Monique Vianey-Liaud

Bio: Monique Vianey-Liaud is an academic researcher from University of Montpellier. The author has contributed to research in topics: Taxon & Clade. The author has an hindex of 29, co-authored 87 publications receiving 2334 citations. Previous affiliations of Monique Vianey-Liaud include Panjab University, Chandigarh.

Mosaic convergence of rodent dentitions.

Abstract: Background Understanding mechanisms responsible for changes in tooth morphology in the course of evolution is an area of investigation common to both paleontology and developmental biology. Detailed analyses of molar tooth crown shape have shown frequent homoplasia in mammalian evolution, which requires accurate investigation of the evolutionary pathways provided by the fossil record. The necessity of preservation of an effective occlusion has been hypothesized to functionally constrain crown morphological changes and to also facilitate convergent evolution. The Muroidea superfamily constitutes a relevant model for the study of molar crown diversification because it encompasses one third of the extant mammalian biodiversity. Methodology/Principal Findings Combined microwear and 3D-topographic analyses performed on fossil and extant muroid molars allow for a first quantification of the relationships between changes in crown morphology and functionality of occlusion. Based on an abundant fossil record and on a well resolved phylogeny, our results show that the most derived functional condition associates longitudinal chewing and non interlocking of cusps. This condition has been reached at least 7 times within muroids via two main types of evolutionary pathways each respecting functional continuity. In the first type, the flattening of tooth crown which induces the removal of cusp interlocking occurs before the rotation of the chewing movement. In the second type however, flattening is subsequent to rotation of the chewing movement which can be associated with certain changes in cusp morphology. Conclusion/Significance The reverse orders of the changes involved in these different pathways reveal a mosaic evolution of mammalian dentition in which direction of chewing and crown shape seem to be partly decoupled. Either can change in respect to strong functional constraints affecting occlusion which thereby limit the number of the possible pathways. Because convergent pathways imply distinct ontogenetic trajectories, new Evo/Devo comparative studies on cusp morphogenesis are necessary.

The role of Asia in the origin and diversification of hystricognathous rodents

Abstract: In the absence of a comprehensive pre-Oligocene fossil record, the origin and early evolution of hystricognathous rodents have long been the subject of much uncertainty. Baluchimyinae (Rodentia) were initially interpreted as a subfamily of the ctenodactyloid Chappatimyidae (sciurognathous), a group considered to be endemic to the Indian subcontinent and to be closely related to hystricognathous rodents. A newly discovered early Oligocene hystricognathous rodent, Bugtimys zafarullahi gen. n. et sp. n., described herein, from the Bugti Hills (Balochistan, Pakistan) sheds new light on the higher level taxonomy of the previously described Baluchimyinae. As a contribution to the phylogenetic debates regarding the origin of Hystricognathi, we present a cladistic assessment of the dental evidence for the Palaeogene hystricognathous rodent cladogenesis. Our phylogenetic results consistently support the monophyly of the Hystricognathiformes clade (including Tsaganomyidae plus Hystricognathi) of which baluchimyine rodents are clearly members. There is, however, no support for the monophyly of a baluchimyine clade. Nonetheless, ‘baluchimyines’ are for the moment reinterpreted as Hystricognathi incertae sedis. Hystricognathous rodents appear to be well diversified at least since the early Oligocene, both in Africa and South America (phiomorphs and caviomorphs, respectively), and also now in south Asia. Furthermore, our phylogenetic results support close relationships between early hystricognathous and Asian ‘ctenodactyloid’ rodents, which clearly points to an Asian origin for Hystricognathi. In this phylogenetic framework, ‘baluchimyines’ and tsaganomyids are representatives of an initial phase of diversification of hystricognathous rodents in Asia. Oligocene phiomorphs and caviomorphs (sister groups) seem therefore to share a common ‘Asian’ hystricognathous ancestor. This reinforces the possibility that the early dispersal of hystricognathous rodents to South America was not from Africa but from Asia.

Possible Evolutionary Relationships among Eocene and Lower Oligocene Rodents of Asia, Europe and North America

Abstract: A previous review by Dawson (1977) summarized the late Eocene rodent faunas of Asia, Europe and North America. Numerous new data provide information about the origin of rodents, and their evolution and radiation within the different continents. Many of these new findings will be discussed elsewhere in this volume.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals

Abstract: To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.

Timing of the Ethiopian flood basalt event and implications for plume birth and global change

Abstract: Continental flood basalts are often considered as fossil evidence of mantle plume heads impinging on the lithosphere1,2 and have been related to continental breakup3,4,5. Many of these flood basalts erupted within a short time span—of the order of 1 Myr—and were apparently synchronous with crises in global climate and with mass extinctions6. Here we present geochronological (40Ar/39Ar) and magnetostratigraphic results for the Ethiopian traps, one of the last remaining flood basalts for which few such data were available. The bulk of the traps, which have been inferred to mark the appearance of the Ethiopian-Afar plume head at the Earth's surface, erupted approximately 30 Myr ago, over a period of 1 Myr or less. This was about the time of a change to a colder and drier global climate, a major continental ice-sheet advance in Antarctica, the largest Tertiary sea-level drop and significant extinctions.