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

FORDYCE, EWAN; VIGLINO, MARIANA; BUONO, MÓNICA; CUITIÑO, JOSÉ IGNACIO

Salt Lake

Congreso; SVP 76th Annual Meeting; 2016

Society of Vertebrate Paleotology

Shark-tootheddolphins (clade Squalodontidae) are pelagic, Late Oligocene - Late Miocene,long-jawed odontocetes with heterodont teeth. Most of the key named species arefrom shelf strata around the North Atlantic Ocean and Mediterranean. Recentphylogenetic analyses place the group just basal to or in the Platanistoidea.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 withlongirostral skulls and postcrania, but lacking earbones and most of thebasicrania. No new specimens have since been described, and the species has notbeen included in published phylogenetic analyses. A new specimen of P. arctirostris(MPEF-PV 10883; Playa Magagna, Chubut), allows a redescription, and the firstphylogenetic analysis for Phoberodon. The fossil, from the Gaiman Formation,comprises a partial skull, a partial mandible, vertebrae and ribs, and bothscapulae, but no earbones. The 3 Phoberodon fossils were used in a cladisticanalysis based on a published morphological matrix totalling 84 taxa and 292characters. Phoberodon has 49% missing data (particularly earbones, and alsoincluding soft tissues). In the resulting strict consensus of 7488equally-parsimonious trees, Platanistoidea includes Waipatiidae,Squalodelphinidae, and Platanistidae, defined by 6 synapomorphies, 4 of themrelated to the periotic. Squalodon is immediately basal to Platanistoidea, withPhoberodon in a more-basal polytomy with Prosqualodon and other stemOdontoceti. The iterPCR procedure did not identify Phoberodon as an unstabletaxon. An implied weight analysis (K=3) places (Phoberodon+Papahu)+Squalodon inthe Platanistoidea; in other published analyses, Papahu is crownward ofplatanistoids. Results reiterate that the earbones (tympanoperiotics) andbasicranium are important in odontocete morphological phylogenetics, and thattaxa like Phoberodon which do not fully preserve these structural complexescommonly plot basal to their expected position. Phoberodon is for now a stemOdontoceti, but is likely to move more crownward, clustering with Squalodon, asnew material is added to analyses.