Diversity of late Neogene Monachinae (Carnivora, Phocidae) from the North Atlantic, with the description of two new species

While the diversity of 'southern seals', or Monachinae, in the North Atlantic realm is currently limited to the Mediterranean monk seal, Monachus monachus, their diversity was much higher during the late Miocene and Pliocene. Although the fossil record of Monachinae from the North Atlantic is mainly composed of isolated specimens, many taxa have been erected on the basis of fragmentary and incomparable specimens. The humerus is commonly considered the most diagnostic postcranial bone. The research presented in this study limits the selection of type specimens for different fossil Monachinae to humeri and questions fossil taxa that have other types of bones as type specimens, such as for Terranectes parvus. In addition, it is essential that the humeri selected as type specimens are (almost) complete. This questions the validity of partial humeri selected as type specimens, such as for Terranectes magnus. This study revises Callophom obscure, Homiphoce capensis and Phophoca etrusca, all purportedly known from the Lee Creek Mine, Aurora, North Carolina, in addition to their respective type localities in Belgium, South Africa and Italy, respectively. C. obscure is retained as a mona chine seal taxon that lived both on the east coast of North America and in the North Sea Basin. However, FL capensis from North America cannot be identified beyond the genus level, and specimens previously assigned to Pl. etrusca from North America clearly belong to different taxa. Indeed, we also present new material and describe two new genera of late Miocene and Pliocene Monachinae from the east coast of North America: Auroraphoca atlantica nov. gen. et nov. sp., and Virginiaphoca magurai nov. gen. et nov. sp. This suggests less faunal interchange of late Neogene Monachinae between the east and west coasts of the North Atlantic than previously expected

Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans

The evolution of filter feeding in baleen whales (Mysticeti) facilitated a wide range of ecological diversity and extreme gigantism. The innovation of filter feeding evolved in a shift from a mineralized upper and lower dentition in stem mysticetes to keratinous baleen plates that hang only from the roof of the mouth in extant species, which are all edentulous as adults. While all extant mysticetes are born with a mandible lacking a specialized feeding structure (i.e., baleen), the bony surface retains small foramina with elongated sulci that often merge together in what has been termed the alveolar gutter. Because mysticete embryos develop tooth buds that resorb in utero, these foramina have been interpreted as homologous to tooth alveoli in other mammals. Here, we test this homology by creating 3D models of the internal mandibular morphology from terrestrial artiodactyls and fossil and extant cetaceans, including stem cetaceans, odontocetes and mysticetes. We demonstrate that dorsal foramina on the mandible communicate with the mandibular canal via smaller canals, which we explain within the context of known mechanical models of bone resorption. We suggest that these dorsal foramina represent distinct branches of the inferior alveolar nerve (or artery), rather than alveoli homologous with those of other mammals. As a functional explanation, we propose that these branches provide sensation to the dorsal margin of the mandible to facilitate placement and occlusion of the baleen plates during filer feeding

Data from: A new basal chaeomysticete (Mammalia: Cetacea) from the late Oligocene Pysht Formation of Washington, USA

Modern baleen-bearing mysticetes are descendant from archaic, toothed mysticetes known from the Late Eocene and Oligocene of the Pacific Ocean. These toothed mysticetes, such as aetiocetids and mammalodontids, dominate the Oligocene fossil record. However, larger bodied eomysticetids have recently been described from the Oligocene of the Pacific and western Atlantic. These eomysticetids lack functional teeth as adults and are thus considered to be the earliest members of Chaeomysticeti. A new fossil from the Olympic Peninsula, Washington State, including a partial skull, tympanic bullae, mandibles and postcrania, is here described as Sitsqwayk cornishorum gen. et sp. nov. S. cornishorum is a Late Oligocene mysticete lacking functional teeth and is the most phylogenetically basal chaeomysticete. Accordingly, S. cornishorum exhibits a mosaic of aetiocetid and eomysticetid characteristics. The presence of S. cornishorum in the North Pacific, and its phylogenetic position relative to the eomysticetids from the Southern Ocean, suggests a possible a North Pacific point of origin for Chaeomysticeti

Figure S4 from <i>Salishicetus meadi</i>, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution

Cross sections of left (a, b) and right (c, d) mandibles of <i>Salishicetus meadi</i> (UWBM 50004) revealed via computed tomography (CT) scanning. White arrows point to mental foramina branching laterally from the mandibular canal

Figure S1 from <i>Salishicetus meadi</i>, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution

Photographs of holotype bulla of <i>Salishicetus meadi</i> (UWBM 50004) in (a) dorsal; (b) ventral; (c) medial; (d) lateral; (e) anterior; and (f) posterior view; and photographs of holotype incus of <i>Salishicetus meadi</i> (UWBM 50004) in (g) dorsal and (h) ventral views

Figure S3 from <i>Salishicetus meadi</i>, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution

Photographs of holotype thoracic vertebra of <i>Salishicetus meadi</i> (UWBM 50004) in (a) anterior and (b) posterior views

Figure S2 from <i>Salishicetus meadi</i>, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution

Photographs of holotype mandibles of <i>Salishicetus meadi</i> (UWBM 50004). Right mandible in (a) medial, (b) dorsal, and (c) lateral views. Left mandible in (d) medial, (e) dorsal, and (f) lateral views

Dinoflagellate cyst biostratigraphy from Diversity of late Neogene Monachinae (Carnivora, Phocidae) from the North Atlantic, with the description of two new species

Dinoflagellate cyst biostratigraphy of sediment samples associated with the lectotype specimen of Callophoca obscura, and one specimen that has formerly been assigned to C. obscura, but that is currently deemed Monachinae indet

List of specimens scanned, location of scan, and number of CT slices.

<p>List of specimens scanned, location of scan, and number of CT slices.</p

Generalized phylogeny showing the transition in mysticetes from toothed ancestors to the edentulous, baleen bearing extant taxa.

<p>Phylogeny of Cetacea with an emphasis on mysticete evolution. Blue represents the ancestral condition of adults bearing teeth. Extant mysticetes (green) are edentulous as adults, bear baleen on the palate, and dorsal foramina on the mandible. Eomysticetidae is traditionally interpreted as edentulous, though some taxa preserve possible alveoli potentially indicative of a dentition [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178243#pone.0178243.ref009" target="_blank">9</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178243#pone.0178243.ref011" target="_blank">11</a>].</p