Rodolfo Salas-Gismondi

Western Amazonia as a Hotspot of Mammalian Biodiversity Throughout the Cenozoic

A state-of-the-art review of the Cenozoic fossil record from Western Amazonia is provided, based on literature and new data (regarding Paleogene native ungulates). It allows summarizing the evolution and dynamics of middle Eocene–Holocene mammalian guilds, at the level of species, families, and orders. Major gaps in the Western Amazonian mammal record occur in the pre-Lutetian and early Miocene intervals, and in the Pliocene epoch. Twenty-three orders, 89 families, and 320 species are recognized in the fossil record, widely dominated by eutherians from the middle Eocene onward. Probable Allotheria (Gondwanatheria) occur only in the earliest interval, whereas Metatheria and Eutheria are conspicuous components of any assemblage. Taxonomic diversity was probably fairly constant at the ordinal level (~12–14 orders in each time slice considered) and much more variable in terms of family and species richness: if most intervals are characterized by 40–50 co-occurring species and 19–31 co-occurring families, the early Miocene period illustrates a depauperate fauna (21 species, 17 families), strongly contrasting with the late Miocene climactic guild (82 species, 38 families). Recent mammalian taxonomic diversity from Western Amazonia (12 orders, 37 families, and 286 species) is at odds with all past intervals, as it encompasses only three orders of South American origin (Didelphimorphia, Cingulata, and Pilosa) but four North American immigrant orders (Artiodactyla, Perissodactyla, Carnivora, and Lagomorpha). In terms of taxonomic diversity, recent mammalian guilds are fully dominated by small-sized taxa (Chiroptera, Rodentia, and Primates). This overview also confirms the scarcity of large mammalian flesh-eaters in ancient Neotropical mammalian assemblages. The pattern and the timing of mammalian dispersals from northern landmasses into Western Amazonia are not elucidated yet.

Neotropics provide insights into the emergence of New World monkeys: New dental evidence from the late Oligocene of Peruvian Amazonia.

Recent field efforts in Peruvian Amazonia (Contamana area, Loreto Department) have resulted in the discovery of a late Oligocene (ca. 26.5xa0Ma; Chambira Formation) fossil primate-bearing locality (CTA-61). In this paper, we analyze the primate material consisting of two isolated upper molars, the peculiar morphology of which allows us to describe a new medium-sized platyrrhine monkey: Canaanimico amazonensis gen. et sp. nov. In addition to the recent discovery of Perupithecus ucayaliensis, a primitive anthropoid taxon of African affinities from the alleged latest Eocene Santa Rosa locality (Peruvian Amazonia), the discovery of Canaanimico adds to the evidence that primates were well-established in the Amazonian Basin during the Paleogene. Our phylogenetic results based on dental evidence show that none of the early Miocene Patagonian taxa (Homunculus, Carlocebus, Soriacebus, Mazzonicebus, Dolichocebus, Tremacebus, and Chilecebus), the late Oligocene Bolivian Branisella, or the Peruvian Canaanimico, is nested within a crown platyrrhine clade. All these early taxa are closely related and considered here as stem Platyrrhini. Canaanimico is nested within the Patagonian Soriacebinae, and closely related to Soriacebus, thereby extending back the soriacebine lineage to 26.5xa0Ma. Given the limited dental evidence, it is difficult to assess if Canaanimico was engaged in a form of pitheciine-like seed predation as is observed in Soriacebus and Mazzonicebus, but dental microwear patterns recorded on one upper molar indicate that Canaanimico was possibly a fruit and hard-object eater. If Panamacebus, a recently discovered stem cebine from the early Miocene of Panama, indicates that the crown platyrrhine radiation was already well underway by the earliest Miocene, Canaanimico indicates in turn that the homunculid radiation (as a part of the stem radiation) was well underway by the late Oligocene. These new data suggest that the stem radiation likely occurred in the Neotropics during the Oligocene, and that several stem lineages independently reached Patagonia during the early Miocene. Finally, we are still faced with a layered pattern of platyrrhine evolution, but modified in terms of timing of cladogeneses. If the crown platyrrhine radiation occurred in the Neotropics around the Oligocene-Miocene transition (or at least during the earliest Miocene), it was apparently concomitant with the diversification of the latest stem forms in Patagonia.

A New Carodnia Simpson, 1935 (Mammalia, Xenungulata) from the Early Eocene of Northwestern Peru and a Phylogeny of Xenungulates at Species Level

In spite of a scarce fossil record and poor diversity, xenungulates cover a wide spatial range throughout South America: a new representative of Carodnia Simpson, 1935, attests to the northernmost occurrence of a carodniid xenungulate, ~4,500km away from previous occurrences (Saõ José de Itaboraí, Rio de Janeiro, Brazil; Chubut Province, Patagonia, Argentina) and very close to the Pacific Coast. A phylogenetic analysis of Xenungulata at thexa0species level shows that Xenungulata and Carodniidae are monophyletic, while Etayoidae are potentially paraphyletic, at least with the selected taxonomic sample. Phylogenetic relationships among Xenungulata are [Notoetayoa gargantuai, Etayoa bacatensis [Carodnia sp. nov. [Carodnia feruglioi, C. cf. feruglioi, C. vieirai]]]. The new species is well differentiated from other xenungulates in having the m3 slightly smaller than m2 in terms of occlusal area and the entoconid and hypoconid almost at the same level on m3. It further differs from all other xenungulates but Etayoa bacatensis in possessing a transverse protolophid on m3. It is distinct from all other representatives of Carodnia in showing a precingulid strongly developed on m2-m3. Referral of the locality to the well-constrained early Eocene Mogollón Formation also confirms (i) the persistence of both carodniid and etayoid xenungulates well after the Paleocene-Eocene transition in South America and (ii) the absence of paleogeographic barrier for such large terrestrial mammals at the scale of South American landmass.