If the fissures were the dens of predators, at least some and probably
many of the bones would show tooth marks. A predator feeding on other
animals would be expected to leave some evidence of its habits on the
bones of its prey. No such evidence is known to me, either from my own
examination of several thousand bones or from the reports in the
literature by others who have studied aspects of the early Permian fauna
of Fort Sill.
If the predators were larger than _Captorhinus_ and occupied the
fissures for a long enough time to account for the accumulation of the
tremendous numbers of individuals that are represented, a considerable
amount of the skeletal material of the larger animals would be present
in the fissure deposits. Even if for some reason the predators died in
areas other than within the fissures, thereby accounting for the absence
of large bones, coprolites should appear in the deposits if, in fact,
the fissures were feeding places. In view of the nearly undamaged
condition of many of the bones recovered from the fissures, it is
reasonable to expect that fecal material would be preserved.
The character of the matrix of the deposits varies from a homogeneous
clay to clay interrupted by layers of soft, limey, conglomeratic rock,
to a hard, well-cemented, calcareous conglomerate. In general the bone
in each kind of matrix is colored characteristically and exhibits a
characteristic degree of wear. The bones entrapped in the homogeneous
clay are relatively few, black, usually disarticulated, little worn and
not unduly fragmented; consequently the discovery of undamaged limb
bones, for example, from this kind of matrix is not unusual. The bones
found in the stratified portion of the matrix are more numerous within
the layers of conglomerate than between. The bones are black, brown or
white, highly fragmented and waterworn to a variable degree. The
fragments recovered from the hard, calcareous matrix are numerous, range
in color from white through various shades of brown, to black, are
highly fragmented, and are usually worn by water.
These categories for bone and matrix, however, are not mutually
exclusive, since bones of any of these colors and exhibiting any degree
of wear and fragmentation are found in any of the kinds of matrix
described above. That water was the agent of wear is suggested by the
highly polished appearance of the worn bones and pebbles that are found
in the matrix.
The variability of the matrix and of the color and condition of the
bones indicates that the agencies of burial and fossilization differed
from time to time and that the agency of transportation of the bones
from the site of burial to the fissures was running water. One can
easily visualize a stream coursing the early Permian landscape that was
subject to periodic flooding and droughts. Along the banks of the stream
and in its pools lived a variety of microsaurs, captorhinids, small
labyrinthodonts and small pelycosaurs. Some of the animals, after they
died, were either buried near the site of their death or were swept
along and buried in sediments further downstream. Burial was for a
length of time sufficient to impart a color to the bones characteristic
of the site in which they were buried. Later floods reexposed the sites
of burial, picked up the bones and carried them to the openings into the
fissures. Presumably, too, a proportion of the bones was carried to the
fissures without previous burial.
The differences in wear exhibited by different bones within the same
block of matrix is attributable to differences in distance that the
bones were transported before final deposition. The final sites of
deposition, the fissures, were inundated occasionally by floods alone,
or because of changes in location of the channel of the stream at the
time of flooding. The periodicity of deposition of the sediments within
portions of the fissures is indicated by the stratification of the bone
conglomerate mentioned earlier.
In summary, it seems that there is little or no evidence beyond the
numbers of bones involved to support the hypothesis that the
concentration of bones in the fissures of Fort Sill represents the
remains of food of predators, and that the fissures were used as dens by
their predatory occupants. On the contrary, the evidence indicates that
the deposition of the bones in the fissures was secondary and that the
agency of transportation, deposition and accumulation of the bones was
an early Permian stream characterized by periodic flooding.