A review of kentriodontine dolphins (Cetacea; Deiphinoidea; Kentriodontidae): Systematics and biogeography

BackgroundCetacea (dolphins, porpoises, and whales) is a clade of aquatic species that includes the most massive, deepest diving, and largest brained mammals. Understanding the temporal pattern of diversification in the group as well as the evolution of cetacean anatomy and behavior requires a robust and well-resolved phylogenetic hypothesis. Although a large body of molecular data has accumulated over the past 20 years, DNA sequences of cetaceans have not been directly integrated with the rich, cetacean fossil record to reconcile discrepancies among molecular and morphological characters.ResultsWe combined new nuclear DNA sequences, including segments of six genes (~2800 basepairs) from the functionally extinct Yangtze River dolphin, with an expanded morphological matrix and published genomic data. Diverse analyses of these data resolved the relationships of 74 taxa that represent all extant families and 11 extinct families of Cetacea. The resulting supermatrix (61,155 characters) and its sub-partitions were analyzed using parsimony methods. Bayesian and maximum likelihood (ML) searches were conducted on the molecular partition, and a molecular scaffold obtained from these searches was used to constrain a parsimony search of the morphological partition. Based on analysis of the supermatrix and model-based analyses of the molecular partition, we found overwhelming support for 15 extant clades. When extinct taxa are included, we recovered trees that are significantly correlated with the fossil record. These trees were used to reconstruct the timing of cetacean diversification and the evolution of characters shared by "river dolphins," a non-monophyletic set of species according to all of our phylogenetic analyses.ConclusionsThe parsimony analysis of the supermatrix and the analysis of morphology constrained to fit the ML/Bayesian molecular tree yielded broadly congruent phylogenetic hypotheses. In trees from both analyses, all Oligocene taxa included in our study fell outside crown Mysticeti and crown Odontoceti, suggesting that these two clades radiated in the late Oligocene or later, contra some recent molecular clock studies. Our trees also imply that many character states shared by river dolphins evolved in their oceanic ancestors, contradicting the hypothesis that these characters are convergent adaptations to fluvial habitats.

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“…Ichishima et al [77] and Steeman et al [21] mentioned a specimen from the Oligocene of New Zealand which they referred to as " Kentriodon ? sp."…”

Section: Discussionmentioning

confidence: 99%

A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea

et al. 2011

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“…Although several attempts have been made to clarify the phylogenetic relationships among established subfamilies and genera (e.g. Barnes 1978Barnes , 1985Muizon 1988aMuizon , 1988bDawson 1996a), the monophyly of the subfamilies could not be demonstrated synapomorphically (Muizon 1988a(Muizon , 1988bIchishima et al 1994).…”

Section: Systematic and Phylogenetic Considerationsmentioning

confidence: 99%

“…The Kentriodontidae is used herein as a grade family, because no synapomorphies of the included taxa are known (Muizon 1988b;Ichishima et al 1994). …”

Section: Introductionmentioning

confidence: 99%

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A new kentriodontid (Cetacea: Delphinoidea) from the Middle Miocene of Hungary

Kazár¹

2005

Foss. Rec.

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Mediocris commenticius n. gen., n. sp. is herein described as a kentriodontid dolphin from the Sarmatian (late Middle Miocene) of south Hungary, territory of the ancient Central Paratethys Sea. The type specimen is an incomplete skeleton including a distorted skull and mandibles with teeth, ear bones, elements of both flippers, and numerous vertebrae. Mediocris commenticius has a nasal bone morphology that differs from all delphinoid taxa, but is most similar to members of the Pithanodelphininae Barnes, 1985. The nasals are triangular, not inflated, have a faint anterolateral notch, and diverge posteriorly. On the basis of the nasal bone morphology, the new species shows affinities to Pithanodelphis, and is less derived than Atocetus and Sarmatodelphis. Due to the incompleteness of the cranial vertex of the type and only known skull, however, the species is only tentatively referred to the subfamily Pithanodelphininae.Schlü sselwö rter: Odontoceti, Kentriodontidae, Pithanodelphininae, Miozä n, Sarmatium, Ungarn. ZusammenfassungMediocris commenticius n. gen., n. sp. wird als Kentriodontide aus dem Sarmatium (spä tes Mittelmiozä n) von Sü dungarn beschrieben, aus dem Gebiet des ehemaligen zentral-paratethyschen Meeres. Der Holotypus ist ein unvollstä ndiges Skelett; erhalten sind der zusammengepresste Schä del, Unterkiefer mit Zä hnen, Gehö rknochen, Knochenelemente beider Brustflossen sowie zahlreiche Wirbel. Die Morphologie der Nasale der neuen Art unterscheidet sich von allen beschriebenen Taxa der Kentriodontidae, weist aber auf Verwandtschaft mit den Pithanodelphinen hin. Die Nasalia sind dreieckig, nicht extrem vergrö ßert, sie haben eine schwach ausgebildete anterolaterale Kerbe und sie divergieren in caudaler Richtung. Anhand der Morphologie der Nasale steht M. commenticius der Art Pithanodelphis cornutus nahe und ist weniger stark spezialisiert als Atocetus und Sarmatodelphis. Wegen der unvollstä ndigen Erhaltung des cranialen Vertex ist Mediocris commenticius allerdings nur mit Vorbehalt in die Unterfamilie Pithanodelphininae einzuordnen.

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“…Signi¢cant sea-level rise would transform these regions into shallow waterways of mixed £uvial and marine origin. Several fossil locales in nearby Japan con¢rm the presence of odontocetes in the western Paci¢c during the Miocene (Ichishima et al 1995), potential colonizers of the Asian epicontinental seas. Our scenario is consistent with the geographical occurrence of the mandibular fragment known as Prolipotes, inland of the Yujiang river delta in southern China.…”

Section: (A) the Fossil Record Of River Dolphinsmentioning

confidence: 99%

Evolution of river dolphins

Hamilton

Caballero²,

Collins

et al. 2001

Proc. R. Soc. Lond. B

185

149

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The world's river dolphins (Inia, Pontoporia, Lipotes and Platanista) are among the least known and most endangered of all cetaceans. The four extant genera inhabit geographically disjunct river systems and exhibit highly modi¢ed morphologies, leading many cetologists to regard river dolphins as an unnatural group. Numerous arrangements have been proposed for their phylogenetic relationships to one another and to other odontocete cetaceans. These alternative views strongly a¡ect the biogeographical and evolutionary implications raised by the important, although limited, fossil record of river dolphins. We present a hypothesis of river dolphin relationships based on phylogenetic analysis of three mitochondrial genes for 29 cetacean species, concluding that the four genera represent three separate, ancient branches in odontocete evolution. Our molecular phylogeny corresponds well with the ¢rst fossil appearances of the primary lineages of modern odontocetes. Integrating relevant events in Tertiary palaeoceanography, we develop a scenario for river dolphin evolution during the globally high sea levels of the Middle Miocene. We suggest that ancestors of the four extant river dolphin lineages colonized the shallow epicontinental seas that inundated the Amazon, Parana¨, Yangtze and Indo-Gangetic river basins, subsequently remaining in these extensive waterways during their transition to freshwater with the Late Neogene trend of sea-level lowering.

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A review of kentriodontine dolphins (Cetacea; Deiphinoidea; Kentriodontidae): Systematics and biogeography

Cited by 30 publications

References 8 publications

A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea

A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea

A new kentriodontid (Cetacea: Delphinoidea) from the Middle Miocene of Hungary

Evolution of river dolphins

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