Extensive Diversity and Disparity of the Early Miocene Platanistoids (Cetacea, Odontoceti) in the Southeastern Pacific (Chilcatay Formation, Peru)

Abstract

Several aspects of the fascinating evolutionary history of toothed and baleen whales (Cetacea) are still to be clarified due to the fragmentation and discontinuity (in space and time) of the fossil record. Here we open a window on the past, describing a part of the extraordinary cetacean fossil assemblage deposited in a restricted interval of time (19–18 Ma) in the Chilcatay Formation (Peru). All the fossils here examined belong to the Platanistoidea clade as here redefined, a toothed whale group nowadays represented only by the Asian river dolphin Platanista gangetica. Two new genera and species, the hyper-longirostrine Ensidelphis riveroi and the squalodelphinid Furcacetus flexirostrum, are described together with new material referred to the squalodelphinid Notocetus vanbenedeni and fragmentary remains showing affinities with the platanistid Araeodelphis. Our cladistic analysis defines the new clade Platanidelphidi, sister-group to Allodelphinidae and including E. riveroi and the clade Squalodelphinidae + Platanistidae. The fossils here examined further confirm the high diversity and disparity of platanistoids during the early Miocene. Finally, morphofunctional considerations on the entire platanistoid assemblage of the Chilcatay Formation suggest a high trophic partitioning of this peculiar cetacean paleocommunity.

Distribution and paleoenvironmental framework of middle Miocene marine vertebrates along the western side of the lower Ica Valley (East Pisco Basin, Peru)

“…in the plain that extends northwest of Cerro Submarino and at the northern edge of Cerro Buque; 35 specimens (26.9%, including the birds and one specimen tentatively identified as a reptile) were found at Dos Cerritos (including the vicinities of Cerro Yesera de Amara); 17 (13.1%) at Cerro Los Tinajones; and 12 (9.2%) at Cerro Las Tres Piramides. The P0 tetrapod assemblage differs from those hosted in the Chilcatay strata exposed at Ullujaya and Zamaca (Bianucci et al, 2018;Di Celma et al, 2019) in its far greater proportion of baleen whales, perhaps reflecting a global trend in mysticete abundance and habitat occupancy (Marx et al, 2019), as well as by the absence of members of the odontocete clade Platanidelphidi (Bianucci et al, 2020). This assemblage also contrasts with that of P1 by the lower abundance of odontocetes, and especially by the apparent absence of ziphiids (beaked whales), whereas it mainly differs from the P2 assemblage by the absence of pinnipeds (seals).…”

A stem delphinidan from the Caribbean region of Venezuela

“…The middle-to-late Miocene fossil record of cetaceans indicates, that along with the global temperature drop by the end of the middle Miocene Climatic Optimum, Odontoceti diversity also entered a phase of change where marine platanistoids (Bianucci et al 2020 ) and some lineages of early odontocetes disappeared, being replaced by a more modern community that included the earliest relatives of crown delphinoids, but also a fair diversity of other groups as sperm whales (Lambert et al 2017a ; Benites-Palomino et al 2020 ; Collareta et al 2020 ), inioids (Lambert et al 2017b , 2020 ) and beaked whales (Bianucci et al 2016 ). The fossil record indicates that the earliest representatives of crown Delphinida coexisted along with early diverging forms, thus sharing world oceans for at least a couple of millions of years.…”

“…During the middle-to-late Miocene the odontocete diversity worldwide included a wide array of sperm whales (Lambert et al 2017a ; Benites-Palomino et al 2020 ), beaked whales (Bianucci et al 2016 ), stem delphinidans (Peredo et al 2018 ; Kimura and Hasegawa 2019 ), and several longirostrine taxa belonging to Eurhinodelphinidae and Platanistoidea (Bianucci et al 2020 ). Most of these groups have been found in multiple localities across the world, especially in the case of stem delphinidans.…”

Hearing from the ocean and into the river: the evolution of the inner ear of Platanistoidea (Cetacea: Odontoceti)

“…The latter has already been found to be correlated with skull shape (McCurry and Pyenson 2018), and we suggest that paleoecology is the primary driving factor here. It is also noteworthy that during the late Oligocene-early Miocene, a variety of rostra and associated tooth morphologies among platanistoids coexisted (Tanaka and Fordyce 2017;Viglino et al 2018aViglino et al , 2020Bianucci et al 2020), implying a range of feeding strategies existed within Platanistoidea, similar to extant odontocetes (Werth 2006;Hocking et al 2017a,b).…”