Laurent Marivaux

Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography

The long-term isolation of South America during most of the Cenozoic produced a highly peculiar terrestrial vertebrate biota, with a wide array of mammal groups, among which caviomorph rodents and platyrrhine primates are Mid-Cenozoic immigrants. In the absence of indisputable pre-Oligocene South American rodents or primates, the mode, timing and biogeography of these extraordinary dispersals remained debated. Here, we describe South Americas oldest known rodents, based on a new diverse caviomorph assemblage from the late Middle Eocene (approx. 41 Ma) of Peru, including five small rodents with three stem caviomorphs. Instead of being tied to the Eocene/Oligocene global cooling and drying episode (approx. 34 Ma), as previously considered, the arrival of caviomorphs and their initial radiation in South America probably occurred under much warmer and wetter conditions, around the Mid-Eocene Climatic Optimum. Our phylogenetic results reaffirm the African origin of South American rodents and support a trans-Atlantic dispersal of these mammals during Middle Eocene times. This discovery further extends the gap (approx. 15 Myr) between first appearances of rodents and primates in South America.

Early Tertiary mammals from North Africa reinforce the molecular Afrotheria clade

The phylogenetic pattern and timing of the radiation of mammals, especially the geographical origins of major crown clades, are areas of controversy among molecular biologists, morphologists and palaeontologists. Molecular phylogeneticists have identified an Afrotheria clade, which includes several taxa as different as tenrecs (Tenrecidae), golden moles (Chrysochloridae), elephant-shrews (Macroscelididae), aardvarks (Tubulidentata) and paenungulates (elephants, sea cows and hyracoids). Molecular data also suggest a Cretaceous African origin for Afrotheria within Placentalia followed by a long period of endemic evolution on the Afro-Arabian continent after the mid-Cretaceous Gondwanan breakup (approx. 105–25 Myr ago). However, there was no morphological support for such a natural grouping so far. Here, we report new dental and postcranial evidence of Eocene stem hyrax and macroscelidid from North Africa that, for the first time, provides a congruent phylogenetic view with the molecular Afrotheria clade. These new fossils imply, however, substantial changes regarding the historical biogeography of afrotheres. Their long period of isolation in Africa, as assumed by molecular inferences, is now to be reconsidered inasmuch as Eocene paenungulates and elephant-shrews are here found to be related to some Early Tertiary Euramerican ‘hyopsodontid condylarths’ (archaic hoofed mammals). As a result, stem members of afrotherian clades are not strictly African but also include some Early Paleogene Holarctic mammals.

Laonastes and the "Lazarus effect'' in recent mammals

The living Laotian rodent Laonastes aenigmamus, first described in early 2005, has been interpreted as the sole member of the new family Laonastidae on the basis of its distinctive morphology and apparent phylogenetic isolation from other living rodents. Here we show that Laonastes is actually a surviving member of the otherwise extinct rodent family Diatomyidae, known from early Oligocene to late Miocene sites in Pakistan, India, Thailand, China, and Japan. Laonastes is a particularly striking example of the “Lazarus effect” in Recent mammals, whereby a taxon that was formerly thought to be extinct is rediscovered in the extant biota, in this case after a temporal gap of roughly 11 million years.

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.

Late middle Eocene epoch of Libya yields earliest known radiation of African anthropoids

Reconstructing the early evolutionary history of anthropoid primates is hindered by a lack of consensus on both the timing and biogeography of anthropoid origins. Some prefer an ancient (Cretaceous) origin for anthropoids in Africa or some other Gondwanan landmass, whereas others advocate a more recent (early Cenozoic) origin for anthropoids in Asia, with subsequent dispersal of one or more early anthropoid taxa to Africa. The oldest undoubted African anthropoid primates described so far are three species of the parapithecid Biretia from the late middle Eocene Bir El Ater locality of Algeria and the late Eocene BQ-2 site in the Fayum region of northern Egypt. Here we report the discovery of the oldest known diverse assemblage of African anthropoids from the late middle Eocene Dur At-Talah escarpment in central Libya. The primate assemblage from Dur At-Talah includes diminutive species pertaining to three higher-level anthropoid clades (Afrotarsiidae, Parapithecidae and Oligopithecidae) as well as a small species of the early strepsirhine primate Karanisia. The high taxonomic diversity of anthropoids at Dur At-Talah indicates either a much longer interval of anthropoid evolution in Africa than is currently documented in the fossil record or the nearly synchronous colonization of Africa by multiple anthropoid clades at some time during the middle Eocene epoch.

The anthropoid status of a primate from the late middle Eocene Pondaung Formation (Central Myanmar): Tarsal evidence

Primate dental and postcranial remains from the Eocene Pondaung Formation (Myanmar) have been the subject of considerable confusion since their initial discoveries, and their anthropoid status has been widely debated. We report here a well preserved primate talus discovered in the Segyauk locality near Mogaung that displays derived anatomical features typical of haplorhines, notably anthropoids, and lacks strepsirhine synapomorphies. Linear discriminant and parsimony analyses indicate that the talus from Myanmar is more similar structurally to those of living and extinct anthropoids than to those of adapiforms, and its overall osteological characteristics further point to arboreal quadrupedalism. Regressions of talar dimensions versus body mass in living primates indicate that this foot bone might have belonged to Amphipithecus. This evidence supports hypotheses favoring anthropoid affinities for the large-bodied primates from Pondaung and runs contrary to the hypothesis that Pondaungia and Amphipithecus are strepsirhine adapiforms.

Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa

Reconstructing the origin and early evolutionary history of anthropoid primates (monkeys, apes, and humans) is a current focus of paleoprimatology. Although earlier hypotheses frequently supported an African origin for anthropoids, recent discoveries of older and phylogenetically more basal fossils in China and Myanmar indicate that the group originated in Asia. Given the Oligocene-Recent history of African anthropoids, the colonization of Africa by early anthropoids hailing from Asia was a decisive event in primate evolution. However, the fossil record has so far failed to constrain the nature and timing of this pivotal event. Here we describe a fossil primate from the late middle Eocene Pondaung Formation of Myanmar, Afrasia djijidae gen. et sp. nov., that is remarkably similar to, yet dentally more primitive than, the roughly contemporaneous North African anthropoid Afrotarsius. Phylogenetic analysis suggests that Afrasia and Afrotarsius are sister taxa within a basal anthropoid clade designated as the infraorder Eosimiiformes. Current knowledge of eosimiiform relationships and their distribution through space and time suggests that members of this clade dispersed from Asia to Africa sometime during the middle Eocene, shortly before their first appearance in the African fossil record. Crown anthropoids and their nearest fossil relatives do not appear to be specially related to Afrotarsius, suggesting one or more additional episodes of dispersal from Asia to Africa. Hystricognathous rodents, anthracotheres, and possibly other Asian mammal groups seem to have colonized Africa at roughly the same time or shortly after anthropoids gained their first toehold there.

Anthropoid versus strepsirhine status of the African Eocene primates Algeripithecus and Azibius: craniodental evidence.

Recent fossil discoveries have demonstrated that Africa and Asia were epicentres for the origin and/or early diversification of the major living primate lineages, including both anthropoids (monkeys, apes and humans) and crown strepsirhine primates (lemurs, lorises and galagos). Competing hypotheses favouring either an African or Asian origin for anthropoids rank among the most hotly contested issues in paleoprimatology. The Afrocentric model for anthropoid origins rests heavily on the >45 Myr old fossil Algeripithecus minutus from Algeria, which is widely acknowledged to be one of the oldest known anthropoids. However, the phylogenetic position of Algeripithecus with respect to other primates has been tenuous because of the highly fragmentary fossils that have documented this primate until now. Recently recovered and more nearly complete fossils of Algeripithecus and contemporaneous relatives reveal that they are not anthropoids. New data support the idea that Algeripithecus and its sister genus Azibius are the earliest offshoots of an Afro–Arabian strepsirhine clade that embraces extant toothcombed primates and their fossil relatives. Azibius exhibits anatomical evidence for nocturnality. Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, a feature that is entirely compatible with the long and procumbent lower canine included in the toothcomb of crown strepsirhines. These results strengthen an ancient African origin for crown strepsirhines and, in turn, strongly challenge the role of Africa as the ancestral homeland for anthropoids.

A new primate from the Eocene Pondaung Formation of Myanmar and the monophyly of Burmese amphipithecids

The family Amphipithecidae is one of the two fossil primate taxa from Asia that appear to be early members of the anthropoid clade. Ganlea megacanina, gen. et sp. nov., is a new amphipithecid from the late middle Eocene Pondaung Formation of central Myanmar. The holotype of Ganlea is distinctive in having a relatively enormous lower canine showing heavy apical wear, indicating an important functional role of the lower canine in food preparation and ingestion. A phylogenetic analysis of amphipithecid relationships suggests that Ganlea is the sister taxon of Myanmarpithecus, a relatively small-bodied taxon that has often, but not always, been included in Amphipithecidae. Pondaungia is the sister taxon of the Ganlea + Myanmarpithecus clade. All three Pondaung amphipithecid genera are monophyletic with respect to Siamopithecus, which is the most basal amphipithecid currently known. The inclusion of Myanmarpithecus in Amphipithecidae diminishes the likelihood that amphipithecids are specially related to adapiform primates. Extremely heavy apical wear has been documented on the lower canines of all three genera of Burmese amphipithecids. This distinctive wear pattern suggests that Burmese amphipithecids were an endemic radiation of hard object feeders that may have been ecological analogues of living New World pitheciin monkeys.

Cynocephalid dermopterans from the Palaeogene of South Asia (Thailand, Myanmar and Pakistan): systematic, evolutionary and palaeobiogeographic implications

Cynocephalid dermopterans (flying lemurs) are represented by only two living genera (Cynocephalus and Galeopterus), which inhabit tropical rainforests of South‐East Asia. Despite their very poor diversity and their limited distribution, dermopterans play a critical role in higher‐level eutherian phylogeny inasmuch as they represent together with Scandentia (tree‐shrew) the sister group of the Primates clade (Plesiadapiformes + Euprimates). However, unlike primates, for which the fossil record extends back to the early Palaeogene on all Holarctic continents and in Africa, the evolutionary history of the order Dermoptera sensu stricto (Cynocephalidae) has so far remained undocumented, with the exception of a badly preserved fragment of mandible from the late Eocene of Thailand (Dermotherium major). In this paper, we described newly discovered fossil dermopterans (essentially dental remains) from different regions of South Asia (Thailand, Myanmar, and Pakistan) ranging from the late middle Eocene to the late Oligocene. We performed microtomographic examinations at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) to analyse different morphological aspects of the fossilized jaws. The abundant material from the late Oligocene of Thailand (Nong Ya Plong coal mine) allows us to emend the diagnosis of the genus Dermotherium and to describe a new species: Dermotherium chimaera sp. n. This species exhibits an interesting mosaic of plesiomorphic cynocephalid characters shared with Cynocephalus and Galeopterus, and as such, it probably documents a form close to the ancestral morphotype from which the two extant forms are derived (supported by cladistic assessment of the dental evidence). The discovery of Palaeogene cynocephalids is particularly significant since it attests to the great antiquity of the order Dermoptera in Asia, and besides, it provides the first spatio‐temporal glimpse into the evolutionary history of that enigmatic mammal group. In that respect, these fossils testify to a long history of endemism in South Asia for dermopterans, and demonstrate that their modern geographic restriction in south‐eastern Asia is clearly a relictual distribution. Cynocephalids had a more widespread distribution during the Palaeogene, which extended from the Indian subcontinent (the rafting Greater India) to South‐East Asia. Their subsequent extinction on the Indian subcontinent was probably mediated by the major palaeogeographic and geomorphologic events related to the India‐Eurasia collision (retreat of the Paratethys Sea, formation of orogenic highlands) that have strongly affected the climate of South Asia at the end of the Oligocene.