Living baleen whales (mysticetes) are bulk filter feeders that use keratinous baleen plates to filter food from prey laden water. Extant mysticetes are born entirely edentulous, though they possess tooth buds early in ontogeny, a trait inherited from toothed ancestors. The mandibles of extant baleen whales have neither teeth nor baleen; teeth are resorbed in utero and baleen grows only on the palate. The mandibles of extant baleen whales also preserve a series of foramina and associated sulci that collectively form an elongated trough, called the alveolar groove. Despite this name, it remains unclear if the alveolar groove of edentulous mysticetes and the dental structures of toothed mammals are homologous. Here, we describe and quantify the anatomical diversity of these structures across extant mysticetes and compare their variable morphologies across living taxonomic groups (i.e., Balaenidae, Neobalaenidae, Eschrichtiidae, and Balaenopteridae). Although we found broad variability across taxonomic groups for the alveolar groove length, occupying approximately 60–80 percent of the mandible’s total curvilinear length (CLL) across all taxa, the relictual alveolar foramen showed distinct patterns, ranging between 15–25% CLL in balaenids, while ranging between 3–12% CLL in balaenopterids. This variability and the morphological patterning along the body of the mandible is consistent with the hypothesis that the foramina underlying the alveolar groove reflect relictual alveoli. These findings also lay the groundwork for future histological studies to examine the contents of these foramina and clarify their potential role in the feeding process.

中文翻译：

---

须鲸下颌骨残留牙槽结构的形态变异

活须鲸（mysticetes）是散装滤食动物，它们使用角蛋白鲸须板从富含猎物的水中过滤食物。现存的神秘动物出生时完全没有牙齿，尽管它们在个体发育早期就具有牙芽，这是从有齿祖先那里遗传的特征。现存须鲸的下颌骨既没有牙齿也没有须鲸；牙齿在子宫内被吸收，鲸须只在上颚生长。现存须鲸的下颌骨还保留着一系列的孔和相关的沟，它们共同形成一个细长的槽，称为牙槽沟。尽管有这个名字，但仍不清楚无牙龟的牙槽沟和有齿哺乳动物的牙齿结构是否同源。这里，我们描述和量化了这些结构在现存神秘动物中的解剖多样性，并比较了它们在现存分类群（即鲢科、新鲽科、鳉科和鲱科）中的可变形态。尽管我们发现不同分类群的牙槽沟长度存在很大差异，约占所有分类群下颌骨总曲线长度 (CLL) 的 60-80%，但残留的牙槽孔显示出不同的模式，在 balaenids 中占 15-25% CLL , 而在 balaenopterids 中的 CLL 范围在 3-12% 之间。这种变异性和沿下颌骨体的形态图案与牙槽沟下方的孔反映残留牙槽的假设一致。