英美科學家進行的一項化石研究顯示,，大象3700萬年前的祖先曾生活在水中,。生活方式類似河馬。這項研究發(fā)表在最新一期美國《國家科學院院刊》（PNAS）上,。
據英國廣播公司4月15日報道,，英國牛津大學和美國紐約州立大學石溪分校的科學家對從埃及北部出土的兩種牙齒化石進行了分析，它們同屬于一個遠古哺乳動物家族的兩個物種,。這一遠古哺乳動物家族的動物都是大象的祖先,，它們的外形介于馬和犀牛之間。
研究人員說,，這兩個物種分別叫做鈍獸和始祖象,，它們生活在3700萬年前的埃及北部。當時埃及北部被亞熱帶雨林和沼澤地覆蓋,。這兩種動物大體上是水生的哺乳動物,，以河流或沼澤中的淡水植物為食。（來源：新華網 葛秋芳）
生物谷推薦原始出處：
（PNAS）,，vol. 105 | no. 15 | 5786-5791 ,，Alexander G. S. C. Liu, Erik R. Seiffert, and Elwyn L. Simons
Stable isotope evidence for an amphibious phase in early proboscidean evolution
Alexander G. S. C. Liu*,, Erik R. Seiffert, and Elwyn L. Simons,
*Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, United Kingdom; Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794-8081; and Division of Fossil Primates, Duke Lemur Center, 1013 Broad Street, Durham, NC 27705
Contributed by Elwyn L. Simons, February 7, 2008 (received for review December 19, 2007)
The order Proboscidea includes extant elephants and their extinct relatives and is closely related to the aquatic sirenians (manatees and dugongs) and terrestrial hyracoids (hyraxes). Some analyses of embryological, morphological, and paleontological data suggest that proboscideans and sirenians shared an aquatic or semiaquatic common ancestor, but independent tests of this hypothesis have proven elusive. Here we test the hypothesis of an aquatic ancestry for advanced proboscideans by measuring 18O in tooth enamel of two late Eocene proboscidean genera, Barytherium and Moeritherium, which are sister taxa of Oligocene-to-Recent proboscideans. The combination of low 18O values and low 18O standard deviations in Barytherium and Moeritherium matches the isotopic pattern seen in aquatic and semiaquatic mammals, and differs from that of terrestrial mammals. 13C values of these early proboscideans suggest that both genera are likely to have consumed freshwater plants, although a component of C3 terrestrial vegetation cannot be ruled out. The simplest explanation for the combined evidence from isotopes, dental functional morphology, and depositional environments is that Barytherium and Moeritherium were at least semiaquatic and lived in freshwater swamp or riverine environments, where they grazed on freshwater vegetation. These results lend new support to the hypothesis that Oligocene-to-Recent proboscideans are derived from amphibious ancestors.
