Collaborative Resarch: Cetacean Phylogeny: A Reconciliation of Fossil and Neontological Data and the Importance of Taxonomic Sampling

[903964 . o’leary]生物学家假设，鲸类动物（鲸鱼）是在6000万年前或更早的时候从陆地哺乳动物进化而来的。这种进化转变是已知的最显著的转变之一，因为它涉及到大小和形状的巨大变化。如果我们能够理解这种进化转变，它就可以作为描述进化新颖性如何出现的模型问题。像陆行鲸（Ambulocetus）这样的化石是鲸曾经有腿并在陆地上行走的绝佳证据。然而，在它们漫长的进化史中，鲸鱼失去了后肢和毛发，发育出专门的头骨来在水下觅食和倾听，在某些情况下，相对于它们5000万年前的祖先，它们的体型超过了最大的恐龙。为了了解这种进化转变发生的方式、原因和时间的细节，为鲸鱼及其近亲建立一个得到充分证实的系统发育树（家族史）是很重要的。理想情况下，研究与鲸鱼密切相关的所有物种的解剖学和分子生物学将是一件有趣的事情。其中包括现存的和灭绝的类群：偶蹄目或偶趾有蹄哺乳动物（骆驼、猪、反刍动物、河马及其亲戚），异蹄目或奇趾有蹄哺乳动物（马、犀牛、貘及其亲戚），以及原足目、尖锐肢目和Mesonychia，这些完全灭绝的有蹄哺乳动物类群。特别是在已灭绝的类群中，美索甲纲可能与鲸类非常接近。大多数（90%）的分类群构成了上面列出的感兴趣的组已经灭绝。因此，无论是研究现存的动物还是灭绝的动物，试图为鲸鱼生成系统发育树的科学家们都被迫只能使用部分数据。那些研究活体动物的人（新生生物学家）利用非常详细的生物学特征（例如，所有生物体的解剖学、分子生物学、组织学等），但只涉及一个瞬间：现在。那些研究灭绝物种的人（古生物学家）所利用的化石证据几乎完全由骨骼数据组成。然而，这些数据可以为更多的物种打分，其中一些可能更接近最早的鲸鱼的祖先状况。在此，我们建议整合新学和古生物学数据，以更好地研究鲸类的系统发育树。这在目前是至关重要的，因为科学家们研究不同的数据类型，不断找到关于谁是鲸鱼最近的亲戚的不同答案：现存的分类群表明它是河马，而灭绝的分类群表明它是中尼索目动物。我们的目标是1)增加灭绝的和现存的鲸鱼及其近亲的分类群和特征采样，2)研究某些生物属性（例如分子，形态）如何以及为什么具有与整个家族树不匹配的进化史。我们的目标是使我们的形态学工作的结果尽可能标准化与出版的插图。这个项目的数据收集方面很大，我们将以此为契机，指导那些可能对进化和系统学研究感兴趣的高中生和本科生，他们可以学习实验室、计算机和数据分析技能以及进化理论。

9903964O'Leary Biologists hypothesize that cetaceans (whales) evolved from terrestrial land mammals as many as 60 million years ago or more. This evolutionary transformation is one of the most remarkable known because it involved dramatic changes in size and shape. If we can understand this evolutionary transition it may serve as a model problem describing how evolutionary novelties appear. Fossils, like Ambulocetus, are excellent evidence that whales once had legs and walked on land. During their long evolutionary history whales have, however, lost their hind limbs and hair, developed specialized skulls to feed and hear underwater, and in some cases exceeded the largest dinosaur in body size relative to their ancestors of over 50 million years ago. In order to understand the details of how, why and when this evolutionary transformation occurred, it is important to develop a well-corroborated phylogenetic tree (family history) for whales and their close relatives. Ideally it would be of interest to study the anatomy and molecular biology of all species that are closely related to whales. These include living and extinct groups: Artiodactyla, or even-toed hoofed mammals (camels, pigs, ruminants, hippopotamids and relatives), Perissodactyla, or odd-toed hoofed mammals (horses, rhinos, tapirs and relatives), as well as Procreodi, Condylarthra and Mesonychia, completely extinct groups of hoofed mammals. In particular among the extinct groups, Mesonychia may be very closely related to cetaceans. Most of the taxa ( 90%) that make up the group of interest outlined above are extinct. As a result, scientists trying to generate a phylogenetic tree for whales are forced to work with only part of the data whether they study living animals or extinct animals. Those working on living animals (neontologists) draw on very detailed biological characters (e.g., all of the organisms' anatomy, molecular biology, histology, etc) but only in one instant of time: the present. Those working on extinct species (paleontologists) draw on fossil evidence which almost exclusively comprises skeletal data. However, these data can be scored for many more species, some of which may more closely approximate the ancestral condition of the earliest whales. Here we propose to integrate neontological and paleontological data, to better examine the phylogenetic tree of cetaceans. This is critical to do at this time because scientists working on different data types continue to find different answers as to who is the closest relative of whales: living taxa indicate that it is the hippopotamus and extinct taxa indicate that it is mesonychians. We aim 1) to increase the taxon and character sampling for both extinct and living whales and relatives, and 2) to examine how and why certain biological attributes (e.g., molecules, morphology) have evolutionary histories that do not appear to match the overall family tree. We aim to make the results of our morphological work as standardized as possible with published illustrations. The data collection aspect of this project is large and we will use this as an opportunity to mentor high school and undergraduate students who may be interested in research in evolution and systematics and who can be taught laboratory, computer, and data analysis skills as well as evolutionary theory.