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.
The Angels Peak faunule, as Granger stated, is of Torrejonian age.
This fact is clearly evident for the genera are all, with the exception
of the forms referred to the Primates, represented in beds of
that age elsewhere in the Nacimiento. Further, approximately two-thirds
of the known "Torrejon" genera are recorded by specimens
from the Angels Peak pocket. The primate remains present no evidence
for suspecting a difference in age, because the order is otherwise
unrecorded in the Torrejonian of New Mexico. The species are
in most instances identical or closely allied with those hitherto recognized.
It is evident from this that the Angels Peak faunule is
more closely correlated in time with the San Juan Torrejonian fauna
as a whole than with either the Dragon fauna or the Tiffanian. In
respect to the San Juan Torrejonian, closest resemblance is to the
Deltatherium zone fauna rather than to the Pantolambda zone fauna
(Osborn, 1929:62). The difference in the faunas of these two
zones is largely, if not entirely, facial in character.
It is not clearly evident, however, that we are dealing with exactly
contemporaneous assemblages when comparison is made between
the Angels Peak faunule and the rest of the San Juan fauna which
serves collectively to define the typical Torrejonian. It may be:
(1) that the Angels Peak faunule is of slightly different age than
the latter, or (2) that the latter is susceptible of stratigraphic subdivision,
and the Angels Peak faunule marks one stage of a sequence
in time. This problem will not be easily solved, and perhaps may
never be, for concentrations similar to that of the Angels Peak faunule
are of infrequent occurrence. It is beyond the scope of the present
paper, and of the present stage of our knowledge of the "Torrejon"
fauna, to discuss at length the possible difference in age, but the following
remarks summarize the matter for the Angels Peak material.
Many of the Angels Peak specimens differ in minor ways from
those previously described from the Torrejonian of the San Juan
Basin. Some of these differences are sufficiently great for the recognition
of new species. Other differences at present are not clearly
valid on a specific level, and it may become necessary to restudy the
entire fauna if satisfactory conclusions ever are reached.
A direct comparison can be made between the Angels Peak
faunule, and a numerically smaller and less well preserved one obtained
by the University of Kansas from a bone concentration near
the head of Kimbetoh Arroyo. The latter faunule presumably is
from the "Deltatherium zone," and hence does not occupy a demonstrably
high position in the "Torrejon," rather, one seemingly down
toward the first known appearance of the fauna. Closely related or
identical species of nine genera occur at both localities. Of these,
the specimens of one species seem to be indistinguishable; the specimens
of another Angels Peak member are perhaps slightly more advanced;
and seven include specimens, distinguishable in greater or
lesser degree, which suggest, principally in smaller size, a less advanced
stage for the Angels Peak faunule.
In general, the non-ferungulate part of the Angels Peak faunule
seems to depart more widely from what is typical of the "Torrejon"
fauna than do the Carnivora and Condylarthra. Because the former
is very poorly represented in the faunule, and not too well known
elsewhere in the San Juan Basin, it may be argued that the apparent
differences would disappear with the acquisition of more material.
This may be so, but at present the point can not be demonstrated.
It is not justified at present to maintain that the Angels Peak species
occupy an earlier position in the Torrejonian than do those obtained
from outcrops between Kimbetoh and the heads of the two
forks of Arroyo Torrejon. Indeed, the stratigraphic position of the
Angels Peak pocket with a considerable thickness of Torrejonian
strata beneath it, tends to argue against such a view. Nevertheless,
it is possible, if not probable, that such is the case, or at least that
detailed work would reveal a series of faunules of slightly different
ages in the Torrejonian stage of the Nacimiento formation. Of
course, chance in collecting, as well as geographic and ecologic differences,
play their part in giving such a local faunule as that at
Angels Peak its somewhat different aspect, but these factors may
not account altogether for the observed differences.
