El tipo scratch-digger en dos armadillos (Dasypodidae, Xenarthra): ontogenia esqueletaria de las manos y variaciones de dígitos

Ontogenetic and comparative studies on the hand skeleton of armadillos (Dasypodidae, Xenarthra) are scarce. In this paper adult autopodial skeleton of two species of extant armadillos, Dasypus hybridus (Dasypodinae) and Chaetophractus villosus (Euphractinae), are characterized. In addition, fetal morphology of the cartilaginous hands is compared to that of the bony adult hands. Adult specimensincluded 38 skeletons of C. villosus (n=34), and D. hybridus (n=4). Fetal cartilaginous hands were studied from serial histological sectioning of two specimens, belonging to D. hybridus and C. villosus. A comprehensive description of the adult hand skeleton, and a qualitative comparison with the fetal hand of both species is provided. The hand of C. villosus is clearly pentadactylous, being the third finger the larger one. In the carpus, elements are largely interlocked betwen them, and with the metacarpals. Therefore, this species fits well into the scratch-digger category. In contrast, D. hybridus shows a reduced five digit, narrowing the entire hand, and there is a similar size of digits II and III. This condition is tie to a series of modifications in the carpus, including a less contact among carpals and metacarpals. Fetal carpus of C. villosus is similar to adult skeleton, while in D. hybridus some differences are recorded. Considering that a relict of the fifth finger is present in D. hybridus, the presence of this finger as a diagnostic character of D. (Hyperoambon) kappleri should be discarded. In addition, a comprehensive revision of this character should be extensive to the rest of the species of Dasypus.Los estudios comparativos y ontogenéticos referidos al esqueleto de las manos de los armadillos (Dasypodidae, Xenarthra), son escasos. En este trabajo se caracterizan los autopodios anteriores adultos en dos especies de armadillos actuales, Dasypus hybridus (Dasypodinae) y Chaetophractus villosus (Euphractinae). Se contrasta además su morfología con estadios previos al comienzo de la osificación esqueletaria. Se estudiaron 38 especímenes adultos, correspondientes a Chaetophractus villosus (n=34) y Dasypus hybridus (n=4). Se utilizaron además los autopodios anteriores de 2 fetos pertenecientes a las mismas especies que se seccionaron histológicamente con el fin de reconstruir la estructura cartilaginosa de la mano en desarrollo. Se realizó una descripción exhaustiva de la región carpal, metacarpal y falangeal del esqueleto adulto de ambas especies que luego se contrastó con el esqueleto preosteogénico de los fetos. En C. villosus hay una clara pentadactilia y el dedo III es el más robusto. En el carpo, los elementos tienden a una condición de diplartría, a relacionarse en mayor medida entre ellos y con el metacarpo. Así, esta especie es la que más se ajusta al tipo scratch-digger. Por su parte, en D. hybridus hay una tendencia a la reducción del dedo V, angostando la mano, y una relación de tamaño similar entre el dedo II y el III. A esta condición la acompañan modificaciones en el carpo que incluyen la reducción de los contactos entre carpales y entre ellos y los metacarpales. La región carpal fetal de C. villosus es muy similar a la del adulto y en ella ya están presentes los rasgos más sobresalientes. En el caso de D. hybridus, se pueden apreciar algunas diferencias con el esqueleto adulto. En este trabajo se han encontrado relictos del quinto dedo en D. hybridus. Así, se debería descartar, como un carácter diagnóstico de D. (H.) kappleri, la presencia de un quinto dedo, y a la vez realizar una revisión exhaustiva y extensiva al resto de las especies de Dasypus

Evolution of the axial skeleton in armadillos (Mammalia, Dasypodidae)

Intraspecific and interspecific variation in cervical, thoracic, and lumbar region of the vertebral column of Dasypodidae were examined in a phylogenetic framework. The number of vertebrae for each region were recorded for 86 specimens and metric data for each vertebra (centrum length, high, and width) were recorded for 72 specimens, including eight of the nine living genera. The number of vertebrae and degree of fusion between them were used to define four characters which were plotted on two alternative phylogenies of Dasypodidae. The ratio between centrum height and width is similar across all taxa analyzed except for Chlamyphorus, which exhibits a deviation in the last two lumbars. Tolypeutes matacus is unique among the taxa examined in having a second co-osified bone called postcervical bone, which is a fusion of the seventh cervical and first thoracic vertebrae. The thoraco-lumbar numbers of dasypodids are reduced when compared with other xenarthrans and are more diverse than those of some other mammalian clades of similar geological age and higher ecomorphological diversity. Changes in size are somewhat coupled with changes in the number of body segments. Independent of the phylogenetic framework taken, changes in size are accompanied with small changes in numbers of thoracolumbar vertebrae within each genus. There are functional and phylogenetic correlates for changes in number of thoraco-lumbar vertebrae in dasypodids

New insights into the genital musculature of Macrostomum johni (Platyhelminthes, Macrostomorpha), revealed with CLSM

The genital system is the most thoroughly studied morphological feature in the genus Macrostomum (Platyhelminthes, Macrostomorpha), for two main reasons: 1) taxonomic identification and 2) understanding different mating strategies. In the present study the musculature of the genital system of the freshwater flatworm Macrostomum johni was visualized using phalloidin-linked fluorescent dye by confocal laser scanning microscopy (CLSM), and a 3D model was provided. In the female antrum, two muscular chambers are observed, both attached to the muscular body wall by muscle fibers. In the male system, three muscle sets associated with the stylet are recognized. Finally, we discuss about the interspecific variability of sexual musculature arrangement within Macrostomun and other related genus, and speculate whether there is a common pattern in the musculature of genital organs related to different mating-behavior.Fil: Adami, Mariana Laura. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Cátedra de Histología y Embriología Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Brusa, Francisco. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Galliari, Fernando Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lachowicz, C.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Damborenea, Maria Cristina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Skeletogenesis and sequence heterochrony in rodent evolution, with particular emphasis on the African striped mouse, Rhabdomys pumilio (Mammalia)

Data documenting skeletal development in rodents, the most species-rich ‘order’ of mammals, are at present restricted to a few model species, a shortcoming that hinders exploration of the morphological and ecological diversification of the group. In this study we provide the most comprehensive sampling of rodent ossification sequences to date, with the aim of exploring whether heterochrony is ubiquitous in rodent evolution at the onset of skeletal formation. The onset of ossification in 17 cranial elements and 24 postcranial elements was examined for eight muroid and caviomorph rodent species. New data are provided for two non-model species. For one of these, the African striped mouse, Rhabdomys pumilio, sampling was extended by studying 53 autopodial elements and examining intraspecific variation. The Parsimov method of studying sequence heterochrony was used to explore the role that changes in developmental timing play in early skeletal formation. Few heterochronies were found to diagnose the muroid and caviomorph clades, suggesting conserved patterning in skeletal development. Mechanisms leading to the generation of the wide range of morphological diversity encapsulated within Rodentia may be restricted to later periods in development than those studied in this work. Documentation of skeletogenesis in Rhabdomys indicates that intraspecifc variation in ossification sequence pattern is present, though not extensive. Our study suggests that sequence heterochrony is neither pivotal nor prevalent during early skeletal formation in rodents

An overview of xenarthran developmental studies with a focus on the development of the xenarthrous vertebrae

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