Variación no alométrica en el cráneo del perezoso bayo Bradypus variegatus (Schinz, 1825) (Mammalia, Pilosa, Bradypodidae)

Brown-throated sloth Bradypus variegatus (Schinz, 1825) is a monomorphic mammal, and its skull ontogeny is poorly known. Here, we present a study of the ontogenetic allometric relationship between skull size and shape in 21 specimens of different sizes, for which size and shape were determined by means of geometric morphometric methods. Results indicate that skull shape variation can hardly be explained by skull size. Several studies have shown unique morphological traits of sloths from mammalian norms, affecting varied phenotypic traits from skeletal parts to soft tissues. This non-allometric scaling of skull form in sloth can be seen as another uniqueness of this taxonomic group.El perezoso bayo Bradypus variegatus (Schinz, 1825) es un mamífero monomórfico, de ontogenia craneal poco conocida. En este estudio analizamos la alometría estática entre tamaño y forma, utilizando 21 especímenes diferentes de edades diversas. El tamaño y la forma fueron determinados mediante técnicas de morfometría geométrica. De los resultados obtenidos se desprende que la variación en la forma craneal queda muy poco explicada por la variación en el tamaño. Muchos estudios han señalado características morfológicas únicas en los perezosos en relación al resto de mamíferos, características fenotípicas que van de la estructura esquelética a tejidos blandos. En este caso, el escalado no alométrico del cráneo debería ser visto como otra característica única de este grupo taxonómico

Mechanical adaptation of trabecular bone morphology in the mammalian mandible

Alveolar bone, together with the underlying trabecular bone, fulfils an important role in providing structural support against masticatory forces. Diseases such as osteoporosis or periodontitis cause alveolar bone resorption which weakens this structural support and is a major cause of tooth loss. However, the functional relationship between alveolar bone remodelling within the molar region and masticatory forces is not well understood. This study investigated this relationship by comparing mammalian species with different diets and functional loading (Felis catus, Cercocebus atys, Homo sapiens, Sus scrofa, Oryctolagus cuniculus, Ovis aries). We performed histomorphometric analyses of trabecular bone morphology (bone volume fraction, trabecular thickness and trabecular spacing) and quantified the variation of bone and tooth root volumes along the tooth row. A principal component analysis and non-parametric MANOVA showed statistically significant differences in trabecular bone morphology between species with contrasting functional loading, but these differences were not seen in sub-adult specimens. Our results support a strong, but complex link between masticatory function and trabecular bone morphology. Further understanding of a potential functional relationship could aid the diagnosis and treatment of mandibular diseases causing alveolar bone resorption, and guide the design and evaluation of dental implants

Size, but not shape, would reflect mandibular differences in two spear-nosed bats (<em>Phyllostomus</em> Lacépède, 1799) (Chiroptera, Phyllostomidae)

The mandible is a model for the evolution of complex morphological structures because it presents a developmental integration of its different parts. Unlike other parts of the skull that harbour different functions (protecting the brain and sensory organs), the mandible’s main functional demands are related to feeding, and dietary changes are expected to be the main selective agent for its structure. Here it is presented a geometric morphometric study of mandibles belonging to two species of New World leaf-nosed bats, Phyllostomidae: Pale Spear-nosed Bat (Phyllostomus discolor Wagner, 1843) (n= 29) and Greater Spear-nosed Bat [Phyllostomus hastatus (Pallas, 1767)] (n= 6), both of them with an omnivorous with a nectarivorous shift feeding habit. Differences in size and shape of mandible were examined using 13 landmarks plotted on lateral aspect. The results revealed species differences for size but not for shape, being allometry an unimportant component of interspecific variation. It is concluded that similar feeding specialization in both species would have evolved towards similar mandibular shape, with size having evolved quite independently in both species