善于航海的维京人，壮举之一就是横跨大西洋。但在维京人之前数百万年，鳄鱼就已经乘风破浪，跋涉数千公里，从非洲到达了美洲繁衍。今天，鳄属（Crocodylus）的动物已经遍布四海。
图：漂洋过海的鳄鱼
来自纽约福德姆大学（Fordham University）的E.Hekkala及其同事利用鳄属11个种的线粒体DNA，建立了完整的鳄属演化树，从而得出了以上结论。11个种中的8个，之前都没有进行过线粒体DNA测序。
研究发现，美洲的4种鳄鱼都与东非的尼罗鳄亲缘最近，它们在700万年前开始分异，这一时间远晚于非洲大陆和南美洲分裂的时间（1.3亿年前）。700万年前，非洲鳄鱼所面对的是2800多公里的大海。
尽管古生物学家们一直猜测鳄鱼漂洋过海并扎根美洲，但一直没有确凿证据。Hekkala的发现让鳄鱼远渡重洋的情景更加有说服力了。
鳄鱼能在咸水体中生活，最多可以坚持6个月不进食。更令人称奇的是，在交配完成之后，雌性可以将精子保存在体内达数月之久，因此一旦一只受精雌性游过了大西洋，这一物种便能在新的土地上扎根了。虽然一两次的漂洋过海并不足以演化出所有种类的美洲鳄，但Hekkala指出，动物可以乘着向西的赤道洋流，从非洲海岸到达美洲，所以鳄类穿越大西洋到达美洲并形成规模，还是很有可能的。（生物谷Bioon.com）
生物谷推荐原文出处：
Marine Biology DOI: 10.1007/s00227-009-1174-5
Between introgression events and fragmentation, islands are the last refuge for the American crocodile in Caribbean Mexico
Salima Machkour-M’Rabet, Yann Hénaut, Pierre Charruau, Muriel Gevrey, Peter Winterton and Luc Legal
Habitat loss and degradation in the Mexican Caribbean, caused by the development of tourism, have decreased the potential nesting area for the American crocodile (Crocodylus acutus) and have fragmented the populations of the Yucatan peninsula. Our study investigated five populations (three continental: North, South, Sian Ka’an, and two insular: Cozumel, Banco Chinchorro) of C. acutus in the Mexican Caribbean using seven different inter simple sequence repeat (ISSR) markers as tools for genetic variability and population differentiation. Three classification methods were tested and compared: distance analysis, self-organizing map, and Bayesian methods, to evaluate the resolution of each method with ISSR markers. The 77 loci selected revealed a high variability between populations (polymorphism from 17% for Sian Ka’an to 75% for Banco Chinchorro) with a total polymorphism of 84% and a global coefficient of gene differentiation (G ST ) of 0.296, but low values of Nei’s Gene diversity (from 0.065 for Sian Ka’an to 0.233 for Banco Chinchorro). Our results suggest elevated inbreeding in all local populations with higher indices for Banco Chinchorro and lower indices for Sian Ka’an. Three independent classification methods gave similar results, and suggested that most continental individuals are admixtures, with different levels of introgression, with the sympatric species Crocodylus moreletii. We propose that the islands/atolls remain the sole areas with genetically “pure” American crocodiles and we discuss these results for future conservation of this endangered crocodile species.
