The Americas

A large group of terrestrial mammals unique to the Americas and rich in vanished giants is Xenarthra ("strange joint"), formerly called Edentata ("toothless"), although only the anteaters have a reduced dentition. Originating in South America, Xenarthra includes such living and extinct representatives as armadillos, giant armadillos, and glyptodonts (order Cingulata, "banded"), as well as anteaters, ground sloths, and tree sloths (order Pilosa, "hairy").

Except for wide variation in scale, the extinct cingulates generally resembled the nine-banded armadillo (Dasypus novemcinctus), the bony-shelled creature is found in the southern United States today. The extinct species include the "beautiful armadillo" (Dasypus bellus), perhaps twice the length of a living nine-banded armadillo and heavy enough to be considered large as defined here. Much larger was the pampathere, Holmesina, about 1 meter (40 inches) high and 2 meters (80 inches) long. It weighed 180 kilograms (400 pounds).

As for the glyptodonts, the largest species, Glyptodon clavipes of South America, weighed over 1,800 kilograms (4,000 pounds)—by an order of magnitude the largest "giant armadillo" of all (Lyons, Smith, and Brown 2004). North America had just one species of glyptodont in near time, which ranged south from Florida (and also central Sonora, at the same latitude as Florida); South America harbored many more species of giant edentates, both glyptodonts and ground sloths. With the solitary exception of the recently described Pachyarmatherium, only known earlier in the Pleistocene, all eight glyptodont genera recorded

Figure 6. Extinct American megafauna, scaled. A. giant beaver; B. mastodon; C. bison; D. saber-toothed cat; E. giant ground sloth; F. Shasta ground sloth. From Murray 1991, in P.V. Rich et al., Vertebrate paleontology of Australasia.

in the last four million years vanished in the late Pleistocene, very likely in near time.

Because the ground sloths play an important role in this book, and given their importance in focusing Thomas Jefferson's interest over two centuries ago on the unknown large animals of America, their record is of more than ordinary interest.

I consider the ground sloths to be the hallmark, the defining group of mammals for the Americas. Ground sloths ranged from Alaska to Patagonia, including the West Indies. Lyons, Smith, and Brown (2004) list 14 extinct species in 12 extinct genera from South America; 10 of the extinct species exceeded 450 kilograms (1,000 pounds) adult body weight. As the hallmark of South America I nominate the largest ground sloth, Megatherium americanum, tipping the scales at over 6,000 kilograms (13,000 pounds), matching or exceeding the mass of a large bull Asian elephant. The largest giant ground sloth in North America,

Figure 7. Extinct North American megafauna, scaled: a. giant armadillo; b. giant ground sloth; c. Columbian mammoth; d. mylodon ground sloth; e. mastodon; f. Shasta ground sloth; g. glyptodont; h. camel; i. tapir; j. giant peccary; k. capybara; l. saber-toothed cat; m. American lion; n. horse; o. woodland musk ox; p. Harrington's mountain goat; q. antilocaprid. Reprinted from Stuart 1991. Used with permission of Cambridge University Press.

Figure 7. Extinct North American megafauna, scaled: a. giant armadillo; b. giant ground sloth; c. Columbian mammoth; d. mylodon ground sloth; e. mastodon; f. Shasta ground sloth; g. glyptodont; h. camel; i. tapir; j. giant peccary; k. capybara; l. saber-toothed cat; m. American lion; n. horse; o. woodland musk ox; p. Harrington's mountain goat; q. antilocaprid. Reprinted from Stuart 1991. Used with permission of Cambridge University Press.

Eremotherium rusconii, is estimated to have weighed a little more than half as much.

In the late Quaternary, until their extinction, the ground sloths, of the order Xenarthra, comprised four genera in North America north of Mexico and twelve in South America (see table 4). These animals are a bit harder to envision than the armadillos. Their closest living relative, South America's giant anteater (Myrmecophaga), at around 20 to 40 kilograms (40 to 85 pounds), is the largest survivor of this stunning lineage. The giant anteaters walk on their knuckles to protect the claws of their forefeet, and the giant ground sloths may have done the same. Like the anteaters, they may also have carried their young on their backs. However, they did not have the anteaters' long snout, very long tongue, reduced dentition, and specialized digestive tract, all designed to mop up and process termites or ants. The ground sloths had teeth and a digestive tract resembling those of a tree sloth, designed to process foliage.

Tree sloths spend most of their time suspended in tropical trees. Ground sloths may not have been quite as languid and slow moving, but their bulk, robust bones, and long, unretractable claws must have made it impossible for them to move quickly or to climb very well, and thus difficult for them to escape predators. Extrapolating from the fact that the related anteaters, tree sloths, and armadillos "are chiefly solitary but may form small, loose associations," Ronald Nowak (1999) writes that the ground sloths were probably solitary except in the breeding season. Thus, unlike elephants, camels, horses, bison, and the extinct relatives of those groups, they not only were not fleet of foot but also lacked the protection of a herd. They must nevertheless have succeeded somehow in defending themselves against nonhuman carnivores, perhaps by sitting up on their haunches, propped by their tails, and, like giant anteaters, using the curving claws on their long front legs to rip attackers. This defense would have had little effect against stones or spears flung from a distance by human hunters.

The ground sloths were the largest of the xenarthrans. Those that are estimated to have exceeded 450 kilograms (1,000 pounds) in weight were the true giant ground sloths. They would include Eremotherium rusconii, known from the southeastern United States south into South America; Paramegatherium spp.; and Lestodon armatus (Lyons, Smith, and Brown 2004). As mentioned above, the most massive of all was South America's Megatherium americanum. It is thought that Megatherium (which had four digits and three well-developed front claws) and Eremotherium (with three fully developed digits and two claws) were able to reach tree

TABLE 4 Near-Time Genera of Extinct Ground Sloths

Family Mylodontidae

1. Mylodon Owen, 1839, SA

2. Glossotherium Owen, 1839, NA, SA

3. Paramylodon Brown, 1903, NA

4. Oreomylodon Hoffstetter, 1949, SA

5. Mylodonopsis Cartelle, 1991, SA

6. Lestodon Gervais, 1855, SA

7. Lestodontidion Roselli, SA (Uruguay)

8. Scelidotherium Owen, 1839, SA

9. Catonyx Ameghino, 1891, SA

Family Megatheriidae

10. Megatherium G. Cuvier, 1796, SA

11. Eremotherium Spillmann, 1948, NA, SA

Family Nothrotheriidae

12. Ocnopus Reinhardt, 1875, SA

13. Prezfontanatherium Roselli, 1976, SA (Uruguay)

14. Nothropus Burmeister, 1882, SA

15. Nothrotherium Lydekker, 1889, SA

16. Nothrotheriops Hoffstetter, 1954, NA

Family Megalononychidae

17. Diodomus Ameghino, 1885, SA

18. Paulocnus Hooijer, 1962, Curaçao

19. Synocnus Paula Couto, 1967, Hispaniola

20. Valgipes Gervais, 1874, SA (Brazil)

21. Megalonyx Harlan, 1825, NA, SA (Colombia)

22. Megalocnus Leidy, 1868, Cuba

23. Neocnus Arredondo, 1961, Cuba, Hispaniola (Microcnus Matthew, 193l, and Cubanocnus Kretzoi, 1968)

24. Parocnus Miller, 1929, Cuba, Hispaniola

25. Miocnus Matthew, 1931, Cuba

26. Acratocnus Anthony 1916, Cuba, Puerto Rico, Hispaniola

27. Xenocnus Paula Couto, 1980, Brazil note: NA = North America, SA = South America. Taxonomy follows McKenna and Bell, revised by Greg McDonald and Ross MacPhee. Eighteen genera of ground sloths are confined to the Americas, from Alaska to Patagonia, with a secondary center of radiation of seven genera of dwarf (under 50 kg) animals in the Caribbean (Greater Antilles plus Curaçao). Living tree sloths—Choelepus, the two-toed sloth, and Bradypus, the three-toed sloth—occur in tropical America.

branches at least as high as those browsed by giraffes. The molar cusps of these monstrous beasts resembled giant pinking shears, suggesting that they were superbly adapted for browsing. The Uruguayan paleontologist Fariña (1996) proposed that in the absence of more suitable carnivores, Megatherium could have also been a facultative carnivore or scavenger, and this behavior is depicted in the Discovery Channel's 2001 television special Walking with Prehistoric Beasts. But Megatherium lacks carnassials, the shearing teeth that are a hallmark of most carnivores.

Recently some have speculated that giant ground sloths used their claws to prey on their relatives, the armored glyptodonts, an idea I find as fanciful as Peter Lund's proposal of 150 years ago that giant ground sloths, like living tree sloths, would clamber about in the giant trees of the tropics (Wallace 2004, 171). To suggest that the ground sloths were predators or even scavengers is a reach. The ground sloth dung deposits I have studied in the Grand Canyon and in caves in Nevada, New Mexico, and West Texas harbor no more traces of bone than I have seen in horse, mule, and burro manure, namely none.

Two medium-sized genera were America's Paramylodon, "near molar tooth" (sometimes known as Glossotherium, "tongue beast"), and North America's Megalonyx ("great claw"). The mylodons were rhinoceros-sized and possessed a dermal armor formed of closely spaced, pea-sized bones embedded in their thick hides, which presumably helped shield them from predators.

The megalonychids include the first ground sloth discovered in North America, Jefferson's ground sloth (Megalonyx jeffersonii). Thomas Jefferson informally named the genus when in 1799 he was sent bones, including claws, from a cave in what is now West Virginia. Because Jefferson, along with many others of his time, believed in a "great chain of being" in which all species were interdependent (if one link was broken, the chain would fail), he did not believe in extinction. Megalonyx must be alive! Jefferson originally interpreted the claws as coming from a large cat, and because they were three times the length of an African lion's claws, he assumed that the animal was three times the size of that beast— and hoped Lewis and Clark might catch sight of it. Later he came to realize that they were from an animal similar to the Megatherium described by the French paleontologist Georges Cuvier. Jefferson also believed that mammoths roamed unknown parts of the West. These ideas were not entirely fabulous. Subsequent fossil discoveries revealed that until the end of the last ice age, ground sloths and various proboscideans, including mammoths, had indeed been native to America. In addition, the fossil record would show that there had been lions in America contemporary with the extinct ground sloths and elephants of near time. Despite having filled Monticello with the bones of late-Pleistocene mastodons and other large mammals, Jefferson is still regarded by some paleontologists as unworthy of being called the "father of paleontology." His interest in this aspect of American prehistory is nevertheless prescient of the theme I develop here, that an understanding of what the New World once harbored is far from irrelevant; indeed, it is crucial to how future management might be envisioned and designed. Jefferson focused on fossils of large extinct animals that only now are beginning to gain their full measure of appreciation. If he was wrong in believing that America might harbor a lion three times larger than its close relatives in the Old World, America nevertheless harbored until not long ago not only lions, but also many other large predators eclipsing the ones we know historically and from the last hundred centuries. I think Jefferson's curiosity would have been aroused. What is the full implication of America's extinct lions, mammoths, and ground sloths?

For those of us in the Southwest, the North American ground sloth most likely to draw attention, with a reconstructed carcass on exhibit at Kartchner Caverns near Benson, Arizona, is the Shasta ground sloth, Noth-rotheriops shastensis. It was about the size of a black bear, with a body mass of 135 to 545 kilograms (300 to 1,200 pounds). This made it the smallest continental North American ground sloth, at less than one-tenth the weight of the true giant ground sloths, which some taxonomists place in the same family. It was more than an order of magnitude more massive than the tree sloths, which weigh up to 10 kilograms (roughly 20 pounds). Its dung and soft parts are found occasionally in dry caves that also harbor preserved plant remains gathered by packrats, revealing details about the habitat as well as the diet of the Shasta ground sloth. In its heyday, the animal ranged from northern California and the Texas Panhandle south into the Sierra Madre Oriental of northern Mexico.

Five genera of elephants in three families (all in the order Proboscidea) occurred in the Quaternary of North America. Three of the genera— Mammuthus (mammoths), Mammut (mastodons), and Cuvieronius (gom-photheres)—survived into near time, close to 13,000 years ago. Both mammoths and mastodons stood roughly 3 meters (8 to 10 feet) high at the shoulder, weighed 6,000 kilograms (9,000 to 13,000 pounds), and had long, curving tusks and in some cases long hair. Mammoths are the extinct genus most likely to be found processed or butchered at prehis toric kill sites in North America. The largest terrestrial mammal in the hemisphere was the imperial mammoth, Mammuthus imperator, at 10,000 kilograms (22,000 pounds). Another elephant, Stegomastodon superbus, tipped the scales at 7,580 kilograms (16,700 pounds) and was South America's only mammal more massive than Megatherium.

Three or more species of elephantlike gomphotheres (Gomphotheri-idae) lived in South America until the end of the Pleistocene. The genus Cuvieronius ranged north of Mexico to overlap in Florida with the mammoths and mastodons. Bones dating from the early Quaternary have been found in Arizona. The gomphotheres had relatively straight tusks supporting a strip of enamel, rather than tusks entirely enclosed in enamel. They had elongated lower jaws. Some species, though probably not the American ones, had lower as well as upper tusks. The Central American gomphotheres may have eaten (and hence dispersed) the large fruits of wild avocado, oil palm, and guanacaste trees. Ecologist Dan Janzen believes that they played a major role in the dispersal of the seeds of palatable fruits, just as today's elephants do in Africa. After the extinctions, humans—and later, domestic livestock—may have unknowingly substituted for the gomphotheres in dispersing such seeds (Janzen and Martin 1982; Barlow 2000; Dudley 2000).

The South American notoungulate and litoptern orders, which together spun off 19 families in over 60 million years (McKenna and Bell 1997), are the least familiar of America's extinct big herbivores of near time. Four genera survived to the end of the ice age. They were diverse groups, and envisioning them is a challenge. Notoungulates may have resembled rhinos with a mouth full of buck teeth, while litopterns resembled horses, camels, or chalicotheres (also extinct), large horse-like animals that had claws rather than hooves. The litoptern Macrauchenia looked vaguely like a large llama, with a much longer neck and an elongated, bootlike nose resembling a short trunk, with the nasal apertures on top of its head rather than terminal. Toxodon, a notoungulate, and Macrauchenia made rare appearances on the Discovery Channel's Walking with Prehistoric Beasts.

The order Carnivora comprises bears, cats, hyenas, mongooses, raccoons, seals, skunks, viverrids (civet cats and their kin), walruses, weasels, and wolves. Six genera of large carnivores disappeared considerably before near time; five more disappeared within near time, and four have survived (see table 2). Besides living wolves, bears, jaguars, and pumas, a zoological garden stocked with the American carnivores of near time would include the dire wolf, Canis dirus; two bears, Tremarctos flori-danus and Arctodus; a scimitar cat and a saber-toothed cat, Homotherium and Smilodon; a lion, Panthera leo atrox; and a cheetah, Miracinonyx.

At least some of these carnivores, such as the cheetah, dire wolf, and lion, are very close to living species. The dire wolf may have been more robust and less cursorial than living timber wolves. Hundreds of its skulls from the tar pits at Rancho La Brea decorate a wall panel at the Page Museum in Hancock Park, Los Angeles. Most paleontologists interpret the abundance of dire wolf and saber-toothed cat remains at Rancho La Brea as reflecting the fate of opportunistic scavengers who came to feast on whatever was trapped in the asphalt and became trapped themselves.

Judged by measurements of its carnassial teeth, the short-faced bear, Arctodus simus, was larger than any living bear, even the polar bear. The Florida cave bear, Tremarctos floridanus, while smaller than Arctodus, was much larger than its living relative, the spectacled bear, a vegetarian that survives in South America.

Two medium-sized North American carnivores that went extinct in near time were the dhole (Cuon alpinus) and a short-faced skunk (Brachy-protoma). The skunk may have suffered extinction when the reduction in megafauna deprived it of sufficient carrion. The dhole, a type of wild dog, survives in Asia, where it hunts in packs. Asian dholes weigh up to 21 kilograms (about 45 pounds) and are reddish in color with black, bushy tails; in appearance they would appeal to any dog lover. They emit distinctive whistling calls to reassemble separated pack members.

Of the odd-toed ungulates (order Perissodactyla), only horses and tapirs survived into near time. New World equids declined from 12 genera over 10 million years ago (S. Webb 1984) to only three genera in near time: Equus, Hippidion, and Onohippidium. Apart from these three, American horse extinctions long predate the arrival of humans. The genus Equus remained highly variable, with many species in the Americas, until near time. The explosive spread of free-ranging horses into grasslands of both North and South America following their reintroduction by the Spanish suggests a return of the native. Tapirs, too, went extinct in the United States in the late Quaternary, having previously lived not only in Florida but also in California, Kansas, and in Arizona, from the Sono-ran lowlands to an elevation of over 6,000 feet in the Colorado Plateau. Three species of tapir survive from southern Mexico through Central and into South America, from tropical lowlands into the cold, wet, high elevations of the cordillera.

In North America the large living genera of the order Artiodactyla (the even-toed ungulates) include musk ox (Ovibos), bison (Bison), moose (Alces), wapiti or elk (Cervus), caribou (Rangifer), deer (Odocoileus), bighorn (Ovis), mountain goat (Oreamnos), and pronghorn (Antilocapra). There were twice as many species of North American artiodactyls before the extinctions of near time.

To the surprise of those who do not know the fossil record, these included three genera of camels and llamas (family Camelidae), all now extinct. Camelops was the size of a dromedary, with longer legs and steeply sloping hindquarters. There were various species of llama in the genera Paleolama and Hemiauchenia. The latter is considered more closely related to the living South American genus, Lama. Some paleontologists find it ironic that for tens of millions of years both camelids and equids evolved in North America, only to migrate into and survive in Eurasia and South America, while they vanished in near time in their evolutionary heartland (Hulbert 2001).

Two now-extinct genera of peccary (piglike animals larger than the three living species) also roamed the continental United States. Both stood about 75 centimeters (30 inches) tall at the shoulder and had downward-pointing tusks. Fossils of the long-nosed peccary, Mylohyus nasutus, are often found in caves. Its low-crowned cheek teeth suggest that it ate fruits, nuts, and succulent vegetation. Platygonus, the flat-headed peccary, with its higher-crowned teeth, probably ate more cacti and other coarse vegetation (Hulbert 2001). Represented at 116 localities east of the continental divide and one-tenth as many to the west, Platygonus compres-sus may have been the most common of the medium-sized extinct mammals. It probably lived in herds. Attaining 50 kilograms (110 pounds), the weight of an Old World boar, Platygonus was considerably heavier than the three living species, the collared and white-lipped peccaries and the relatively recently discovered Chacoan peccary, Catagonus wagneri, a rare South American species that can attain 40 kilograms (almost 90 pounds).

Extinct cervids (members of the deer family) include Cervalces, the stag moose, commonly found in eastern Quaternary faunas; Torontoceros, a recently described and poorly known deer; Bretzia, a very large deer dating from the early and evidently also the late Quaternary; and Navaho-ceros, the mountain deer, thought to be related to living Andean deer.

Extinct bovids (members of the cattle family) include the woodland musk ox, which has mistakenly been given two generic names (Booth-erium for the female, Symbos for the male; the former has priority), and the brush ox, Euceratherium. The extinct antilocaprids, Capromeryx,

Stockoceros, and Tetrameryx, all had divided (V-shaped) horns, rather than Antilocapra's pronghorn. Capromeryx and Stockoceros were also smaller than the pronghorn, an exception to the rule that smaller members of a lineage were more likely to survive extinction in near time.

The largest American rodent to go extinct in near time was the bear-sized giant beaver, Castoroides. This creature did not build dams like living beaver. It would have been a major drawing card in an imaginary pre-extinction zoo, rivaled by the similarly sized extinct capybara, Neo-choerus, found fossil in Florida. Another capybara, Hydrochoerus, persists in tropical America and is a popular "giant rodent" in zoos.

In the last four million years the North American continent north of Mexico lost 26 genera of small rodents. What is of interest for our analysis is that all of these extinctions predated the Rancholabrean and near time (Martin and Steadman 1999, table 2). Extinctions of rodent species in near time occurred on oceanic islands but rarely on the continent. Arthur Harris has described two extinct species of packrats (Neotoma), also known as wood rats, from the arid West. Ethnographic data indicate that packrats were popular prey for hunter-gatherers in much of their range. Possibly the extinction of the two species described by Harris came at the hands of prehistoric foragers.

Of the two genera of North American sirenians known north of Mexico, Trichechus, the manatee (600 kilograms, or roughly 1,300 pounds), survives in the coastal waters of Florida. In the Quaternary, Hydrodamalis stelleri, Steller's sea cow (over an order of magnitude heavier than a manatee), disappeared from the coastal waters of California and Alaska, and a related species disappeared from Japan. A population that probably did not exceed 1,000 to 2,000 animals survived in the kelp beds of the undiscovered and uninhabited Commander Islands of the northwestern Pacific. By 1768, less than 30 years after the arrival of explorers and fur traders, the genus was biologically extinct. This is the only historical extinction of a megaherbivore, apparently by overkill.*

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