Ricardo Montero

Embryonic development of the skeleton of Amphisbaena darwini heterozonata (Squamata: Amphisbaenidae)

An assemblage of amphisbaenian embryos has allowed us to characterize the external morphology of the developing embryos as well as the chondrification and ossification sequences of their skeletal elements. The external characterization of embryos serves as an incomplete developmental table. In contrast to the condition in other squamates, the premaxilla seems to arise azygously from the beginning or to represent very early fusion during embryogenesis. The tabulosphenoid forms from two cartilages to which are added extensive membranous ossifications. The two parietals engage in medial fusion at the midline, where the anterior process of the synotic tectum ossifies and forms the sagittal crest. The lateral element‐X does not ossify until very late in embryogenesis and is interpreted as an epiphysial ossification. The compound mandibular bone arises from the ossification of the posterior part of Meckels cartilage and the fusion of at least two dermal centers, interpreted as surangular and splenial. The vertebral column shows an antero‐posterior gradient of vertebral differentiation. The number of vertebrae is fixed from the beginning of their differentiation. The remnants of pectoral and pelvic girdles are represented by cartilaginous rods. Some reproductive data obtained during the collection of data could be compared with those from the literature. J. Morphol. 239:1–25, 1999.

How common are cranial sesamoids among squamates

Sesamoids are elements that originate as intratendinous structures due to genetic and epigenetic factors. These elements have been reported frequently in vertebrates, although cranial sesamoids have been recorded almost exclusively in non‐tetrapod Osteichthyes. The only tetrapod cranial sesamoids reported until now have been the transiliens cartilage (of crocodiles and turtles), and another one located in the quadrate‐mandibular joint of birds. Here, we examined seven squamate species using histological sections, dissections of preserved specimens, dry skeletons, cleared and stained specimens, computed tomographies (CT), and report the presence of other cranial sesamoids. One is attached to the cephalic condyle of the quadrate, embedded in the bodenaponeurosis and jaw adductor muscles of Ophiodes intermedius (Anguidae). The other sesamoid is found at the base of the basicranium of several squamates, capping the sphenoccipital tubercle, on the lateral side of the basioccipital–basisphenoid suture. This bone has previously been reported as “element X.” We reinterpret it as a basicranial sesamoid, as it is associated with tendons of the cranio‐cervical muscles. This bone seems to have the function of resisting tension‐compression forces generated by the muscle during flexion the head. This element was previously known in several squamates, and we confirmed its presence in three additional squamate families: Gymnophthalmidae, Gekkonidae, and Pygopodidae. The evidence suggests that cranial sesamoids are a widespread character in squamates, and it is possible that this feature has been present since the origin of the group.

The Skull of Phyllomedusa sauvagii (Anura, Hylidae)

The hylid genus Phyllomedusa comprises charismatic frogs commonly known as monkey, leaf or green frogs, and is the most diverse genus of the subfamily Phyllomedusinae, including about 31 species. Although there is some information about the anatomy of these frogs, little is known about the osteology. Here the adult skull of Phyllomedusa sauvagii, both articulated and disarticulated, is described and the intraspecific variation is reported. Additionally, cartilage associated with the adult skull, such as the nasal capsules, auditory apparatus, and hyobranchial apparatus, are included in the analysis. Further examination of disarticulated bones reveals their remarkable complexity, specifically in the sphenethmoid and of the oocipital region. The description of disarticulated bones is useful for the identification of fossil remains as well as providing morphological characteristics that are phylogenetically informative. When comparing the skull morphology with the available information of other species of the genus, Phyllomesusa sauvagii skull resembles more that of P. vaillantii and P. venusta than P. atelopoides. Anat Rec, 299:557–572, 2016.

Políticas científicas, optimalidad y sistemas complejos

Considerando que el sistema cientifico es un sistema complejo que debe adaptarse a los cambios del conocimiento, doy mi parecer sobre la necesidad de establecer politicas que favorezcan esta evolucion. Haciendo analogias con otros sistemas complejos, considero que es importante mantener la diversidad y redundancia del sistema. Creo que una forma de conseguir esta meta es mantener y promover grupos y proyectos que usualmente no son considerados de excelencia en el momento de su evaluacion.