D e s e r t E x p o s u r e
May 2012
Southwest Wildlife
A Lost World
How an 11,000-year-old sloth found near Las Cruces taught us about the world of the last Ice Age.
by Jay W. Sharp
One day about 11,000 years ago, as the last Ice Age drew slowly to a close, an immature shasta ground sloth — a pale yellowish animal roughly the size of a modern black bear — found disaster in southwestern New Mexico. The lumbering creature, probably by misstep or from predatory pursuit, evidently stumbled and plunged into a fumarole, or gas vent, at the rim of Aden Crater — a low-lying volcanic lava cone located in the 500-square-mile Portrillo Basalt Field, southwest of Las Cruces.
Although, apparently, the sloth somehow survived the initial fall, it would find no escape. "A most appalling death trap," Professor Chester R. Longwell of Yale University called the fumarole after exploring it in 1928. The sloth would perish, the remains of its last meal still in its paunch.
How was the carcass of the shasta ground sloth (Northrotheriops shastensis) discovered after its plummet into such a forbidding place so many millennia ago?
A Window to the Past
It was in late 1927 or early 1928 that three young men — C. Ewing Waterhouse, Wilson Esterly and Carlos Rushing — came to the Aden Crater planning to explore the fumarole. They were either Boy Scouts, according to the website Desert Diary, or musicians, according to the Berkeley Daily Gazette of Feb. 1, 1929. Perhaps they were both. In any event, they came prepared for adventure, but they could scarcely have anticipated what they were about to find as they lowered themselves by rope to the floor of the fumarole.
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Looking across the southern and western rim of Aden Crater, a low-lying volcanic lava cone located in the 500-square-mile Portrillo Basalt Field, southwest of Las Cruces. (Photo by Jay W. Sharp) |
"The descent into the pit is difficult," said Longwell, quoted in Richard Swann Lull's "A Remarkable Ground Sloth," a scholarly report on the animal. "It is necessary to use a rope, taking advantage of occasional irregularities in the wall for foot rests. The descent is nearly vertical for the first 40 feet. From the first landing the pipe continues down irregularly by a series of steep slopes, nearly horizontal stretches, and vertical drops, and the diameter varies greatly."
After a tortuous passage, Longwell recounted, he arrived in a "large room some 15 feet in width by 30 in length." Like other rooms, he said, "This also contains a large quantity of bat guano." It was on the floor of this chamber that Waterhouse and his friends — to their surprise — had come upon the sloth skeleton, "almost completely buried in the dry, loose guano, and at a distance of about 100 feet vertically below the mouth of the pit." Along the way, they may have also seen the more recent remains of coyotes and a bobcat lying atop the guano.
Waterhouse, an obviously bright young man who had guided Longwell to Aden Crater and the fumarole, had earlier notified Yale University's Peabody Museum of the find by a letter dated Feb. 25, 1928. He had enclosed photographs and drawings that alerted the museum to the fact that he and his two friends had come upon something extraordinary. "It was at once evident," as Lull put it, "that a ground sloth had been discovered in a remarkable state of preservation."
Their find would draw national attention. Time magazine's Jan. 7, 1929, edition reported that after the sloth died, "the indifferent bats dropped their guano on its dead body. Good for modern paleontology was their filthy covering. It preserved the sloth-bones, teeth, tendons, hide and even a food ball in its stomach." Time said that the sloth lived "1,000,000 years ago, certainly 500,000." The Berkeley Daily Gazette, by contrast, said that the sloth was "believed to have lived 50,000 years ago." This was, of course, before the development of radiocarbon dating technology, which would later indicate an age in the range of 11,000 years.
The Peabody Museum — realizing that the partially mummified sloth offered an important window to the past — promptly made arrangements to acquire and study the remains. "The specimen was complete," said Lull, "the bones being held in articulation by their original ligaments and tendons. There are also present some of the periosteum [connective tissue covering the bones], patches of skin, and the mucous membrane lining the hard palate, as well as some muscle fibers."
Even some of the animal's coarse yellowish-colored hair had been preserved. Astonishingly, the sloth had broken none of its bones in its fall into the fumarole. They remained largely preserved, suggesting that the animal had been able to search for an escape before it died.
A Striking Animal
Today, thanks especially to the find at Aden Crater, as Björn Kurtén and Elaine Anderson wrote in Pleistocene Animals of North America, "More is known about the external appearance of Northrotheriops shastensis than any other ground sloth."
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Young man, probably a friend of Ewing Waterhouse, at the mouth of the fumarole, sometime in the late 1920s. (Photo made available by the University of Texas at El Paso Library, Special Collections Department. C. E. Waterhouse papers, MS458) |
A mature adult shasta ground sloth — one of the smallest of the giant ground sloths, all now extinct — measured more than seven feet from the tip of its nose to the tip of its tail. It stood more than three feet high at the shoulder. It likely weighed around 400 pounds. (By comparison, another one-time species of late Ice Age giant ground sloth — the Eremotherium — measured some 20 feet in length and weighed a ton.)
Like other members of its taxonomic family, the shasta ground sloth had a relatively small head with prehensile (grasping) lips and tongue, something like a modern giraffe. It had a long flexible neck, long and relatively slender forelimbs, muscular hindquarters and a muscular tail. On its forefeet, long claws may have been used to dig food plants from the soil and to pluck edible fruit from thorny plants such as the prickly pear, as well as to defend itself from predators such as the sabertooth cat or the dire wolf.
Standing upright to take foliage from shrubs and trees, the animal likely used its back legs and tail much like a tripod, giving it stability and reach. Walking, it probably moved clumsily, with a waddle, on the knuckles of its front feet and the heel and outer edges of its hind feet.
A Very Different World
The young shasta ground sloth's territory southwest of Las Cruces featured — as it still does — low mountain ranges, scattered volcanoes, massive lava flows, rocky and sandy soils and playa lake beds. But, measured by the climate, the plant and wildlife communities and the late Ice Age human community, its world looked very different from what we see today.
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Photo of skull and ribs of the shasta ground sloth, probably shot by Waterhouse soon after discovery of the animal. (Photo made available by the University of Texas at El Paso Library, Special Collections Department. C. E. Waterhouse papers, MS458) |
Reflecting the waning Ice Age, the sloth knew a climate that was much cooler than ours today, with mild winters and summers and moderate rainfall. The playa lakes held water through the year. The sloth foraged in a plant community that resembled an African savannah, or a grassy open woodland. The land bore a blanket of grasses such as bush muhly, alkali sacaton and several gramas with scattered stands of trees such as piñon pine, juniper and live oak interspersed with various species of arid-land vegetation such as prickly pear cacti, agave, yuccas and desert globemallow.
The sloth belonged to a rich community of "mega" mammals distributed across southwestern New Mexico. These included, for just a few examples, mammoths, mastodons, camels, three-toed horses, short-faced bears, sabertooth cats, dire wolves and tapirs — all now extinct for reasons that have puzzled paleontologists for years. As Arthur H. Harris wrote in "Plio-Pleistocene Vertebrate Fossils of the El Paso Area," "a virtual Noah's ark of vertebrate diversity [now extinct]" lies embedded in the late Ice Age sediments within our region.
As the last Ice Age wound down, the shasta ground sloth, some archaeological evidence suggests, may have been hunted by the earliest Americans, the Paleo Indians, according to Michael Cannon and David Meltzer in Quaternary Science Reviews. Nomadic big-game hunters probably moving as compact family units, the Paleo Indians had arrived at an unknown time from undetermined origins by uncertain trails. Armed with spears tipped with exquisitely crafted stone points, they shadowed the big game of the time. Given the opportunity, they drove their spears into the great animals, killing them for food, hides and bones. They also scavenged the bodies of the big game that fell to injury or illness. Some archaeologists think that the Paleo Indians may have been such a powerful force that they contributed substantially to the extinction of the Pleistocene big game, the "megafauna."
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