Wing Musculature Reconstruction in Extinct Flightless Auks (Pinguinus and Mancalla) Reveals Incomplete Convergence with Penguins (Spheniscidae) Due to Differing Ancestral States.

Despite longstanding interest in convergent evolution, factors that result in deviations from fully convergent phenotypes remain poorly understood. In birds, the evolution of flightless wing-propelled diving has emerged as a classic example of convergence, having arisen in disparate lineages including penguins (Sphenisciformes) and auks (Pan-Alcidae, Charadriiformes). Nevertheless, little is known about the functional anatomy of the wings of flightless auks because all such taxa are extinct, and their morphology is almost exclusively represented by skeletal remains. Here, in order to re-evaluate the extent of evolutionary convergence among flightless wing-propelled divers, wing muscles and ligaments were reconstructed in two extinct flightless auks, representing independent transitions to flightlessness: Pinguinus impennis (a crown-group alcid), and Mancalla (a stem-group alcid). Extensive anatomical data were gathered from dissections of 12 species of extant charadriiforms and 4 aequornithine waterbirds including a penguin. The results suggest that the wings of both flightless auk taxa were characterized by an increased mechanical advantage of wing elevator/retractor muscles, and decreased mobility of distal wing joints, both of which are likely advantageous for wing-propelled diving and parallel similar functional specializations in penguins. However, the conformations of individual muscles and ligaments underlying these specializations differ markedly between penguins and flightless auks, instead resembling those in each respective group's close relatives. Thus, the wings of these flightless wing-propelled divers can be described as convergent as overall functional units, but are incompletely convergent at lower levels of anatomical organization-a result of retaining differing conditions from each group's respective volant ancestors. Detailed investigations such as this one may indicate that, even in the face of similar functional demands, courses of phenotypic evolution are dictated to an important degree by ancestral starting points.

La reconstruction de la musculature des ailes d'espèces éteintes de pingouins non-volants (Pinguinus et Mancalla) révèle une convergence incomplète avec les manchots (Spheniscidae) expliquée par des états ancestraux différentsMalgré un intérêt de longue date pour l'évolution convergente, les facteurs limitant l'evolution de phénotypes entièrement convergents restent mal compris. Chez les oiseaux, l'évolution de la plongée propulsée par les ailes, associée à une perte de la capacité de vol, est devenue un exemple classique de convergence, apparue dans des lignées disparates telles que les manchots (Sphenisciformes) et les pingouins (Pan-Alcidae, Charadriiformes). On sait cependant peu de choses sur l'anatomie fonctionnelle des ailes des pingouins non-volants, car tous sont éteints et leur morphologie est presque exclusivement représentée par des restes squelettiques. Ici, afin de réévaluer l'étendue de la convergence évolutive chez les espèces non-volantes d'oiseaux plongeurs propulsés par leurs ailes, les muscles des ailes et les ligaments ont été reconstruits chez deux espèces éteintes de pingouins non-volants. Ces espèces représentent des transitions indépendantes vers l'inaptitude à voler : Pinguinus impennis (un alcidé du groupe-couronne) et Mancalla (un alcidé du groupe-tronc). Des données anatomiques approfondies ont été recueillies à partir des dissections de 12 espèces actuelles de Charadriiformes et de 4 espèces d'oiseaux d'eau Aequornithes, dont un manchot. Les résultats suggèrent que les ailes des deux taxons de pingouins non-volants étaient caractérisées par un avantage mécanique accru des muscles alaires élévateurs / rétracteurs, et par une mobilité réduite des articulations distales de l'aile. Ces deux éléments sont probablement avantageux pour la plongée propulsée par les ailes, et représentent des spécialisations fonctionnelles similaires à celles des manchots. Cependant, les conformations des muscles et des ligaments individuels sous-jacents à ces spécialisations diffèrent nettement entre les manchots et les pingouins non-volants. Ces conformations ressemblent ainsi plutôt à celles des taxons proches de chaque groupe respectif. Chez ces oiseaux plongeurs non-volants propulsés par les ailes, les ailes peuvent être décrites comme convergentes en tant qu'unités fonctionnelles globales, mais sont incomplètement convergentes à des niveaux inférieurs d'organisation anatomique. C'est le résultat du maintien de conditions différentes héritées des ancêtres volants respectifs de chaque groupe. Des recherches détaillées comme celle-ci peuvent indiquer que, même face à des exigences fonctionnelles similaires, le cours de l'évolution phénotypique est dicté, de manière importante, par le point de départ ancestral.(Translated by Simon L. Ducatez).

La reconstrucción de la musculatura del ala en álcidos extintos no voladores (Pinguinus y Mancalla) revela una convergencia incompleta con los pingüinos (Spheniscidae) debido a sus distintos estados ancestralesA pesar del gran interés que tradicionalmente ha despertado la evolución convergente, los factores que limitan la evolución de fenotipos completamente convergentes siguen siendo poco conocidos. En las aves, la evolución del buceo mediante propulsión alar asociado a una pérdida de la capacidad de vuelo ha emergido como un ejemplo clásico de convergencia evolutiva, habiendo aparecido en linajes dispares que incluyen los pingüinos (Sphenisciformes) y los álcidos (Pan-Alcidae, Charadriiformes). Sin embargo, el conocimiento sobre la anatomía funcional de los álcidos no voladores es limitado, dado que dichos taxones están completamente extintos y su morfología está representada de modo prácticamente exclusivo por restos esqueléticos. En este trabajo, reconstruimos los ligamentos y los músculos del ala de dos álcidos extintos no voladores que representan dos transiciones independientes hacia la condición no voladora: Pinguinus impennis (un álcido del grupo corona) y Mancalla (un álcido del grupo troncal), con el objetivo de reevaluar el alcance de la convergencia evolutiva entre los distintos grupos de aves no voladoras que bucean mediante propulsión alar. A tal efecto, recolectamos información anatómica exhaustiva a partir de la disección de 12 especies existentes de caradriformes y 4 aequornitinas acuáticas, incluyendo un pingüino. Los resultados sugieren que las alas de ambos álcidos no voladores estaban caracterizadas por una mayor ventaja mecánica de los músculos elevadores/retractores del ala, y por una disminución de la movilidad de las articulaciones distales del ala. Ambas características son probablemente ventajosas para el buceo mediante propulsión alar y representan especializaciones funcionales similares a las de los pingüinos. Sin embargo, la configuración de los ligamentos y músculos individuales ligados a dichas especializaciones difiere marcadamente entre pingüinos y álcidos no voladores, siendo similar a la configuración en los respectivos parientes cercanos de cada grupo. En consecuencia, las alas de estas aves no voladoras que bucean mediante propulsión alar pueden ser descritas como convergentes si son consideradas como unidades funcionales generales, pero esta convergencia es incompleta en niveles inferiores de su organización anatómica. Esto es el resultado de la retención de las distintas condiciones presentes en los antepasados voladores de ambos grupos. Investigaciones detalladas como la presente pueden indicar que, incluso frente a requerimientos funcionales similares, el curso de la evolución fenotípica está fuertemente dictado por el punto de partida ancestral.(Translated by Juan Benito Moreno).

Publisher Correction: A new viewpoint on antlers reveals the evolutionary history of deer (Cervidae, Mammalia).

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A new viewpoint on antlers reveals the evolutionary history of deer (Cervidae, Mammalia).

Recent molecular phylogeny of deer revealed that the characters of antlers previously focused on are homoplasious, and antlers tend to be considered problematic for classification. However, we think antlers are important tools and reconsidered and analysed the characters and structures to use them for classification. This study developed a method to describe the branching structure of antlers by using antler grooves, which are formed on the antlers by growth, and then projecting the position of the branching directions of tines on the burr circumference. By making diagrams, comparing the branching structure interspecifically, homologous elements (tines, beams, and processes) of the antlers of 25 species of 16 genera were determined. Subsequently, ancestral state reconstruction was performed on the fixed molecular phylogenetic tree. It was revealed that Capreolinae and Cervini gained respective three-pointed antlers independently, and their subclades gained synapomorphous tines. We found new homologous and synapomorphous characters, as the antler of Eld's deer, which has been classified in Rucervus, is structurally close to that of Elaphurus rather than that of Rucervus, consistent with molecular phylogeny. The methods of this study will contribute to the understanding of the branching structure and phylogeny of fossil species and uncover the evolutionary history of Cervidae.

First fossil occurrence of a filefish (Tetraodontiformes; Monacanthidae) in Asia, from the Middle Miocene in Nagano Prefecture, central Japan.

A new fossil filefish, Aluterus shigensis sp. nov., with a close resemblance to the extant Aluterus scriptus (Osbeck), is described from the Middle Miocene Bessho Formation in Nagano Prefecture, central Japan. It is characterized by: 21 total vertebrae; very slender and long first dorsal spine with tiny anterior barbs; thin and lancet-shaped basal pterygiophore of the spiny dorsal fin, with its ventral margin separated from the skull; proximal tip of moderately slender first pterygiophore of the soft dorsal fin not reaching far ventrally; soft dorsal-fin base longer than anal-fin base; caudal peduncle having nearly equal depth and length; and tiny, fine scales with slender, straight spinules. The occurrence of this fossil filefish from the Bessho Formation is consistent with the influence of warm water currents suggested by other fossils, but it is inconsistent with the deep-water sedimentary environment of this Formation. This is the first fossil occurrence of a filefish in Asia; previously described fossil filefishes are known from the Pliocene and Pleistocene of Italy, the Pliocene of Greece, and the Miocene and Pliocene of North America. These fossil records suggest that the genus Aluterus had already been derived and was widely distributed during the Middle Miocene with taxa closely resembling Recent species.

[Jaws of birds].

Birds (Class Aves) have been hypothesized to have evolved from theropod dinosaurs, which belong to the group known as diapsid reptiles, during the Mesozoic era. They subsequently acquired derived characters relating to flying ability in all parts of their body, including the jaws, which were toothed in the ancestral forms but beaked in later members. When the fore limbs became modified as wings specialized for flight, they became incapable of grasping food, which function was then assumed by the avian bill. Avian bills consequently evolved great morphological diversity reflecting very divergent modes of feeding. To illustrate the progression of "the evolution of vertebrate jaws," the comparative osteology of avian cranial bones is exemplified by reference to Mesozoic birds and the morphological and functional variations observed among the bills of Neornithes.