A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales

Bajpai, Sunil; Gingerich, Philip D.

doi:10.1073/pnas.95.26.15464

Cited by 134 publications

(87 citation statements)

References 14 publications

(14 reference statements)

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“…12) was calibrated first with a 55-million-year (Myr) date for the separation of Cetacea from the hippopotamus (35). Using this calibration, the baleen͞toothed whale separation was estimated at 32.3 ϩ͞Ϫ5.1 Myr B.P.…”

Section: Resultsmentioning

confidence: 99%

Retroposon analysis of major cetacean lineages: The monophyly of toothed whales and the paraphyly of river dolphins

Nikaido

Matsuno

Hamilton

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

231

164

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SINE (short interspersed element) insertion analysis elucidates contentious aspects in the phylogeny of toothed whales and dolphins (Odontoceti), especially river dolphins. Here, we characterize 25 informative SINEs inserted into unique genomic loci during evolution of odontocetes to construct a cladogram, and determine a total of 2.8 kb per taxon of the flanking sequences of these SINE loci to estimate divergence times among lineages. We demonstrate that: (i) Odontocetes are monophyletic; (ii) Ganges River dolphins, beaked whales, and ocean dolphins diverged (in this order) after sperm whales; (iii) three other river dolphin taxa, namely the Amazon, La Plata, and Yangtze river dolphins, form a monophyletic group with Yangtze River dolphins being the most basal; and (iv) the rapid radiation of extant cetacean lineages occurred some 28 -33 million years B.P., in strong accord with the fossil record. The combination of SINE and flanking sequence analysis suggests a topology and set of divergence times for odontocete relationships, offering alternative explanations for several long-standing problems in cetacean evolution.SINE ͉ evolution ͉ divergence times

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Section: Resultsmentioning

confidence: 99%

Retroposon analysis of major cetacean lineages: The monophyly of toothed whales and the paraphyly of river dolphins

Nikaido

Matsuno

Hamilton

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

231

164

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“…For the Murphy et al (2001a) data, the Boreoeutheria/Afrotheria/Xenarthra divergence (the basal divergence in Eutheria) was constrained to be between 90 and 130 mya . Following Cao et al (2000), we gave constraints of 52-58 mya on the basal divergence of Perissodactyla (horse/rhinoceros) and the whale/hippopotamus divergence (McKenna and Bell, 1997;Bajpai and Gingerich, 1998;Waddell et al, 1999b), and of 13-18 mya on the orangutan/human divergence (Waddell and Penny, 1996). According to the fossil record, the Rodentia/Lagomorph divergence should be 61-90 mya, because Zalambdalestidae which is regarded as the sister group of the Rodentia/Lagomorph clade (Archibald, Averianov, and Ekdale, 2001) is known to be 90 my old and because the ancestors of rodent and rabbit (the Eurymylidae and the Mimotonidae) are known from the early Paleocene (61-65 mya).…”

Section: Application Of the Methods To Eutherian Evolutionmentioning

confidence: 99%

Time scale of eutherian evolution estimated without assuming a constant rate of molecular evolution.

2003

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Controversies over the molecular clock hypothesis were reviewed. Since it is evident that the molecular clock does not hold in an exact sense, accounting for evolution of the rate of molecular evolution is a prerequisite when estimating divergence times with molecular sequences. Recently proposed statistical methods that account for this rate variation are overviewed and one of these procedures is applied to the mitochondrial protein sequences and to the nuclear gene sequences from many mammalian species in order to estimate the time scale of eutherian evolution. This Bayesian method not only takes account of the variation of molecular evolutionary rate among lineages and among genes, but it also incorporates fossil evidence via constraints on node times. With denser taxonomic sampling and a more realistic model of molecular evolution, this Bayesian approach is expected to increase the accuracy of divergence time estimates.Key words: Bayesian method, divergence times, variation of evolutionary MOLECULAR CLOCKSince Pauling (1962, 1965) first recognized the possibility that proteins evolve at steady rates, the notion has aroused many controversies (Wilson et al., 1977;Kimura, 1983;Britten, 1986;Gillespie, 1991;Graur and Li, 2000). This hypothetical constancy of molecular evolution is called the molecular clock.The neutral theory provides a simple and successful explanation for a large number of observations of molecular evolution (Kimura, 1968(Kimura, , 1983). Yet the theory does not necessarily predict the molecular clock, since it simply predicts that the rate of molecular evolution is equal to the rate of neutral mutation, and the mutation rate may possibly be related to generation time rather than absolute time as suggested by many authors (e.g., Laird et al., 1969;Kohne, 1970). The generation time in rodents is much shorter than that in humans, and therefore the number of germline replications per year might be much higher in rodents than in humans.Britten (1986) showed that the rate of DNA evolution has been retarded in anthropoids compared with the rates in prosimians and in rodents. Wu and Li (1985) suggested that the rate of nucleotide substitution in rodents such as mice and rats is higher than that in humans, and that the ratio of the number of nucleotide substitutions in the rodent line to that in the human line since their divergence is 1.3 for nonsynonymous (amino acid replacing) substitutions and 2.0 for synonymous substitutions. It seems plausible that mice and rats evolve more rapidly than higher primates in the nuclear genes (Waterston et al., 2002), but the difference of the rate between rodents and humans seems smaller than the difference of the generation time between the two lineages. Genetic changes in evolution are the results of fixation of mutations that occurred in the germ cells, that is, eggs and sperms, and mutation rate may differ between female and male gametogenesis. Since the number of germ cell divisions is expected to be larger in males than in females, males are expected to ...

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“…In delphinid cetaceans, the osmolality of urine is always higher than that of plasma and usually markedly exceeds that of the surrounding ocean (except during fasting). Urine osmolalities are typically 1,300-2,000 mosmol/kgH 2 O and, under fasting conditions, have been reported to be 800-900 mosmol/kgH 2 O (28, 34).…”

mentioning

confidence: 99%

Molecular and functional characterization of a urea transporter from the kidney of a short-finned pilot whale

Janech

Chen²,

Klein

et al. 2002

American Journal of Physiology-Regulatory, Integrative and Comp

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Cetaceans (whales and dolphins) always excrete urine with an osmolality markedly higher than that of plasma. Although the mechanisms by which cetaceans concentrate urine have not been elucidated, data support a role for medullary urea accumulation in this process, as is the case for terrestrial mammals. Therefore, we hypothesized that facilitated urea transporters are present in the kidney of cetaceans. Using 5′/3′-rapid amplification of cDNA ends, we cloned a 2.7-kb cDNA from the kidney of the short-finned pilot whale Globicephala macrorhynchus. The putative open-reading frame encoded a 397-amino acid protein [pilot whale urea transporter A2 (whUT-A2)] that has 94% amino acid sequence identity to the A2 isoform of the human urea transporter (hUT-A2). Heterologous expression of whUT-A2 cRNA in Xenopus oocytes induced phloretin-inhibitable urea transport. Although Northern analysis and RT-PCR indicated that whUT-A2 was exclusively expressed in kidney, Western blotting using a polyclonal antibody to rat UT-A1/UT-A2 detected various immunoreactive proteins in kidney and other tissues. Furthermore, RT-PCR analysis suggested the presence of alternatively spliced UT-A transcripts in the kidney as well as extrarenal tissues. We conclude that renal urea transporters are highly conserved among mammals inhabiting terrestrial and pelagic environments. A urea-based concentrating mechanism, presumably evolved to meet the demands of an arid terrestrial environment, may have contributed a fortuitous preadaptation that enabled the ancestors of cetaceans to reinvade the sea.

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A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales

Cited by 134 publications

References 14 publications

Retroposon analysis of major cetacean lineages: The monophyly of toothed whales and the paraphyly of river dolphins

Retroposon analysis of major cetacean lineages: The monophyly of toothed whales and the paraphyly of river dolphins

Time scale of eutherian evolution estimated without assuming a constant rate of molecular evolution.

Molecular and functional characterization of a urea transporter from the kidney of a short-finned pilot whale

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