The Borchers fauna is the oldest known interglacial fauna of Kansas. Sorex taylori Hibbard, Perognathus sp. (the same as found at Meade County, Loc. no. 3), and Synaptomys cf. vetus Wilson are forms previously known only from the upper Pliocene. The presence of S. cf. vetus Wilson, previously known only from the upper Pliocene of Idaho, though not known from the Rexroad fauna, may be a form whose range was extended southward by the advance of the continental and the Rocky Mountain glaciers, thus arriving in the area after the Rexroad fauna had been forced southward by a changing climate.
The presence of Onychomys and Sigmodon in abundance indicates a warm climate for the region. Many of the genera of mammals occurring in the Borchers fauna have species or subspecies occurring in this region or still farther southward at the present time. Zapus has been reported by Blair (1939, p. 127) from Oklahoma. Although the species are different, the fauna seems to show a close relationship to the Curtis ranch fauna of Arizona--closer than to any other known Pleistocene fauna of North America.
The volcanic ash from which the fossils were taken was deposited in a small lake or in partly ponded streams. The ash fall itself did not bring about the death of the forms collected from the edge of the lens. No bones have been found articulated, and jaws predominate over other skeletal parts. Inasmuch as most microvertebrate faunas have been recovered from trapped deposits, such as caves, fissures, tar pits, or sinks, and few small fossils are known from fluvial deposits, it seems in order at least to postulate a method for the deposition of such faunas as the Borchers and the Rexroad.
In four years of intensive trapping in Meade County, 1936 to 1939, no harvest mice were caught, although more than 50 skulls and lower jaws were taken from a slide consisting of debris and dirt below an old barn owl nest, which had been in the bluff above the debris for at least 2 years previous to 1936. The summer of 1940 the mouse was abundant in the area; many were caught while they were running around on the ground in the day time, and remains of them were found in fresh owl pellets. Everyone who has collected fossils along a bank where owls roost or nest has been impressed by the tremendous number of rodent remains; most of these become covered as a result of the constant slumping of the bank or cliff, and later may be carried away and redeposited, or may be covered in place by a greater slump. A series of barn owl or great horned owl roosts and nests along the banks of a tributary stream, upstream from a lake or a body of water of low gradient, would produce a constant supply of rodent material to be trapped and covered in the ponded water. The owls' constant hunting would, in a few years, assemble even the rarest small mammals in a region, although specimens of the most abundant mammal species would make up the majority of the number caught. The pellets would provide a constant supply of material, much of which would be deposited along the stream's course.
This brief explanation of technical terms is given for the use of readers who may not be acquainted with them.
Alveolus--Socket in the jaw where a tooth is situated.
Boreal region--The northern Boreal region includes approximately all of North and Central America in which the mean temperature of the hottest season does not exceed 64.4° F.
Canine--Teeth in upper and lower jaws that correspond to the large biting or holding teeth of dogs and cats.
Coronoid process--Portion of lower jaw behind the alveolar border and above the condyle, which extends upward and is laterally compressed, being concave on its outer surface to allow for muscle attachment.
Dental formula--Only one half of the total number of teeth is written in the formula. The number written is added and multiplied by 2. The teeth of the right or left upper jaw are written as the numerator and those of the lower jaw as the denominator. The dental formula for man is I 2/2, C 1/1, P 2/2, M 3/3 = 32. Thus, in man there are 8 teeth in each side of the upper and lower jaw when the wisdom teeth or the third molars are through.
Entoconid--Postero-internal cusp of the lower molar.
Fauna--The animal life characteristic of a region, locality, or geological horizon.
Fossorial--Said of animals that spend most of their life burrowing, or living in burrows.
Glacial age--Part of Pleistocene time when much of northern North America and mountain regions were covered with ice.
Hypoconid--Postero-external cusp of the lower molar.
Incisor--Gnawing teeth of rodents or front teeth of any mammal.
Interglacial age--Part of Pleistocene time when glaciers had nearly or completely receded from the continent.
Labiad--Toward the lips.
Mental foramen--Opening in lower jaw or ramus situated on outer side near anterior end and through which a branch of the fifth nerve and blood vessels pass.
Metacone--The postero-external cusp of the upper molars.
Metaconid--Second antero-internal cusp lying just posterior to the paraconid, which is the first antero-internal cusp of the lower molars.
Metaloph--Posterior crest of certain molars formed by the union of cusps in the wearing down of the tooth.
Metastyle--Posterior ridge of certain upper molars formed from the cingulum.
P.--Premolar; P1 first lower premolar; P1 first upper premolar.
Parastyle--The anterior ridge of certain upper molars formed from the cingulum, an enamel ridge at the base of the tooth, as in the upper molars of the ground squirrel.
Pleistocene--Glacial epoch; ice age; pertaining to the epoch following the Tertiary and next before the present. The Pleistocene is divided into 4 glacial and 3 interglacial ages in North America: (1) Nebraskan glacial, Aftonian interglacial; (2) Kansan glacial, Yarmouth interglacial; (3) Illinoian glacial, Sangamon interglacial; (4) Wisconsin glacial.
Pliocene--Latest epoch of the Tertiary period, next preceding Pleistocene time.
Protocone--Antero-internal cusp of the upper molars.
Protoconid--Antero-external cusp of the lower molars.
Protoloph--Anterior crest of certain upper molars; in the pocket mice it is formed by three cusps.
Quaternary--Division of geologic time that includes Pleistocene and Recent.
Ramus--Right or left half of lower jaw; plural, rami.
reentrant valley--Fold in enamel of a tooth between the cusps.
Talonid--Heel of lower molars formed by the following cusps, hypoconid, entoconid, and hypoconulid.
Trigonid--Triangle formed by the anterior cusps (protoconid, paraconid, and metaconid) on the lower molars of certain animals, especially those of the carnivores.
Blair, W.F., 1939, Faunal relationships and geographic distribution of mammals in Oklahoma: Am. Midland Naturalist, vol. 22, no. 1, pp. 85-133.
Cragin, F.W., 1896, Preliminary notice of three late Neocene terranes of Kansas: Colorado College Studies, vol. 6, 51-54.
Frye, J.C., 1940, A preliminary report on the water supply of the Meade artesian basin, Meade County, Kansas: Kansas Geol. Survey, Bull. 35, pp. 1-39, figs. 1-7, pls. 1-5. [available online]
Hibbard, C.W., 1938, An upper Pliocene fauna from Meade County, Kansas: Kansas Acad. Sci. Trans., vol. 40, pp. 239-265.
Smith, H.T.U., 1940, Geological studies in southwestern Kansas: Kansas Geol. Survey, Bull. 34, pp. 1-211, figs. 1-212, pls. 1-34. [available online]
Wilson, R.W., 1933, A rodent fauna from later Cenozoic beds of southwestern Idaho: Carnegie Inst. Washington Pub. 440, pp. 117-135.
Kansas Geological Survey, Geology
Placed on web June 15, 2007; originally published July 1941.
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