macaronesian islands as well.     

Horizontal gene transfer from extinct and extant lineages: biological innovation and the coral of life

Horizontal gene transfer (HGT) is often considered to be a source of error in phylogenetic reconstruction, causing individual gene trees within an organismal lineage to be incongruent, obfuscating the ‘true’ evolutionary history. However, when identified as such, HGTs between divergent organismal lineages are useful, phylogenetically informative characters that can provide insight into evolutionary history. Here, we discuss several distinct HGT events involving all three domains of life, illustrating the selective advantages that can be conveyed via HGT, and the utility of HGT in aiding phylogenetic reconstruction and in dating the relative sequence of speciation events. We also discuss the role of HGT from extinct lineages, and its impact on our understanding of the evolution of life on Earth. Organismal phylogeny needs to incorporate reticulations; a simple tree does not provide an accurate depiction of the processes that have shaped life''s history.     

On the origins of birds: the sequence of character acquisition in the evolution of avian flight

Assessment of competing theories for the evolution of avian flight is problematic, and tends to rest too heavily on reconstruction of the mode of life of one or a few specimens representing still fewer species. A more powerful method is to compare the sequence of character acquisition predicted by the various theories with the empirical sequence provided by cladistic phylogeny. Arboreal and cursorial theories incorrectly predict the sequence of character acquisition for several key features of avian evolution. We propose an alternative ''pouncing proavis'' model for the evolution of flight. As well as being both biologically and evolutionarily plausible, the pouncing proavis model correctly predicts the evolutionary sequence of all five key features marking the evolution of birds.     

Early-Middle Pleistocene leaves of extinct and extant Proteaceae from western Tasmania, Australia

Fossil leaves of six species of Proteaceae which are no longer native to Tasmania occur in Early Pleistocene sediments at Regatta Point, western Tasmania, Australia. These species probably became extinct during the Early or Middle Pleistocene as the direct or indirect result of glacial/interglacial cycles. Only one extinct species of Proteaceae is known from younger sediments. Leaves of another four species which can be confidently assigned to extant Tasmanian species, and from an extant genus also occur in these sediments. Another extant species occurs in Early Pleistocene sediments at the Huskisson/Marionoak Divide, western Tasmania, and another extant species occurs in Early-Middle Pleistocene sediments at Regatta Point. These fossils imply that the number of species and of genera of Proteaceae in western Tasmania has not increased since the Early Pleistocene, and may have declined. More species of Banksia and Telopea and at least as many species of Orites occurred in Early Pleistocene western Tasmania than now occur in that region. The presence of extant species in the Early Pleistocene suggests that the turnover time of many proteaceous species is of the order of millions of years. Two new species, Telopea strahanensis and Orites truncata , are proposed.     

The position of Cetacea within mammalia: phylogenetic analysis of morphological data from extinct and extant taxa

Knowledge of the phylogenetic position of the order Cetacea (whales, dolphins, and porpoises) within Mammalia is of central importance to evolutionary biologists studying the transformations of biological form and function that accompanied the shift from fully terrestrial to fully aquatic life in this clade. Phylogenies based on molecular data and those based on morphological data both place cetaceans among ungulates but are incongruent in other respects. Morphologists argue that cetaceans are most closely related to mesonychians, an extinct group of terrestrial ungulates. They have disagreed, however, as to whether Perissodactyla (odd-toed ungulates) or Artiodactyla (even-toed ungulates) is the extant clade most closely related to Cetacea, and have long maintained that each of these orders is monophyletic. The great majority of molecule-based phylogenies show, by contrast, not only that artiodactyls are the closest extant relatives of Cetacea, but also that Artiodactyla is paraphyletic unless cetaceans are nested within it, often as the sister group of hippopotamids. We tested morphological evidence for several hypotheses concerning the sister taxon relationships of Cetacea in a maximum parsimony analysis of 123 morphological characters from 10 extant and 30 extinct taxa. We advocate treating certain multistate characters as ordered because such a procedure incorporates information about hierarchical morphological transformation. In all most-parsimonious trees, whether multistate characters are ordered or unordered, Artiodactyla is the extant sister taxon of Cetacea. With certain multistate characters ordered, the extinct clade Mesonychia (Mesonychidae + Hapalodectidae) is the sister taxon of Cetacea, and Artiodactyla is monophyletic. When all fossils are removed from the analysis, Artiodactyla is paraphyletic with Cetacea nested inside, indicating that inclusion of mesonychians and other extinct stem taxa in a phylogenetic analysis of the ungulate clade is integral to the recovery of artiodactyl monophyly. Phylogenies derived from molecular data alone may risk recovering inconsistent branches because of an inability to sample extinct clades, which by a conservative estimate, amount to 89% of the ingroup. Addition of data from recently described astragali attributed to cetaceans does not overturn artiodactyl monophyly.     

Cranial mechanics compared in extinct marsupial and extant African lions using a finite-element approach

Few species have generated more or longer running controversy than Australia's extinct marsupial lion Thylacoleo carnifex ( Owen, 1859 ). Over the last century and a half, feeding behaviours as disparate as osteophagy and specialized herbivory have been suggested and T. carnifex has been placed in both phalangeriform and vombatiform clades. Phylogenetic placement remains uncertain, but broad consensus has been achieved regarding diet, with all recent authors agreeing that T. carnifex was a carnivore. However, the marsupial lion's extraordinary cranial and dental morphologies remain without clear analogy, leaving many questions unanswered regarding how this most atypical mammalian predator killed its prey. Here I apply a rapidly emerging new approach in comparative biology, finite-element analysis, to the examination of cranial mechanics in T. carnifex . Comparisons are made with an extant lion Panthera leo (Linnaeus, 1758) under simulations designed to model stress distributions imposed by biting (intrinsic loads) and interaction with struggling prey (extrinsic loads). Modelling that approximates the 3-D architecture of jaw adductors suggests that both the placental and marsupial lions could generate considerably greater bite forces than has been predicted using 2-D approaches, but with relatively greater forces in the marsupial. The distribution of cranial stress is in many respects similar in both species, but results from simulations of extrinsic forces suggest that the marsupial was particularly well adapted to resist the high stresses that would be expected in dealings with relatively large prey. On the other hand, relatively high stress recorded in the rostrum of T. carnifex under intrinsic loadings suggests that it may have deployed a very different modus operandi , wherein the carnassial teeth played an active role in effecting a kill.     

Barb geometry of asymmetrical feathers reveals a transitional morphology in the evolution of avian flight

The geometry of feather barbs (barb length and barb angle) determines feather vane asymmetry and vane rigidity, which are both critical to a feather''s aerodynamic performance. Here, we describe the relationship between barb geometry and aerodynamic function across the evolutionary history of asymmetrical flight feathers, from Mesozoic taxa outside of modern avian diversity (Microraptor, Archaeopteryx, Sapeornis, Confuciusornis and the enantiornithine Eopengornis) to an extensive sample of modern birds. Contrary to previous assumptions, we find that barb angle is not related to vane-width asymmetry; instead barb angle varies with vane function, whereas barb length variation determines vane asymmetry. We demonstrate that barb geometry significantly differs among functionally distinct portions of flight feather vanes, and that cutting-edge leading vanes occupy a distinct region of morphospace characterized by small barb angles. This cutting-edge vane morphology is ubiquitous across a phylogenetically and functionally diverse sample of modern birds and Mesozoic stem birds, revealing a fundamental aerodynamic adaptation that has persisted from the Late Jurassic. However, in Mesozoic taxa stemward of Ornithurae and Enantiornithes, trailing vane barb geometry is distinctly different from that of modern birds. In both modern birds and enantiornithines, trailing vanes have larger barb angles than in comparatively stemward taxa like Archaeopteryx, which exhibit small trailing vane barb angles. This discovery reveals a previously unrecognized evolutionary transition in flight feather morphology, which has important implications for the flight capacity of early feathered theropods such as Archaeopteryx and Microraptor. Our findings suggest that the fully modern avian flight feather, and possibly a modern capacity for powered flight, evolved crownward of Confuciusornis, long after the origin of asymmetrical flight feathers, and much later than previously recognized.     

On the origin of avian flight: Compromise and system approaches

Based on evolutionary morphological analysis of the fore and hind limbs of extinct and extant birds, a new compromise hypothesis of the origin of flight in birds and theropod dinosaurs is proposed. The bipedalism and anisodactylous foot suitable for various functions were key adaptations for the development of flight. The bipedalism freed forelimbs from the supporting function and promoted transformation into wings, as animals moved from one tree branch to another and descended from trees. At the initial stage, the strong hind limbs provided the opportunity to climb and leap onto trees, bushes, or eminence, while the anisodactylous foot provided a firm support on both dry land and trees. The support provided by this foot allowed the reduction of the tail, which was initially composed of a long row of vertebrae. Thus, a stage of gliding flight was not necessarily passed by early birds. In the other lineages of feathered creatures, functional changes in forelimbs that resulted in the formation of wings developed in parallel and followed almost the same scenario.