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ENVIRONMENT

The faunal list is rather long for one obtained from such a restricted
area. It is not exceptional in this regard, however, for even longer
lists have been made from single quarry sites in the Paleocene
(Simpson, 1937:33-34). The exact number of genera and species
represented is still uncertain. It seems that twenty-one genera and
twenty-four species are present and that they are distributed among
eleven to twelve families and five to six orders. A greater number of
genera and species may be recorded eventually.

The ferungulate cohort constitutes most of the fauna (91 percent),
and this fact indicates a floodplain facies as the most probable
depositional environment. The small representation of multituberculates,
insectivores, and insectivore derivatives, however, may be attributed
in part to the difficulties inherent in surface collecting of minute
specimens.

Some resemblance in percentage composition is shown to the faunules of
the Fort Union Group if those forms too small to be seen readily in
collecting of surface material are omitted from the Montanan lists, but
differences exist not entirely the result of either geographic or
stratigraphic separation. Thus, the phenacodontids of the Angels Peak
are relatively abundant, matching figures obtained for surface
collecting in the Fort Union of Montana (Simpson, 1937:61).

That the faunule is not completely of floodplain type is seen in the
absence or rarity of such relatively large carnivores as _Claenodon
ferox_, the larger species of _Chriacus_, _Triisodon_, and the entire
absence of the Mesonychidae. The absence of the mesonychids might, but
probably should not, be explained as a result of stratigraphic
differences. There seems to be no reason for thinking that the Angels
Peak faunule antedates the appearance of the Mesonychidae. They are
absent from the Dragon and earlier levels, but are also extremely rare
in the Lebo of the Fort Union Group. In the ungulate population, the
absence of species of _Ellipsodon_ other than _E. acolytus_ (_E.
inaequidens_ is so rare everywhere that it hardly seems an exception to
this statement), and the complete absence of _Haploconus_ likewise
suggest some, presumably local, peculiarity of environment. The latter
genus is absent from the Lebo, but is recorded from the Dragon (Gazin,
1941:3), a fact which prevents a