Marx Felix G, Buono Mónica R, Fordyce R Ewan, Boessenecker R W
Department of Geology, University of Otago, Dunedin, New Zealand.
Naturwissenschaften. 2013 Mar;100(3):257-61. doi: 10.1007/s00114-013-1012-y. Epub 2013 Jan 29.
The origin of the pygmy right whale (Caperea marginata) has long been one of the most vexing conundrums of marine mammal evolution. The extremely disparate skeletal structure of Caperea and a patchy fossil record have left morphology and molecules at odds: whereas most morphological analyses ally Caperea with right whales (Balaenidae), most molecular studies instead suggest a close relationship with rorquals (Balaenopteridae) and grey whales (Eschrichtiidae). The morphological evidence supporting a Caperea-balaenid clade consists of several shared features of the skull and mandible, as traditionally observed in adult individuals. Here, we show that at least two of these features, the ascending process of the maxilla and the coronoid process, arise from substantially different precursors early during ontogeny and therefore likely do not represent genuine synapomorphies. Both of these juvenile morphologies have adult counterparts in the fossil record, thus indicating that the ontogenetic variation in the living species may be a genuine reflection of differing ancestral states. This new evidence contradicts previous morphological hypotheses on the origins of Caperea and may help to reconcile morphological and molecular evidence.
侏露脊鲸（Caperea marginata）的起源长期以来一直是海洋哺乳动物进化中最令人困惑的难题之一。侏露脊鲸截然不同的骨骼结构以及零散的化石记录使得形态学和分子学观点产生了分歧：大多数形态学分析将侏露脊鲸与露脊鲸科（Balaenidae）归为一类，而大多数分子研究则表明它与须鲸科（Balaenopteridae）和灰鲸科（Eschrichtiidae）关系密切。支持侏露脊鲸与露脊鲸科形成进化枝的形态学证据包括传统上在成年个体中观察到的头骨和下颌骨的几个共同特征。在这里，我们表明，这些特征中至少有两个，即上颌骨的上升突和冠状突，在个体发育早期源自截然不同的前体，因此可能并不代表真正的共有衍征。这两种幼年形态在化石记录中都有成年对应形态，因此表明现存物种的个体发育变异可能真实反映了不同的祖先状态。这一新证据与之前关于侏露脊鲸起源的形态学假说相矛盾，可能有助于调和形态学和分子学证据。
