Bianucci Giovanni, Geisler Jonathan H, Citron Sara, Collareta Alberto
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126 Pisa, Italy.
Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Northern Boulevard, Old Westbury, NY 11568, USA; Research Associate, Department of Paleobiology, National Museum of Natural History, Washington D.C. 20560, USA.
Curr Biol. 2022 Apr 25;32(8):1843-1851.e2. doi: 10.1016/j.cub.2022.02.041. Epub 2022 Mar 7.
The killer whale (Orcinus orca) and false killer whale (Pseudorca crassidens) are the only extant cetaceans that hunt other marine mammals, with pods of the former routinely preying on baleen whales >10 m in length and the latter being known to take other delphinids. Fossil evidence for the origins of this feeding behavior is wanting, although molecular phylogenies indicate that it evolved independently in the two lineages. We describe a new extinct representative of the killer whale ecomorph, Rododelphis stamatiadisi, based on a partial skeleton from the Pleistocene of Rhodes (Greece). Five otoliths of the bathypelagic blue whiting Micromesistius poutassou are associated with the holotype, providing unexpected evidence of its last meal. The evolutionary relationships of R. stamatiadisi and the convergent evolution of killer whale-like features were explored through a broad-ranging phylogenetic analysis that recovered R. stamatiadisi as the closest relative of P. crassidens and O. orca as the only living representative of a once diverse clade. Within the clade of Orca and kin, key features implicated in extant killer whale feeding, such as body size, tooth size, and tooth count, evolved in a stepwise manner. The tooth wear in Rododelphis and an extinct species of Orcinus (O. citoniensis) are consistent with a fish-based diet, supporting an exaptative Pleistocene origin for marine mammal hunting in both lineages. If correct, predation by the ancestors of Pseudorca and Orca did not play a significant role in the evolution of baleen whale gigantism. VIDEO ABSTRACT.
虎鲸（Orcinus orca）和伪虎鲸（Pseudorca crassidens）是现存仅有的捕食其他海洋哺乳动物的鲸类动物，前者的群体经常捕食体长超过10米的须鲸，而后者则以捕食其他海豚科动物而闻名。尽管分子系统发育表明这种捕食行为在这两个谱系中是独立进化的，但关于这种捕食行为起源的化石证据却很匮乏。我们基于来自希腊罗德岛更新世的部分骨骼，描述了一种虎鲸生态形态的新灭绝代表——斯塔马蒂亚迪斯罗德海豚（Rododelphis stamatiadisi）。与该正模标本相关联的有五条深海蓝鳕（Micromesistius poutassou）的耳石，这为其最后一餐提供了意想不到的证据。通过广泛的系统发育分析，探究了斯塔马蒂亚迪斯罗德海豚的进化关系以及类似虎鲸特征的趋同进化，该分析将斯塔马蒂亚迪斯罗德海豚确定为伪虎鲸的最近亲缘种，而虎鲸是一个曾经多样化的分支中唯一现存的代表。在虎鲸及其近亲的分支中，与现存虎鲸捕食相关的关键特征，如体型大小、牙齿大小和牙齿数量，是逐步进化的。罗德海豚和一种已灭绝的虎鲸物种（O. citoniensis）的牙齿磨损情况与以鱼类为基础的饮食一致，这支持了两个谱系中海洋哺乳动物捕食行为在更新世起源时具有适应性改变的观点。如果这一观点正确，那么伪虎鲸和虎鲸祖先的捕食行为在须鲸巨型化的进化过程中并未起到重要作用。视频摘要。
