Mol Phylogenet Evol. 2005 Dec;37(3):743-50. Epub 2005 Jul 19.
Molecular phylogenetics of 'river dolphins' and the baiji mitochondrial genome.
 Yan J,
 Zhou K,
 Yang G.
Jiangsu Key Laboratory for Bioresource Technology, College of Life Sciences, Nanjing Normal
University, Nanjing 210097, China.
It is well known that the classical river dolphins are not a natural group, but up to now
the phylogenetic relationships among them are not very clear because different views
have been referred from different studies. In the present study, we determined the
complete nucleotide sequence of the mitochondrial (mt) genome of the baiji (Lipotes
vexillifer), the most endangered cetacean species, and conducted phylogenetic analyses
for the classical river dolphins based on data from cetacean mitochondrial genomes
available. In our analyses, the classical river dolphins split into two separate lineages,
Platanista and Lipotes+(Inia+Pontoporia), having no sister relationship with each other,
and the Platanista lineage is always within the odontocete clade instead of having a
closer affinity to Mysticeti. The position of the Platanista is more basal, suggesting
separate divergence of this lineage well before the other one. The Lipotes has a sister
relationship with Inia+pontoporia, and they together formed the sister group to the
Delphinoidea. This result strongly supports paraphyly of the classical river dolphins, and
the nonplatanistoid river dolphins do represent a monophyletic grouping, with the
Lipotidae as the sister taxa to (Iniidae+Pontoporiidae), and is well congruent with the
studies based on short interspersed repetitive elements (SINEs).
Proc Biol Sci. 2001 Mar 7;268(1466):549-56.
Erratum in:
Proc R Soc Lond B Biol Sci 2001 Dec 22;268(1485):2615.
Evolution of river dolphins.
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Hamilton H,
Caballero S,
Collins AG,
Brownell RL Jr.
Museum of Paleontology and Department of Integrative Biology, University of California, Berkeley
94720, USA. heals@socrates.berkeley.edu
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 modified 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 affect 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 first 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 epicontintental 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.