Conard Fissure

It's been a while since we've done a good old-fashioned Pleistocene cave fauna, and there's one more wanting to complete the Big Three of Irvingtonian eastern North America. We've already spent some time with Cumberland Bone Cave and Port Kennedy Bone Cave, so now it's the turn of Conard Fissure in northwestern Arkansas.

The eastern half of North America is good for many things, but if you're looking for Cenozoic deposition and you're not on the coastal plain, it's basically fissure fills or bust. If your area had karst development before, say, 50,000 years ago, and you can access said karst, you can occasionally find glimpses of otherwise completely lost times. (Hey, we've got karst in southeastern Minnesota—never give up hope for a pre-Late Pleistocene assemblage!) Conard Fissure is a classic example. Located near Buffalo National River in an area laced with caves, this site was discovered in 1903 on the Conard farm by Waldo Conard, who was hoping to find lead. The report of bones made its way to the American Museum of Natural History, and that fall Barnum Brown was there to investigate. He reported collecting "about three hundred jaws and many disassociated limb bones and vertebrae from the dump" (Brown 1908). This seemed promising, so he returned the next year to make a collection of several thousand bones. (If that seems like a lot, he also relates that the fragility of the bones resulted in dozens being broken for every one collected, and many bones had been broken before collecting by the weight of rocks that had fallen on them.) Later the University of Arkansas would make collections from the "tailings" (Dowling 1958).

The fissure with windlass in place for specimen retrieval. Figure 2 from Brown (1908).

The bones were almost entirely disassociated. Although fragile, they required little preparation beyond washing off clay and soaking them in a preservative. They filled spaces and pockets and weasel lairs. The top of the deposit had been sealed by mineral deposition (Brown 1908). Unlike Cumberland and Port Kennedy, Conard Fissure had not been disrupted by quarrying or modification to lay rail, and so excavation took place in a less disturbed setting. The fissure, albeit choked up by fallen rocks, bones, and clay, still had stalactites and other cave formations. Other fissures nearby did not yield bones (Brown 1908).

Brown had this model made of the upper part of the fissure, showing cave formations and fill. From Brown (1908), plate XXV.

Brown identified 51 mammal species (the modern number would be somewhat smaller), as well as several species each of amphibians, reptiles, and birds, but did not differentiate the members of those groups to any great degree. 4,034 specimens were attributed to mammals, 1,136 to amphibians and reptiles, and "many bones" to birds. The great abundance of small animals is striking if you've grown up with the narrative that old-time paleontologists only cared about big skulls and skeletons. By far the most abundant taxon in Brown's analysis was the deer mouse Peromyscus, at 1,500 specimens, followed by 1,000 specimens of undetermined snakes. Animals larger than, say, a coyote were limited to wolves, black bears, a couple of species of lynx, cougar, American cheetah, saber-toothed cats, horses, peccaries, elk, deer, and muskox. Of these, none had more than 20 specimens except for an undetermined species of the peccary Mylohyus (200; later appropriately named M. browni in Gidley 1920, but now considered a synonym of M. fossilis) and black bear (110). Brown coined 19 new species and subspecies, but only one is still in use: an extinct species of muskrat, Fiber annectens, now Ondatra annectens.

Some of the many, many peccary bones of Conard Fissure. From Brown (1908), plate XXIV.

Other authors took cracks at other parts of the fauna. Dowling (1958) identified a dozen snake species and noted that they were primarily terrestrial (non-burrowing or cave-dwelling) species active during the day. He suggested that rather than being attracted by frogs, as Brown proposed, the snakes represent food items from similarly diurnal predators such as the abundant weasels and skunks. Gilmore (1928) identified Brown's lizard as a horned toad. Shufeldt (1913) gave a further look at Brown's bird material. It is not, as Wetmore (1959) noted, the author's most distinguished work, but he does end up being credited with a new species of prairie chicken (Tympanuchus ceres) thanks mostly to Wetmore (Shufeldt had suggested that some material be given the species name ceres if it proved to be distinct, and Wetmore provided the assist 46 years later).

Micropaleontology in the early 1900s: sieving for bones. Figure 3 in Brown (1908).

The age of the cave deposits has never been tightly established, and probably spans a long interval. Brown (1908) decided it wasn't pre-Pleistocene because of the fauna, and thought it dated to the time of the most recent glacial retreat (very late Pleistocene) due to the absence of typical Pleistocene megafauna, such as mammoths, mastodons, and giant sloths. (He missed what would seem to be an obvious trick here, that the fissure entrance may simply have been too small to fit something like an elephant.) It was soon thought to be older, though. For example, Hay (1924) suggested an Illinoian age (the glaciation before the most recent glaciation) on faunal grounds and the Illinoian being the stage with the closest glacial approach to Arkansas. Today it is recognized as older still, in the Irvingtonian North American Land Mammal Age of the Early to Middle Pleistocene (e.g., Kurtén and Anderson 1980).

Brown (1908) described the accumulation as gradual rather than catastrophic, and a result of the activities of several kinds of predators. Larger remains probably represent things brought in by cats and bears, whereas smaller remains are probably leftovers from weasels and owls. There is also a probable packrat influence as well. Tooth marks are abundant. Brown attempted to record stratigraphic context but found it "impracticable" and misleading. He did note that the most abundant forms (such as bears and peccaries) appeared to be present at about the same abundance throughout, whereas saber-toothed cats disappeared ten feet from the upper surface. There has never been a comprehensive review of the site since Brown's report (not uncommon for even well-known sites, which may get just one key publication early on, followed by a long tail of commentary). It would be interesting for someone to take another holistic look with the benefit of nearly 120 years of advances in paleontology; look at the differences in opinion since then concerning age and the source of the snakes, for example.

A typical chunk of bone-bearing matrix from Conard Fissure. From Brown (1908), plate XXV.

References

Brown, B. 1908. The Conard fissure, a Pleistocene bone deposit in northern Arkansas: with descriptions of two new genera and twenty new species of mammals. Memoirs of the American Museum of Natural History 9(4): 155–208. (linked scan above has great plates but useless in-text figures, this scan has usable in-text figures but mediocre plates)

Dowling, H. G. 1958. Pleistocene snakes of the Ozark Plateau. American Museum Novitates 1882.

Gidley, J. W. 1920. Pleistocene peccaries from the Cumberland cave deposit. Proceedings of the United States National Museum 57(2324):651–678.

Gidley, J. W. and C. L. Gazin. 1938. The Pleistocene vertebrate fauna from Cumberland Cave, Maryland. United States National Museum Bulletin 171: 1–99.

Gilmore, C. W. 1928. Fossil lizards of North America. Memoirs of the National Academy of Science 22.

Graham, R. W. 1972. Biostratigraphy and paleoecological significance of the Conard Fissure local fauna with emphasis on the genus Blarina. Thesis. University of Iowa, Iowa City.

Hay, O. P. 1924. The Pleistocene of the middle region of North America and its vertebrated animals. Carnegie Institute of Washington Publication 322A.

Kurtén, B., and E. Anderson. 1980. Pleistocene mammals of North America. Columbia University Press, New York, New York.

Shufeldt, R. W. 1913. Further studies of fossil birds with descriptions of new and extinct species. Bulletin of the American Museum of Natural History 33: 285–306.

Wetmore, A. 1959. Notes on certain grouse of the Pleistocene. The Wilson Bulletin 71(2): 178–182.