Oligocene-Miocene marine mammals from Belgrade Quarry, North Carolina

New Skeletons of the Ancient Dolphin Xenorophus sloanii and Xenorophus simplicidens sp. nov. (Mammalia, Cetacea) from the Oligocene of South Carolina and the Ontogeny, Functional Anatomy, Asymmetry, Pathology, and Evolution of the Earliest Odontoceti

“…Boessenecker [41] further identified an isolated xenorophid bulla (CCNHM 936) from the Pungo River Formation, and speculated that such specimens perhaps represent reworking of Oligocene fossils into the base of the Pungo River Formation or perhaps the survival of these archaic taxa into the earliest Miocene. More recent discoveries of xenorophid specimens apparently straddling the Oligocene-Miocene boundary [7] lend support to this latter hypothesis.…”

“…This clade represents one of the earliest diverging lineages amongst odontocetes and sheds considerable light upon the early evolution of echolocation, feeding adaptations, and encephalization within Odontoceti [1][2][3][4][5]. Fossils of Xenorophidae are restricted to South and North Carolina and Virginia [6] along the Atlantic Coastal Plain and do not occur in well-sampled Oligocene marine mammal assemblages in other ocean basins [1][2][3][4][5][7][8][9], suggesting that the Xenorophidae represent an early and localized diversification of stem odontocetes in the Western North Atlantic. Their skull morphology includes a number of plesiomorphic and unusual derived features.…”

Echericetus novellusn. gen. n. sp. (Cetacea, Mysticeti, Eomysticetidae), an Oligocene baleen whale from Baja California Sur, Mexico

“…The eomysticetid fossil record represents one of the best-sampled stem mysticete clades, but large-scale questions remain, such as the origin, adaptive traits, and functional morphology (whether eomysticetids were skim feeders, similar to right baleen whales), and the causes that drove their extinction after the Oligocene–Miocene transition (Boessenecker and Fordyce, 2015b, 2017b). The oldest eomysticetid fossils are Micromysticetus rothauseni and Yamatocetus canaliculatus , close to 30 Ma (Marx and Fordyce, 2015), whereas the youngest geological occurrence is the early Miocene Waharoa (~22.28 Ma, Aquitanian; Boessenecker and Fordyce, 2017b; also see Boessenecker, 2022), indicating that eomysticetids thrived at least for 8 to 11 Myr. Not only the longevity of eomysticetid lineage but also the high disparity and diversity, at least nine genera and 13 species (including Echericetus novellus n. gen. n.…”

“…from the Oligocene of Mexico (slightly older than 27.95 Ma, latest Rupelian) adds to the growing list of new eomysticetids in the North Pacific (e.g., Hernández-Cisneros and Nava-Sánchez, 2022). The eomysticetid fossil record represents one of the bestsampled stem mysticete clades, but large-scale questions remain, such as the origin, adaptive traits, and functional morphology (whether eomysticetids were skim feeders, similar to right baleen whales), and the causes that drove their extinction after the Oligocene-Miocene transition (Boessenecker andFordyce, 2015b, 2017b). The oldest eomysticetid fossils are Micromysticetus rothauseni and Yamatocetus canaliculatus, close to 30 Ma (Marx and Fordyce, 2015), whereas the youngest geological occurrence is the early Miocene Waharoa (∼22.28 Ma, Aquitanian; Boessenecker and Fordyce, 2017b; also see Boessenecker, 2022), indicating that eomysticetids thrived at least for 8 to 11 Myr.…”

“…Groups such as eomysticetid are examples of great diversity and disparity, where developmental processes (Boessenecker and Fordyce, 2015b) and environmental factors (e.g., climate change; Marx et al, 2019) likely drove their evolutionary pathways. Eomysticetid display a widespread geographic distribution, unique longirostrine skull morphology, and possible ecological role as a planktivore (Sanders and Barnes, 2002b;Clementz et al, 2014;Boessenecker andFordyce, 2015b, 2017b). More interestingly, eomysticetid represent a transitional step between the *Corresponding author.…”