Fig. 18 in Geology And Paleontology Of The Upper John Day Beds, John River Valley, Oregon: Lithostratigraphic And Biochronologic Revision In The Haystack Valley And Kimberly Areas (Kimberly And Mt. Misery Quadrangles)

Fig. 18. The Great Plains oreodont Merycochoerus from the Childs Frick collection of the American Museum of Natural History provides biochronologic control for the occurrence of this indicator taxon in the upper John Day Formation, Oregon. Because many upper John Day taxa are represented by few individuals, the larger Frick samples of Arikareean/Hemingfordian mammals are critical to accurate age assessment. The graph measures the progressive fusion and posterior extension of the premaxillae in time, most likely related to ongoing development of a tapirlike proboscis in this large oreodont. The triangle labelled ''Rose Creek'' refers to UCMP 76848 from Picture Gorge 36.