Late quaternary land snails from the north coast of Jamaica: Local extinctions and climatic change

Palaeogeography, Palaeoclimatology, Palaeoecology, 63 (1988): 293 311 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

293

LATE QUATERNARY LAND SNAILS FROM THE NORTH COAST OF JAMAICA: LOCAL EXTINCTIONS AND CLIMATIC CHANGE G L E N N A. G O O D F R I E N D 1 a n d R I C H A R D M. M I T T E R E R 2 1Isotope Department, Weizmann Institute of Science, 76100 Rehovot (Israel) 2Geosciences Program, University of Texas at Dallas, Richardson, TX 75083-0688 (U.S.A.) (Received February 23, 1987; revised and accepted June 15, 1987)

Abstract Goodfriend, G. A. and Mitterer, R. M., 1988. Late Quaternary land snails from the north coast of Jamaica: local extinctions and climatic change. Palaeogeogr, Palaeoclimatol., Palaeoecol., 63: 293-311. Analysis of the land snail faunas and chronology (14C and amino acid epimer ratios) of six late Quaternary deposits from a site on the north coast of Jamaica provides a basis for reconstruction of local extinction events and their relation to paleoclimate. Paleotemperature estimates are derived from epimerization rates at an interior site and indicate an average Holocene-late last glacial temperature difference of c. 4-5°C. Size variation in land snails indicates relatively dry conditions during the late last glacial and moist conditions in the late Holocene, followed by drier conditions beginning sometime during the last millennium. The rich faunas of the latter half of the last glacial are represented today at the same site by only a relatively few remnant species. Two major periods of extinction are identified. During latest last glacial to early Holocene time, a number of species became locally extinct, probably due to increased temperatures; many survive today in the cooler interior of the island. Extensive extinctions occurred again during the last millennium. These apparently resulted largely from habitat disturbance by man. A similar pattern of late Holocene extinctions has also been documented for vertebrates on other tropical islands and is also thought to result from human disturbance.

Introduction Tropical islands have experienced extensive e x t i n c t i o n s s i n c e t h e P l e i s t o c e n e . T h i s phen o m e n o n h a s b e e n s t u d i e d m o s t l y in v e r t e b r a t e s (e.g., P r e g i l l a n d Olson, 1981; O l s o n a n d J a m e s , 1982; S t e a d m a n et al., 1984; S t e a d m a n a n d Olson, 1985; M a c P h e e , 1986; P r e g i l l , 1986) b u t l a n d s n a i l s h a v e a l s o b e e n s t u d i e d (Christ e n s e n a n d K i r c h , 1986). In t h e W e s t I n d i e s , m a n y of t h e e x t i n c t v e r t e b r a t e s p e c i e s a r e t h o u g h t to h a v e o c c u p i e d r e l a t i v e l y d r y habitats and their extinctions have been hypothesized to r e s u l t from i n c r e a s e d m o i s t u r e d u r i n g t h e H o l o c e n e , w h i c h r e d u c e d t h e e x t e n t of s u i t a b l e h a b i t a t s for t h e s e s p e c i e s ( P r e g i l l a n d Olson, 1981). H o w e v e r , s i n c e t h e n , d a t i n g of 0031-0182/88/$03.50

d e p o s i t s from A n t i g u a i n d i c a t e s t h a t v e r t e b r a t e e x t i n c t i o n s o c c u r r e d t h e r e v e r y l a t e in the Holocene, and thus suggest a human cause for t h i s case ( S t e a d m a n et al,, 1984). S i m i l a r late Holocene vertebrate extinctions have also o c c u r r e d in t h e H a w a i i a n I s l a n d s ( O l s o n a n d J a m e s , 1982), a n d M a d a g a s c a r ( M a c P h e e , 1986). The late Q u a t e r n a r y land snail deposits c o n s i d e r e d here, from G r e e n G r o t t o C a v e on t h e n o r t h c o a s t of J a m a i c a , c o n t a i n a l a r g e n u m b e r of s p e c i e s w h i c h no l o n g e r e x i s t at t h e site or in t h e a r e a t o d a y . A l t h o u g h t h e s e e x t i n c t i o n s a r e of a l o c a l n a t u r e , t h e y m a y r e l a t e to t h e s a m e p r o c e s s e s p r o d u c i n g e x t i n c t i o n s of v e r t e b r a t e species. T h e c h r o n o l o g y of t h e l a n d s n a i l s p e c i e s a t G r e e n G r o t t o a n d its

:'c~1988 Elsevier Science Publishers B.V.

294 r e l a t i o n to p a l e o c l i m a t e is e x a m i n e d in this study. The land snail f a u n a of the island of J a m a i c a is quite r e m a r k a b l e in several respects: its v e r y high diversity (some 400-450 species), its p r o n o u n c e d endemism (c. 95% of the species

o c c u r only in J a m a i c a ) , and the s t r o n g l y r e g i o n a l c h a r a c t e r of the f a u n a s of different parts of the island (Jarvis, 1902, 1903; J a r v i s in Pilsbry, 1903; Paul, 1982; Goodfriend, 1986a, b; Goodfriend and M i t t e r e r , submitted). The n o r t h - c e n t r a l coast is typical with r e g a r d to

Fig. 1. Photographs of land snail shells. A. Pleurodonte lucerna, deposit $4. B. Pleurodonte sublucerna, $4. C. Apoma gracilis, $4 (note secondary deposits). D. Colobostylus albus, in matrix, B2. E. Colobostylus albus, with heavy secondary deposits, $4. F. Colobostylus albus, with very light secondary deposits, $4. G. Alcadia major, B1. H. Modern specimen of Alcadia major from the interior of Jamaica. I. Eutrochatella pulchella, $4. J. Eutrochatella costata, $4.

295 30 I

40 I

" r

i

50

77°W I

___

•

....... .--* .... V ~

--

'

'

"

u

Fig.2. Distribution of Eutrochatella costata and E. pulchella in the north-central region of Jamaica. E. pulchella occurs over most of the island. Mean annual rainfall isohyets (in mm/yr)are shown. See legend for Fig.3. GGC = Green Grotto Cave. CC = Cockpit Country. Parish abbreviations: S J = St. James; T R = Trelawny; S N = St. Ann; S M = St. Mary.

this last aspect, having a number of endemic species. The regions of endemism tend to correspond to different climatic regions: the dry and warm central north coast (1000-1500 mm mean annual rainfall; Jamaican Meteorological Service, unpublished ms) (Fig.2), the moister eastern north coast (1800-2000 mm/yr), the moist and cool north-central interior plateau (1300-2300 mm/yr), and the wet and cool Cockpit Country (1500-3000 mm/yr). Very little information is presently available concerning changes in the composition of land snail faunas in West Indian low,land areas during the Quaternary. A single, still extant species of land snail was reported from Quaternary deposits in the Bahamas (Garret and Gould, 1984) and from Curacao (Gould, 1971). From Cuba, two species are known from undated Pleistocene deposits (Richards, 1935) and undated, probably late Holocene deposits have been described from the Havana area (Aguayo and Jaume, 1939). No Quaternary lowland deposits have been described from Jamaica, but two rich faunas are known from the interior plateau of the island (Goodfriend, 1986a; Goodfriend and Mitterer, submitted). Six deposits were collected from around and in Green Grotto Cave, east of Discovery Bay, St. Ann, Jamaica (Jamaican grid coordinates 420,566; elevation 15 m). The cave is developed within the Hope Gate Formation, an interglacial reef terrace of dolomitized limestone (Cant, 1972). Five of the deposits came from

small solution holes in the limestone, exposed by blasting activity in 1975-1976. The sixth came from the floor of an entrance chamber of the cave. In two samples, the soil matrix is indurated with calcite to form a shell breccia, whereas the other deposits consist of friable or weakly indurated sediments. The snails in the deposits are derived from the forest growing on the hill in which the cave is developed. None of the species is an inhabitant of caves, although Jamaican caves are occasionally inhabited by introduced species or species that occur in highly disturbed habitats. Dating of cave deposits is problematic due to the frequent occurrence of mixed-age deposits (Goodfriend and Mitterer, submitted). Furthermore, the amount of material available is often not sufficient for conventional ~4C dating. In order to get around these problems, an integrated approach was used which combines 14C and amino acid epimer (alloisoleucine/isoleucine; hereafter, A / I ) dating. Radiocarbon analysis was performed on land snail shells in a deposit in which a sufficient number of large shells was available. This sample served as a time calibration for A / I ratios measured in other shells. A major advantage of the amino acid analyses is that individual shells can be analyzed, so that the chronology of species within a mixed-age deposit can be unscrambled. A / I is a good predictor of age in fossil land snails (Goodfriend, 1987d; Goodfriend and Mitterer, submitted).

296 Paleoclimatic information was obtained from shell size, which relates to rainfall (Goodfriend, 1986c; Goodfriend, 1987b); from the timing of karst development, as indicated by the age distribution of the deposits; and from variations in amino acid epimerization rates, which are a function of temperature history (Schroeder and Bada, 1973). Methods and materials Samples of the two breccias were removed from the field by a hammer and chisel. In the laboratory they were broken apart to remove the embedded land snail shells. Samples of the three solution hole fills with unconsolidated sediments were removed and sorted in the laboratory. Representative shell material of the cave chamber deposit was selected in the field; a sample of sediments was also collected and sorted in the laboratory. Before analysis for dating, thorough removal of secondary carbonate deposits was carried out (Goodfriend, 1987c). A sample of Pleurodonte lucerna shells from breccia B2 was analyzed for 14C at the Weizmann Institute of Science Radiocarbon Laboratory. Amino acid epimer ratio analyses were mostly carried out by RMM [see Hare (1969) for methodology] but some were also carried out by GAG and by Prof. Y. Borstein (WIS), for several very small samples. The uncertainty of the A/I ratios averages _ 0.01. A variety of species, belonging to different genera and families, was analyzed. Land snail shell carbonate from limestone areas shows age anomalies, due to incorporation into the shell of carbon derived from ingested limestone (Goodfriend and Stipp, 1983). Consequently, 14C dates must be corrected for this factor. In Jamaican snails, this age anomaly averages 1800 yr but is quite variable ( _ 1180 yr standard deviation) (Goodfriend, 1987a). However, live-collected specimens of Pleurodonte lucerna (the fossil species that was dated) from the forest at Green Grotto Cave showed an age anomaly of only 500 yr (Goodfriend and Stipp, 1983). Since the causes of variability of age anomalies of Jamaican

snails are not understood (e.g., whether it is site-specific), an intermediate figure of 1000 yr was selected as the best estimate of the age anomaly. This amount was therefore subtracted from the age reported by the laboratory. The uncertainty of the age anomaly adds to the uncertainty of the estimated age of the fossils but only by a small amount in this case, since the error of measurement of the apparent age of the fossils greatly exceeds the uncertainty of the age anomaly. The date reported here has been corrected for the age anomaly and for fractionation (Goodfriend, 1987a) and the reported error includes the uncertainty of the age anomaly correction. Size variation was studied in both fossil and, for comparison, modern specimens of two species (Pleurodonte lucerna and Alcadia major). Both species reach a final adult size (characterized by the flaring out of the lip of the shell; Fig.lA, H), which facilitates size comparisons among samples. Shell diameter was measured from the point behind the lip where the lip first begins to flare. Measurements to the nearest 0.1 mm were made by a dial caliper. The living land snail fauna at the site was sampled during numerous visits at different times of the year and included a nocturnal visit under wet conditions (when most species are active). The modern distributions of the species occurring in the fossil deposits were based primarily on the collections of G.A.G. (c. 550 stations in Jamaica) but also on the collections at the Florida State Museum at the University of Florida, the collection of Dr. C. R. C. Paul (University of Liverpool), and literature records in Baker (1934a, b) and Pilsbry and Brown (1911). Locations are cited in Jamaican grid coordinates. Description o f deposits B designates breccia samples (indurated matrix) and S designates samples from weakly or non-indurated sediments. BI: Sediments reddish-tan, with inclusions of a few red soil peds; matrix well indurated, very

297

hard; abundant shells; fill of solution fissure; collected 17 Dec., 1981. Illustrated in lower left corner of cover photo of Geology, 11(9) (Sept., 1983) - - Sagda montegoensis in matrix. B2: Sediments tan, moderately indurated but locally slightly crumbly, with numerous voids between shells; shells account for c. 50~o of the volume; rounded mass, c. 70 x 60 × 50 cm, which fell out of blasted cliff, and was later brought to the Rose Hill Estate; collected 9 Oct., 1983. See Fig.lD. $1: Matrix of peddy red bauxitic soil, generally friable but locally indurated; shells mostly heavily coated; fill of solution hole; collected 17 Dec., 1981. $2: Matrix of red-brown bauxitic soil, with smaller, weaker peds than $1, mostly friable but with a small amount of local induration; shells mostly heavily coated; fill of solution hole; collected 17 Dec., 1981. $3: Matrix of red-brown, peddy bauxitic soil; matrix completely friable; partially fills solution hole; shells mostly not coated or weakly coated; collected 9 Oct., 1983. $4: Sediments tan, peddy to finely-textured, friable, 3 4cm deep; shells collected nonquantitatively from on and in sediments; most shells not coated or weakly coated but some moderately heavily coated; collected from floor

of entrance chamber of cave, c. 15 m inside SE entrance; collected 9 Oct., 1983.

Dating of the deposits Within each of the six deposits, there is a considerable range of A/I values (Table I). This indicates that each contains to some degree a mixture of shells of different ages (Goodfriend, 1987c). Deposits B1, B2, and $3 show the most uniform A/I values (SD is _ 0.04) and are thus of more uniform age. A radiocarbon date of 30,400_+2580 yr B.P. was obtained from a sample of Pleurodonte lucerna shells from B2 (Table I). Sufficient material for 14C analysis of deposits B1, S1, and $2 was not available. The abundant shells in $3 and $4 were not analyzed for 14C because their low A/I values indicate late Holocene ages. In such material, the uncertainty in the true 14C age is quite large, due to the uncertainty of the age anomaly correction. In this case, more precise age estimates can be obtained from the A/I ratios. From the radiocarbon date and the associated mean A/I ratio of shells from B2 (several species), it is possible to estimate the mean ages of the other deposits from their mean A/I ratios, assuming that the epimerization rate

TABLEI Chronology of deposits at Green G r o t t o Cave, based on 1"C a n a l y s i s and alloisoleucine/isoleucine ratios (mean, s t a n d a r d error, s t a n d a r d deviation, and range), with estimates of m e a n ages based on m e a n A/I ratios Deposit

Alloisoleucine/isoleucine :~+_ SE

SD

Range

0.61 +_0.02 0.51 + 0.02

0.04 0.04

0.54-0.65 0.45-0.58

4 5

0.08 0.16 0.039 0.107

0.26-0.42 0.21-0.52 0-0.10 0 0.37

4 4 24 36

14C age (yr B.P.)

Est. m e a n age (yr B.P.)

-30,400 + 2580 (RT-674)

41,000 --

-----

16,000 19,000 1400 --

N

Breccias B1 B2

Unconsolidated sediments $1 $2 $3 $4

0.36 + 0.04 0.39 + 0.08 0.034 _ 0.008 0.103 + 0.018

298

Epimerization rates at Coco Ree

constant did not change over time. However, because Holocene temperatures were on average warmer th an late last glacial temperatures, shells y o unger t han the calibration sample would have experienced higher average temperatures th an the calibration sample, whereas shells older than the calibration sample would have experienced lower average temperatures. Consequently, the ages of younger samples would be overestimated and the ages of older samples underestimated. To circumvent this problem, different epimerization rate constants for the Holocene and for the late last glacial at Green Grotto were estimated based on data from snails from a cave at Coco Ree in the interior of J a m ai ca (Goodfriend and Mitterer, submitted). The Coco Ree radiocarbon dates of 13,400 yr B.P. and 30,100 y r B.P. and the associated A / I values were used to calculate epimerization rate constants between 0 and 13,400 yr B.P. (taken to represent Holocene) and between 13,400 and 30,100 yr B.P. (taken to represent late last glacial). From these rates and the difference in temperatures between the sites, the rate constants for the corresponding periods at Green Grotto can be calculated. This temperature difference was assumed to be constant over time and was estimated from the epimerization rates themselves, for the period 0-30,000 yr B.P., for which radiocarbon dates and associated mean A / I values were conveniently available from both sites. Details of these procedures and the results follow.

Table II gives the 14C dates and associated

A / I ratios for two Coco Ree samples, t a k e n from Goodfriend and Mi t t erer (submitted). The rate constants (k) were calculated according to the formula of Mitterer (1975), but with the integration constant taken as 0 (since values of A/I=O were measured in the youngest samples): k = 0.565 In \0.565 - At

t

(1)

where A, = A/(A + 1) = (A/I)/(1 + All) of a sample with age t. From the two ~4C dates, rates were calculated for the periods 0-13,400 yr B.P. and 0-30,000 yr B.P. (Table II). The rate constant for 13,400-30,000 yr B.P. was calculated from the corresponding ~4C dates and A / I ratios from the formula: rln~ 0.565 k = 0.565 [_ \~}.5~-~4,1- ] 0.565

- ln(o.5~-~--A,2)]/(tl - t2) (2) where tl and t2 refer to the two sample ages.

Temperature difference between sites The epimerization rate constant for Green Grotto for 0-30,000 yr B.P. (Table II) was calculated from the data in Table I, using Eq. 1. The average temperature difference between

TABLEII Alloisoleucine]isoleucineepimerization rate constants (k) for land snails in deposits at Coco Ree and Green Grotto, for different periods Time period (yr B.P.) 0-30,000 0-13,400 13,400-30,000

Coco Ree

Green Grotto

mean A]I

'4C age

k ( x 10-s)

mean A/I

14C age

k ( x 10- s)

0.25 0.16 --

30,100 13,400 --

0.82 1.18 0.53"

0.51 0.33a --

30,400 ---

1.70 2.44" 1.09a

"Calculated from other data in table; see text.

299

the sites was then calculated using the following formula: T 1 - T 2 = A T - RT1T2 In (k2/kl) 1

Eo

(3)

where T is the average sample temperature (in oK), R is the gas constant (=1.987×10 -3 kcal/deg mol), E a is the Arrhenius activation energy (taken as 29 kcal/mol; Mitterer, 1975), and subscripts 1 and 2 refer to the two samples. This equation cannot be solved explicitly. However, as pointed out by Schroeder and Bada (1973), the calculation of A T is relatively insensitive to the absolute temperature values substituted into the right side of the equation. It is convenient to use the present measured temperature of the deposit (21.5°C=294.7°K) for both T 1 and T 2 on the right side, calculate AT, then estimate T 2 again as T 1 - A T , and recalculate the new AT. A temperature difference of 4.2°C is thus calculated between Green Grotto and Coco Ree for the period 0-30,000 yr B.P. This is somewhat higher than the estimated temperature difference between the sites based on meteorological data. For Coco Ree (elevation 410 m), the temperature would be slightly lower than the nearby Worthy Park station (50 m elevation below Coco Ree), which has a mean annual air temperature of 22.5°C (slightly warmer than the measured soil temperature in the cave). For Green Grotto, the nearest north coast station is Montego Bay, with a mean annual temperature of 25.4°C (Jamaican Meterological Service, 1973). Thus the calculated temperature difference based on meteorological data (2.9°C) is a little smaller than the 4.2°C difference estimated from A / I values of the Pleistocene samples. The slightly greater temperature difference based on the amino acid data may be the result of higher temperatures within the cave at Green Grotto (due to the presence of numerous bats) or may reflect a higher adiabatic cooling rate during ~This equation is modified from Eq. 3 of Schroeder and Bada (1973), in which "ln" was written instead of "log"; we use the In form here and therefore omit the factor (2.303) which converts In to log.

glacial times due to drier air. Or the apparent difference may be simply a result of the uncertainty of the estimate, which results from the uncertainties of the estimates of 14C ages and mean A / I ratios.

Estimation of epimerization rates at Green Grotto

From the calculated value of AT (between sites) and the calculated epimerization rate constants at Coco Ree, the epimerization rate constants at Green Grotto for the periods 0-13,400 and 13,400-30,000 yr B.P. were calculated, using Eq. 3 (Table II). Based on these estimates of k, equations for calculating the mean ages (t) of the deposits lacking 14C dates were obtained. For 0-13,400 yr B.P., substitution into Eq. 1, rearrangement, and simplification gives 0.565 ) t = 2.320 x 104 In \0.565 - A t

(4)

From this, a value of 0.33 is calculated for the expected A / I at Green Grotto for 13,400 yr B.P. (Table II). For the period 13,400-30,000 yr B.P., substitution into Eq. 2, rearrangement, and simplification gives t = 5.208 x 104 [ l n ( \0.5650"565At) - 0"584] + 13'400

(5) This equation is used also to extrapolate the age of the sample with higher A / I than the calibration sample. From Eq. 5 and the mean A / I values of the older deposits, the following mean ages were calculated: 16,000 yr B.P. for S1, 19,000 yr B.P. for $2, and 41,000 yr B.P. for B1 (Table I). From Eq. 4, the mean age of $3 is calculated at 1400 yr B.P. No calculation is made for the mixedage deposit $4. But as a point of reference for A / I values of individual shells (presented below), the expected A / I ratio at the Pleistocene-Holocene transition (taken as 10,000 yr B.P.) is calculated as 0.24 from Eq. 4. For A / I

300

ratios less than or equal to this value, A/I is nearly linear with respect to time. In general, it can be seen that there is a correlation between the amount of secondary carbonate deposition on the shells or in the matrix and the age of the deposit, as determined by A/I ratios. The two breccias show the greatest ages, with the more indurated of the two (B1) being older. Also of last glacial age but younger than the two breccias are samples S1 and $2, in which the shells have heavy secondary carbonate deposits. The Holocene $3 and mostly Holocene $4 samples show generally lighter, but variable, secondary deposits. In order to see if the amount of secondary deposits on shells in these samples might be able to be used as an approximate indicator of age, amino acid analyses were carried out on shells of Colobostylus albus having varying amounts of secondary deposits. The secondary deposits on the shells were subjectively classified as light ( < 5% of surface) or moderate to heavy (>5%). It was found (Table III) that shell with heavier deposits had higher A/I ratios. For the shells with moderate to heavy secondary deposits, A/I ratios indicate a range of latest last glacial (0.27-0.37) to middle-late Holocene ages (0.08-0.09, or c. 3000 yr B.P.), whereas the shells with light secondary deposits are all of late Holocene age (A/I< 0.10). No difference in A/I ratios of shells with similar amounts of secondary deposits is seen between samples $3 and $4. Thus, for the Green Grotto deposits, the amount of deposition of secondary carbonates can be taken as

an approximate indication of age. This relationship is particularly useful for dating individual shells too small for amino acid analysis (< c. 15 mg). The presence of predated shells of Poteria in deposits $3 and $4 may also be used as an indicator of age. The shells appear to have been eaten by rodents: the periphery of the shell has been chewed away along all or most of the last whorl. No such shells occur in the four late last glacial deposits. Amino acid epimer ratios of these predated shells (two specimens in $3, both with A/I=O) is consistent with rats being the source of predation, as these were introduced by the Spanish in the 16th century. The land snail faunas -- general patterns

A total of 36 species was found in the deposits (Table IV). Of these, only 12 are presently living at the site (Table IV). Only two species presently living at the site (Stauroglypta spreta and Varicella sp.) are not represented in any of the deposits. The former species appears to represent a very recent introduction; nothing can be said of the latter unidentified species, represented by a single freshly-dead specimen. All of the other species living at the site occur in Pleistocene deposits (B1, B2, S1, and/or $2), except for Brachypodella robertsi. This is a rare species (found alive at the site only once) which occurs as only a single specimen in $3. Therefore its absence from Pleistocene deposits cannot be taken to indicate that it was not present at the site

TABLE III Alloisoleucine/isoleucine values of individual Colobostylus albus shells (from deposits $3 and $4) with light and with moderate to heavy secondary carbonate deposits on shell Deposit

Light secondary deposits

Moderate-heavy secondary deposits

$3 $4 both: mean range N

0.03, 0.05, 0.05, 0.05, 0.10 0.03, 0.05, 0.06, 0.06, 0.09 0.06 0.03-0.10 10

0.09, 0.16 0.08, 0.15, 0.18, 0.27, 0.33, 0.36, 0.37 0.22 0.08-0.37 9

301 TABLE IV Land snails in six fossil deposits and species living at the site today (marked w i t h X). N indicates the presence of > 10 specimens Species

Living at site

Deposit 83

$4 a

$2

$1

B2

1

5

B1

Helicinidae

Alcadia brownei (Gray) Alcadia major (Gray) Eutrochatella costata (Sow.) Eutrochatella pulcheUa (Gray) Fadyenia fadyeniana (C.B. Ads.) Helicina aurantia Gray Helicina neritella Lam. Lucidella aureola (F~r.) Lucidella persculpta Pils. and B r o w n

--

/1

1

--

N

N/N

N

N

9

--

--

/3

4

--

5

--

-8/1 -4/1 2/

4 5 -3 6

2 --N 2

--2 --

------

N

N/9

4

N

N

N 1

N/N --

N 3

N 5

N 6

X

4

7 1 9 6

X X

4

--

3

--

1

N

Poteriidae

Poteria varians (C.B. Ads.)

X

4

Chondropomidae

Colobostylus albus (Sow.) Parachondria fecunda (C.B. Ads.)

4 -

-

Truncatellidae

Geomelania vicina C.B. Ads. Subulinidae

LameUaxis monodon (C.B. Ads.)

1/-

1

Urocoptidae

Apoma gracilis (Wood) Geoscala robertsi (C.B. Ads.) Spirostemma teneUa (C.B. Ads.) Urocoptis brevis (Pfr.) Urocoptis hendersoni Pils. Urocoptis ovata (Desh.)

--

/N

1

N

.

1

.

N

.

1/

2

- -

2

6

N/3

1

1

-/1

- -

-

.

1

-

.

1 - -

1

--

--

- -

- -

--

2

Helicodiscidae

Helicodiscus apex (C.B. Ads.)

N

7

-

-

Sagdidae

Lacteoluna omissa (Pils.) Proserpinula opalina (C.B. Ads.) Sagda bondi V a n a t t a Sagda centralis Goodfriend Sagda montegoensis Pils. and B r o w n Sagda spei Pils. and B r o w n Stauroglypta peraffinis (C.B. Ads.) Stauroglypta spreta (C.B. Ads.) Strialuna sincera (C.B. Ads.)

- -

- -

- -

--

i/

.

.

.

.

.

.

N --

--

.

- -

.

.

.

.

-

-

.

2

i

1

N

/1 N/1

. N

N

1/-

N

2

3

3/-

1

3

--

X X

.

5/

3

.

. N

N

N

. --

-2

Oleacinidae

Varicella propinqua (C.B. Ads.) Varicella sp. Varicella sp. Sigmataxis annae (Pils.)

-L

X N

--

N

4

--

302 TABLE IV (continued) Species

Living at site

Camaenidae Pleurodonte jamaicensis (Gruel.) Pleurodonte lucerna (Mfiller) Pleurodonte sinuata (Miiller) Pleurodonte sublucerna (PUs.)

Deposit $3

$4 a

$2

S1

B2

B1

5 N N 3

1/1 N/4 5/4 8/ .

-7 6 .

-3 7 .

1 N N

-5 8

22

19/15

26

20

14

12

X X

Total species

14

.

.

"Shells were enumerated separately according to whether they had light secondary carbonate deposits or moderate to heavy secondary carbonate deposits (left: light secondary deposits/right: m o d e r a t e - h e a v y secondary deposits).

site today): Helicina aurantia (see Goodfriend and Mitterer, submitted), Poteria varians, and Urocoptis ovata. Thus fossil evidence indicates that the regional endemic character of the north coast fauna had already been established by the last glacial period. On the other hand, seven species occurring in the fossil deposits no longer occur on the north coast (Table V) but are now limited to the interior plateau. Examples include Alcadia major (Fig.lG; Fig.3), and Sagda bondi (Goodfriend, 1986b). Another two species of the interior, Alcadia brownei (Goodfriend and Mitterer, submitted) and Eutrochatella pulchella (Fig.lI, 2), extend down to the coast only in the wetter area to the east of the cave. The deposits contain combinations of species which do not occur together anywhere today:

during the last glacial period. The history of the fauna at the cave can therefore be viewed as involving primarily the loss of species. The local character of the land snail fauna is evident even in the Pleistocene deposits. Abundant in almost all deposits are two species which are today endemic to the north coast of Jamaica (and still occur at the site today): Eutrochatella costata (Fig.lJ, 2) and Colobostylus albus (see Jarvis (1903) for distribution) (Fig.ID-F). Other north coast endemics occurring in the deposits (but not living at the site today) are Urocoptis hendersoni (in the Pleistocene $2 deposit) and Sigmataxis annae (Holocene and Pleistocene). Also occurring in Pleistocene and Holocene deposits are several species presently endemic to the north-central region of the island (and still occurring at the I

'

i

r" ~ - ~ ~ . i ~ ,~

.

....

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~" -==-~-~I

re

.:

...

-40

t

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•

,.""., ~,, " ...... "~

I

'

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'

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'

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I

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.

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km - 30

,

78°W I

,

40 ,

,

77=W I

60 ,

Fig.3. Distribution of Alcadia major [and showing location of Green Grotto Cave (star)].

SO ,

,

303 TABLE V Times of extinction and earliest appearance of land snail species now extinct at Green Grotto (GGC), with a summary of the present geographic ranges of the species Species

Earliest record

Present range

Extinction during late last glacial Urocoptis hendersoni late last glacial Sagda montegoensis late last glacial Alcadia major late last glacial Geomelania vicina late last glacial Sagda bondi late last glacial Lacteoluna omissa late last glacial VariceUa sp. late last glacial

N coast, E of GGC N coast, W of GGC interior plateau interior plateau interior plateau unknown unknown

Extinction in latest last glacial/early Holocene Alcadia brownei late last glacial Eutrochatella pulchella late last glacial Apoma gracilis late last glacial Sagda spei latest last glacial/early Holocene

interior interior interior interior

Extinctions in late Holocene late Helicina neriteUa late Lucidella persculpta late Parachondria fecunda late Proserpinula opalina late Sagda centralis late Strialuna sincera late Varicella propinqua late Sigmataxis annae late Fadyenia fadyeniana late Pleurodonte jamaicensis late Pleurodonte sublucerna late Lamellaxis monodon late Helicodiscus apex

includes GGC area includes GGC area includes GGC area includes GGC area includes GGC area includes GGC area includes GGC area N coast, E of GGC interior plateau interior plateau interior plateau b unknown unknown

last glacial last glacial last glacial Holocene Holocene last glacial last glacial last glacial last glacial last glacial Holocene last glacial last glacial

plateau ~ plateau a plateau plateau a

aExtending to coast in wetter area to the east. bExtending to top of N coastal slope. species n o w limited to the i n t e r i o r t o g e t h e r with n o r t h c o a s t a l endemics. These assemblages a r g u e for the existence in the late Q u a t e r n a r y of e n v i r o n m e n t a l c o n d i t i o n s not h a v i n g a m o d e r n analog. The p a u c i t y of small species in B2 is likely the r e s u l t of sampling bias in this deposit. The deposit consists m o s t l y of quite large shells (Pleurodonte, S a g d a ) p a r t i a l l y c e m e n t e d together, b u t c o n t a i n i n g n u m e r o u s voids. The deposit appears to r e p r e s e n t shells c a u g h t in a s o l u t i o n hole and l a t e r cemented. Smaller shells w o u l d h a v e been w a s h e d out t h r o u g h the holes b e t w e e n the l a r g e r shells before cementation. Thus we see in the cave f a u n a s long-term persistence of some local species as well as

extensive e x t i n c t i o n s of b o t h local species and species n o w o c c u r r i n g only outside the n o r t h coastal region. The c h r o n o l o g y of these e x t i n c t i o n s at G r e e n G r o t t o Cave is followed in g r e a t e r detail in the following section. The chronology Grotto Cave

of extinctions

at Green

The t e m p o r a l r a n g e s of the locally extinct species are s u m m a r i z e d in Table V. F o r m a n y species, the a p p r o x i m a t e time of d i s a p p e a r a n c e could be d e t e r m i n e d from the age of the y o u n g e s t deposit in w h i c h t h e y occur. A n u m b e r of species o c c u r only in deposits d a t i n g to the last glacial: A l c a d i a major, Geomelania vicina, Urocoptis brevis, U. hendersoni, Lacteo-

304

luna omissa, Sagda bondi, S. montegoensis, and Varicella sp. It is not clear whether their disappearance coincided with the end of the last glacial, because this period is poorly represented in the fossil deposits and because many of these species are too rare for their absence from a particular deposit to be taken as evidence of extinction. However, it is perhaps significant that the more abundant species Alcadia major and Sagda montegoensis do occur in the younger (S1 and/or $2), as well as the older (B1 and B2), last glacial deposits. A large number of the locally extinct species have their last appearance in the late Holocene $3 deposit: Fadyenia fadyeniana, Helicina neri-

tella, Lucidella persculpta, Parachondria fecunda, Helicodiscus apex, Sagda centralis, Strialuna sincera, Varicella propinqua, Sigmataxis annae, Pleurodonte jamaicensis, and Pleurodonte sublucerna. The chronologies of some of the locallyextinct species in $3 and $4 were examined in greater detail through amino acid epimer analysis of individual shells (Fig.4). Because epimerization rates in different genera of mollusks may differ by c. + 10% (Lajoie et al., 1980; Miller et al., 1983; G. Goodfriend, unpublished data), the time calibration of these PLeisL deposits

Livinq at site

Sagda ~ 2 centr Alcadia A browne/

,.

.A .p

Eutroch h

.p

Apoma grad/is A -

.p

pulch

Pleuro, A" subluc.

8ooo

Pleuro. /ul:erna P" otis Cofob. albus P"

o

.A

• ~,

•

o

080

•o

0.10

o

.p -p

• 0.20 ' ~'

'

' 0,30'

A/I

Fig.4. Chronologyof some species in deposits $3 and $4, based on alloisoleucine/isoleucineanalyses of individual shells. Data also includedfor Pleurodentelucernawith low A/I values in $2. Also indicated is the presence or absence of each species at the site today and in the Pleistocene deposits at Green Grotto. The estimated A/I value at the Pleistocene-Holocene boundary is given by the asterisk.

individual A/I values based on the calibration of mean values of several species given above must be taken as approximate. Alcadia brownei: Present in all Pleistocene deposits and last appearing as a single specimen with heavy secondary deposits in $4. Analysis of a piece of this shell gave A/I= 0.26, which indicates a latest last glacial/early Holocene age. Eutrochatella pulchella: Present in low abundance in two of the last glacial deposits and last appearing as encrusted specimens in $4. Amino acid analysis of two shells gave A/I = 0.21 and 0.25, which indicates a latest last glacial/early Holocene age. Apoma gracilis: Last appearance as numerous specimens, all with heavy secondary deposits (Fig.lE), in $4. A/I measurements of three shells gave A/I= 0.22-0.27, which cluster around estimated average A/I at time of the Pleistocene-Holocene transition. Extinction must have occurred in latest last glacial to early Holocene times. Sagda centralis: Abundant in the late Holocene $3 deposit and with few uncoated specimens in $4. A/I measurements of $4 specimens (n=4) yielded values of 0.02-0.03. Thus the extinction of this species at the site is very recent - - sometime in the last 1000yr. It appears to have lived at the site only for a short time in the late Holocene. Pleurodonte sublucerna: Present only in $3 and $4. Analysis of specimens from $4 (n = 5) yielded A/I values ranging from 0.02 to 0.07. Thus, like S. centralis, this species also went extinct sometime in the last 1000 yr and existed at the site only during late Holocene times. The single specimen of Sagda spei in $4, comprising the base of the shell, was not sacrificed for amino acid analysis. However, the heavy encrustation of the shell, as well as the presence of well-indurated matrix inside the shell, is similar to Colobostylus albus (Table III) shells with A/I ratios indicating late last glacial to early Holocene ages. The single Proserpinula opalina in $4 has light secondary deposits and is therefore probably of late Holocene age; the shell is too small for amino acid analysis.

305 estimate lies in the middle of the range of values estimated for the glacial maximum (18,000 yr B.P.)-present t em perat ure change for neotropical areas (Van der Hammen, 1974; Webster and Streten, 1978; Peterson et al., 1979; Rind and Peteet, 1985; Liu and Colinvaux, 1985). Information on late Q u a t e r n a r y rainfall conditions at Green Grotto Cave is provided by variation in shell size of some of the species in the deposits. Pleurodonte lucerna (Fig.lA) shows tremendous geographic variation in size in relation to rainfall, with larger snails occurring in wetter areas (Goodfriend, 1983; Goodfriend, 1987b). A comparison of livecollected shells from Green Grotto (Fig.5A) with fossil specimens (Fig.5B) shows t hat all the Pleistocene shells are smaller than the average of the modern snails, thus implying conditions drier t han present during late last glacial times. The Holocene fossils fall into two size groups: a series of shells much smaller than the modern average (with A / I between 0.02 and 0.05) and a series with mostly larger than average sizes, occurring between A / I from 0 to 0.02 and from 0.06 to 0.08. Thus, except for the period corresponding to A/I=:0.02-0.05, generally wetter conditions

Late Quaternary paleoclimate in J a m a i c a Some controversy exists over the degree of temperature depression in lowlands or sea surfaces in the tropics during glacial times (Rind and Peteet, 1985). Epimerization rate calculations based on 1"C dated snails from a c a v e at Coco Ree (Goodfriend and Mitterer, submitted) provide a basis for evaluating temperature changes in Jamaica (cf. Miller et al., 1987). Using Eq. 3 and the calculated epimerization rate constants for the periods 0 13,400 yr B.P. and 13,400-30,000 yr B.P. (Table II), we obtain a difference of 4.6°C between the average temperatures of these two periods. This estimate represents the average H o l o c e n e - l a t e last glacial temperature difference but is r a t h e r approximate. The major source of error is the u n c e r t a i n t y of the mean A / I of the younger Coco Ree sample (+0.02). For example, using a value of 0.14 for the mean A / I of the 13,400 yr old sample (one standard error less th an the estimated mean), a temperature difference of 2.8°C is obtained. Significant uncertainties also exist in the 1"C dates. However, the calculations do indicate significantly cooler conditions during last glacial times as compared to the Holocene. The 3/,- A

B

-34 -32

32 30

I,

28 i,I

-30

i

•

m

-28 -26

26•

w

!

24-

•

1

living

6 'o. 2

•

, , , ,

0.04

-2t~

"--HOLOEENEI PLEtSTOZENE--" "/

l

i/

I

"/

I

, ~" i . . . . . 0.06 r 0.~8 "~"0.22 0. 0 . (0.36) (0.39) (0.51)

$I

$2

B2

A/I Fig.5. Shell diameter of Pleurodonte lucerna. A. Living population at site, showing mean ()~) + standard deviation. B. Fossil P. lucerna, plotted as a function of the A/I ratios of individual shells (for A/I = 0 to 0.30), or of the mean A/I of the deposits (for deposits S1, $2, and B2). The mean diameter for the B2 shells is given and the position of the Pleistocene Holocene boundary is indicated. Dashed line represents the mean of modern shells, for comparison with the fossils.

306

than at present are suggested for the late Holocene. The presence of unusually large shells even with A/I=O suggests the persistence of relatively moist conditions up until very recent time. Given the uncertainties of the A / I measurements (±0.01), the advent of the present drier conditions probably occurred later than the time represented by A/I= 0.01, or in the last c. 500 yr, according to the calibration of A / I against time. The unusually high variability of the sizes of shells with A / I - 0 (cf. scatter for modern and B2 samples) suggests a shift in the mean size, and thus in moisture conditions, within this time period. The widespread occurrence of diminution of shell size in P. lucerna in Jamaica argues for a deterioration of moisture conditions resulting from decreased rainfall (Goodfriend, 19875) rather than desiccation of sites due to thinning of the forest by selective cutting of trees. The interpretation of the very small shells with A/I= 0.02-0.05 is problematic. On the face of it, dry conditions are suggested. However, in the interior of Jamaica, there exist numerous sites with gigantic fossil specimens of P. lucerna having A / I ratios of 0.02-0.03 (Goodfriend, 1987b). Given the cooler temperatures in the interior, these would correspond in age with ratios of 0.04-0.06 at Green Grotto, according to the Coco Ree calibration. The huge size of these shells implies that very wet conditions were widespread in the interior of Jamaica at that time. This apparent conflict is resolved if the very small size of the Green Grotto P. lucerna at this time were the result not of drier conditions but of an interaction with its (here larger) sister semispecies P. sublucerna (Fig.lB). Size diminution (at A/I= 0.05) is recorded shortly after the first record of P. sublucerna at the site (A/I= 0.07) and continues until the apparent time of extinction of P. sublucerna at the site (at A/I=O.02). It is noteworthy that in the small area in the interior where these two semispecies occur together today, they differ markedly in shape (with P. lucerna keeled and P. sublucerna rounded, the converse of the situation in the Green Grotto deposits). Such character dis-

placement has been shown with respect to shell shape in fossil land snails from Bermuda (Schindel and Gould, 1977) and has been suggested for other cases although the evidence is weak (discussed in Goodfriend, 1986c). The diminution of P. lucerna may represent a response to competition between the two species or, perhaps more likely, the development of a reproductive isolation mechanism. Furthermore, the contemporaneity of drierthan-present conditions at the coast and unusually wet conditions in the interior is most unlikely. Therefore the interpretation of late Holocene times (A/I
19A

18-

+ I+

~I"/E .to

16-

i_I++

15B1 52 Sampte

15'00'

'

'

' 2000 '

~

~

'

~ 2500 J

Mean annuat rainfatl(mm)

Fig.6. Shell d i a m e t e r of Alcadia major. A. Shells m deposits B1 a n d $2, w i t h m e a n _ 1 s t a n d a r d d e v i a t i o n i n d i c a t e d for s a m p l e B1. B. M e a n s of m o d e r n p o p u l a t i o n s ( _ 1 s t a n d a r d d e v i a t i o n ) from n i n e sites, in r e l a t i o n to t h e m e a n a n n u a l r a i n f a l l at t h e sites.

307 variety of evidence implying drier conditions in tropical areas during glacial times (e.g., Van der Hammen, 1974; Webster and Streten, 1978; Colinvaux, 1979). The general paucity of early to middle Holocene fossils is noteworthy: the latest Pleistocene deposits S1 and $2 stop accumulating during or before this time; $3 postdates this period; and $4 has relatively few shells dating to this time. A similar paucity of early Holocene material is also seen at Coco Ree (Goodfriend and Mitterer, submitted) and at Bonafide Cave (G. A. Goodfriend, unpublished data). Thus this pattern seems to be a widespread phenomenon in Jamaica. The period would seem to be one of reduced karst development, which probably relates to drier conditions. A single Pleurodonte lucerna shell of probable early Holocene age (A/I=0.22) is somewhat smaller than the mean of living specimens (Fig.5B), which is consistent with this climatic interpreation. Taken together, the data suggest the following climatic pattern: cool and relatively dry conditions during the late last glacial, with the dry conditions perhaps continuing well into the Holocene. Late Holocene times (
Late Holocene extinctions The extreme recency of many of the extinctions at Green Grotto Cave strongly suggests human disturbanqe, through habitat destruction, as a cause. Jamaica was first inhabited by people of the Little River culture around 600 A.D. (Rouse, 1982) and settlements of this period are known from the north coast in the vicinity of the cave (Lee, 1980). Following the arrival of the Spanish in the 16th century and the British in the 17th century, population increase and destruction of forests rapidly ensued (Asprey and Robbins, 1953). Today the north coast of Jamaica is almost completely

deforested, with a few areas of secondary forests and small r e m n a n t patches of hillslope forest which have been thinned in the past but probably not clearcut (such as the present forest at Green Grotto). The present distributions of the species which became extinct at Green Grotto at this time sheds some light on the probable causes of their disappearance. Of the 13 species that became extinct at Green Grotto in late Holocene times, the modern distributions of 11 are known (Tab]e V). Of these 11, seven occur within the vicinity of Green Grotto today, while another (Sigmataxis annae) is known from the north coast not far to the east (Pilsbry, 1907, p. 39). Since these extinctions are strictly local and did not occur at some other sites along the north coast, habitat disturbance would seem to be the most likely cause of their disappearance. The remaining three do not occur along the north coast today. Pleurodonte jamaicensis occurs only on the interior plateau. However, little significance can be attached to its occurrence in the Green Grotto deposits, since the shells of this species are utilized by hermit crabs which inhabit the north coast and north coastal slope; the species may never have actually lived in the vicinity of the cave. Pleurodonte sublucerna occurs today near the top of the coastal slope (Goodfriend, 1983). Subfossil material, presumably also of late Holocene age as the Green Grotto shells, is also known from other north coastal sites (e.g., SN-240 of G.A.G.; 426,563). P. lucerna, still living at Green Grotto, is also known as a subfossil from numerous sites along the north coast but only one other living population is known from this area. Fadyenia fadyeniana is a minute species known only from the interior plateau. It seems probable that most and possibly all of these local extinctions resulted from habitat destruction, apparently even before the arrival of Europeans. A similar pattern of late Holocene local extinctions of land snails in the Galapagos has also been attributed to this process (Chambers and Steadman, 1986).

308

Latest last glacial to early Holocene extinctions Several species occurring in last glacial deposits at Green Grotto disappeared sometime toward the end of the last glacial or beginning of the Holocene. In each case, these species are either limited to the interior (Apoma gracilis) or occur today on the north coast only in wetter areas to the east (Eutrochatella pulchella, Fig.2; Alcadia brownei, see Goodfriend and Mitterer, submitted; Sagda spei, see Goodfriend, 1986b). The onset of higher temperatures during this time period may have caused these species to become restricted to moister areas, the combination of warm temperatures and low rainfall being unfavorable.

Late last glacial extinctions The combination of poor time resolution and the lack of information on short-term climatic fluctuations makes analysis of extinctions during this time period problematic. There are seven species for which only Pleistocene records occur at Green Grotto. Urocoptis hendersoni is the only species which lives nearby the caves today. It has been found only in a very small area on the north coast of St. Ann Parish, 7-8 km east of Green Grotto [sta. SN-40 (451,566) and SN-229 (448,561) of G.A.G.]; no large change in range is indicated. Urocoptis brevis is present in deposit $2. This species has an unusual distribution: it is the common Urocoptis of the south coast of Jamaica (Jarvis, frontispiece in Pilsbry, 1903) but was also reported from Falmouth on the north coast by Pilsbry (1903, p. 124), who interpreted it as a possible case of accidental introduction. The occurrence of the species in this latter area (30-35 km east of Green Grotto) has been confirmed by recent collections by G.A.G. (sta. Tr-28; 302,574) and by Dr. C. R. C. Paul (sta. J 11/2; 291,583). The presence of this species in the fossil record at Green Grotto favors the interpretation of the occurrence of this species to the east as a relict distribution rather than a recent introduction. The area in

which it occurs today is somewhat drier (1100 mm mean annual rainfall at Falmouth, Trelawny) than Green Grotto. Its restriction to the area might have occurred as a result of the onset of wetter conditions in the Holocene. Alcadia major (Fig.3), Geomelania vicina, and Sagda bondi (Goodfriend, 1986b) are all species restricted to the interior of Jamaica. Their disappearance might have been related to increased temperatures toward the end of the last glacial, as suggested above for the other species of the interior. However, S. bondi persisted higher up on the coastal slope (at 200 m elevation) near Green Grotto until late Holocene time (Goodfriend, 1986b). A. major is the only relatively abundant species of these three in the deposits. Its absence from deposit $4, which includes some latest Pleistocene to early Holocene material, thus suggests that it disappeared earlier than the several species whose last appearance is in $4. Sagda montegoensis, common in the Pleistocene deposits, now occurs along the north coast and coastal slope in the region not far to the west of Green Grotto (Goodfriend, 1986b). This species was succeeded by S. spei (in $4), which was succeeded by S. centralis (in $3 and $4). For none of the species of Sagda is the modern distribution clearly related to climate (Goodfriend, 1986b). Biological interactions among the species would seem to be a probable cause of these faunal changes but these in turn may vary according to climatic conditions. Nothing is known about Lacteoluna omissa apart from Baker's (1935) record from Manchester, in the southern interior plateau region.

Comparison to other Jamaican fossil land snail records Quaternary land snail faunas have been described from the central interior plateau at Coco Ree (Goodfriend and Mitterer, submitted) and from Sheep Pen Cave in the Cockpit Country at the western end of the interior plateau (Goodfriend, 1986a). At Coco Ree, all except two of the 37 species occurring within

309 the deposit (which has radiocarbon dates as old as 36,000 yr B.P.) are living in the same area today. One species (Pleurodonte lucerna) was replaced at the site by its sister species P. sublucerna at c. 24,000 yr B . P . P . lucerna now lives within 4 km of the site, in the same climatic regime. Another species, Helicina jamaicensis, persisted until mid-Holocene time. Thus nothing comparable to the late last glacial to early Holocene extinctions at Green Grotto occurred at Coco Ree - - the fauna passed through this period unchanged. No information is available on extinctions that may have occurred at Coco Ree in latest Holocene, since the fauna living on the hill in which the cave formed has not been thoroughly sampled. The forest there appears to be disturbed and the fauna somewhat depauperate. The very rich fauna from Sheep Pen Cave (47 species) is probably of Middle Pleistocene age, although no secure date is available. Three species within the deposit are not known from modern collections or other fossil deposits and appear to be extinct. Of the remaining species, the great majority lives in the area today. The six which do not live in the area now occupy ranges to the north, south, or west, usually in similar climatic regimes. An exception is Sagda montegoensis, which now occurs several kilometers north of Sheep Pen, in a drier area. So, despite the considerable age of this deposit, the extinctions (species extinctions or local extinctions) are not as extensive as the late last glacial early Holocene extinctions at Green Grotto. At Sheep Pen the modern fauna at the site has not been sampled. The forest on the hill is mostly cut down, so most species are probably extinct there now. But the great majority of the fossil species whose present range includes the Sheep Pen area have been found living on neighboring hills, where the forest is in good condition. Thus it appears that the extensive late last glacial-early Holocene extinctions represent a coastal phenomenon, with no parallel occurrence in the interior. The following general scenario is envisioned: with the warming of temperatures during this period, populations

of some species in the warmer coastal area died off. Although interior populations would also have experienced warming, their survival may have been made possible by the introduction and spread of alleles adapted to warmer temperatures from the coastal area. Holocene temperatures in the interior are probably not much different from late last glacial temperatures along the coast, as indicated by the comparative rates of amino acid epimerization. R e l a t i o n to v e r t e b r a t e e x t i n c t i o n s in t h e West Indies

As was the case with the Green Grotto land snails, vertebrates in drier areas in the West Indies also underwent extensive local or species extinctions (Pregill and Olson, 1981; Steadman et al., 1984; Pregill, 1986). Some of these have been supposed to date from the end of the last glacial and be the result of the onset of moister climatic conditions, restricting or eliminating drier habitats (Pregill and Olson, 19811). The land snail extinctions occurring at Green Grotto, on the dry north coast of Jamaica, at around this time clearly do not relate to the increasingly moist conditions that may have occurred then. Only careful dating of appropriate deposits will indicate whether indeed parallel extinctions in vertebrates occurred around the same time. Better dated are late Holocene occurrences of extinct or locally extinct vertebrates in the West Indies and other tropical islands (Olson and James, 1982; Steadman et al., 1984; Steadman and Olson, 1985; MacPhee, 1986; Pregill, 1986). These disappearances have occurred sometime during the last c. 500-3000 yr and have been attributed to human impact through habitat destruction, hunting, and introduction of predators. The occurrence of Holocene extinctions of land snails at Green Grotto emphasizes the probable impact of human disturbance on tropical island biotas. However, evidence of recent desiccation further complicates the picture and must be taken into consideration with regard to vertebrates - - but

310 the land snail extinctions appear to predate the beginning of the present dry conditions.

Eutrochatella costata: GG: SN-12 (405,569); SN-37 (420,566); SN-209 (407,564); SN-211 (418,569); SN-220 (399,564); Tr-41 (386,572). Baker (1934b): VCN (c. 249,588). CRCP: J 11/2 (291,583).

Acknowledgements Field work and preliminary analysis of the materials were carried out when G.A.G. was e n r o l l e d i n g r a d u a t e s t u d i e s in t h e D e p a r t m e n t of Zoology, University of Florida. Mr. Clive Lazarus kindly allowed collection of the fossil deposits at Green Grotto. The radiocarbon a n a l y s i s w a s p r o v i d e d b y M r . I. C a r m i . A m i n o acid analyses of several very small samples were p r o v i d e d b y Prof. Y. B o r s t e i n a n d Ms. I. L e h a v o t . Dr. C . R . C . P a u l ( D e p a r t m e n t o f Geology, University of Liverpool) kindly made his collection of Jamaican land snails available f o r s t u d y . Dr. F. G. T h o m p s o n p r o v i d e d a c c e s s to t h e F l o r i d a S t a t e M u s e u m c o l l e c t i o n . W o r k w a s s u p p o r t e d b y a U.S. N a t i o n a l S c i e n c e F o u n d a t i o n g r a n t ( E A R 8508298) t o R M M a n d by the Minerva Foundation.

Appendix Locality records for points on distribution maps (Figs.2 and 3). Station number is followed by location in Jamaican grid coordinates in parentheses. Sources of records: GG (collection of G.A. Goodfriend), FSM (Florida State Museum collection), Baker (Baker, 1934a, b), P&B (Pilsbry and Brown, 1911), CRCP (collection of C.R.C. Paul). Eutrochatella pulcheUa: GG: SN-46 (463,551); SN-50 (454,547); SN-51 (452,548); SN-59 (463,539); SN-72 (425,532); SN-76 (423,522); SN-86 (419,534); SN-90 (437,527); SN-95 (443,553); SN-97 (458,552); SN-105 (426,477); SN-111 (474,480); SN-115 (474,487); SN-123 (476,473); SN-128 (411,483); SN-139 (445,493); SN-140 (440,506); SN-141 (437,514); SN-145 (445,506); SN-167 (465,528); SN-173 (531,512); SN-175 (481,526); SN-182 (469,539); SN-187 (425,510); SN-189 (427,503); SN-194 (425,490); SN-232 (506,537); SN-234 (515,544); SN-237 (516,546); SN-245 (505,539); SM-5 (562,543); SM-7 (573,548); C1-BH (416,475); Tr-29 (384,547); Tr-30 (325,527); Tr-32 (359,537); Tr-34 (355,539); Tr-49 (339,534); Tr-51 (302,530); Tr-52 (326,535); Tr53 (323,542); Tr-54 (316,552); Tr-56 (346,541); Tr-58 (318,539); Tr-60 (305,536); Tr-63 (334,499); SE-1 (307,484); SE-4 (c. 268,479); SE-7 (c. 304,478); SJ-6 (249,529); SJ-18 (283,526); SJ20 (278,522); SJ-24 (232,524); SJ-25 (244,515); SJ-26 (238,509); SJ-28 (249,503). FSM: FGT 2801 (374,530); FGT 2802 (c. 371,521); FGT 2841 (541,545); FGT 2642 (543,538); RF 19 (c. 332,481); RF 20 (331,471); RF 22 (c. 303,495); RF 23 (c. 300,503). P&B: Orange Hill (c. 258,556). B a k e r (1934b): VF (234,558); NMT (c. 335,490).

Alcadia major: GG: SN-2 (415,481); SN-88 (415,534); SN-138 (426,488); SN-186 (418,503); SN-206 (419,542); SN-215 (405,510); SN-244 (404,540); Tr-25 (376,492); Tr-26 (353,513); Tr-34 (355,539); Tr-48 (362,541); Tr-56 (346,541); Tr-57 (367,543); Tr-63 (334,499); SE-1 (307,484); SE-5B (262,466); SE-17 (262,459); SJ-6 (249,529); SJ-18 (283,526); SJ-20 (278,522); SJ-21 (276,530); SJ-22 (264,528); SJ-25 (244,515); SJ-26 (238,509); SJ-27 (249,502). FSM: FGT 2801 (374,530); FGT 2803 (369,515); FGT 2868 (c. 322,496); FGT 2870 (c. 369,515); RF19 (c. 332,481); RF27 (c. 294,513). Baker (1934a): MN3 (c. 357,425); NMM (c. 334,445); NM2 (c. 340,465).

References Aguayo, C. G. and Jaume, M. L., 1939. Moluscos semifossiles del "Bosque de la Habana". Mere. Soc. Cubana Hist. Nat., 13: 229-245. Asprey, G. F. and Robbins, R. G., 1953. The vegetation of Jamaica. Ecol. Monogr., 23: 359-412. Baker, H. B., 1934a. Jamaican land snails, 1. Nautilus, 48: 6-14. Baker, H. B., 1934b. Jamaican land snails, 2. Nautilus, 48: 60-67. Baker, H. B., 1935. Jamaican land snails, 6. Nautilus, 49: 52-58. Cant, R. V., 1972. Jamaica's Pleistocene reef terraces. J. Geol. Soc. Jam., 12: 13-17. Chambers, S. M. and Steadman, D. W., 1986. Holocene terrestrial gastropod faunas from Isla Santa Cruz and Isla Floreana, Gal~pagos: evidence for late Holocene declines. Trans. San Diego Soc. Nat. Hist., 21: 89-110. Christensen, C. C. and Kirch, P. V., 1986. Nonmarine mollusks and ecological change at Barbers Point, O'ahu, Hawai'i. Occas. Pap. Bishop Mus., 26: 52-80. Colinvaux, P., 1979. The ice-age Amazon. Nature, 278: 399-400. Garrett, P. and Gould, S. J., 1984. Geology of New Providence Island, Bahamas. Bull. Geol. Soc. Am., 95: 209 220. Goodfriend, G. A., 1983. Clinal variation and natural selection in the land snail Pleurodonte lucerna in western St. Ann Parish, Jamaica. Thesis. Univ. of Florida, Gainesville. Goodfriend, G. A., 1986a. Pleistocene land snails from Sheep Pen Cave in the Cockpit Country of Jamaica. Proc. 8th Int. Malacol. Congr. Budapest, 1983, pp. 87-90. Goodfriend, G. A., 1986b. Radiation of the land snail genus Sagda (Pulmonata: Sagdidae): comparative morphology, biogeography and ecology of the species of north-central Jamaica. Zool. J. Linn. Soc., 87: 367-398. Goodfriend, G. A., 1986c. Variation in land-snail shell form and size and its causes: a review. Syst. Zool., 35: 204-223. Goodfriend, G. A., 1987a. Radiocarbon age anomalies in shell carbonate of land snails from semi-arid areas. Radiocarbon, 29: 159-167.

311 Goodfriend, G. A., 1987b. Late Holocene morphological changes in a J a m a i c a n land snail: evidence for changes in rainfall. In: W. H. Berger and L. D. Labeyrie (Editors), Abrupt Climatic Change - Evidence and Implications. Reidel, Dordrecht, pp. 123-126. Goodfriend, G. A., 1987c. Chronostratigraphic studies of sediments in the Negev Desert, using amino acid epimerization analysis of land snail shells. Quat. Res., 28: 374-392. Goodfriend, G. A., 1987d. Evaluation of amino acid racemization/epimerization dating using radiocarbon-dated fossil land snails. Geology, 15: 698-700. Goodfriend, G. A. and Mitterer, R. M., submitted. Late Quaternary land snail faunal history and chronostratigraphy of cave sediments at Coco Ree, Jamaica. Goodfriend, G. A. and Stipp, J. J., 1983. Limestone and the problem of radiocarbon dating of land-snail shell carbonate. Geology, 11:575 577. Gould, S. J., 1971. The paleontology and evolution of Cerion II: age and fauna of Indian shell middens on Curacao and Aruba. Breviora, 372: 1-26. Hare, P. E., 1969. Geochemistry of proteins, peptides, and amino acids. In: G. Eglinton and M . T . J . Murphy (Editors), Organic Geochemistry. Springer, New York, N.Y., pp. 438 463. J a m a i c a n Meteorological Service, 1973. The Climate of Jamaica. Climatology Branch, J a m a i c a n Meterological Service, Kingston. J a m a i c a n Meteorological Service, in ms. Monthly and a n n u a l rainfall totals in Jamaica (averages for the period 1931-1960). Jarvis, P. W., 1902. Notes on the distribution of the Pleurodonte sinuata group. Nautilus, 16:1 4. Jarvis, P. W., 1903. Distribution of J a m a i c a n species of Colobostylus. Nautilus, 17: 62-65. Lajoie, K. R., Wehmiller, J. F. and Kennedy, G. L., 1980. Inter- and intrageneric trends in apparent racemization kinetics of amino acids in Quaternary mollusks. In: P. E. Hare, T. C. Hoering and K. King, Jr. (Editors), Biogeochemistry of Amino Acids. Wiley, New York, N.Y., pp. 305 340. Lee, J. W., 1980. J a m a i c a n redware. In: S. M. Lewenstein (Editor), Proc. Eighth Int. Congr. for the Study of the Pre-Columbian Cultures of the Lesser Antilles. Anthropol. Res. Pap., Ariz. State Univ., 22: 597-609. Liu, K. B. and Colinvaux, P. A., 1985. Forest changes in the Amazon Basin during the last glacial maximum. Nature, 318:556 557. MacPhee, R. D. E., 1986. Environment, extinction, and Holocene vertebrate localities in southern Madagascar. Natl. Geogr. Res., 2: 441-455. Miller, G. H., Sejrup, H.P., Mangerud, J. and Andersen, B. G., 1983. Amino acid ratios in Quaternary molluscs and foraminifera from western Norway: correlation, geochronology and paleotemperature estimates. Boreas, 12: 107-124. Miller, G.H., Jull, A. J. T., Linick, T., Sutherland, D., Sejrup, H.P., Brigham, J.K., Bowen, D.Q. and Man-

t

gerud, J., 1987. Racemization-derived late Devensian temperature reduction in Scotland. Nature, 326: 593-595. Mitterer, R. M., 1975. Ages and diagenetic temperatures of Pleistocene deposits of Florida based on isoleucine epimerization in Mercenaria. E a r t h Planet. Sci. Lett., 28: 275 282. Olson, S. L. and James, H. F., 1982. Fossil birds from the Hawaiian Islands: evidence for wholesale extinction by man before western contact. Science, 217: 633-635. Paul, C. R. C., 1982. The J a m a i c a n land snail genera Geoscala and Simplicervix (Pulmonata: Urocoptidae). J. Conchol., 31: 101-127. Peterson, G. M., Webb, T , III, Kutzbach, J. E., Van der Hammen, T., Wijmstra, T. A. and Street, F. A., 1979. The continental record of environmental conditions at 18,000 yr B.P.: an initial evaluation. Quat. Res., 12: 47-82. Pilsbry, H. A., 1903. Manual of Conchology, 2" ser., 15. Academy of Natural Sciences of Philadelphia, Philadelphia. Pilsbry, H. A., 1907. Manual of Conchology, 2 ~' ser., 19. Academy of Natural Sciences of Philadelphia, Philadelphia. Pilsbry, H. A. and Brown, A. P., 1911. The land Mollusca of Montego Bay, Jamaica; with notes on the land Mollusca of the Kingston region. Proc. Acad. Nat. Sci. Phila., 63: 572 588. Pregill, G., 1986. Body size of insular lizards: a pattern of Holocene dwarfism. Evolution, 40: 997-1008. Pregill, G. K. and Olson, S. L., 1981. Zoogeography of West Indian vertebrates in relation to Pleistocene climatic cycles. Annu. Rev. Ecol. Syst., 12: 75-98. Rich~rds , hi. ~ . 1935. Pleistocene mollusks from western Cuba. J. Paleontol., 9:253 258. Rind, D. and Peteet, D., 1985. Terrestrial conditions at the last glacial maximum and CLIMAP sea-surface temperature estimates: are they consistent? Quat. Res., 24: 1-22. Rouse, I., 1982. Ceramic and religious development in the Greater Antilles. J. New World Archaeol., 5: 45-55. Schindel, D. E. and Gould, S. J., 1977. Biological interaction between fossil species: character displacement in Bermudian land snails. Paleobiology, 3: 259-269. Schroeder, R. A. and Bada, J. L., 1973. Glacial-postglacial temperature difference deduced from aspartic acid racemization in fossil bones. Science, 182:479 482. Steadman, D. W. and Olson, S. L., 1985. Bird remains from an archaeological site on Henderson Island, South Pacific: man-caused extinctions on an " u n i n h a b i t e d " island. Proc. Natl. Acad. Sci. U.S.A., 82:6191 6195. Steadman, D. W., Pregill, G. K. and Olson, S. L., 1984. Fossil vertebrates from Antigua, Lesser Antilles: evidence for late Holocene human-caused extinctions in the West Indies. Proc. Natl. Acad. Sci. U.S.A., 81: 4448-4451. Van der Hammen, T., 1974. The Pleistocene changes of vegetation and climate in tropical South America. J. Biogeogr., 1:3 26. Webster, P. J. and Streten, N. A., 1978. Late Quaternary ice age climates of Tropical Australasia: interpretations and reconstructions. Quat. Res., 10: 279-309.