Ontogenetic criteria to distinguish vertebral types on the debated xenarthran synsacrum

Observations of different types of sacra in Greyhounds based on the occurrence of sacrocaudal fusion

Little attention has been paid to the normal fusion of the vertebrae of greyhounds despite the common occurrence of sacrocaudal fusion. The current study aimed to investigate and provide data on the morphology of different types of fused sacra (B, C and D) in greyhounds and also to determine the potential association between the sex, body mass and morphology of fused sacra (S. Weight, S. Length and S. Width) in greyhounds. The sacra were collected from 171 greyhounds from Melbourne, Australia. After classifying the sacra based on the occurrence and types of the sacrocaudal fusion, they were measured for weight of the sacrum, length of sacrum and the width of sacrum. Multiple linear regression analyses were used to quantify the association between weight of the sacrum (as the outcome variable) type of sacrum (A, B, C and D), body mass and sex (as explanatory variables). The results proved that there are measurable differences between each type of fused sacra (B, C and D) and the standard sacra (A). In addition, this study showed that sex or body mass do not influence the occurrence of different types of fusion. The results of this study showed that the occurrence of sacrocaudal fusions was independent of body size in this population of greyhounds. Sacrocaudal fusion might affect the biomechanics in greyhounds independently of effects of body size.

Size and shape regional differentiation during the development of the spine in the nine-banded armadillo (Dasypus novemcinctus)

Xenarthrans (armadillos, anteaters, sloths, and their extinct relatives) are unique among mammals in displaying a distinctive specialization of the posterior trunk vertebrae-supernumerary vertebral xenarthrous articulations. This study seeks to understand how xenarthry develops through ontogeny and if it may be constrained to appear within pre-existing vertebral regions. Using three-dimensional geometric morphometrics on the neural arches of vertebrae, we explore phenotypic, allometric, and disparity patterns of the different axial morphotypes during the ontogeny of nine-banded armadillos. Shape-based regionalization analyses showed that the adult thoracolumbar column is divided into three regions according to the presence or absence of ribs and the presence or absence of xenarthrous articulations. A three-region division was retrieved in almost all specimens through development, although younger stages (e.g., fetuses, neonates) have more region boundary variability. In size-based regionalization analyses, thoracolumbar vertebrae are separated into two regions: a prediaphragmatic, prexenarthrous region, and a postdiaphragmatic xenarthrous region. We show that posterior thoracic vertebrae grow at a slower rate, while anterior thoracics and lumbars grow at a faster rate relatively, with rates decreasing anteroposteriorly in the former and increasing anteroposteriorly in the latter. We propose that different proportions between vertebrae and vertebral regions might result from differences in growth pattern and timing of ossification.

RADIOGRAPHIC ANATOMY OF THE FORELIMB IN THE NORTHERN TAMANDUA (TAMANDUA MEXICANA)

The thoracic limb anatomy of anteaters in the family Myrmecophagidae is specialized for accessing termite and ant nests and for defense purposes. In the case of the northern tamandua (Tamandua mexicana), the forelimbs are also adapted for arboreal and terrestrial locomotion. Unfortunately, this species faces many conservation threats, such as habitat loss and traffic accidents, and injured individuals are frequently taken to wildlife rehabilitation centers. However, lack of knowledge of the radiographic osteoanatomy of this species may prevent appropriate management of injuries and thereby reduce the chances of successful release and survival. In order to fill this knowledge gap, this article describes for the first time the radiographic anatomy of the thoracic limb of the northern tamandua using four standard views and one additional view. The additional orthogonal view helps visualize structures, such as the hamatus process and the sesamoid bone, that are otherwise difficult to visualize due to the natural forearm position of anteaters. Additionally, some fractures and physeal growth plates were identified in one juvenile individual. Further radiographic investigations should be conducted on anteaters to provide more tools for diagnosis, treatment, and rehabilitation of these animals.

Pelvic sexual dimorphism among species monomorphic in body size: relationship to relative newborn body mass

Females have larger pelves than males among eutherians to mitigate obstetrical difficulty. This study addresses 3 issues concerning pelvic sexual dimorphism using 8 species that are sexually monomorphic in nonpelvic size: Aotus azarae , Castor canadensis , Dasypus novemcinctus , Hylobates lar , Saguinus geoffroyi , Sciurus carolinensis , Sylvilagus floridanus , and Urocyon cinereoargenteus . Using published data to compute the index of relative newborn body mass (RNBM = [newborn body mass/adult female body mass]100%) for 266 eutherian species, A. azarae , H. lar , and S. geoffroyi are characterized as giving birth to relatively large newborns and the other 5 species as giving birth to relatively small newborns. The 3 issues are, compared to species giving birth to relatively small newborns, whether species that give birth to relatively large newborns have 1) higher magnitude of pelvic sexual size dimorphism (SSD), 2) lower prevalence of pelvic joint fusion, and 3) dissociation between pelvic and nonpelvic sizes. Nine measures of the pelvis were taken, and fusion of interpubic and sacroiliac joints was observed. Species grouped by high and low RNBM do not differ significantly in magnitude of SSD of pelvic inlet circumference. Species with high RNBM have significantly lower prevalence of interpubic joint fusion than those with low RNBM. Sexes do not differ in their multiple correlation coefficients between inlet circumference and nonpelvic body size in 7 of 8 species. Results suggest that 1) there are multiple anatomical pathways for pelvic obstetrical sufficiency, 2) an unfused interpubic joint is obstetrically advantageous, and 3) relative newborn size does not change the association between pelvic and nonpelvic size in females and males.