Marcelo R Sánchez-Villagra

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The development of distinct regions in the amniote vertebral column results from somite formation and Hox gene expression, with the adult morphology displaying remarkable variation among lineages. Mammalian regionalization is reportedly very conservative or even constrained, but there has been no study investigating vertebral count variation across Amniota(More)
We combine osteological, dental, and soft tissue data with sequences from three nuclear and five mitochondrial genes, sampling all major living clades of marsupials plus several extinct taxa, to perform a simultaneous analysis of marsupial interrelationships. These data were analyzed using direct optimization and sensitivity analysis on a parallel(More)
A major gap in our knowledge of the evolution of marsupial mammals concerns the Paleogene of the northern continents, a critical time and place to link the early history of metatherians in Asia and North America with the more recent diversification in South America and Australia. We studied new exceptionally well-preserved partial skeletons of the Early(More)
Data on the relative sequence of ossification of postcranial elements for eight therian mammals (Myotis lucifugus, Homo sapiens, Rattus norvegicus, Mus musculus, Mesocricetus auratus, Cavia porcellus, Didelphis albiventris, and Sminthopsis macroura) and three outgroups (Chelydra serpentina, Alligator mississippiensis, and Lacerta vivipara) were taken from(More)
Northern South America and South East Asia are today's hotspots of crocodylian diversity with up to six (mainly alligatorid) and four (mainly crocodylid) living species respectively, of which usually no more than two or three occur sympatrically. In contrast, during the late Miocene, 14 species existed in South America. Here we show a diversity peak in(More)
Mammals show a very low level of variation in vertebral count, particularly in the neck. Phenotypes exhibited at various stages during the development of the axial skeleton may play a key role in testing mechanisms recently proposed to explain this conservatism. Here, we provide osteogenetic data that identify developmental criteria with which to recognize(More)
It has been hypothesized that most morphological evolution occurs by allometric differentiation. Because rodents encapsulate a phenomenal amount of taxonomic diversity and, among several clades, contrasting levels of morphological diversity, they represent an excellent subject to address the question: how variable are allometric patterns during evolution?(More)
Postcranial ossification sequences in 24 therian mammals and three outgroup taxa were obtained using clear staining and computed tomography to test the hypothesis that the marsupial forelimb is developmentally accelerated, and to assess patterns of therian postcranial ossification. Sequence rank variation of individual bones, phylogenetic analysis, and(More)
We analyzed a comprehensive data set of ossification sequences including seven marsupial, 13 placental and seven sauropsid species. Data are provided for the first time for two major mammalian clades, Chiroptera and Soricidae, and for two rodent species; the published sequences of three species were improved with additional sampling. The relative timing of(More)
Although we are starting to understand the molecular basis of shell development based on the study of cryptodires, basic comparative ontogenetic data for the other major clade of living turtle, the pleurodires, are largely missing. Herein, the developmental and phylogenetic relation between the bony shell and endoskeleton of Pleurodira are examined by(More)