Pre-Wisconsinan mammals from Jamaica and models of late Quaternary extinction in the greater Antilles

QUATERNARY

RESEARCH

31, %106

(1989)

Pre-Wisconsinan Mammals from Jamaica and Models of Late Quaternary Extinction in the Greater Antilles R.D.

E. MACPHEE

Department of Mammalogy, American Museum of Natural History, New York, New York 10024

DEREK C.FORD Departments of Geography and Geology, McMaster

University, Hamilton, Ontario, Canada L&S 4Rl

AND DONALD A. MCFARLANE Section of Birds and Mammals, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, California, 90007 Received March 14, 1988 The vertebrate fauna recovered from indurated conglomerates at Wallingford Roadside Cave (central Jamaica) is shown to be in excess of 100,000 yr old according to uranium series and electron spin resonance dating. The Wallingford local fauna is therefore pre-Wisconsinan in age, and Roadside Cave is now the oldest radiometrically dated locality in the West Indies containing identifiable species of land mammals. In the absence of a good radiometric record for Quatemary paleontological sites in the Caribbean, there is no satisfactory basis for determining whether most extinct Antillean mammals died out in a “blitzkrieg”-like event immediately following initial human colonization in the mid-Holocene. Fossils of Clidomys (Heptaxodontidae, Caviomorpha), the giant Wallingford rodent, have never been found in situ in sediments of demonstrably Holocene age, and its extinction may antedate the middle Holocene. This is also a possibility for the primate Xenothrix mcgregori, although its remains have been found in loose cave earth. A major, climatedriven bout of terrestrial vertebrate extinction at about 14,00&12,000 yr B.P. has been hypothesized for the West Indies by G. Pregill and S. L. Olson (Annual Review of Ecology and Systematics 12,75-98, 1981), but at present there is nothing to connect the disappearance of Clidomys with this event either. Quatemary extinctions in the Caribbean may prove to be of critical significance for evaluating the reality of New World blitzkrieg, but not until an effort is mounted to constrain them rigorously using modem radiometric approaches. 8 1989 University of Washington.

INTRODUCTION

et al., 1983; MacPhee, 1984) have demonstrated that the available hypodigm contains only one good genus with two species (Clidomys osborni and C. parvus), referable to the Antillean family Heptaxodontidae. Like most lineages in Heptaxodontidae, the Jamaican forms were exceptionally large by rodent standards (MacPhee, 1984). The size and robusticity of limb elements of C. osborni imply a body mass close to that of a small capybara (Hydrochaeris; -25-30 kg). C. parvus would have been somewhat less massive. By comparison, the largest

The first discoveries of fossil terrestrial vertebrates in Jamaica were made in 19191920 by Anthony (1920a, b), who collected and described several nominal species of large caviomorph rodents from cave sites in the central and northwestern parts of the island. The large number of species which he named (five, distributed among two families) implied that a diverse rodent fauna had once existed in Jamaica, but it is now clear that Anthony seriously oversplit his taxa. Recent systematic studies (MacPhee 94 0033-5894189 $3.00 Copyright All rights

8 1989 by the University of Washington. of reproduction in any form reserved.

PRE-WISCONSINAN

known

JAMAICAN

West Indian heptaxodontid, Aminundutu (from St. Martin and Anguilla) was literally megafaunal; according to Cope (1883), it had a body size comparable to that of the cervid Odocoileus virginiunus (50-145 kg; Nowak and Paradiso, 1983). In addition to his perceptive remarks on the morphological distinctiveness of the Jamaican heptaxodontids, Anthony (1920a, b) also commented briefly on their probable geological age. Because most of the heptaxodontid fossils which he collected in Jamaica came from indurated conglomerates lining gallery walls, he was unable to correlate them stratigraphically or temporally with anything else (e.g., cultural vs noncultural layers in loose cave earth). Nevertheless, Anthony felt certain that his big rodents were older than most of the other extinct terrestrial vertebrates previously collected in the West Indies, and he went on to state that they must have lived “in the Pleistocene, probably a matter of 100,000 years ago” (Anthony, 192Ob, p. 161). Although this is scarcely a daring estimate by modem standards, to most paleontologists in the 1920s a date of 100,ooO yr B.P. would have meant earliest Pleistocene (e.g., Keith, 1925). Unfortunately, Anthony’s finds failed to excite the interest which they deserved, and 30 yr elapsed before another major fossil-collecting expedition was mounted in Jamaica (Williams and Koopman, 1952). Anthony had no settled opinions regarding the cause or date of final disappearance of the Jamaican heptaxodontids. He thought that humans or their commensals (e.g., Ruttus) were primarily responsible for the local disappearance of the rice rat Oryzomys couesi untillurum, but “the cause of the disappearance of the older, Pleistocene [Mlammalia is not so apparent” (Anthony, 192Ob, p. 161). In Anthony’s time, the human colonization of the West Indies was believed to have been a comparatively recent occurrence, and this is still the accepted view. The Casimiroid of blyrhiza

95

MAMMALS

Hispaniola (-4500 yr B.P.) is the oldest dated culture tradition in the Greater Antilles, and the first Amerindian colonization efforts probably antedated it by only a millennium or so (Rouse and Alhrire, 1978). The points considered so far suggest that if Anthony’s age assessment for Clidomys is even approximately accurate, anthropogenie factors cannot be responsible for the disappearance of heptaxodontids in Jamaica. This contention runs counter to Martin’s (1984a, b) preliminary inferences concerning the cause of Quatemary extinctions in the West Indies: It is not clear that any of the Greater Antillean extinct endemic mammals disappeared as early as 11,000 years ago, the time of fauna1 catastrophe on the continent. At least some extinct genera survived to a later date to be incorporated in archaeological middens. Unless it can be shown that the others definitely disappeared before human arrival, most West Indian extinctions may he attributed to “blitzkrieg” or to more gradual impacts accompanying the growth of sizable prehistoric populations (Martin, 1984a, p. 393). [But blitzkrieg] can also be rejected if endemic ground sloths and giant rodents in the West Indies became extinct around 11,000 years ago, long before human invasion of the West Indies (Martin, 1984b, p. 183).

Determining how and when Clidomys disappeared may therefore have wide implications. The purpose of this paper is twofold: (1) to present radiometric dates for the first pre-Wisconsinan land mammal locality recognized in the West Indies, and (2) to assess the significance of this new information for existing models of Quaternary extinctions in this part of the Neotropics. MATERIALS

AND METHODS

Heptaxodontid fossils nave been recovered from only live sites in Jamaica (Fig. 1): Wallingford and Wallingford Roadside Caves (St. Elizabeth), Sheep Pen (Trelawney), and unlocated caves near Lluidas Vale (St. Catherine) and Molton (Manchester). Information on these sites and their vertebrate fossils was recently summarized by MacPhee (1984; see also

MACPHEE,

FORD, AND MCFARLANE

FIG. 1. Location map of localities in text. Heptaxodontid rodents have been recovered from the two major caves at Wallingford (Main and Roadside), Sheep Pen, and unlocated caves near Lluidas Vale and Molton. Long Mile and Coca Ree caves have yielded remains of endemic primates and Somerville Cave is one of the earliest dated archeological sites on the island (710 2 60 yr B.P.; AA-1793). Shaded areas mark the approximate maximum extent of marine transgression during the last interglaciation (130,000-115,000 yr B.P.).

Koopman and Williams, 1951; Williams, 1952; MacPhee et al., 1983; McFarlane and Gledhill, 1985). Wallingford Roadside Cave, the best known locality, is the source of the materials for dating described here (Fig. 2). This cave is an abandoned flood conduit for the One Eye River, the bed of which is now situated some 30 m below the cave’s entrance. Valley downcutting rates indicate that abandonment cannot have

been recent (McFarlane and Gledhill, 198% and exogenous sediments and materials have probably been accumulating in Roadside for an appreciable period. Fossils are found in two different deposits in Roadside Cave (Fig. 2a): in unconsolidated cave earth on the floor, and in a calcareous conglomerate plastered over the rear wall (“hard breccia” of Koopman and Williams, 1951). The cave earth is indis-

/

,OTlll

’

JAMWAL 3 JAMWAL

58 5

FIG. 2. Section sketch (a) and detail (b) of Wallingford Roadside Cave. Detail illustrates approximate size of remaining bone-bearing conglomerate and position of central flowstone. With the exception of 3 JAMWAL BONES, all samples listed in Table 1 came from this flowstone (or its interface with the upper conglomerate in the case of JAMWAL 3 and 3 JAMWAL 3A). Detail illustrates source of four of these samples collected by DAM in June 1985. For additional information on cave morphology, see MacPhee (1984) and McFarlane and Gledhill (1985).

PRE-WISCONSINAN

tinctly stratified. It has yielded abundant remains of post-Columbian Rattus as well as several vertebrate species probably or certainly extinct in Jamaica (Oryzomys couesi, Tonatia saurophila, and an unidentified species of Celestus). Oryzomys teeth and bone from 20-30 cm below the surface of the cave earth, collected by D. A. McFarlane (unpubl. data), have been dated at 270 + 67 yr B.P. (University of Arizona Accelerator Laboratory No. AA-1795). The calcareous conglomerate at Roadside Cave was almost entirely removed by earlier excavators, so that its original stratigraphic relationship to the cave earth is uncertain. Remnants of it preserved in crevices and sampled for this study are described in detail by MacPhee (1984). The best surviving section (Fig. 2b) comprises a bone-bearing and indurated cave earth that is separated into upper and lower units by a central layer of calcite flowstone (cave floor precipitate). The flowstone was probably discontinuous; where preserved it is 0.5-10.0 cm thick in aggregate. Contact relationships seen in laboratory specimens suggest that the calcite was precipitated upon the lower earth and that the upper earth was then laid upon it; that is, the flowstone is in correct stratigraphic position and is not a later intrusion. However, there was insufficient sample for this point to be established conclusively. By contrast, both the lower and upper earths contain many thin seams and stringers (0.1-0.3 cm) of calcite that definitely are later intrusions. The red earth is a typical karst residuum of clay and silt rich in iron and alumina. In a few spots it displays evidence of regular layering but most often lacks any structure. It is variably indurated with calcite. These features are characteristic of cave earths that have cracked due to varying compaction and subsidence, usually as a consequence of wetting and drying episodes. Snail shells and bone are abundant in both the lower and upper earths. Vertebrate remains include bones of chelonians, crocodiles, and the extant hutia Geocupromys, in addition to those of heptaxodontids

JAMAICAN

MAMMALS

97

(for the complete species list, see MacPhee. 1984). A few heptaxodontid limb bones were found in articulation, which suggests that redeposition has not been an important factor in this cave. The mix of terrestrial, amphibious, and aquatic taxa is unusual, even for a thanatocoenose. This fact, combined with the dating information supplied below, warrants recognition of the assemblage from the conglomerate as a local fauna (hereafter, Wallingford fauna). A first attempt to date the Wallingford fauna radiometrically was made using a small sample of turtle shell from the upper conglomerate that yielded associated Cfidomys remains. The apparent 14C age of the sample, 33,650 + 2550 yr B.P. (Geochron No. GX-9438, corrected), had to be based on the apatite-carbonate fraction because the shell did not contain enough dateable organic matter (MacPhee, 1984). This value is near the limit of conventional radiocarbon dating, implying that the real age of the Wallingford fauna might be significantly older. Therefore, two samples of the central flowstone were submitted to Dr. Richard Lively of the Minnesota Geological Survey to attempt uranium (U) series dating (Gascoyne et al., 1978; Ivanovich and Harmon, 1982; Schwartz and Gascoyne, 1984). His first two results, MGS 356 and MGS 357, are reported in Table 1. Replicate measurements to check these results yielded “infinite” ages (>350,000 yr B.P.), suggesting that the uranium system was open to postdepositional disturbance by later waters percolating through the conglomerate. Further dating attempts were then undertaken at the McMaster University laboratory. The results of the completed analyses are reported in Table 1. A further four analyses failed due to loss of all thorium or of all uranium during chemical separation. Speleothem calcite ages may also be estimated by the electron spin resonance (ESR) decay method (Hennig and Grtin, 1983; Griin, 1985). Although the dating principles are less reliable than those of U series, the method may be more effective

98

MACPHEE, TABLE

Lab No. JAMWAL JAMWAL JAMWAL JAMWAL JAMWAL JAMWAL JAMWAL

Description

1 IR 2 3 4 SA 5B

3 JAMWAL BONES 3 JAMWAL 3 JAMWAL MGSb 356 MGS 357

3A 5

Layered calcite Layered calcite Layered calcite Calcite stringers Nailhead calcite Layered calcite Botryoidal overgrowths Clidomys long bones Calcite stringers Layered calcite Layered calcite Layered calcite

FORD, AND MCFARLANE

1. U SERIES AGE DETERMINATIGNS~ Yield @)

U(ppm)

U

Th

0.17 0.09 0.25 0.73 0.03 0.09 0.11

28 85 42 38 8 20 37

28 56 21 56 21 22 17

0.95 0.90 0.99 1.04 0.70 1.07 0.98

0.98 0.94 1.25 0.59 5.18 0.92 0.33

79 214 84 1000 58 80 9

5.62

11

12

1.01

2.73

40

>350*

0.39 0.16 0.21 0.22

22 27 7 7

8 33 15 35

0.89 1.23 1.05 1.06

0.99 0.85 0.70 0.78

15 76 59 34

>350*d 180 2 40 129 2 12 161 2 16

Age [234UP38U] [23@Th/234Ul [23@Th/232Thl (lo3 yr B.P.) >350*’ >350* >350* 95 2 4d >350* 250 f 96 4426

LISamples collected December 1981 (RDEM) and June 1985 (DAM). b MGS, Minnesota Geological Survey; JAMWAL, McMaster Spleleothem Laboratory. ‘, *, Leached sample. d Equivalent isochron age for samples JAMWAL 3 and 3 JAMWAL 3A is 120,000 yr B.P. (slope = 0.558).

where U concentrations are very low as they were in a majority of the Roadside Cave deposits considered here. Portions of samples of the central flowstone, of calcite stringers, and of long bones prepared for U series analysis were irradiated. Internal dose rates of gamma radiation were calculated from the measured U contents. For the external (or “environmental”) rate, minimum and maximum doses of 30 and 100 mrad a-l were assumed. From these data “model age ranges” were calculated and are reported in Table 2. The central flowstone is described as “layered calcite” in Tables I and 2. The samples consisted of calcite layers no more than 0.5 to 2.0 mm thick separated by paper-thin layers of the red clay. The aggreTABLE Lab No. 3 JAMWAL BONES 3 JAMWAL 3 JAMWAL

2. ESR MGDAL

Description

3A 5

gate thickness of the calcite layers was 1.5 4 to 6.0 cm; this probably represents no more than a few thousand years of deposition. Much of the calcite displayed a sugary tex- ’ ture, suggesting that it had recrystallized. This would increase the effective porosity and thus leave the material exposed to preferential leaching of U by later percolating waters; leaching results in too great an age being determined by the 230Th:234U method. To attempt to overcome this problem and that posed by the abundance of clay, crystals were hand-separated from the least recrystallized patches and cleaned by ultrasonic sweeping and hydrogen peroxide washes. Seven completed U series analyses yielded four finite ages, ranging from 120,000 f 12,000 to 250,000 + 96,000 yr ESTIMATES

OF AGE”

U hw-4

Range of modal ages

Clidomys long bones

1.17

136-253 (k20%)

Calcite stringers Layered calcite

0.42 0.27

92-188 (k20%) 65-150 (?20%)

n Analyses by Dr. R. Grim. External gamma radiation dose estimated at 30 mrad a-* minimum, 100 mrad a-r maximum.

PRE-WISCONSINAN

JAMAICAN

B.P. One ESR measurement gave a “modal age range” of 65-150,000 yr B.P. + 20%, which is in good agreement. JAMWAL 4 was sampled from nailhead spar that grew in a vug inside the central flowstone (Fig. 2b). Its deposition represents a local prolonged wetting because it is a subaqueous precipitate. The spar appears to be very leached or derived from a leachate (23@Th:234U = 5.18) and was probably deposited during a main recrystallization episode. The calcite stringers are intrusive. Those above the central flowstone almost certainly postdate it. Two of them were analyzed. JAMWAL 3 was 1 mm thick and contained within an unusually indurated earth. The cementation appears to have protected this particular stringer from subsequent leaching because it yielded the best analytical result and most certain date in the series, 95,000 & 4000 yr B.P. There was insufficient calcite to attempt a replication. A stringer from a different sample of indurated earth was recrystallized and gave an infinite age (3 JAMWAL 3A): however, the ESR modal age range obtained from it (Table 2) is in excellent agreement with the U series age for JAMWAL 3. A U isochron method can be applied to samples contaminated with earth to obtain an approximate age (Schwartz, 1980). The isochron for the stringer samples is equivalent to an age of -120,000 yr B.P. (Table 1). No isochrons could be derived from the analytical data obtained from the central flowstone. JAMWAL 5B consisted of fine, bulbous overgrowths upon a portion of the central flowstone close to the vug (Fig. 2b). It is an evaporite deposit, representing wellaerated conditions such as the modern cave will experience. It was the only evaporitic calcite among the samples submitted to the McMaster laboratory. It was expected to represent a late stage precipitate and this was confirmed by a quite reliable determination of 44,000 + 6000 yr B.P. Three U series analyses and an ESR measurement were made upon 16 g of Cli-

99

MAMMALS

domys long bones from the upper and lower

conglomerates. The bones were very decayed. All thorium was lost during two analyses and the third yielded an infinite age. The ESR modal age range is in good agreement with all finite ages discussed above. INTERPRETATION The combined U series and ESR dates establish beyond reasonable doubt that the Wallingford fauna is older than 100,000 yr B.P. but most probably younger than 200,000 yr B.P. The central flowstone was probably deposited over a span of a few thousand years, at most, during the period 180,000-130,000 yr B.P. Using the chronology of Shackleton and Opdyke (1973) the Wallingford Roadside conglomerate and its vertebrates were deposited during oxygen isotope stage 6 and shortly thereafter, while the intercalated calcite was laid down no later than stage 5. Stage 5e is usually considered to be coterminous with the Sangamonian or last interglaciation (-130,000-115,000 yr B.P.) of the familiar glacial-interglacial succession. The minimum probable age for the Wallingford fauna may therefore be set at or near the SangamoniatV early Wisconsinan boundary as defined by Andrews and Barry (1978). DISCUSSION A great deal of attention is currently being focused on insular extinctions, particularly those which occurred during the very recent past (e.g., Olson and James, 1984; Diamond, 1984; Steadman, 1986; MacPhee, 1986; James ef al., 1987). One impetus for this high level of interest is practical: oceanic islands may be the only geographical contexts where it will be possible to test, with the necessary control and with adequate sample sizes, the validity of competing extinction models (MacPhee, 1986; Burney and MacPhee, 1988; on testing, see Grayson, 1977, 1984). Distinguishing between potential “natural” and anthropogenie factors in the post-Wisconsinan wave of extinctions in North America has proven

100

MACPHEE,

FORD,

exceptionally difficult, in part because acceptable criteria for eliminating the “wrong” set of factors in a given instance have yet to be identified [cf. divergence of views in papers collected by Martin and Klein (1984)]. By contrast, there is much less disagreement about extinctions which occurred within the last thousand years or so, since in these cases whole categories of normative “natural” causes (e.g., glaciationinduced climate changes) can be justifiably excluded from consideration. In the best documented cases of recent insular extinctions, good archeological or written records are usually available to confirm that population collapses occurred shortly subsequent to human colonization or exploitation. These may be appropriately denoted as examples of “island unequivocal examples of this blitzkrieg”; extinction process include the loss of much of the tortoise fauna in the western Indian Ocean during the 17th and 18th centuries (Stoddart and Peake, 1979; Bour, 1984) and the disappearance of numerous flightless bird species on small islands during the past 500-1000 yr (Diamond, 1984; Olson and James, 1984). However, in many other instances of apparently recent extinctions on islands, good evidence of blitzkrieg is lacking, and arguments favoring human causes tend to rely on assumed analogies with better-substantiated examples. In the past, frequent appeal has been made to analogy in discussions of Quaternary extinctions in the West Indies, because so little information exists on the precise time of their occurrence. The importance of this point can be emphasized by reference to Morgan and Woods’ (1986) recent and comprehensive assessment of late Quaternary extinctions in the Caribbean. Using what little good radiometric and archeological evidence is available, these authors show that almost 90% of the known species of Antillian nonvolant mammals became extinct in the last 20,000 yr. This raw figure is of limited value, however, because it covers essentially all of postpleniglacial time and does not reveal relationships be-

AND

MCFARLANE

tween climate change, human colonization, and extinction. In an effort to define such relationships, they divided the late Quaternary into three subperiods-“late Pleistocene” (>20,000 yr B.P. to Amerindian arrival ca. 2500 B .C .), Amerindian (ca. 2500 B.C.-1500 A.D.), and post-Columbian (1500 A.D. to present)-and then disbursed the extinct Caribbean taxa according to subperiod of probable extinction. Their tabular presentation (Morgan and Woods, 1986, pp. 202-203) contains several surprises. Of the total number of named taxa listed (72 species, of which only 9 are still extant), 28 or 39% fall into the “late Pleistocene” category, while 14 are postColumbian (19%), and only 16 are Amerindian (22%). Five others (7%) died out in the last 100 yr and are not included in the postColumbian total. Using a slightly different species count (76 taxa) and extinction schedule, they infer that a minimum of 37 species (49%) have died out since 4500 yr B.P. By either count, roughly half of the known extinctions are relegated to the period prior to human colonization, although it should be noted that the authors were attempting to be as conservative as possible. With better records, they expect to find that many, if not most, of the “late Pleistocene” extinctions will eventually fall into one of the other groupings. Interestingly, Morgan and Woods (1986) allowed that Clidomys may represent a significant counterexample, and the dates reported here may seem to confirm this. However, it is important to realize that the Wallingford Roadside dates are chronomettic point sources which establish for certain only that Clidomys was still extant approximately 100,000 yr ago. As in most paleontological situations, the actual date of final disappearance will have to be determined probablistically, from many samples drawn from many sites. Only in this way will it become possible to identify cause-effect relationships with some precision. In the meantime, one must be content with scenarios. In the case of Clidomys, it is fairly clear what implications would flow from

PRE-WISCONSINAN

sufficient proof of disappearance within one of these time spans: 140,000 to 15,000 yr B.P. New World vertebrate extinctions which occurred well before the terminal Wisconsinan would be accepted as nonanthropogenic by supporters of blitzkrieg, because they would have significantly antedated the consensus date for the peopling of North America (approximately 12,000 yr B.P.; Martin, 1984b). Using the best U series age estimates for the Roadside heptaxodontids as a terminus, the earliest that Clidomys could have disappeared is 120,000-140,000 yr ago, or roughly the interval between the latest Illinoian and the middle Sangamonian. So early a disappearance might be correlated with rising sea level during the Sangamonian (Cronin et al., 1981; Mann ef al., 1985) and consequent reduction of the land area of Jamaica (Fig. 1). In fact, MacPhee (1984) inferred from the composition of the species list for Roadside Cave that the sea might have been higher and therefore closer to the cave mouth at the time that the vertebrate remains were deposited. However, in North America the Sangamonian does not seem to have been a time of heightened extinction rates (Martin, 1984a), and in any event a + lo- to 20-m rise in sea level seems too inconsiderable to cause mammalian extinction on a large island like Jamaica. Similarly, there is no paleontological indication that the renewal of severe glacial conditions subsequent to 80,000 yr B.P. (Andrews and Barry, 1978) prompted massive fauna1 losses in the Northern Hemisphere. 14,000 to 11,000 yr B.P. Increase in the volume of continental ice during Wisconsinan time reduced sea level to - 120 m below the present level by approximately 18,000 yr B.P. (Bloom et al., 1974). During pleniglacial times, many islands and emergent banks in the West Indies would have been dramatically larger in subaerial extent than they are today (Fig. 3). In addition, they might have been quite different environmentally. Pregill and Olson (1981; Pregill, 1981) maintain that, because of reduced rainfall, or cooler temperatures, or

JAMAICAN

MAMMALS

101

both, much of the Wisconsinan land area of the West Indies would have been vegetated by arid savanna, grassland, and xeric scrub forest. As yet no detailed late Pleistocene palynological records for the central Caribbean have been published, and thus no direct evidence for this hypothesis can be offered. For corroboration, Pregill and Olson (1981) rely principally on the biogeographical observation that the patchy distributions of surviving xeric-adapted vertebrates in the West Indies are best explained as inevitable sequelae to drastic reductions in appropriate habitat. They postulate that following full glacial retreat, the onset of more humid conditions beginning about 14,000 yr B.P. permitted rapid expansion of mesic vegetation in the Caribbean. This had the ultimate effect of greatly reducing the habitats of some xerophilous species while actually promoting the extinction of others. At present, only a handful of radiocarbon dates from Antillean paleontological localities antedate the beginning of the Holocene (cf. Pregill, 1981; Morgan and Woods, 1986), and there is no conclusive evidence that any West Indian vertebrate actually suffered complete extinction in the terminal Pleistocene as defined here. Pregill (1981) cites examples of lizard species that might have become extinct in Puerto Rico approximately 13,000 yr B.P., but he also notes, as an evident paradox, that some fossil species thought to have been adapted to xeric conditions do not occur in sites in the semiarid (and therefore most Pleistocent-like) southwestern portion of the island. Another potential weakness of the Pregill-Olson hypothesis is that xeric environments in the West Indies must have been very limited in extent during the Sangamonian interglaciation, which in North America was apparently warmer (and wetter?) at some times than the present interglaciation (Adam et al., 1981). If the dryadapted fauna was already in existence at this time, as it logically must have been given the short time spans involved, where was it and what happened to it during the last interglaciation?

102

MACPHEE,

FORD, AND MCFARLANE

r land

surface

exposed

CB. 125,000

yr B.P.,

land

surface

exposed

ca. 18.000

2

PUERTO

yr S.P.

RICO

HISPANIOLA

WEST INDIES LATE PLEISTOCENE 0

200

km

L

FIG. 3. Sketchmap of the West Indies and adjacent continental areas comparing maximum and mimimum exposures of land during the late Pleistocene: sea levels set to +20 m at ca. 125,000 yr B.P. and - 120 m at ca. 18,008 yr B.P. (Mann et al., 1985), with no allowances for uplift/subsidence (base map provided by J. D. Laze11 of The Conservation Agency). Because of the amount of vertical motion experienced by Florida during the Quatemary (cf. Alt and Brooks, 1%5), coastline reconstructions are highly conjectural. In Jamaica, rising sea levels during the Sangamonian interglaciation would have had a noticeable effect on low-lying areas along the south coast, converting coastal swamps into shallow marine embayments and making islands of the Hellshire Hills and Portland Ridge (see Fig. 1). Conversely, attainment of minimum sea level during pleniglacial times would have led to progressive exposure of much of the island’s shelf. Given the direction of prevailing winds, much of this “new land” could have had a comparatively dry climate during late Wisconsinan time, although this remains to be confirmed.

In contrast to the herpetological evidence (Williams, 1969), there is no good indication that any of the extinct mammals of the West Indies were specifically adapted to savanna conditions (contra Buskirk, 1985). Although frequently described as sloths, the extinct megalony“ground” chids of Cuba, Hispaniola, and Puerto Rico are more likely to have been arboreally adapted (Webb, 1985) and therefore true forest dwellers. The primates of the West Indies are represented by very poor mate-

rial (Williams and Koopman, 1952; MacPhee and Woods, 1982; Ford, 1986), but since no living platyrrhines are adapted to savanna conditions it is hard to imagine that the Antillean ones were. Caviomorphs are more diversely adapted, but only a few (none AntilIean) can be described as opencountry dwellers (e.g., Kerodon, Dolichotis). The short limbs and robusticity of Clidomys do not preclude open-country adaptation, although living Dinomys (which heptaxodontids resemble postcranially in

PRE-WISCONSINAN

important respects) is a forest/cliff dweller (Nowak and Paradiso, 1983). Even if Jamaica and the rest of the West Indies became environmentally more diverse during the later Quatemary, this provides no good basis for inferring that Clidomys was adaptively tied to a narrow range of ecological conditions. Although direct evidence of a terminal Pleistocene event in the West Indies is still wanting, the Pregill-Olson hypothesis merits most serious consideration. The reason for this is simple: proof that a major terminal Pleistocene event occurred in the Caribbean would be a severe and possibly fatal test of blitzkrieg as a general explanation for postglacial extinction in the New World. Disappearances of numerous West Indian taxa around 11,000 yr B.P., for example, would be coeval with the “spike” evident in grouped radiometric data for sloth dung and sabertooth bones from North American sites (Meltzer and Mead, 1983; Martin, 1984b, 1987)-and would count as suggestive evidence that both the insular and mainland extinctions occurring at this time were driven by nonanthropogenie forces.
JAMAICAN

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lasted into the period during which people were expanding through the Greater Antilles, but, as it is not clear exactly where Xenothrix was found at Long Mile, this late date may be misleading. Goodfriend and Mitterer (1987) have dated bulk samples of land snails (Poteriu variuns) from Coca Ree Cave (St. Catherine), where a primate femur was recently found (Ford and Morgan, 1986). They obtained a date of 36,300 + 4300 yr B .P. for the layer in which the bone was discovered. For reasons discussed by the authors, this should be considered as a minimum age. It is not known whether this femur belongs to Xenothrix; Ford and Morgan (1986) think that it may represent a different platyrrhine species (see note added in proof). In any case, it needs to be borne in mind that Jamaican primates may have disappeared much earlier than the time implied by MacPhee’s (1984) indirect date. Whatever the facts may turn out to be for Xenothrix, is there any other indication that Clidomys survived into the modem era? The rarity of a fossil species is not logically correlated with its antiquity. However, it is pertinent to note that, by our estimate, fossil collectors have now prospected in over 100 different Jamaican caves-but with the exception of the ones listed above, none has yielded any sign of Clidomys. Finally, all Clidomys finds have been made in indurated conglomerates, with the exception of a few loose specimens at Roadside Cave that probably eroded out of matrix (MacPhee, 1984). These points are indicative rather than dispositive, but together they support Anthony’s original assessment that Clidomys osborni and C. parvus did not survive long enough to be incorporated into the recent fills that abound in caves throughout the island. This conclusion forces another, which is that at present there is no positive indication that human factors played a role in the disappearance of Clidomys or Xenothrix. While our findings do not, in themselves, amount to a sufftcient test of the blitzkrieg model as applied to the Antilles, they are a start in the right direction. What our find-

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ings do illustrate is the importance of having adequate temporal fixes on extinct faunas before reconstructing the cause of their disappearance-and on this point we are in firm agreement with Martin. CONCLUSION

Until a dense Quaternary radiometric record is assembled for extinct Antillean vertebrates, scenarios for their extinction will remain unsatisfactory. At present we can offer no persuasive support for the notion that Clidomys died out comparatively early; but by the same token, we have no indication that it survived until the midHolocene, the consensus date for initial human occupation of the Caribbean. We are intrigued by the Pregill-Olson hypothesis of coordinated but nonanthropogenic extinctions in the West Indies immediately after postglacial times, but we are bothered by its dependence on postulated environmental changes that seem insufficiently catastrophic to drive large mammals to extinction. Mammal hairs found in Paleogene Dominican amber may be the earliest physical evidence of land mammals in the West Indies (Poinar, 1988), but Wallingford Roadside Cave is now the earliest conventional paleontological locality in the insular Neotropics with a land mammal fauna. We hope that this new record will be short-lived as a result of other workers finding-and dating !- many more such localities in Jamaica and elsewhere in the Caribbean. ACKNOWLEDGMENTS Fieldwork funding for RDEM and DAM was provided by the National Science Foundation (DEB 8021735) and the Cave Research Foundation, respectively. Richard E. Gledhill and Veronica Mahanger MacPhee provided invaluable field assistance. Charles A. Woods, Veronica MacPhee, and David A. Bumey criticized an earlier version of this paper, for which we are grateful. RDEM acknowledges a debt to P. S. Martin for demonstrating to him that good thoughts about Pleistocene extinctions are dependent on good dates. We are indebted to Dr. Richard Lively, Minnesota Geological Survey, for the U series dating of MGS 356

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and 357. The speleothem dating programs at McMaster University are supported by research grants to H. P. Schwartz and to D.C.F. from the Natural Sciences and Engineering Research Council of Canada. Chemical extractions for a-counting were made by Mrs. Nicolette Caesar. ESR determinations were made by Dr. Rainer Grim during the tenure of a postdoctoral fellowship at McMaster. Dr. A. J. T. Jull (University of Arizona TAMS facility) kindly dated the bone samples reported here as AA-1793 and 1795. Note added in proof. The number of late Quatemary primate taxa from Jamaica is rising. Ford and Morgan (1988) have recently announced the discovery of a primate femur from Sheep Pen that differs in many important respects from the Coca Ree specimen (Ford and Morgan, 1986). Ford and Morgan (1988: 209) have described the Sheep Pen femur as probably being of “Middle Pleistocene” age; however, it has not yet been dated radiometrically, and no information is available as to its association (if any) with heptaxodontid remains from the same locality (Susan M. Ford, personal communication, 1988).

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