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Despite a considerable interest among researchers in understanding the variation in skull shapes of birds and the factors influencing it, some of the drivers associated with the design features of an entire bird body, which are important for both successful terrestrial locomotion and flight, have been overlooked. One such factor, in our opinion, is relative skull size (skull length in relation to body mass), which can affect the position of the body's center of gravity. We tested the effects of relative skull size, allometry (i.e., absolute skull size), and diet on variation in skull shape. The study was conducted on 50 songbird species representing a wide range of body masses (8.3-570 g) and dietary preferences (granivores, insectivores/granivores, insectivores, omnivores). Skull shape was analyzed using two-dimensional geometric morphometrics. We found that similar patterns of skull shape occur among passerines with different body sizes and diets. Relative skull size predicted skull shape to a similar extent and with a similar pattern as the absolute size. The effect of relative skull size on skull shape variation is likely due to biomechanical constraints related to flight. Key words: granivores, insectivores, omnivores, geometric morphometry, allometry, songbirds, passerine birds. Bien que la question des variations de la forme du crane des oiseaux et des facteurs qui l'influencent est d'interet considerable pour les chercheurs, certains facteurs associes aux elements de conception de l'ensemble d'un corps d'oiseau, qui sont importants pour le succes de la locomotion terrestre et du vol, ne sont pas pris en consideration. Un de ces facteurs, selon nous, est la taille relative du crane (la longueur du crane par rapport a la masse corporelle), qui peut influencer la position du centre de gravite du corps. Nous avons examine les effets de la taille relative du crane, de l'allometrie (c.-a-d., la taille absolue du crane) et du regime alimentaire sur les variations de la forme du crane. L'etude a porte sur 50 especes d'oiseaux chanteurs couvrant de grandes fourchettes de masses corporelles (de 8,3 a 570 g) et de preferences alimentaires (granivores, insectivores/granivores, insectivores, omnivores). La forme du crane a ete analysee a l'aide de parametres morphometriques bidimensionnels. Nous avons trouve des motifs semblables de forme du crane chez des passereaux de tailles de corps et de regimes alimentaires differents. La taille relative du crane predit la forme du crane dans une mesure semblable et selon un motif similaire a la taille absolue. L'influence de la taille relative du crane sur les variations de la forme du crane est vraisemblablement due a des contraintes biomecaniques reliees au vol. [Traduit par la Redaction] Mots-cles : granivores, insectivores, omnivores, morphometrie geometrique, allometrie, oiseaux chanteurs, passereaux., Introduction Birds have a dramatically wide variety of skull shapes, the subject of considerable research interest (Hospitaleche and Tambussi 2006; Degrange and Picasso 2010; Klingenberg and Marugan-Lobon 2013; Bright et [...]

Covariation patterns of dental traits vary greatly among mammals due to the effect of evolutionary factors. Studies of integration and modularity in dentition in closely related species could provide insights into evolutionary patterns at higher taxonomic levels. We studied the initial stage of trait divergence using two subspecies of closely related bat species, Myotis myotis myotis and M. blythii oxygnathus (family Vespertilionidae), utilizing a collection of 105 specimens from Ukraine and 63 paired quantitative characters. We identified modularities in the dentitions. For vestigial teeth, we found decreased correlations with other teeth and increased variation. The overall modularity of odontometric characters was slightly higher in M. b. oxygnathus. The internal constraints on evolutionary change were unexpectedly high. Variation and covariation in tooth sizes were critically limited in the studied Myotis species, which could be attributed to the need to maintain accurate occlusion. Using the example of M. myotis and M. blythii dentition, we observe the initial stage of the divergence in a highly canalized structure. [ABSTRACT FROM AUTHOR]

As bats are long-lived mammals, insight into the age of individuals is important for studies relating to population ecology and conservation biology, as well as longevity. Thus, there is a need to develop methods to estimate the age of bats, and teeth are excellent means to do so. The work detailed here involves an assessment of age-related changes and variation in tooth wear, dentine growth layers, and pulp cavity size in two bat species with differing life history strategies, i.e. Nyctalus noctula (n = 149) and Eptesicus serotinus (n = 49). Both the gross morphology and the histology of teeth in both species were found to display age-related variation. Morphological indicators like tooth wear and pulp-cavity size showed considerable variation at the individual level, and corresponding with broadly defined age categories. Dentine growth layering was consistent with presumed age and had annual growth layers in both species, along with accessory layers. Aspects of interpreting growth layers and tooth wear based on photographs and histological preparations associated with observer bias are important to consider, as are the sampling of multiple readings. [ABSTRACT FROM AUTHOR]

Morphological integration of the bird skeleton is of great interest because it relates to issues of specialization, plasticity, and rate of evolutionary transformations of a skeleton as a whole and its anatomical regions. Despite growing interest, the integration and modularity of the skeleton of birds, in general, remain little studied. We evaluated the change of relative sizes and integration of shapes of skull, sternum and pelvis, and factors that influence the covariation of these regions among passerines. Results of both standard and phylogenetic reduced major axis showed that the relative lengths of the most studied skeletal traits were largely determined by body mass. The length of the skull scaled isometrically on body mass, and the lengths of both synsacrum and ilium showed positive allometry. Within the skull, beak length was positively allometric, whereas cranium length was negatively allometric with body mass. We found the presence of covariation between shapes of skull, sternum and pelvis using standard partial least squares (PLS) analysis and absence of covariation between most of these blocks using evolutionary PLS analysis on phylogenetic independent contrasts. Evolutionary integration is confirmed only for shapes of skull and pelvis (dorsal view). [ABSTRACT FROM AUTHOR]

As bats are long-lived mammals, insight into the age of individuals is important for studies relating to population ecology and conservation biology, as well as longevity. Thus, there is a need to develop methods to estimate the age of bats, and teeth are excellent means to do so. The work detailed here involves an assessment of age-related changes and variation in tooth wear, dentine growth layers, and pulp cavity size in two bat species with differing life history strategies, i.e. Nyctalus noctula (n = 149) and Eptesicus serotinus (n = 49). Both the gross morphology and the histology of teeth in both species were found to display age-related variation. Morphological indicators like tooth wear and pulp-cavity size showed considerable variation at the individual level, and corresponding with broadly defined age categories. Dentine growth layering was consistent with presumed age and had annual growth layers in both species, along with accessory layers. Aspects of interpreting growth layers and tooth wear based on photographs and histological preparations associated with observer bias are important to consider, as are the sampling of multiple readings. [ABSTRACT FROM AUTHOR]

The genus Myotis is unique among mammals in its high taxonomic diversity and global distribution. Their phylogenetic relationships reflect biogeographic affinities rather than phenotypes. Myotis diverged from other bats in the early Miocene, with a subsequent split between Old and New World lineages about 19 million years ago. Similar ecomorphs ('Leuconoe' [near-water hunters], 'Myotis' [gleaners], 'Selysius' [aerial hawkers]) emerged independently in different lineages of Myotis. We retrieved the probable ancestral ecomorph for each lineage. Phenetic diversity was estimated from the analysis of body and skull traits. It seems that evolution of Myotis fluctuated between 'Leuconoe', 'Selysius', and larger 'Myotis'. [ABSTRACT FROM AUTHOR]