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 attaching any age significance to its absence from the Angels Peak faunule. It should be mentioned, however, that no remains of Haploconus were reported as a result of the more extensive collecting by Granger in the Angels Peak area. Incidentally, the type of Haploconus angustus is said to come from near Huerfano Peak (Matthew, 1937:156).
The high ratio of carnivores to ungulates is a peculiarity shared with, but far exceeded by, the Lebo fauna if figures obtained from surface collections of the latter are used. It seems unlikely that this ratio is the result of selective trapping in the accumulating sediments. Perhaps, this high ratio reflects the imperfectly carnivorous habits of the Paleocene creodonts as a group. One obvious explanation, regardless of probability or merit, is that some of these do not belong to the Carnivora.
The percentage composition of the Angels Peak faunule based on 148 identifiable mammalian specimens, is as follows:
| Percent | |||
| Insectivora: | 5 | ||
| Carnivora: | |||
| Arctocyonidae: | 32 | ||
| Miacidae: | 4 | ||
| —— | 36 | ||
| Condylarthra: | |||
| Hyopsodontidae: | 22 | ||
| Phenacodontidae: | 18 | ||
| Periptychidae: | |||
| Anisonchinae: | 10 | ||
| Periptychinae: | 5 | ||
| —— | 15 | ||
| —— | 55 | ||
| Others: | 4 | ||
| —— | |||
| 100 |
The most common forms in the Angels Peak faunule are: Tricentes cf. T. subtrigonus, Chriacus truncatus, Ellipsodon acolytus, Tetraclaenodon nr. T. puercensis, and Anisonchus sectorius.
Post-cranial skeletal elements are of relatively rare occurrence in the pocket. The presence of several more or less complete skulls, and the relatively frequent association of upper and lower dentitions, however, seem to be points against ascribing the accumulation to the activities of predators and scavengers, otherwise perhaps indicated by the large amount of resistant tooth material.