The Catastrophic Extinction of North American Mammoths and Mastodonts
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The catastrophic extinction of North American mammoths and mastodonts Gary Haynes Abstract Archaeological and theoretical evidence reviewed here indicates that Clovis-era foragers extermi- nated mammoths and mastodonts in North America around 11,000 radiocarbon years ago. The process unfolded quickly as human foragers explored and dispersed into fragmenting habitats where megamammal populations were ecologically stressed. Megamammal extinctions were eco-catastro- phes with major ripple effects on oral and faunal communities. Keywords Mammoth; mastodont; extinction; Palaeoindian; North America; patch choice. Introduction Mammoths and mastodonts became extinct in North America soon after 11,000 radio- carbon years before present (RCYBP) (Taylor et al. 1996; Martin and Stuart 1995; Stuart 1991). Thirty-three genera of large mammals (body mass over 44 kg) died out around the same time (Martin and Klein 1984). Distinctive Clovis uted projectile points (Plate 1) also appeared then (see the papers in Bonnichsen and Turnmire 1991). Prehistorians such as C. V. Haynes, Jr. [who is not related to me] have proposed that uted point assem- blages represent North America’s earliest archaeological culture because they are the oldest found at virtually every site, locale or subregion where they have been dated. The exceptions are few, such as in Alaska’s Tanana river valley sites (Hamilton and Goebel 1999) or in scattered locales such as Cactus Hill, Virginia (McAvoy and McAvoy 1997) and Meadowcroft Rockshelter, Pennsylvania (Adovasio et al. 1999). But examples of pre- uted-point components are extremely rare (Fiedel 2000). The people who made the Clovis-type uted points are incontestably the rst to arrive in most parts of late Pleisto- cene North America, and therefore are closely linked chronologically with the disap- pearance of mammoths and mastodonts. World Archaeology Vol. 33(3): 391–416 Ancient Ecodisasters © 2002 Taylor & Francis Ltd ISSN 0043-8243 print/1470-1375 online DOI: 10.1080/0043824012010744 0 392 Gary Haynes Plate 1 Fluted point (cast) from the Vail site in Maine. Fluted points compared over space and time may differ in morphology and manufacturing techniques. We know that human hunting can limit or exterminate ungulates with or without climate stress (Alroy 2000; Kay 1994, 1995; Martin 1967, 1982, 1984, 1990; Martin and Steadman 1999; Mithen 1993; Stuart 1999). If the rst settlers in North America targeted large mammals as preferred prey, their opportunistic foraging (Kelly and Todd 1988; Meltzer 1993: 305) may have eradicated mammoth and mastodont populations that had survived earlier cycles of ecological stress during rapid climatic oscillations (Alroy 1999; Martin and Steadman 1999). The removal of mammoths and mastodonts from the New World was an eco- catastrophe that happened swiftly and unexpectedly. Fossils of large mammals show no evidence of climate-caused chronic ill-health or increased vulnerability just before they disappeared (see, for example, Fisher (1996) for information about mastodonts and Duckler and van Valkenburgh (1998) for information about predators). The large mammals – including mammoths and mastodonts – were exterminated so quickly that the geological record provides no direct clues about how it happened. The disappearance of America’s largest forms of animal life would have been a memo- rable event for humans to experience. As well, the disappearance of animals large enough to be true ‘ecosystem engineers’ (see Owen-Smith 1987, 1988, 1999) would have had profound effects on North American ecosystems. Owen-Smith (1987, 1999: 67) has argued that the extinction of megamammals – the animals weighing over 1,000 kg – transformed a minor extinction pulse affected by climate change into a major extinction cascade, because mammoths and mastodonts were ‘keystone’ species that had greatly raised diver- sity at the patch level. With the megamammals gone, natural processes such as woody regeneration and shrub invasions of grassy glades progressed unimpeded, thus reducing carrying capacity for nonmigratory grazers. Zimov et al. (1995) presented a simulation model showing that the removal of Beringia’s megafauna by human overhunting was as important as climate in shifting the vegetation from highly productive, grass-dominated steppe to poorly productive moss- tundra. Large herbivore feeding has major effects on ecosystems and is known to increase primary productivity in African grassland savanna (Bell 1971), an effect also postulated for California grasslands (Edwards 1992). The process of biome shift due to herbivore Catastrophic extinction of mammoths and mastodonts 393 feeding is now being observed in Yakutia, where large grazers were recently re-introduced into tundra-taiga habitats that may be transformed to steppe in the future (Stone 1998; Zimov et al. 1995: 782–3). lf human foragers did wipe out mammoths and mastodonts in North America and indi- rectly caused the extinctions of other animal species, can we ever discover why and how they managed to do it? My explanation of the process is founded on three propositions: (1) the timing and direction of climate-caused habitat changes were not coupled with extinctions; (2) megamammals were demonstrably killed by human hunters in North America; (3) late Pleistocene foraging in mammoth and mastodont ranges was an optimal strategy for opportunistic hunter-gatherers. These will now be discussed. Climate-caused changes in habitat were not coupled with extinctions At the end of the Pleistocene, severe climate reversals occurred out of phase with the extinction event. The Younger Dryas chronozone – a northern hemisphere geological interval of cold that had abruptly reversed warm and wet conditions beginning around 11,000 RCYBP and ending nearly a millennium later (duration and timing are problemati- cal in different world areas (Rutter et al. 2000)) – is sometimes thought to have been the last straw for larger mammals, killing them off completely after they had suffered through several cold to warm reversals following the last Glacial Maximum. Yet the current best-guess chronosequence of events during the glacial to deglacial tran- sition (for example, Fiedel 1999: 106, g. 6) does not support this scenario of extinction based solely on climate. The earliest appearance of foragers who made Clovis uted points was about 11,500 RCYBP (Fig. 1). Some large mammals may have become extinct around 11,200 RCYBP, followed by a near-continental drought beginning 10,900 RCYBP, and the extinctions of all large fauna including mammoths and mastodonts by around 10,800 RCYBP (Graham et al. 1997; Stafford et al. 1997a, 1997b; Holliday 2000; Haynes, C. V. 1991). The Younger Dryas reversal to cold conditions may not have occurred every- where, and, where it did occur, it followed some extinctions but preceded mammoth and mastodont extinction. In southern South America there may have been no Younger Dryas at all (Bennett et al. 2000; Rodbell 2000), and thus the New World pattern of extinctions is not a direct result of the abrupt onset or end of the Younger Dryas. It is worth noting again that megafauna such as ground sloths, horses, camels, mammoths and mastodonts had universally survived earlier abrupt climate reversals. No clear model can explain how the extinction process tracked changes in climate and habitat at the end of the Pleistocene (see Krech 1999: 38–40 for a précis of the ambigu- ity). But the extinctions do seem to be synchronous with the existence of human foragers who dispersed through the continent within a few centuries of rst appearing. The Clovis foraging strategy involved killing megamammals The makers of Clovis-like uted points were present over almost all of North America south of the last glacial ice-fronts, between around 11,500 and 10,500 years ago (Table 1). 14C years B.P. Climate Chronozone or Faunal Event Cultural Event Event 19,500-16,100 Very cold, dry Last Glacial (No extinctions) (Archaeological Maximum remains rare to nonexistent anywhere in continent) 13,000 Warm Bølling (No extinctions) (Archaeological remains rare to nonexistent anywhere in continent) 12,000 Warm Allerød (No extinctions) (Archaeological remains rare to nonexistent anywhere in continent) 11,500 Cold Intra-Allerød (No extinctions) Earliest Clovis cold period radiocarbon dates, very restricted range 11,200 Warm (Unnamed Some large-mammal Clovis present in wide warm interval) extinctions area 10,900 Cold, drier Younger Dryas Clovis becoming locally begins abruptly more variable 10,800 Cold continues All megafauna Clovis-like materials extinctions complete, distributed continent- including mammoths wide and mastodonts 10,200 Warm, wetter Younger Dryas Fluted points no longer ends abruptly made Figure 1 Correlation of climate changes, hypothesized extinction events and culture in North America. Catastrophic extinction of mammoths and mastodonts 395 A small but inuential literature has argued that Clovis uted point makers were big-game hunters, directly descended (biologically and culturally) from Eurasian Upper Palae- olithic steppe explorers (see, for example, Haynes, C. V. 1987). Scholars who accept this probable connection nevertheless recognize that smaller game and plant resources also would have been eaten (Jennings 1989; Willey 1966). On the other side of the debate are arguments that only plants and small animals were regularly targeted as food, in direct proportion to their existence in Clovis-era habitats (Dent 1995; Dincauze 1993: 285; Meltzer 1993; Meltzer and Smith 1986).