Monique Vianey-Liaud

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

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.

Mosaic convergence of rodent dentitions

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.

Dinosaur eggshells as biochronological markers in Upper Cretaceous continental deposits

Abstract European dinosaur eggshells are now well organized in a parataxonomic classification and can be used as reliable biochronological markers for Upper Cretaceous continental deposits. The Rognacian (Campanian–Maastrichtian) continental deposits of southern France can be divided into three successive associations of megaloolithidae taxa. A maximum in ootaxa diversity occurs in Upper Campanian deposits, followed by a decrease at the Campanian–Maastrichtian transition; this correlates with a climatic change recorded in the palynological floras. The stratigraphic distribution of the oospecies demonstrates that the ‘Rognac Limestone’ found in the west and east areas of the Arc basin is diachronic.

Les rongeurs de l'Eocène terminal et de l'Oligocène d'Europe comme indicateurs de leur environnement

Abstract Palaeoecological interpretation of the occurrence of certain rodents in Late Eocene and Oligocene strata from western Europe is based on the establishment of five dental categories, roughly linked with diet and environment. Time-changes in species diversity, and relative abundance in these categories, are analyzed for the Late Eocene and Oligocene periods. The sequence is geographically limited (Quercy-Auvergne) to avoid the mixing of environments that results from too general compiling. Cooling at the beginning of the Late Eocene created open areas testified by the occurrence of hypsodont rodents. The great decrease in rodent diversity and species turnover, at the “Grande Coupure” is probably related to the important decrease in temperature at the Eocene-Oligocene boundary. The less important diversity decrease, at the Mas de Pauffie level (MP 26) is perhaps an indication of a recurrent cooling at the beginning of the Late Oligocene. Maximum aridity also occurred at this level. The calibration and correlation of these events with global events, like the 29 Ma decrease in temperature, or the 30 Ma great marine regression are discussed. The decrease in abundance of Issiodoromys with the great increase in species iversity of categories I and II (no-to-weakly hypsodont teeth) during the Late Oligocene, mark the development of forests, related to increased moisture (and temperature). The analysis of time specific changes in the Theridomyidae, from their first occurrence to their extinction is related to the principal environmental events.

Cranial Remain from Tunisia Provides New Clues for the Origin and Evolution of Sirenia (Mammalia, Afrotheria) in Africa

Sea cows (manatees, dugongs) are the only living marine mammals to feed solely on aquatic plants. Unlike whales or dolphins (Cetacea), the earliest evolutionary history of sirenians is poorly documented, and limited to a few fossils including skulls and skeletons of two genera composing the stem family of Prorastomidae (Prorastomus and Pezosiren). Surprisingly, these fossils come from the Eocene of Jamaica, while stem Hyracoidea and Proboscidea - the putative sister-groups to Sirenia - are recorded in Africa as early as the Late Paleocene. So far, the historical biogeography of early Sirenia has remained obscure given this paradox between phylogeny and fossil record. Here we use X-ray microtomography to investigate a newly discovered sirenian petrosal from the Eocene of Tunisia. This fossil represents the oldest occurrence of sirenians in Africa. The morphology of this petrosal is more primitive than the Jamaican prorastomids’ one, which emphasizes the basal position of this new African taxon within the Sirenia clade. This discovery testifies to the great antiquity of Sirenia in Africa, and therefore supports their African origin. While isotopic analyses previously suggested sirenians had adapted directly to the marine environment, new paleoenvironmental evidence suggests that basal-most sea cows were likely restricted to fresh waters.

Hystricognathy vs sciurognathy in the rodent jaw: a new morphometric assessment of hystricognathy applied to the living fossil Laonastes (Diatomyidae).

While exceptional for an intense diversification of lineages, the evolutionary history of the order Rodentia comprises only a limited number of morphological morphotypes for the mandible. This situation could partly explain the intense debates about the taxonomic position of the latest described member of this clade, the Laotian rock rat Laonastes aenigmamus (Diatomyidae). This discovery has re-launched the debate on the definition of the Hystricognathi suborder identified using the angle of the jaw relative to the plane of the incisors. Our study aims to end this ambiguity. For clarity, it became necessary to revisit the entire morphological diversity of the mandible in extant and extinct rodents. However, current and past rodent diversity brings out the limitations of the qualitative descriptive approach and highlights the need for a quantitative approach. Here, we present the first descriptive comparison of the masticatory apparatus within the Ctenohystrica clade, in combining classic comparative anatomy with morphometrical methods. First, we quantified the shape of the mandible in rodents using 3D landmarks. Then, the analysis of osteological features was compared to myological features in order to understand the biomechanical origin of this morphological diversity. Among the morphological variation observed, the mandible of Laonastes aenigmamus displays an intermediate association of features that could be considered neither as sciurognathous nor as hystricognathous.

RELATIONSHIPS BETWEEN EUROPEAN AND INDIAN DINOSAUR EGGS AND EGGSHELLS OF THE OOFAMILY MEGALOOLITHIDAE

Abstract Indian and French dinosaur eggshell oospecies belonging to the oofamily Megaloolithidae are compared and, of the fourteen Megaloolithidae oospecies previously described from the Late Cretaceous of India, seven are considered junior synonyms. Comparisons between nine oospecies from India and France reveal four groupings which show similarities between megaloolithids of these countries: (1) Megaloolithus microtuberculata, M. cylindricus, and M. padiyalensis; (2) M. mamillare and M. jabalpurensis; (3) M. siruguei and M. khempurensis; and (4) M. pseudomamillare and M. baghensis. Five oospecies from India have no French equivalents, whereas the oogenus Cairanoolithus is endemic to France. Updated synonymy Megaloolithus oospecies shows a total of nine distinct oospecies from India: Megaloolithus cylindricus, M. mohabeyi, M. padiyalensis, M. jabalpurensis, M. dholiyaensis, M. dhoridungriensis, M. khempurensis, M. megadermus, and M. baghensis. One oospecies, M. jabalpurensis, is common to India and South America and is considered here to be possibly a senior synonym of M. patagonicus. The similarities in egg taxa suggest close phyletic relationships, as well as the probable existence of a terrestrial connection of dinosaur fauna between India and Europe during the Cretaceous, and between the two gondwanan areas Patagonia and India.

Dinosaur eggshells (Saurischia) from the Late Cretaceous Intertrappean and Lameta formations (Deccan, India)

ABSTRACT Small eggshell fragments (from Takli 1 and Pisdura 2) or complete crushed eggs (Jabalpur) have been discovered in the intertrappean and Lameta beds from Deccan (India; Upper Cretaceous). Their microstructure is generally well preserved, allowing a fine interpretation of the eggshell pattern. They are referred to sauropod dinosaurs because of their single-layered structure, with distinct growth units. These units are fan-shaped and thin for the first two localities. They show parallel radial limits for the last one and are slightly thicker. This attribution is also supported by the discussion on skeletal remains (bones or teeth) found in the same localities.

Late Cretaceous Peruvian eggshells and their relationships with laurasian and eastern Gondwanian material

Abstract The eggshell material from some Late Cretaceous Peruvian sites is reevaluated in light of the results ofeggshell research in the last years. As a preliminary step, a new oospecies is first described from the Aix Basin (France): Megaloolithus pseudomamillare . The eggshells from the Bagua Basin Peru are divided into six types [1, Dinosauroid spherulitic type, Tubospherulitic morphotype and Angusticanaliculate pore system ( M. pseudomamillare ); 2, Dinosauroid spherulitic, undetermined morphotype; 3, Ornithoid type, Ratite morphotype, Angusticanaliculate; 4, Ornithoid type, Ratite morphotype; 5, Ornithoid type, Ratite morphotype or dinosauroid type, Angustispherulitic morphotype; 6, ? Geckonoid type]. Because of presumable loss of the main part of the material, it was not possible to make additional studies on the eggshells from Laguna Umayo. We can only assess that the tuberculate fragments described by Kerourio & Sige (1984) belong to Megaloolithus , and that the type 2 of this locality could be the same as the type 5 of the Bagua basin. The family Megaloolithidae is thus recorded in Europe, India and South America; it seems that the same oospecies exists in these three areas, in Late Cretaceous deposits. The available biochronological data discussed here support the tentative correlation of the Umayo Formation with the Fundo et Triunfo Formation.

Zegdoumyidae (Rodentia, Mammalia), stem anomaluroid rodents from the Early to Middle Eocene of Algeria (Gour Lazib, Western Sahara): new dental evidence

The Palaeogene fossil record of rodents in Africa is very poor compared to that of North America or Eurasia. Despite this, Africa has long appeared to be a centre of adaptive radiation for two distinct groups of Rodentia: Hystricognathi and Anomaluroidea. The >45-million-year-old enigmatic Zegdoumyidae is the oldest and only rodent family known of this age from Africa (Algeria and Tunisia). Zegdoumyids have been tentatively regarded as a possible early African stem group for Anomaluridae, a link that has never been clearly established because of the highly fragmentary nature of zegdoumyid fossils, as well as the major temporal and morphological gaps between zegdoumyids and the first true anomaluroids from the Late Eocene. About 200 rodent teeth have been sorted after acid treatment of indurated sediments from several new localities in the Gour Lazib of western Algeria dating from the late Early or early Middle Eocene. These new fossils allow us to better describe the morphology of the Zegdoumyidae (especially Glibia and Zegdoumys) and to identify a new taxon, Lazibemys zegdouensis gen. et sp. nov. With this material, we investigated the phylogenetic position of the Zegdoumyidae in a high-level rodent phylogeny with cladistic assessment of the dental evidence. Our analyses have yielded six equally most-parsimonious trees in which zegdoumyids represent the earliest offshoots (pectinately arranged) of a large clade that embraces Eocene anomaluroids plus stem and crown Anomaluridae. This phylogenetic assumption underscores the great antiquity of the Anomaluroidea clade in Africa, as expected given the high morphological divergence of the Late Eocene African anomaluroids. Zegdoumyids exhibit a variety of dental morphologies and provide some suggestions on evolutionary trends within the Anomaluroidea (early stages of pentalophodonty, incisor enamel microstructure transitional from the pauciserial to the uniserial condition). The source of Zegdoumyidae is still unclear inasmuch as there is no well-identified sister group among early Palaeogene rodents. Zegdoumyids seem to share a common ancestry with both stem Myodonta and North American Sciuravidae. Given the high degree of dental specialization of zegdoumyids, we cannot exclude the possibility that zegdoumyids are rooted in a more primitive, as yet unknown, African rodent lineage older than the Early-Middle Eocene.