Eotaria citrica, sp. nov., a new stem otariid from the “Topanga” formation of Southern California

Abstract

A new taxon of stem otariid, Eotaria citrica sp. nov., is described from the upper Burdigalian to lower Langhian “Topanga” formation of Orange County, California. The new species is described from mandibular and dental remains that show a unique combination of plesiomorphic and derived characters. Specifically, it is characterized by having trenchant and prominent paraconid cusps in p3–m1, lingual cingula of p2–4 with faint crenulations, premolars and molars with vestigial metaconid, bilobed root of m2 and a genial tuberosity located under p3. Furthermore, additional material of the contemporaneous Eotaria crypta is described, providing new information on the morphology of this taxon. Both species of Eotaria represent the earliest stem otariids, reinforcing the hypothesis that the group originated in the north Eastern Pacific Region. At present, the “Topanga” Fm. pinniped fauna includes Eotaria citrica, Eotaria crypta, the desmatophocid Allodesmus sp., the odobenids Neotherium sp., Pelagiarctos sp. and includes the oldest records of crown pinnipeds in California. Overall this pinniped fauna is similar to the nearly contemporaneous Sharktooth Hill bonebed. However, unambiguous records of Eotaria are still missing from Sharktooth Hill. This absence may be due to taphonomic or paleoenvironmental factors. The new “Topanga” record presented here was integrated into an overview of the late Oligocene through early Pleistocene pinniped faunas of Southern California. The results show an overall increase in body size over time until the Pleistocene. Furthermore, desmatophocids were the largest pinnipeds during the middle Miocene, but were extinct by the beginning of the late Miocene. Odobenids diversified and became the dominant pinnipeds in late Miocene through Pleistocene assemblages, usually approaching or exceeding 3 m in body length, while otariids remained as the smallest taxa. This pattern contrasts with modern assemblages, in which the phocid Mirounga angustirostris is the largest pinniped taxon in the region, odobenids are extinct and medium and small size ranges are occupied by otariids or other phocids.

Oldest record of monk seals from the North Pacific and biogeographic implications

“…enaliarctines and desmatophocids) and other crown pinnipeds (e.g. odobenids and otariids) which are differentially known from the late Oligocene to the Neogene of the North Pacific region [2,3,[8][9][10].…”

A dwarf walrus from the Miocene of Baja California Sur, Mexico

“…7]). Its size was actually closer to that of the early otariid Pithanotaria starri, which is known from California and was sympatric with large odobenids such as Imagotaria downsi and others (figure 4 and table 3) [3,5]. It is possible that Nanodobenus was occupying a niche similar to that of Pithanotaria , and was replaced by otariids such as Thalassoleon mexicanus , known from the overlying Almejas Formation, which occurs sympatrically with the larger odobenids Aivukus cedrosensis and Dusignathus santacruzensis (figure 4) [5,15].…”

“…During their early history odobenids occurred sympatrically with otariids and desmatophocids, with the latter having larger body sizes and presumably occupying higher trophic levels [1–6]. This pattern shifted after the mid–late Miocene extinction of desmatophocids, leading to a greater diversity of odobenids and an overall increase in body size within this group, peaking during the latest Miocene–early Pliocene [3,4]. These multispecies communities were then composed of otariids and usually two or more species of large (greater than or equal to 2.5 m in body length) odobenids [3,4].…”

Evidence for the independent acquisition of aquatic specializations in pinnipeds (seals, sea lions, and walruses): insights from the study of the phylogenetic position, locomotor behaviour, and description of the stem pinniped, Puijila darwini

“…The earliest fossil odobenids and otariids are restricted to the North Pacific (Deméré et al, 2003). Eotaria represents the earliest-known stem otariid (Boessenecker and Churchill, 2015;Velez-Juarbe, 2017), but the taxon is very incompletely known, as are Pithanotaria, "Thalassoleon" mcnallyae and "Thalassoleon" inouei, taxa that likely represent early-diverging members of the Callorhinus (northern fur seal) offshoot (Deméré et al, 2003;Boessenecker and Churchill, 2015). "Thalassoleon" mexicanus, known from the late Miocene of the North Pacific, may be a stem otariid (Churchill and Boessenecker, 2014) or an early-diverging member of a clade containing all otariids excluding the aforementioned clade including Callorhinus.…”

“…Completeness was considered when selecting fossil taxa. For example, Eotaria, the earliest-known otariid (Boessenecker and Churchill, 2015;Velez-Juarbe, 2017), was not included, as it is known only from mandibular and dental elements. A primary goal in the selection of fossil taxa was to sample early-diverging members of each lineage that do not depart significantly from the hypothetical ancestor at the base of Arctoidea.…”