Fossil odontocetes from Patagonia (Argentina) as a key to understand their evolutionary history during the still enigmatic early Miocene

VIGLINO, MARIANA; BUONO, MÓNICA R.; FORDYCE, ROBERT EWAN; CUITIÑO, JOSÉ I.; GAETÁN, MAXIMILIANO

Paris

Congreso; 5th International Paleontological Congress; 2018

National Museum of Natural History (MNHN), the Sorbonne University and the National Scientific Research Center (CNRS)

Cetacean history includes three major adaptive radiations. The first involves the Eocene northern origins of cetaceans. The second involves the Neoceti (Odontoceti + Mysticeti), which diversified from latest Eocene to earliest Miocene as the Southern Ocean opened. This radiation is linked to rise of the Antarctic Circumpolar Current and to increased nutrients, leading to new niches for cetaceans. Details are uncertain for aspects of this second radiation, especially for the earliest Miocene, but clues come from early Miocene dolphins (clade Platanistoidea) from the Gaiman Formation of Patagonia (Argentina). Fossil record suggest that species of Platanistoidea were once diverse and widespread components of global marine ecosystems, but the lineage now includes only one extant species, Platanista gangetica. The radiation and later decline of platanistoids are still poorly understood. In Patagonia, platanistoids are represented by: Notocetus vanbenedeni, Phoberodon arctirostris and Prosqualodon australis. Surprisingly, these widely-cited species have been overlooked in recent phylogenetic studies, and their detailed anatomy and functional complexes need a modern assessment. We are analyzing key anatomical characters of these species to elucidate the different morphotypes represented in the earliest Miocene. Phoberodon has a long and robust rostrum, with a wide and toothed premaxilla. Prosqualodon has a short and narrow rostrum, also with a wide premaxilla. Phoberodon and Prosqualodon are heterodont and polydont; their robust cheek-teeth have highly elevated denticulate crowns, suggesting a component of mastication. Short jaws in Prosqualodon may indicate sarcophagous feeding. In contrast, the small, more ?modern? Notocetus has single-rooted teeth with short conical crowns, reminiscent of the extant Platanista, suggesting a more piscivorous diet. These characteristics indicate wide variation in feeding strategy and prey preferences in the early Miocene Patagonian communities, and are consistent with little or no ecological overlap. Moreover, all species have osteological correlates indicating the presence of the nasofacial sound-producing complex and pterygoid sinus system, consistent with echolocation abilities reported for all crown-clades of odontocetes. These fossils informs us on an important epoch of the evolutionary history of platanistoids, and can help us characterize the early Miocene cetacean communities of Patagonia. The analyses continue.