Annales des Sciences Naturelles - Zoologie et Biologie Animale最新文献

A recent phylogenetic analysis based on a data matrix of 43 taxa and 155 osteological characters has produced a new hypothesis of tetrapod phylogeny that is drastically different from the established consensus. This phylogeny indicates that the centrum of lissamphibians is apparently a pleurocentrum, and is homologous with the centrum of amniotes. The interpretation of the dental characters that have been used to argue for close relationships between lissamphibians and some dissorophoids is more complex and difficult than has been often been suggested. If paedomorphosis was an important process in the origin of lissamphibians, it may have occurred earlier than previously suggested because lepospondyls can be interpreted as paedomorphic stegocephalians.

Amphisbaena alba when in a defensive position adopts a horseshoe posture, raises its head and tail and opens its mouth. The tail is rigid; the dorsal surface often has non-pigmented areas which resemble scars. Leposternon microcephalum lives sympatrically with A. alba; it has a soft tail which does not appear to be involved in defensive display. Both species have been observed in captivity. The height to which A. alba raises head and tail during defensive display was measured. Morphometrics and morphology of the integument structure in both species were studied in the body and in the tail from the collagen bundles organization viewpoint. The results reveal a mechanical resistance of the tail in A. alba, but not in L. microcephalum. It is possible that this structure, formed of a dense piece of collagen, serves as a ‘biting block’ ; lesions caused by potential predators could cause no great harm. The skin of the remainder of the body in A. alba (but not in L. microcephalum) is also very resistant; the animal is practically covered by a flexible armour.

A phylogenetic analysis based on a data matrix of 43 taxa and 155 osteological characters has produced a new hypothesis of tetrapod phylogeny that is drastically different from the established consensus. Among Paleozoic taxa, only diadectomorphs appear to be related to amniotes. In contrast to previous hypotheses, lissamphibians appear to have been derived from lepospondyls. Seymouriamorphs, gephyrostegids, embolomeres, temnospondyls, and loxommatids are stem-tetrapods. The new phylogeny suggests that the absence of a tympanic middle ear in salamanders and gymnophiones is a primitive character.

The transverse and sagittal diameters of the long bones were measured in a sample of 53 species of eutherian mammals and 36 species of birds. The scaling of the transverse and sagittal diameters of each bone to body mass was calculated. For each bone the ratio of sagittal/transverse diameter was calculated, as an expression of the cross-sectional shape of the bones. The distributions of the ratios were not significantly different from normality in all the avian bones and in the mammalian femur and tibia. In most cases, the mean of the distribution was significantly different from 1 (circular shape). The analysis shows that changes in the ratio can be caused by selective factors, considering the correlation predicted between the breaking moments and the radii, but at the same time the cross-sectional shape of mammalian and avian long bones may have a phylogenetic basis. Finally, the previous assumption of relationship between bone curvature and stress predictability, is also discussed.

The morphology of the abdominal and pelvic arterial system was analysed in two talpid species, the common mole (Talpa europaea) and the Pyrenean desman (Galemys pyrenaicus). Animals were studied by injection of coloured latex solution into the aorta by cannulation through the left ventricle of the heart, and subsequent dissection under a surgical microscope. In spite of the intra- and interspecific variation observed in the main abdominal and pelvic vessels examined, the general arrangements observed in talpids are consistent with the patterns described in other Insectivora, such as Soricinae and Crocidurinae. Interspecific morphological comparisons within the Insectivora and with representatives of other mammal orders revealed that the origin and arrangement of certain arteries, such as the renal, gonadal, caudal mesenteric, and median sacral arteries are clearly uncorrelated with function and phylogeny. Similar conclusions can be extended to the common or separate origin of the cœliac and the cranial mesenteric arteries. In contrast, other specific arterial traits can be interpreted from a functional and/or evolutionary standpoint. We discuss these implications for the following characteristics: the absence of gastroepiploic arteries; the presence of double lienal arteries and right gastric artery; the course of the cranial mesenteric artery; the presence of the ductus deferentis artery; and the origin of the cranial gluteal, deep iliac circumflex, and medial and lateral femoral circumflex arteries. Phenetic relationships among Soricomorpha were evaluated by cluster analysis. Congruence between the phenogram obtained and an accepted evolutionary hypothesis corroborates the phylogenetic significance of some arterial arrangements.

A new study was carried out on an increased number of young embryos of Reptile taxa either with well developed limbs or limbless to complete the previous observations devoted to the relationships between the somatic extensions and the formation of limb buds. Results are summarized in table I. In the embryos of Reptiles, the somites involved in limb formation send ventral processes in the somatopleural territory of the future limb and the limb develops only in front of these somatic extensions. In lizards with well developed limbs, there are always eight somites (S6–S13, S1 being the first postotic somite) which send ventral processes in the somatopleure and are thus involved in anterior limb formation. In serpentiform lizards such as Anguis fragilis, Ophisaurus apodus, Scelotes brevipes, only four or five somites (S6–S9 or S6–S10) form ventral extensions; the limb bud develops only in front of these somites, and its size is thus reduced from this early stage. Macroscopic and histological studies of young embryos belonging to four species of snakes (Natrix natrix, Natrix tessellata, Natrix maura and Vipera aspis) shows that none of the thoracic somites of the series S6–S13 form ventral extensions. Several observations suggest that in Reptiles with well developed limbs, the somitic extensions may initiate limb development by liberating a growth factor of the FGF family. In snake embryos, which are devoid of somitic extensions, no growth factor would be liberated and thus no anterior limb would develop. In some species, some pelvian somites form short extensions, which induce a feeble pelvian thickening or a rudimentary posterior limb bud (e.g. Boïdae). It is an embryonic mechanism which is responsible for the limbless condition in Snakes.

Une nouvelle étude portant sur un nombre élevé de jeunes embryons de reptiles, à membres bien développés ou serpentiformes est entreprise pour compléter les observations antérieures relatives aux relations existant entre les prolongements ventraux des somites thoraciques et la formation des ébauches des membres. Tableau I résume toutes les données ainsi obtenues. Chez les embryons d'espèces à membres bien développés (7 espèces sont étudiées), il y a toujours 8 somites thoraciques envoyant chacun un prolongement ventral dans la somatopleure et une ébauche de membre se forme face à ces 8 somites. Chez les embryons de reptiles serpentiformes (3 espèces de Sauriens étudiées), 4 à 5 somites thoraciques seulement forment des prolongements ventraux et l'ébauche du membre ne se soulève qu'à hauteur de ces somites; elle est ainsi réduite dans ses dimensions, dès l'origine. L'étude macroscopique et histologique de jeunes embryons de 4 espèces d'Ophidiens (Natrix natrix, N. tessellata, N. maura, Vipera aspis) montre qu'aucun somite thoracique (postérieur à S5) ne forme de prolongement ventral chez ces espèces. Or, différentes observations suggèren