The timing of Late Pleistocene mammalian extinctions in North America

QUATERNARY

RESEARCH

19, 130- 135 (1983)

SHORT The Timing

of Late Pleistocene Mammalian in North America DAVID

Department

PAPER

of Anthropology,

Extinctions

J. MELTZER

National Museum Washington,

of Natural D.C. 20560

History,

Smithsonian

Institution,

AND JIM I. MEAD Laboratory

for

Paleoenvironmental

Studies, Tucson,

Department Arizona

of Geosciences,

University

of Arizona,

85721

Received August 4, 1982 More than 375 l*C dates from 150 fossil sites in North America have been analyzed to evaluate the question of extinction of Late Pleistocene megafauna. When critically evaluated, no 14Cages for any extinct Pleistocene genera are younger than 10,000 yr B.P.

Numerous theories have been advanced to account for the Late Pleistocene extinction of some 32 genera of large herbivores and carnivores in North America. The theories can be divided into two basic types: those that attribute extinction to the agency of man (Martin, 1967, 1973, 1974), and those that attribute the process to the effects of climatic change (Guilday, 1967; Slaughter, 1967; Graham, 1979). Importantly, the foundation of each is a presumed temporal correlation. In the former instance, extinctions are thought to coincide with the arrival of man in North America, while in the latter case it is presumed that extinctions occur coincidentally with climatic changes of the late Wisconsin and early Holocene. In recent years, archaeological research on early man in the New World has questioned the apparent Late Pleistocene arrival of man (MacNeish, 1979; Bryan, 1978; Bryan ef al., 1978), an important aspect of the overkill model (Mosimann and Martin, 1975). Similarly, the timing of the Pleistocene-Holocene climatic changes, which

is the basis of both the desiccation (Guilday, 1967) and equability (Slaughter, 1967) models of extinction, has proven to be more complex than previously thought. Depending on the region, major environmental changes start well before and continue later than the stratigraphic epoch boundary separating the Pleistocene and Holocene (Wright, 1981). Lost in the debate on the antiquity of man and the end of the Pleistocene, however, is an examination of the timing of the extinction episode itself. Not since Martin (1967, 1974), and before him Hester (1960), has the radiocarbon record for the relevant mammalian taxa been systematically reviewed. This type of analysis is crucial in tracking the spatial and temporal distribution of the extinctions, in determining differences or similarities (i.e., the overall synchrony) in the extinction of the various taxa, and in providing a baseline for establishing the relation between extinctions and the theories called on to account for them. In this paper we report on our examination of the radiocarbon record for the following genera 130

0033-5894/83/010130-06$03.00/O Copyright @ 1983 by the University of Washington. All rights of reproduction in any form reserved.

NORTH AMERICAN

of large extinct North American

MAMMAL

mammals:

Acinonyx, Arctodus, Bootherium, Camelops, Capromeryx, Castoroides, Cervalces, Equus, Euceratherium, Glossotherium, Hemiauchenia, Mammut, Mammuthus, Megalonyx, Mylohyus, Nothrotheriops, Panthera, Platygonus, Sangamona, Smilodon , Stockoceros, Sym bos. and Tapirus

(terminology follows Kurttn and Anderson, 1980). Our data are derived from 23 years of the journal Radiocarbon, additional published reports, and unpublished sources where available. We collected information on site locality, material dated, potential or actual biases or contaminants in the dates, complimentary geological and pollen data, possible association with archaeological materials, and validity of the association between the material dated and the extinct genus. We have included dates on extinct faunas that purportedly range in age from 3000 yr B.P. to the earliest limits of the radiocarbon technique. The total sample amounted to 150 sites, including more than 375 separate 14C determinations. We feel that the sample includes nearly all radiocarbon-dated extinct faunas in North America, and as such is remarkably small when compared with the thousands of extinct vertebrates that have been unearthed on this continent but not dated by radiocarbon (e.g., the samples being dealt with by Dreimanis (1967, 1968) for only one taxon in a limited section of the continent). Because not all radiocarbon determinations are equally reliable (Stuckenrath, 1977), we established a rating system to evaluate all the dates (Table 1). This provided at least a partial control on the vagaries of the dating technique and yielded a set of uniformly sorted and reliable dates. To derive an individual score, the rating in category I is added to the rating in category II. The scores can range from a high of nine to a low of two. These numbers are only on an ordinal scale, and the assigned values do not imply any arithmetic relationship (e.g.. a charcoal date may or may not be twice as

131

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TABLE

1.

RATING

RADIOCARBON WITH

SYSTEM DATES EXTINCT

USED

IN ANALYZING

ASSOCIATED FAUNA

I. Material dated Derived from extinct fauna Body perishables (dung, hide, hair) Collagen Apatite Whole bone (‘bone date’) Derived from other organic material Charcoal Wood (logs, twigs, leaves) Peat Organic mud Soil Shell (freshwater/terrestrial) Terrestrial carbonate

6 5 3 3 3 -I I

II. Strength of association Strong Unknown‘or medium Weak

3 2 I

5 5 3 1

reliable as one derived from peat, but it is reasonable to assume that peat dates are about as reliable as dates derived from gyttja). Note too that a high score for a particular taxon at a site may not carry over to all the taxa represented at the site. For instance, when a 14C date is derived directly from an extinct genus (e.g., a collagen date on the bone), only that genus is given a high value in category II. Other fauna associated with that date but not dated directly are given a lesser rating. The results are summarized in graphic form in a histogram of all 14C dates, regardless of their score on the critical test (Fig. 1). There are in this sample 232 dates from the 150 sites; the initial sample of 375 dates was reduced to 232 by averaging multiple dates at individual sites where appropriate, following the criteria of Long and Rippeteau (1974). No sites or clearly erroneous dates are omitted from this figure in order to illustrate the magnitude and range of the radiocarbon record for extinct Late Pleistocene genera. The structure of this distribution, with the frequency peak occurring in the interval between 11,000 and 11,500 yr B.P., reflects the overall distribu-

132

MELTZER

Rodlocarbon

AND MEAD

yr

E P.

(X10?

FIG. 1. Distribution of 232 14C dates from 150 sites in North America. H, Dates rating 1 to 7, not a critical test. a, collagen dates rating 8, a critical test (but see text). 0, dates rating 8 or 9 on material other than collagen, most critical test.

tion of Wisconsin-age radiocarbon dates and is not indicative of any phenomena related to the extinction process. While nearly 70% of all radiocarbon dates fall between 11,000 and 14,000 yr B.P., this is largely due to sampling of the archaeological and geological records (Mead, 1981, p. 323). As is apparent from Figure 1, many radiocarbon determinations yield ages younger than the age often argued to mark the end of the megafaunal extinction episode (11,000 yr B.P.). A number of dates are scattered through the early and middle Holocene. Before any conclusions are drawn about Holocene vertebrate survivals, however, we caution that this evidence is more apparent than real. When one plots only those dates that are more likely to be reliable determinations (those with a score of eight or nine on the rating system), a different pattern emerges (Fig. 1, open squares). Nearly all of the early and middle Holocene dates from the initial sample are absent from this group. Importantly, all dates after 10,000 yr B.P. that remain in this sample are determinations run on bone collagen (Fig. 1, open squares with a central dot). In recent years it has become apparent that there are analytical and technical reasons to view collagen dates with some suspicion (Taylor, 1980). This is verified in the pattern here, with the collagen dates differing markedly from dates run on other or-

ganic materials, and with the variation apparent in multiple collagen dates run on a single bone (e.g., there are three collagen dates from Sandy, Utah run on the same bone that range in age from 5900 to 8800 yr B.P.). The youngest 14C dates by genera are listed in Table 2. There are three points to be made regarding the table. First, there is an apparent lack of synchrony in the terminal dates of the various genera. The dates range from 17,620 + 1490 - 1820 (Acinonyx from Natural Trap Cave, Wyoming) to 4885 2 160 (Mammuthus from Kassler, Colorado). However this evidence is complicated by the widely varying sample sizes and the reliability of the particular 14C determination. It would thus be premature to infer an early, full-glacial extinction for either Acinonyx or Bootherium based on only one dated occurrence each. Second, it appears that in some instances there was generic survival into the early Holocene (Camelops, Equus, Hemiauchenia), and perhaps as late as the middle Holocene (Mammut, Mammuthus, Platygonus). Yet upon closer examination this is not the case. For all the genera just listed, and for that matter for all genera postdating 10,000 yr B.P., only three (Euceratherium, Nothrotheriops, and Smilodon) have scores on our rating system of eight or better, the cutoff point for what

NORTH AMERICAN TABLE Genus

MAMMAL

2. YOUNGEST i4C DATES FOR EXTINCT GENERA FROM 150 SITES” Number of sites

Youngest 14C date

Acinon.vx

1

1

Arctodus Bootherirrm Camelops

2

12,650 ? 250 17,200 k 600 8240 t 960 10,370 + 350 11,170 2 360 10.230 t 150 10,230 + 150 8240 k 960 10,370 + 350 *8250 2 330 9880 t 270 8527 + 256 5950 t 300 *8910 +- 150 10,395 A 100 4885 2 160 *5985 2 210 10,550 2 350 9380 2 85 11,500 t 500 *9410 k 155 9840 _t 160 10,035 ” 250 10,400 + 275 10,370 t 350 4290 t 150 k12,950 k 550 *9940 t 760 “94102 155 8980 ‘- 300 11,330 2 370 11,100 2 400 9400 t 250

26

Capromeryx Castoroides Cer1~alce.s EqaUs

4 2 2 39

Eaceratheriunr Glossotherium Hemiaachenia Mammat

I 10

3 53

Mammathus

63

Megalonyx

10

Mylohvrrs Nothrotheriops

Panthera Platygonus

133

EXTINCTIONS

3 9

10

Sangamona Smilodon Stockoceros

2

S.vmbos Tapiras

9

Score

Locality* a

3 6

b d

8 7 8 8 2 k m

n 0 P q bb b! t!

u v w

4 6

aa

ClIf the rating for a particular date is under 7 then, where available, the next youngest date with a score of 8 or better is listed. If that date is based on collagen (*), then the next youngest date with a score of 8 or better and not derived from collagen is listed. See for example Mummut. Details of data in Meltzer and Mead (unpublished data). ! = possibly contaminated; ‘-‘C date not replicated. D Fossil localities and radiocarbon laboratory numbers. a Natural Trap Cave, Wyoming, DC-690 b Lubbock Lake, Texas, I-246 Big Bone Lick, Kentucky, W-1617 Whitewater Draw, Arizona, A-184~ Jaguar Cave, Idaho. No lab. number Blackwater Draw, New Mexico, A-481 Ansonia, Ohio, I-5843 Potter Creek, California UCR-381 Hornsby Spring, Florida, No lab. number Gypsum Cave, Nevada, C-222 (solid carbon) Russell Farm, Michigan, M-347 Ferguson Farm, Ontario, Canada GSC-614 m Pleasant Lake. Michigan, BETA-1388 n Kassler, Colorado. W-288

Sandy, Utah, SI-2341b P Rawhide Butte. Wyoming, A-366 9 Glynn, Georgia, UGa-79 First American Bank, Tennessee, I-6125 Aden Crater. New Mexico, Y-l 163a Rampart Cave, Arizona, L-473a, I-442 U Warren Beach, Ohio, M-1516 V Welsh Cave. Kentucky, I-2982 w Brynjulfson, Missouri, ISGS-70 X Ventana Cave, Arizona, A-1081 Y Shelter Cave, New Mexico A-1878 2 Scotts, Michigan, M-1402 aa Evansville, Indiana, W-418 bb Tule Springs, Nevada, UCLA-636 0

134

MELTZER

we consider a reliable 14C date. Of these three exceptions, the Nothrotheriops date from Aden Crater (Y-l 163a) was based on body tissue thought to have been contaminated, and the date has not been replicated. The Euceratherium and Smilodon dates are each derived from bone collagen whose reliability is, again, suspect. Finally, when one considers only those genera for which we have demonstrably reliable dates (those with a score of eight or better on our rating system) that are not derived from bone collagen (Camefops, Equus, Mammut, Mammuthus, Nothrotheriops, Panthera), a familiar pattern appears. These reliable dates, not surprisingly on genera for which we have more than a mere handful of dates, indicate that Late Pleistocene extinctions lasted no later than 10,000 yr B.P. and possibly occurred as early as 10,800 yr B.P. (with a statistical error of lo). Moreover, it appears to indicate that at least among these genera there may be an element of synchrony in the extinction process. Most genera simply do not occur with sufficient frequency that we can draw unequivocal conclusions regarding the last appearance of the taxa. Perhaps more to the point, despite an apparent synchrony of the terminal dates for which we have reliable data, it is still unknown whether the extinction process was a short-term catastrophic episode or a process that began early and lasted for a long period of time (Martin, 1967). Owing to the paucity of the radiocarbon data for the wide variety of taxa that became extinct, it thus remains impossible to determine whether the extinctions coincided with man’s appearance in North America. It is important to observe that the data we have are not a direct measure of the extinction process itself. The fact that the number of dates rises and falls in consort with geological and archaeological activities attests to that. In some sense, the radiocarbon record and the extinction process are related, since the former marks the termi-

AND

MEAD

nation of the latter. In addition, the data show that, when critically evaluated, no radiocarbon determinations for any extinct Pleistocene genera are younger than 10,000 yr B.P. This picture may well change with additional reliable dates. These genera became extinct, and they did so by the end of the Pleistocene, but the process, timing, and patterning across genera and ranges is still unknown. Additional critically analyzed 14C determinations will only refine the timing and possibly the patterning of extinctions, but cannot directly determine the process. ACKNOWLEDGMENTS This paper is an outgrowth of one delivered at a symposium organized by the authors for the 1982 Society for American Archaeology meetings. The symposium included a roundtable discussion of Late Pleistocene extinctions organized by P. S. Martin, and hosted and moderated by H. E. Wright, Jr. (many of the papers presented at the symposium, as well as a transcript of the discussion, will be included in a volume edited by the authors). We thank the participants in both instances for helping us sharpen our own thoughts on the issue. We also thank D. Fisher for providing us with the unpublished date from the Pleasant Lake mastodon. This paper has benefited from the comments and criticisms of C. V. Haynes, G. Haynes, D. W. Steadman, and D. Stanford. E. M. Mean typed the final manuscript.

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