Early Miocene squalodontid, Phoberodon arctirostris (Odontoceti, Platanistoidea), from Patagonia and phylogenetics of the Platanistoidea

VIGLINO, MARIANA; BUONO, MÓNICA R.; FITZGERALD, ERICH M.G.; FORDYCE, ROBERT EWAN; CUITIÑO, JOSÉ I.

Salt Lake

Congreso; 76th Society of Vertebrate Paleotology meeting; 2016

Society of Vertebrate Paleontology

Shark-toothed dolphins (clade Squalodontidae) are pelagic, Late Oligocene - Late Miocene, long-jawedodontocetes with heterodont teeth. Most of the key named species are from shelf strata around the NorthAtlantic Ocean and Mediterranean. Recent phylogenetic analyses place the group just basal to or in thePlatanistoidea. One of the few named squalodontids from the Southern Hemisphere is Phoberodonarctirostris (Gaiman Formation, Burdigalian, Early Miocene) from Patagonia, Argentina. The species,named in the 1920s, includes two informative types with longirostral skulls and postcrania, but lackingearbones and most of the basicrania. No new specimens have since been described, and the species hasnot been included in published phylogenetic analyses. A new specimen of P.arctirostris (MPEF-PV10883; Playa Magagna, Chubut), allows a redescription, and the first phylogenetic analysis forPhoberodon. The fossil, from the Gaiman Formation, comprises a partial skull, a partial mandible,vertebrae and ribs, and both scapulae, but no earbones.The 3 Phoberodon fossils were used in a cladistic analysis based on a published morphological matrixtotalling 84 taxa and 292 characters. Phoberodon has 49% missing data (particularly earbones, and alsoincluding soft tissues). In the resulting strict consensus of 7488 equally-parsimonious trees, Platanistoideaincludes Waipatiidae, Squalodelphinidae, and Platanistidae, defined by 6 synapomorphies, 4 of themrelated to the periotic. Squalodon is immediately basal to Platanistoidea, with Phoberodon in a more-basalpolytomy with Prosqualodon and other stem Odontoceti. The iterPCR procedure did not identifyPhoberodon as an unstable taxon. An implied weight analysis (K=3) places(Phoberodon+Papahu)+Squalodon in the Platanistoidea; in other published analyses, Papahu iscrownward of platanistoids. Results reiterate that the earbones (tympanoperiotics) and basicranium areimportant in odontocete morphological phylogenetics, and that taxa like Phoberodon which do not fullypreserve these structural complexes commonly plot basal to their expected position. Phoberodon is fornow a stem Odontoceti, but is likely to move more crownward, clustering with Squalodon, as newmaterial is added to analyses.