Mammut pacificus is a recently described species of mastodon from the Pleistocene of California and Idaho. We report the easternmost occurrence of this taxon based upon the palate with right and left M3 of an adult male from the Irvingtonian of eastern Montana. The undamaged right M3 exhibits the extreme narrowness that characterizes M. pacificus rather than M. americanum. The Montana specimen dates to an interglacial interval between pre-Illinoian and Illinoian glaciation, perhaps indicating that M. pacificus was extirpated in the region due to habitat shifts associated with glacial encroachment.

中文翻译：

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太平洋猛犸象（长鼻目：猛犸象科）的最东端，基于美国蒙大拿州东部的部分头骨

Mammut pacificus 是最近描述的一种来自加利福尼亚州和爱达荷州更新世的乳齿象。我们根据来自蒙大拿州东部欧文顿人的成年男性的左右 M3 的上颚报告了该分类群的最东端出现。未受损的右侧 M3 表现出极端狭窄，这是 M. pacificus 而不是 M. americanum 的特征。蒙大拿州的标本可以追溯到伊利诺伊州前和伊利诺伊州冰川作用之间的间冰期，这可能表明由于与冰川侵蚀相关的栖息地变化，该地区的太平洋 M. pacificus 已经灭绝。