Micromorphology of osteoderms in Dasypodidae (Cingulata, Mammalia): Characterization and 3D-reconstructions.

Osteoderms are present in a variety of extinct and extant vertebrates, but among mammals, the presence of osteoderms is essentially restricted to armadillos (Cingulata, Dasypodidae). Osteoderms have been proposed to exhibit a variety of functionalities in Dasypodidae, mainly protection and thermoregulation, and they have been considered as one of the synapomorphies of this group. In this study, we use high-resolution microcomputed tomography to describe the osteoderm micromorphology of several extant species of Dasypodidae in a comparative context. This study allowed the identification, 3D-reconstruction and volume quantification of different internal structures of osteoderms as well as their interrelations. This detailed characterization of the internal osteoderm morphology was compared in a phylogenetic context to assess the evolutionary trends of the species involved. This enables the identification of distinctive patterns for the most widely recognized clades, the Dasypodinae and Euphractinae with a morphological homogeneity in the microstructure of their osteoderms, in comparison with Tolypeutinae where it has not been possible to establish a common morphological pattern. The most important features for linage differentiation is the degree of compaction of the osteoderms, the number of cavities and the development of hairs. It is likely that the differential development of the various structures occurred as adaptive response to climate changes.

Adaptations to a semiaquatic lifestyle in the external ear of southern pinnipeds (Otariidae and Phocidae, Carnivora): Morphological evidences.

Pinnipeds are semiaquatic carnivorans that spend most of their lives in water and use coastal terrestrial, or ice pack, environments to breed, molt and rest. Certain characteristics of the ear have been linked to ecological aspects. In our contribution we focus on the study of the macroscopic and microscopic morphology of the external ear (with the exception of the osseous outer ear canal) of six species of Southern pinnipeds. In order to recognize the different components of tissues, sections were stained following several routine protocols. In addition, double-staining and enzymatic clearing (Alcian blue-alizarin red) was performed to assess the arrangement of skeletal elements in the OEC. The basic structure of the pinna in the southern otariids studied match those previously analyzed for Northern Hemisphere species. The cartilage macro anatomy of the OEC of Mirounga leonina and Arctocephallus gazella is different from that of the Northern Hemisphere species, with only one plate of cartilage, but markedly different between them. The histology of the otariids OEC is homogeneous along the entire extension, but phocids has three different regions (distal, middle, and proximal). The cartilage histology of most phocids is also different from that of analyzed otariids, with an elastic cartilage that resembles a myxoid-like tissue, but is not present in M. leonina, were the tissue around the OEC is very rich in adipocytes. The southern elephant seal M. leonina OEC has a combination of features similar to both the rest of the phocids and to the otariids. An auditory organ that is functional both over and under water could be essential for social behavior in these species.

Ontogenetic variation in the stratum granulosum of the epidermis of Chaetophractus vellerosus (Xenarthra, Dasypodidae) in relation to the development of cornified scales.

The epidermis of mammals is characterized by having a stratum granulosum that produces an orthokeratotic stratum corneum, different from the typical reptilian parakeratotic stratum. Nonetheless, some mammals show distinct degrees of parakeratosis in epidermal regions with few or no pilose follicles (e.g., areas subjacent to cornified scales). With respect to the epidermis and the development of cornified scales in the Dasypodidae, previous studies have supported the presence of a continuous stratum granulosum without any variations during ontogeny. This condition, in which the cornified scales develop without a loss of the stratum granulosum, was interpreted as primitive for eutherians. The present contribution expands the knowledge on the epidermis of Chaetophractus vellerosus in distinct ontogenetic stages in order to determine whether the cornified scales show the same developmental pattern as in other eutherians. The presence of a stratum granulosum in C. vellerosus neonates and its reduction in more advanced ontogenetic stages, in direct relationship with cornified scale development, supports the hypothesis that the partial parakeratosis in the xenarthran integument is secondary, as in other eutherians, and can be interpreted as a derived character state.