Miocene baleen whales were highly diverse and included tens of genera. However, their taxonomy and phylogeny, as well as relationships with living whales, are still a subject of controversy. Here, “Mesocetus” argillarius, a poorly known specimen from Denmark, is redescribed with a focus on the cranial anatomy. It was found to represent not only a new genus, Tranatocetus gen. nov., but also a new family; Tranatocetidae. The whales of this family have the rostral bones either overriding or dividing the frontals; the rostral bones are contacting the parietals and nasals dividing the maxillae on the vertex; the occipital shield is dorsoventrally bent. The tympanic bulla is particularly characteristic of this family featuring a short, narrow anterior portion with a rounded or squared anterior end and a wider and higher posterior portion that is swollen in the posteroventral area. A phylogenetic analysis including 51 taxa supports a monophyletic group comprising most Neogene and modern whales, with Tranatocetidae being possibly closer related to Balaenopteridae (rorquals) than to Cetotheriidae. Tranatocetidae exhibit a charahteristic bulla shape. In fact, all Neogene and modern mysticete families examined have a unique shape of the tympanic bulla that is diagnostic at family-level. Inclusion of problematic taxa like Tranatocetus argillarius in phylogenies brings new understanding of the distribution and diagnostic value of character traits. This underlines the need for re-examination of earlier described specimens in the light of the wealth of new information published in later years.
The ecological and conservation status of the geographically isolated Black Sea harbour porpoise is currently unknown. Although it has been suggested that Black Sea harbour porpoises are distinct from other populations, the implementation of specific conservation plans has been hindered by the absence of a genetic and morphological study with large sample sizes. We sought to test the hypothesis that Black Sea porpoises differ from those in the Atlantic Ocean using cranial morphology and mitochondrial DNA variation. A total of 177 adult skulls from the Atlantic coast of France, Danish North Sea including Skagerrak and Inner Danish Waters, Greenland and the Black Sea were scored for 22 morphological variables. A portion of the mitochondrial control region was sequenced for 146 ind. from the eastern north Atlantic, the northern Aegean Sea, the Sea of Marmara and the Black Sea. Within the Black Sea, we found relatively low levels of genetic diversity, and no statistically significant differentiation. However, the Black Sea population shares no haplotypes with the eastern Atlantic populations, suggesting that they have been separated for thousands of years. Black Sea porpoises also show significant morphological differences from other populations, with smaller body and skull size, wider and longer rostrum, smaller orbital length, smaller internal nares and condylar widths and larger occipital ridge. Our results demonstrate that harbour porpoises from the Black Sea, Sea of Marmara and the northern Aegean Sea (eastern region): (1) are genetically differentiated; (2) have been reproductively isolated for a considerable period of time; and (3) are likely to be on an independent evolutionary pathway. We recommend that harbour porpoises from the eastern region be recognized as the subspecies Phocoena phocoena relicta.
All extant porpoise species show paedomorphic skeletal traits. These traits are hypothesized to be connected with rapid growth to reproductive size and could thus show geographic variation according to ecological circumstances. To investigate this, skeletal ontogeny was compared among harbour porpoises from California, West Greenland, the inner Danish waters, and the Sea of Azov. Porpoises from California grew to larger sizes than Danish porpoises, which were again larger than Greenlandic porpoises, whereas Azov porpoises were smallest. Size differences were largely attributable to differences in timing of offset of growth. Expression of paedomorphosis followed the same pattern among populations and sexes as adult sizes; Californian porpoises were less paedomorphic than the other populations across all assessed traits, whereas porpoises from Azov were the most paedomorphic. We propose that the larger size and less profound paedomorphism seen in Californian porpoises are attributable to fluctuation of prey availability, owing to variation in upwelling on which productivity in Californian waters depends. Skull shapes after correction for allometry were significantly different among all populations, Sea of Azov porpoises being most divergent. There was no overlap of skull shapes between the Atlantic, the Pacific, and Azov, supporting the current division of harbor porpoises ( Phocoena phocoena (L., 1758)) into three subspecies ( Phocoena phocoena phocoena (L., 1758), Phocoena phocoena relicta Abel, 1905, and Phocoena phocoena vomerina Gill, 1865).
Nine taxa of Miocene baleen whales were described from the Black Sea region under the name Cetotherium before 1951, and a further four closely related species representing three genera have been added in recent years. This rich diversity requires taxonomic revision and ordering. Here, a new genus, Mithridatocetus, is described from the Tortonian of Crimea and Caucasus, with two species, M. eichwaldi and M. adygeicus (originally Kurdalagonus adygeicus); 'Cetotherium' mayeri (a nomen dubium) is also a member of this genus. In comparison with other Cetotheriinae, Mithridatocetus is distinguished by the autapomorphic shape of the tympanic bulla with the swollen main ridge, the lowered anterior portion of the involucrum and the oblique anterolateral margin; such synapomorphies, as a transversely narrow squamosal with the ventromedially oriented postglenoid process (shared with Eucetotherium), a squamosal cleft (shared with Kurdalagonus) and an oval surface of the compound posterior process of the tympanoperiotic on the posterolateral skull wall (shared with Brandtocetus); and a unique combination of a high neurocranium and a long and robust paroccipital process. The genus Kurdalagonus is redefined here as containing only one described species, K. mchedlidzei. Therefore, the group Cetotheriinae is now restricted to the latest Serravallian and Tortonian of the Eastern Paratethys and includes at least five genera: Cetotherium, Brandtocetus, Kurdalagonus, Mithridatocetus and Zygiocetus. In addition, ?Cetotherium priscum and C. incertum are considered to be nomina dubia; 'Cetotherium' klinderi and 'Cetotherium' pusillum require more complete specimens for reassessment; 'Cetotherium' maicopicum and Eucetotherium helmersenii require further research to identify their taxonomical affinities.
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