ABSTRACT

Twelve new specimens of fossil walruses are described from four Miocene units in California. The new material represents five taxa: (1) a specimen from the Santa Margarita Formation referred to Imagotaria downsi; (2) a specimen from the Valmonte Diatomite Member of the Monterey Formation referred to cf. Pontolis magnus; (3) six specimens from the Monterey Formation referred to a new species of Pontolis (Pontolis barroni, sp. nov.); (4) one specimen from the Oso Member of the Capistrano Formation referred to a new species of Pontolis (Pontolis kohnoi, sp. nov.); (5) three specimens from the Oso Member referred to a new genus and species (Osodobenus eodon, gen. et sp. nov.). A phylogenetic analysis suggests that both the Dusignathinae and an expanded concept of the genus Pontolis represent monophyletic groups. We provide phylogenetic definitions for clade names of odobenids. Two of the new species are represented by specimens of males, females, and juveniles. Analysis of these specimens shows that the dental anatomy of later diverging basal odobenids is more variable than previously considered. The specific pattern of variation is lineage specific and likely corresponds to the intermediate dental morphology of late Miocene odobenids. Osodobenus eodon, gen. et sp. nov., is the first basal odobenid with tusk-like canines, a longitudinally arched palate, and an enlarged infraorbital foramen. These features are plausibly correlated with benthic suction feeding in the odobenins (Pliocene to Recent) and so Os. eodon may represent a case of convergent evolution of benthic feeding in the late Miocene.

http://zoobank.org/urn:lsid:zoobank.org:pub:530A114B-46E9-4E6F-A847-8B17FAFD4327

摘要

从加利福尼亚的四个中新世单元描述了十二个新的化石海象标本。新材料代表了五个分类单元：（1）来自圣玛格丽塔组的标本，称为Imagotaria downsi；（2）来自蒙特雷组的Valmonte硅藻土构件的标本，参见cf. 马尾蓬; （3）六个来自蒙特里组的标本提到了一种新的蓬托利斯物种（Pontolis barroni，sp。nov。）；（4）Capistrano组Oso成员的一个标本提到了一种新的Pontolis（Pontolis kohnoi，sp。nov。）；（5）来自Oso成员的三份标本提到了一个新的属和种（Osodobenus eodon，gen。等。十一月）。系统发育分析表明，Dusignathinae和Pontolis属的扩展概念都代表单系统群体。我们提供了系统进化的odobenids进化枝名称。其中两个新物种以雄性，雌性和幼虫的标本为代表。对这些标本的分析表明，后来散布的基础齿状贝类动物的牙齿解剖结构比以前考虑的要多。变异的特定模式是沿袭特定的，并且可能对应于中新世晚期鄂贝多尼类动物的中间牙齿形态。蛇，gen。等。十一月，是第一个具有象牙似犬齿，纵向拱形上颚和扩大的眶下孔的基底钩齿贝类。这些特征可能与odobenins的底栖吸食有关（上新世至最近），以及Os。eodon可能代表了中新世晚期底栖生物汇聚演化的情况。

http://zoobank.org/urn:lsid:zoobank.org:pub:530A114B-46E9-4E6F-A847-8B17FAFD4327