The myth of the hippo-like anthracothere: The eternal problem of homology and convergence
The myth of the hippo-like anthracothere: The eternal problem of homology and convergence
复制标题
类似河马的炭疽兽的神话：同源性和趋同性的永恒问题
DOI：
--
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
M. Pickford
中科院分区：
文献类型：
--
作者：
M. Pickford
炭疽兽有着与恐龙相似的身体比例、运动方式和生活方式的说法在文献中已经存在了很长时间，并且被重复了很多次，以至于它已经被赋予了不容置疑的真理的光环。然而，从世纪前开始研究炭疽热的关系，观察表明，存在根本性的差异，在牙齿，颅和颅后解剖的两个群体。从1836年到1991年，（下颌角处有一块下降的骨板，眼眶凸起）的发现，在暗示河马和一个炭疽虫属之间的密切关系方面，压倒了所有其他化石（Merycopotamus）后来加入了第二个属，龙，在1991年为下降的角度，2003年为提高轨道（Lihoreau，2003; Pickford，1991）。对这些结构的仔细研究表明，它们在这两个群体中并不同源，但它们在解释它们之间的关系时扮演了一个非常顽固的角色，最近在2005年的论文中也有报道。早在1836年，化石的其余部分和许多颅齿特征就表明，无论是在总体身体平面还是骨骼解剖的细节上，炭疽兽看起来都与河马并不特别相似，从那时起，这些观察结果就被不定期地证实了。然而，尽管形态各异，大多数作者继续将他们研究的炭疽兽类（无论是炭疽兽目还是槽齿兽目）的运动、行为和生态学归因于它们。
两个广泛的主题在长期的河马-炭疽动物关系研究历史中并行不悖，“同源与趋同”和“早期与晚期分歧”，早期分歧意味着存在一个大约3000万年的幽灵原始河马谱系。事实上，这两个主题是联系在一起的，在这个意义上，早期分歧的支持者倾向于将河马和炭疽兽之间的相似性解释为趋同，而那些提出晚期分歧的人通常认为相似性代表同源性。
所有这些解释都是在一个更广泛的背景下进行的，即关于偶蹄动物的单系或并系的辩论，这在维多利亚时代和今天一样被积极讨论。最近，分子研究改变了争论的范围，主要是通过表明鲸鱼和河马之间的亲缘关系比河马和其他偶蹄动物之间的亲缘关系更近。在寻找应该将河马与鲸鱼联系起来的幽灵谱系时，一些作者最近提出，炭疽兽类“强大”地填补了这一角色，而其他人则认为炭疽兽类与河马没有密切关系，而其他人则提出古轮兽科或鲸类可能代表了缺失的谱系。本文综述了炭疽兽在拟步甲科昆虫进化中的作用。结论是，他们没有发挥任何作用，而古choerids很可能代表了鬼血统，已经逃避了科学家超过世纪。
The notion that anthracotheres had hippo-like body proportions, locomotion and lifestyles has been in the literature for so long, and has been repeated so many times, that it has taken on the aura of unquestionable truth. However, right from the beginning of studies into hippo-anthracothere relationships over a century and a half ago, observations were made that revealed the existence of fundamental differences in dental, cranial and post-cranial anatomy in the two groups. From 1836 to 1991 two skeletal characters (a descending plate at the angle of the mandible, and raised orbits) have overshadowed all others in suggesting close relationships between hippos and a single anthracothere genus ( Merycopotamus ) later to be joined by a second genus, Libycosaurus , in 1991 for the descending angle, and 2003 for the raised orbits (Lihoreau, 2003; Pickford, 1991). Close examination of these structures reveals that they are not homologous in the two groups, yet they have played an inordinately stubborn role in interpretations of the relationships between them, featuring in papers as recently as 2005. The rest of the skeleton and many cranio-dental features revealed, as early as 1836, that anthracotheres did not look particularly similar to hippos, either in gross body plan, or in details of the skeletal anatomy, observations that have been confirmed at irregular intervals ever since. Yet, despite the divergent morphology, most authors continued to attribute hippo-like locomotion, behaviour and ecology to the anthracotheres that they studied, whether anthracotheriines or bothriodontines.
Two broad themes have run side by side in the long history of study of hippo-anthracothere relationships, «homology versus convergence» and «early versus late divergence», early divergence implying the existence of a ghost proto-hippo lineage of some 30 million years duration. Indeed these two themes are linked together, in the sense that proponents of early divergence have tended to interpret the similarities between hippos and anthracotheres as convergences, whereas those who have proposed late divergence usually took the perceived similarities to represent homologies.
All these interpretations were played out within the context of a much broader background debate about monophyly or paraphyly of the artiodactyls, which was actively discussed in the Victorian era just as it is today. More recently, molecular studies have altered the scope of the debate, principally by indicating closer affinities between whales and hippos than between hippos and other artiodactyls. In the search for the ghost lineage that should link hippos to whales, some authors have recently suggested that anthracotheres fill the role «robustly», whereas others have suggested that anthracotheres are not closely related to hippos, whilst yet others have proposed that palaeochoerids or cebochoerids may represent the missing lineage. The aim of this paper is to review the possible role of anthracotheres in the evolution of hippopotamids. It is concluded that they played no part in it, whereas palaeochoerids could well represent the ghost lineage that has evaded scientists for more than a century.