Ground Sloths At Home

When a thing ceases to be a subject of controversy, it ceases to be a subject of interest.

William Hazlitt, "The Spirit of Controversy"

Although I analyzed fossil pollen in sloth dung samples from Rampart Cave in 1958, I did not actually visit the cave itself for another decade. In the meantime I studied glacial-age vegetation change based on fossil pollen records from Costa Rica, Arizona, California, New Mexico, and Utah. I compared large-animal extinctions in East Africa with those in Madagascar. Yet I never made the two-day trip from Tucson to Rampart Cave. My walking was deteriorating and I elected to take longer trips while I still could. By 1969 the time had finally come for a good look at ground sloth dung in situ.

In January, with the help of National Park Service (NPS) rangers and their river patrol boat, I found myself at the west end of the Grand Canyon a few miles downstream from Bat Cave. Scrambling up to a ledge, I caught up with my guides and let my eyes feast on the view. Any view of the Grand Canyon, from the top down, the bottom up, or, like this, from somewhere in between, is stunning. Five hundred feet below our perch, the Colorado River flowed west toward a gap in the Grand Wash Cliffs. The south-facing slopes and canyon walls were sun-baked and supported fewer woody plants than those facing north. On a steep slope to the west of Rampart Cave, only lichens grew on an apron of rock rubble detached from the cliff face above. The talus might once have provided retreats for yellow-bellied marmots, whose bones have been found in Rampart and other caves in the canyon. In contrast, in winter the north-

facing slopes were relatively cool and moist. Near the cave we found a rich crop of shrubs and herbs. Occasionally plants found root space between or on top of great blocks of limestone, evidently once transported down the steep slope by mighty mudflows.

Inside the cave, my NPS guides unlocked a gate and returned downstream, reminding me to lock up when I left. Austin Long and the rest of our party, hiking in from Pierce Ferry, soon arrived. Slowly proceeding deeper into the cave, we fell silent as in a cathedral, thrilled to experience one of the most remarkable fossil deposits in the world. The back of the cave was faintly illuminated by light from the cave mouth. In single file we walked into a trench, through sloth dung. When we stopped we stood chest deep in layers of stratified sloth dung. There was no perceptible airflow, but the deposit had lost any trace of ammonia or other odors of decaying manure; the air smelled resinous, like incense. No one spoke a word. In the stillness I felt the hair rise on the back of my neck. One did not need to be a Sufi or a mystic to sense that this dimly lit, low-ceilinged chamber was a sacred sanctuary. More than a sepulcher for the dead, Rampart Cave venerated the extinct.

The trench walls were packed solid. When fresh, the 40-by-50-foot deposit must have been compressed by the repeated tromping of 500-pound ground sloths. Near the middle of the deposit a layer of plant debris brought in by packrats was interleaved with layers of the compacted dung. Around the edges where the deposit adjoined cave walls and in places on top of it, we found untrampled dung balls 4.5 to 6 inches in diameter, the size of softballs. These should have been the last to be deposited, and we collected some for radiocarbon dating. We sought the final record of a large mammal teetering on the threshold of extinction. We would discover similar opportunities in Stanton's Cave at the upper part of the Grand Canyon.

The dung was remarkably well preserved, not only at the upper levels but also down to at least 4.5 feet, where it dated at over 30,000 years old. One measure of the quality of preservation is the ratio of carbon to nitrogen, which changes rapidly with exposure to the elements. The carbon-to-nitrogen ratio of the ground sloth dung was not appreciably different from that of fresh cow manure (Clark, O'Deen, and Belau 1974). To be certain that the dung was much more than a few hundred years old, we obtained radiocarbon dates on sloth dung from the top to the bottom of the deposit.

From earlier reports we had every reason to expect that Rampart Cave would yield riches, for it had been explored for fossil bones long before

Plate 2. View upstream from mouth of Rampart Cave, April 1971. Photo by Jim King.

Dick Shutler took his samples in the 1950s. I believe that Willis Evans was the first to recognize its paleontological significance. In the mid-1930s Evans, a Pit River Indian from Northern California (Harrington 1933), led a site survey crew that mapped and excavated small shallow caves in the western end of the Grand Canyon. A few years earlier, Evans had helped anthropologist Mark Harrington excavate Gypsum Cave, Nevada, which harbored an extraordinary deposit of ground sloth dung along with bones of various extinct animals and prehistoric artifacts. As a result of his work in Gypsum Cave, Willis Evans knew what he had found when he entered Rampart Cave. It is fair to say that he knew his shit.

In two test pits in a bone-rich deposit in the back of Rampart Cave, Evans excavated through packrat middens and sloth dung to bedrock. The pits yielded fossil bones of Shasta ground sloth, yellow-bellied marmot, jackrabbit, ring-tailed cat, bobcat, an extinct mountain goat (Ore-amnos harringtoni) first collected by Harrington in Nevada, an extinct burro-sized horse, and possibly mountain lion. In addition there were bones of gopher tortoise, chuckwalla, and unidentified birds, later recognized to include California Condors. Some of the fossil bones had tissue attached. There was also hair, apparently that of the ground sloth (Harington 1972; Harrington 1936; R. Wilson 1942). (Dick Harington,

Sloth dung exposed in 1969 Untrampled dung balls Back dirt piles Test pits

Postglacial wood rat deposits

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