Fitzgerald Erich M G
School of Geosciences, Monash University, Clayton, Victoria 3800, Australia.
Proc Biol Sci. 2006 Dec 7;273(1604):2955-63. doi: 10.1098/rspb.2006.3664.
Extant baleen whales (Cetacea, Mysticeti) are all large filter-feeding marine mammals that lack teeth as adults, instead possessing baleen, and feed on small marine animals in bulk. The early evolution of these superlative mammals, and their unique feeding method, has hitherto remained enigmatic. Here, I report a new toothed mysticete from the Late Oligocene of Australia that is more archaic than any previously described. Unlike all other mysticetes, this new whale was small, had enormous eyes and lacked derived adaptations for bulk filter-feeding. Several morphological features suggest that this mysticete was a macrophagous predator, being convergent on some Mesozoic marine reptiles and the extant leopard seal (Hydrurga leptonyx). It thus refutes the notions that all stem mysticetes were filter-feeders, and that the origins and initial radiation of mysticetes was linked to the evolution of filter-feeding. Mysticetes evidently radiated into a variety of disparate forms and feeding ecologies before the evolution of baleen or filter-feeding. The phylogenetic context of the new whale indicates that basal mysticetes were macrophagous predators that did not employ filter-feeding or echolocation, and that the evolution of characters associated with bulk filter-feeding was gradual.
现存的须鲸（鲸目，须鲸亚目）都是大型滤食性海洋哺乳动物，成年后无齿，取而代之的是鲸须，它们大量捕食小型海洋动物。这些顶级哺乳动物的早期演化及其独特的进食方式，至今仍是个谜。在此，我报告一种来自澳大利亚晚渐新世的新的有齿须鲸，它比此前描述过的任何须鲸都更古老。与所有其他须鲸不同，这种新鲸体型小，眼睛巨大，缺乏适应大量滤食的衍生特征。一些形态特征表明，这种须鲸是一种大型食肉类捕食者，在某些方面与中生代海洋爬行动物和现存的豹海豹（Hydrurga leptonyx）趋同。因此，它驳斥了所有原始须鲸都是滤食者以及须鲸的起源和早期辐射与滤食演化相关的观点。显然，在鲸须或滤食演化之前，须鲸就已经辐射演化出了各种不同的形态和进食生态。这种新鲸的系统发育背景表明，原始须鲸是大型食肉类捕食者，不采用滤食或回声定位，与大量滤食相关的特征是逐渐演化而来的。
