A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales
A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales
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DOI：
10.1073/pnas.95.26.15464
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发表时间：
1998-12-22
影响因子：
11.1
通讯作者：
Gingerich, PD
中科院分区：
文献类型：
--
作者：
Bajpai, S;Gingerich, PD
喜马拉雅猴骨是印度北部Subathu组发现的一种新的巴基酸古岩。这种类型的牙齿有一个小的下颌管，表明在更高级的鲸类动物中缺乏听觉特化，它有类似巴基鲸的臼齿，表明它以鱼为食。喜马拉雅猴很重要，因为它是已知最古老的古生物，而且它是在与海洋动物群有关的海洋地层中发现的。喜马拉雅山脉将鲸鱼的化石记录延伸至350万年前的地质时代，即始新世早期中期[大约5350万年前（Ma）]。磷酸盐牙釉质中氧的同位素组成介于淡水和海洋古蚌中所报道的氧的同位素组成之间，表明喜马拉雅古蚌可能在这两种环境中都生活过一段时间。当对古鲸目的时间范围进行辐射校正时，可能性的比较限制了古鲸目和鲸目的起源时间约为54-55 Ma（始新世开始），而它们与现存偶蹄目的分化可能早在64-65 Ma（新生代开始）。
Himalayacetus subathuensis is a new pakicetid archaeocete from the Subathu Formation of northern India. The type dentary has a small mandibular canal indicating a lack of auditory specializations seen in more advanced cetaceans, and it has Pakicetus-like molar teeth suggesting that it fed on fish, Himalayacetus is significant because it is the oldest archaeocete known and because it was found in marine strata associated with a marine fauna. Himalayacetus extends the fossil record of whales about 3.5 million years back in geological time, to the middle part of the early Eocene [approximate to 53.5 million years ago (Ma)]. Oxygen in the tooth enamel phosphate has an isotopic composition intermediate between values reported for freshwater and marine archaeocetes, indicating that Himalayacetus probably spent some time in both environments. When the temporal range of Archaeoceti is calibrated radiometrically, comparison of likelihoods constrains the time of origin of Archaeoceti and hence Cetacea to about 54-55 Ma (beginning of the Eocene), whereas their divergence from extant Artiodactyla may have been as early as 64-65 Ma (beginning of the Cenozoic).