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Robert J. Asher – One of the best experts on this subject based on the ideXlab platform.

  • Dental Eruption and Growth in Hyracoidea (Mammalia, Afrotheria)
    Journal of Vertebrate Paleontology, 2017
    Co-Authors: Robert J. Asher, Erik R. Seiffert, Rodolphe Tabuce, Lionel Hautier, Gf Gunnell, David Pattinson, Hesham M. Sallam
    Abstract:

    ABSTRACT We investigated dental homologies, development, and growth in living and fossil hyracoids and tested if hyracoids and other mammals show correlations between eruption patterns, gestation time, and age at maturity. Unlike living species, fossil hyracoids simultaneously possess replaced P1 and canine teeth. Fossil species also have shorter crowns, an I3/i3, I2, and a hypoconulid on m3. Prenatal specimens of the living Procavia capensis and Heterohyrax brucei show up to three tooth buds posterior to dI1 and anterior to the seven upper cheek teeth that consistently erupt; erupted teeth include an anterior premolar but not a canine. Most lower cheek teeth finish eruption during growth in hyracoids, not after growth as in most other Afrotherians. All hyracoids show the m1 at (lower) or near (upper) the beginning of eruption of permanent teeth; M3/m3 is the last permanent tooth to erupt. The living P. capensis erupts most lower antemolar loci before m2. In contrast, fossil hyraxes erupt lower antemolars…

  • Dental eruption and growth in Hyracoidea (Mammalia, Afrotheria)
    , 2017
    Co-Authors: Robert J. Asher, Erik R. Seiffert, Rodolphe Tabuce, Lionel Hautier, Gf Gunnell, David Pattinson, Hesham M. Sallam
    Abstract:

    We investigated dental homologies, development, and growth in living and fossil hyracoids and tested if hyracoids and other mammals show correlations between eruption patterns, gestation time, and age at maturity. Unlike living species, fossil hyracoids simultaneously possess replaced P1 and canine teeth. Fossil species also have shorter crowns, an I3/i3, I2, and a hypoconulid on m3. Prenatal specimens of the living Procavia capensis and Heterohyrax brucei show up to three tooth buds posterior to dI1 and anterior to the seven upper cheek teeth that consistently erupt; erupted teeth include an anterior premolar but not a canine. Most lower cheek teeth finish eruption during growth in hyracoids, not after growth as in most other Afrotherians. All hyracoids show the m1 at (lower) or near (upper) the beginning of eruption of permanent teeth; M3/m3 is the last permanent tooth to erupt. The living P. capensis erupts most lower antemolar loci before m2. In contrast, fossil hyraxes erupt lower antemolars after m2. Although the early eruption of antemolars correlates with increased gestation time and age at maturity in primates and Tupaia (i.e., ‘Schultz’s rule’), and although modern hyraxes resemble some anthropoid primates in exhibiting long gestation and eruption of antemolars at or before molars, eruption patterns do not significantly covary with either life history parameter among Afrotherians sampled so far. However, we do observe a shift in eruption timing and crown height in Procavia relative to fossil hyracoids, mirroring observations recently made for other ungulate-grade mammals. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Asher, R. J., G. F. Gunnell, E. R. Seiffert, D. Pattinson, R. Tabuce, L. Hautier, and H. M. Sallam. 2017. Dental eruption and growth in Hyracoidea (Mammalia, Afrotheria). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1317638.

  • 4
    , 2016
    Co-Authors: Lionel Hautier, Nigel C Bennett, Hermien Viljoen, Lauren Howard, Michel C. Milinkovitch, Athanasia C. Tzika, Anjali Goswami, Robert J. Asher
    Abstract:

    1 Consensus on placental mammal phylogeny is fairly recent compared to that for vertebrates as a whole. A stable phylogenetic hypothesis enables investigation into the possibility that placental clades differ from one another in terms of their development. Here, we focus on the sequence of skeletal ossification as a possible source of developmental distinctiveness in "northern " (Laurasiatheria and Euarchontoglires) vs. "southern " (Afrotheria and Xenarthra) placental clades. Previous analyses of mammalian ossification sequences have mainly focused on marsupials, monotremes, and northern placentals. We contribute data on cranial and postcranial ossification events during growth in Afrotheria, including elephants, hyraxes, golden moles, tenrecs, sengis, and aardvarks, and also draw on data for Xenarthra. We use three different techniques to quantify sequence heterochrony: continuous method, sequence-ANOVA and event-paring/Parsimov. By controlling for ties and taking into account results that all methods support, we show that Afrotherian

Terence J Robinson – One of the best experts on this subject based on the ideXlab platform.

  • Retroviral envelope syncytin capture in an ancestrally diverged mammalian clade for placentation in the primitive Afrotherian tenrecs
    Proceedings of the National Academy of Sciences of the United States of America, 2014
    Co-Authors: Guillaume Cornelis, Terence J Robinson, François Catzeflis, Michel C. Milinkovitch, Athanasia C. Tzika, Cécile Vernochet, Sébastien Malicorne, Sylvie Souquere, Steven M. Goodman, Gérard Pierron
    Abstract:

    Syncytins are fusogenic envelope (env) genes of retroviral origin that have been captured for a function in placentation. Syncytins have been identified in Euarchontoglires (primates, rodents, Leporidae) and Laurasiatheria (Carnivora, ruminants) placental mammals. Here, we searched for similar genes in species that retained characteristic features of primitive mammals, namely the Malagasy and mainland African Tenrecidae. They belong to the superorder Afrotheria, an early lineage that diverged from Euarchotonglires and Laurasiatheria 100 Mya, during the Cretaceous terrestrial revolution. An in silico search for env genes with full coding capacity within a Tenrecidae genome identified several candidates, with one displaying placenta-specific expression as revealed by RT-PCR analysis of a large panel of Setifer setosus tissues. Cloning of this endogenous retroviral env gene demonstrated fusogenicity in an ex vivo cell–cell fusion assay on a panel of mammalian cells. Refined analysis of placental architecture and ultrastructure combined with in situ hybridization demonstrated specific expression of the gene in multinucleate cellular masses and layers at the materno–fetal interface, consistent with a role in syncytium formation. This gene, which we named “syncytin-Ten1,” is conserved among Tenrecidae, with evidence of purifying selection and conservation of fusogenic activity. To our knowledge, it is the first syncytin identified to date within the ancestrally diverged Afrotheria superorder.

  • phylogenetic relationships of elephant shrews Afrotheria macroscelididae
    Journal of Zoology, 2011
    Co-Authors: H A Smit, Fengtang Yang, Malcolm A Fergusonsmith, Jansen B Van Vuuren, P C M Obrien, Terence J Robinson
    Abstract:

    Elephant-shrews or sengis (Macroscelidea, Afrotheria) are grouped into two subfamilies, Rhynchocyoninae with a single genus and four species, and Macroscelidinae represented by three genera and 13 species. Our current understanding of the evolutionary relationships within this group is largely based on a molecular phylogeny that suffers from incomplete species representation. We present the first complete phylogeny (with the exception of the recently described East African Rhynchocyon udzungwensis) for Macroscelidea based on mitochondrial and nuclear markers. Novel cytogenetic characters as well as previously described allozyme variation and various morphological features are evaluated and mapped to the molecular topology. Our analyses indicate that Elephantulus is paraphyletic, and that Petrodromus and Macroscelides should be subsumed in Elephantulus. A relaxed Bayesian dating approach supports the hypothesis that an arid-adapted Macroscelidinae lineage dispersed from east Africa at ∼11.5 MYA via an African arid corridor to south-western Africa. The timing of speciation within the east African Rhynchocyoninae (8–10 MYA) is coincidental with the diversification of some other forest specialists. In turn, divergence within the Macroscelidinae coincides with major aridification events across Africa.

  • Sex chromosomes of basal placental mammals
    Chromosoma, 2007
    Co-Authors: Paul D. Waters, Aurora Ruiz-herrera, Gauthier Dobigny, Montserrat Garcia Caldès, Terence J Robinson
    Abstract:

    Placental (eutherian) mammals are currently classified into four superordinal clades (Afrotheria, Xenarthra, Laurasiatheria and Supraprimates) of which one, the Afrotheria (a unique lineage of African origin), is generally considered to be basal. Therefore, Afrotheria provide a pivotal evolutionary link for studying fundamental differences between the sex chromosomes of human/mouse (both representatives of Supraprimates and the index species for studies of sex chromosomes) and those of the distantly related marsupials. In this study, we use female fibroblasts to investigate classical features of X chromosome inactivation including replication timing of the X chromosomes and Barr body formation. We also examine LINE-1 accumulation on the X chromosomes of representative Afrotherians and look for evidence of a pseudoautosomal region (PAR). Our results demonstrate that asynchronous replication of the X chromosomes is common to Afrotheria, as with other mammals, and Barr body formation is observed across all Placentalia, suggesting that mechanisms controlling this evolved before their radiation. Finally, we provide evidence of a PAR (which marsupials lack) and demonstrate that LINE1 is accumulated on the Afrotherian and xenarthran X, although this is probably not due to transposition events in a common ancestor, but rather ongoing selection to retain recently inserted LINE1 on the X.

Roscoe Stanyon – One of the best experts on this subject based on the ideXlab platform.

  • RESEARCH ARTICLE Open Access Chromosome painting in three-toed sloths: a cytogenetic signature and ancestral karyotype for
    , 2016
    Co-Authors: Nathália F Azevedo, Roscoe Stanyon, Marta Svartman, Andrea Manchester, Nádia De Moraes-barros, Angela M Vianna-morgante
    Abstract:

    Background: Xenarthra (sloths, armadillos and anteaters) represent one of four currently recognized Eutherian mammal supraorders. Some phylogenomic studies point to the possibility of Xenarthra being at the base of the Eutherian tree, together or not with the supraorder Afrotheria. We performed painting with human autosomes and X-chromosome specific probes on metaphases of two three-toed sloths: Bradypus torquatus and B. variegatus. These species represent the fourth of the five extant Xenarthra families to be studied with this approach. Results: Eleven human chromosomes were conserved as one block in both B. torquatus and B. variegatus: (HSA 5

  • The Chromosomes of Afrotheria and Their Bearing on Mammalian Genome Evolution
    Cytogenetic and genome research, 2012
    Co-Authors: Marta Svartman, Roscoe Stanyon
    Abstract:

    Afrotheria is the clade of placental mammals that, together with Xenarthra, Euarchontoglires and Laurasiatheria, represents 1 of the 4 main recognized supraordinal eutherian clades. It reunites 6 orde

  • chromosome painting in the manatee supports Afrotheria and paenungulata
    BMC Evolutionary Biology, 2007
    Co-Authors: Margaret E Kellogg, Sandra Burkett, Thomas R Dennis, Gary Stone, Brian A. Gray, Peter M Mcguire, Roberto T Zori, Roscoe Stanyon
    Abstract:

    Background Sirenia (manatees, dugongs and Stellar’s sea cow) have no evolutionary relationship with other marine mammals, despite similarities in adaptations and body shape. Recent phylogenomic results place Sirenia in Afrotheria and with elephants and rock hyraxes in Paenungulata. Sirenia and Hyracoidea are the two Afrotherian orders as yet unstudied by comparative molecular cytogenetics. Here we report on the chromosome painting of the Florida manatee.