Archaic toothed mysticetes represent the evolutionary transition from raptorial to bulk filter feeding in baleen whales. Aetiocetids, in particular, preserve an intermediate morphological stage in which teeth functioned alongside a precursor of baleen, the hallmark of all modern mysticetes. To date, however, aetiocetids are almost exclusively Late Oligocene and coeval with both other toothed mysticetes and fully fledged filter feeders. By contrast, reports of cetaceans from the Early Oligocene remain rare, leaving the origins of aetiocetids, and thus of baleen, largely in the dark. Here, we report a new aetiocetid, Fucaia buelli, from the earliest Oligocene (ca 33-31 Ma) of western North America. The new material narrows the temporal gap between aetiocetids and the oldest known mysticete, Llanocetus (ca 34 Ma). The specimen preserves abundant morphological detail relating to the phylogenetically informative ear bones (otherwise poorly documented in this family), the hyoid apparatus and much of the (heterodont) dentition. Fucaia comprises some of the smallest known mysticetes, comparable in size with the smallest odontocetes. Based on their phylogenetic relationships and dental and mandibular morphology, including tooth wear patterns, we propose that aetiocetids were suction-assisted raptorial feeders and interpret this strategy as a crucial, intermediary step, enabling the transition from raptorial to filter feeding. Following this line of argument, a combination of raptorial and suction feeding would have been ancestral to all toothed mysticetes, and possibly even baleen whales as a whole.

译文

:齿状的神秘者代表了鲸鱼从猛禽到大头过滤器的进化过渡。特别是,食醋动物保留了一个中间的形态学阶段,在这个阶段中,牙齿与Baleen的前体一起起作用,而Baleen是所有现代神秘主义者的标志。然而,迄今为止,成鲸类几乎完全是晚渐新世,并且与其他带齿的神秘菌和完全成熟的滤嘴一起进入同卵期。相比之下,来自渐新世的鲸类鲸类的报道仍然很少,留下了鲸蜡类鲸鱼的起源,因此,巴利翁的起源很大程度上是在黑暗中。在这里,我们报道了一种来自北美西部最早的渐新世(ca-33-31 aMa)的新的始祖物种Fucaia buelli。新材料缩小了突触类动物和最古老的神秘者Llanocetus(ca 34 Ma)之间的时间间隔。该标本保留了丰富的形态学细节,涉及系统发育信息丰富的耳骨(否则在该家族中文献不足),舌骨样仪和大部分(异齿)牙列。福卡亚(Fucaia)包括一些最小的已知神秘菌,其大小可与最小的齿突科动物相媲美。基于它们的系统发育关系以及牙齿和下颌的形态(包括牙齿磨损模式),我们建议将突触鲸类作为吸食辅助的食器,并将这一策略解释为至关重要的中间步骤,从而实现了从食到滤食的过渡。按照这一论点,猛禽和吸食的结合对于所有带齿的神秘主义者乃至整个鲸鱼都是祖先。

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