Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
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.
ISSN: 1932-6203

hal-00807308
https://hal.archives-ouvertes.fr/hal-00807308
DOI : 10.1371/journal.pone.0054307

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Although advanced anthropoid primates (i.e., Simiiformes) are recorded at the end of the Eocene in North Africa (Proteopithecidae, Parapithecidae, and Oligopithecidae), the origin and emergence of this group has so far remained undocumented. The question as to whether these primates are the result of a monophyletic radiation of endemic anthropoids in Africa, or several Asian clades colonizing Africa, is a current focus of paleoprimatology. In this article, we report the discovery of a new anthropoid from Djebel el Kébar in central Tunisia, dating from the late middle Eocene (Bartonian). This taxon, Amamria tunisiensis, new genus and species, currently known by only one isolated upper molar, is among the most ancient anthropoids to be recorded in Africa thus far. Amamria displays a suite of dental features that are primarily observed in Eosimiiformes (stem Anthropoidea). However, it is not allocated to any known family of that group (i.e., Asian Eosimiidae and Afro-Asian Afrotarsiidae) inasmuch as it develops some dental traits that are unknown among eosimiiforms, but can be found in African simiiform anthropoids such as proteopithecids and oligopithecids. With such a mosaic of dental traits, Amamria appears to be a structural intermediate, and as such it could occupy a key position, close to the root of the African simiiforms. Given its antiquity and its apparent pivotal position, the possibility exists that Amamria could have evolved in Africa from Asian eosimiiform or Asian "proto"-simiiform ancestors, which would have entered Africa sometime during the middle Eocene. Amamria could then represent one of the earliest offshoots of the African simiiform radiation. This view would then be rather in favor of the hypothesis of a monophyletic radiation of endemic simiiform anthropoids in Africa. Finally, these new data suggest that there must have been at least two Asian anthropoid colonizers of Africa: the afrotarsiids and the ancestor of Amamria.
ISSN: 0002-9483

hal-01053704
https://hal.archives-ouvertes.fr/hal-01053704
DOI : 10.1002/ajpa.22523