Abstract
Abstract. A new monotypic genus of Neogene odontocete (Isoninia borealis) is named on the basis of a partial skull (CMM-V-4061). The holotype was found on the riverbed of the Meherrin River (North Carolina, USA) and probably originated from the Miocene marine Eastover Formation. Deep interdigitation of the cranial sutures indicates that this individual was mature. The new taxon differs from all other delphinidans in the unique combination of the following characters: anteriorly retracted premaxillae and maxillae; premaxillae not contacting nasals; thick nasals with ventrolateral margins deeply imbedded within corresponding troughs in the frontals (this is an apomorphy); nasals with transversely convex dorsal surface; nearly symmetrical vertex; os suturarum (or interparietal or extra folds of the frontals) at the vertex; large dorsal infraorbital foramen level with the posterior margin of the external bony nares; and a postorbital recess on the ventrolateral face of the frontal below and behind the postorbital process of the frontal. This odontocete exhibits two small but pronounced concavities on the cerebral face of the frontal/presphenoid that are presumed to have held vestigial olfactory bulbs in life. Inioidea is only diagnosed by a single unequivocal synapomorphy: width across nasals and nares subequal. Isoninia shares this feature with other inioids and forms the basis for the placement of Isoninia within this clade. A relatively high vertex coupled with a supraoccipital that is deeply wedged between the frontals suggests placement of this new inioid species within the family Iniidae. This is the second inioid described from the Eastover Formation (the other being Meherrinia isoni). This new species adds new cranial morphology and a new combination of cranial characters to this taxonomically small but growing group of mostly marine and mostly Western Hemisphere odontocetes (urn:lsid:zoobank.org:pub:E8B817CA-B250-42B3-9365-36EFBFE351C9).
Highlights
Our goal here is to add to that diversity by describing and naming a new genus and species of inioid from the late Neogene of North Carolina (USA)
The holotype skull (CMM-V-4061) is very dark, so to improve contrast in Figs. 2 and 3, the specimen was lightly dusted with sublimed ammonium chloride
After the specimen was photographed with a Nikon Coolpix 510 camera on a black velvet background under fluorescent light, the ammonium chloride was removed by holding the specimen under running water (Shelburne and Thompson, 2016)
Summary
The extant South American river dolphins (Inia and Pontoporia) are traditionally grouped in the Inioidea (sensu de Muizon, 1988), a conclusion with which more recent work is in agreement; there has been some discussion of whether its sister group is the Yangtze river dolphin (Lipotidae) or modern marine dolphins (Delphinoidea) (Arnason and Guldberg, 1996; Yang and Zhou, 1999; Yang et al, 2005; Cassens et al, 2000; Hamilton et al, 2001; Nikaido et al, 2001; Cozzuol, 2010; Geisler and Sanders, 2003; McGowen et al, 2009; Geisler et al, 2011, 2012; Gatesy et al, 2013; Pyenson et al, 2015; Post et al, 2017; Lambert et al, 2017, 2018, 2020; McGowen et al, 2020). Godfrey et al.: A new odontocete (Inioidea, Odontoceti) from the late Neogene sis (Banguera-Hinestroza et al, 2002) that inhabits the Beni– Mamoré river basin, and possibly Inia araguaiaensis (Hrbek et al, 2014) from the Araguaia–Tocantins river basin. Our goal here is to add to that diversity by describing and naming a new genus and species of inioid from the late Neogene of North Carolina (USA)
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