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Abstract

Research on sediments which were originally mapped as Miocene Colter Formation and subsequently discovered to contain a small pocket of Oligocene deposits continued this summer. This small exposure of Oligocene is of interest for several reasons. The deposits are the western-most exposures of Oligocene rocks known to occur in Wyoming and the relationship to the surrounding Colter Formation is poorly understood at this time. The fauna being recovered indicates that the deposits are Oligocene, and most probably very early Oligocene. The fauna includes a number of good wholly Oligocene genera and a few Eocene "holdovers". Most notable among these latter forms is a multituberculate which was thought to be extinct in the late Eocene. The fauna and nature of the deposits may help in establishing an idea of the ecology in early Oligocene time and, therefore, aid in understanding the disappearance of multituberculates, the longest lived order of mammals. Project Number 181.

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