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, R. EWAN; CUITIÑO, JOSÉ I.; GAETÁN, CARLOS MAXIMILIANO

Congreso; 5th International Paleontological Congress; 2018

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 the 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 fromearly Miocene dolphins (clade Platanistoidea) from the Gaiman Formation of Patagonia (Argentina). The fossil record suggests that species of Platanistoidea were once diverse and widespread components of global marine ecosystems, but the lineage now in cludes only one extant species, Platanista gangetica. Theradiation 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 detailedanatomy 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 andpolydont; 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 extantPlatanista, suggesting a more piscivorous diet. These characteristics indicate wide variation in feeding strategies 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 ofthe nasofacial sound-producing complex and pterygoid sinus system, consistent with echolocation abilities reported for all crown-clades of odontocetes. These fossils inform us on an important epoch of the evolutionary history of platanistoids, and can help us characterizing the early Miocene cetaceancommunities of Patagonia. The analyses continue.