Evolution of the Cetacean Body Plan: Eocene Whales from India

进化是支配地球上所有生物多样性的过程。进化变化的积累是缓慢的，而且，对于大多数生物体来说，不可能在一个观察者的一生中进行研究。最令人印象深刻的进化变化包括动物身体结构各方面的巨大变化。这种宏观进化的变化只有在长时间的积累之后才会变得明显。实际的例子很少，因为化石记录很少给予研究人员这种程度的细节。化石记录中记载的宏观进化变化的最好例子之一是鲸鱼、海豚和鼠海豚的起源。所有现代鲸鱼、海豚和鼠海豚（合构成鲸目动物）都是完全水生的哺乳动物，完全适应了它们的水环境，无法在陆地上生存。然而，鲸目动物的祖先生活在陆地上，它们的身体结构与狼大致相似，与现代鲸目动物非常不同。在不到1500万年的时间里，这种古老的身体计划被修改成现代鲸类动物的身体计划。本提案旨在从几个角度研究这些转变。首先，pi将在印度收集鲸类化石，记录陆地-水过渡。其次，他们将研究运动和感觉器官的进化，因为鲸类动物经历了这一转变。最后，他们将研究海豚胚胎，以便将鲸类胚胎学的变化与进化变化联系起来。鲸类动物的体型在很大程度上是由鲸类动物不寻常的游泳方式（在水中摆动水平尾片）决定的。然而，化石鲸类动物有非常不同的游泳方式，这些可以用化石来研究。鲸类动物身体结构的进化也可以通过确定其与感觉器官的相互作用来间接研究。在这方面，最重要的感觉器官是平衡器官和（与之相关的）听觉器官。这些将使用ct扫描方法进行研究。最后，现代鲸类动物的身体计划也受到胚胎发育的影响，但影响程度尚不清楚，这将用现代海豚的胚胎来研究。

Evolution is the process that governs the entire diversity of living organisms on Earth. Evolutionary changes accumulate slowly, and, for most organisms, cannot be studied within the life span of one human observer. The most impressive evolutionary changes involve great modifications in all aspects of the design of an animal, its bodyplan. Such macroevolutionary changes become obvious only after they accumulate over a long time period. Actual examples are rare because the fossil record rarely grant researchers this level of detail. One of the best examples of macroevolutionary changes that are documented in the fossil record is the origin of whales, dolphins, and porpoises.All modern whales, dolphins, and porpoises (together constituting the Cetacea) are fully aquatic mammals, perfectly adapted to their watery environment and unable to survive on land. However, cetaceans have ancestors that lived on land, with a body plan that roughly resembled that of a wolf, and very unlike that of modern cetaceans. In less than 15 million years, this archaic body plan was modified into that of modern cetaceans. The present proposal aims to study these transformations from several points of view. First, PIs will collect cetacean fossils in India that document the land-water transition. Second, they will study the evolution of locomotor and sense organs, as cetaceans passed through this transition. Finally, they will study dolphin embryos in order to relate changes in cetacean embryology to evolutionary changes. The cetacean bodyplan is determined, to a large extent, by the unusual mode of swimming of cetaceans (swinging the horizontal tail fluke through the water). However, fossil cetacean had very different modes of swimming and these can be studied with fossils. The evolution of the cetacean bodyplan can also be studied indirectly, by determining its interaction with the sense organs. The most important sense organ with respect to this is the organ of balance and (associated with it) the organ of hearing. These will be studied using CT-scan methods. Finally, the modern cetacean bodyplan is also influenced, to an unknown degree, by its embryologic development, and this will be studied using embryos of modern dolphins.