A Prehistoric, Noncultural Vertebrate Assemblage from Tutuila, American Samoa1 David W Steadman2,3 and Gregory K. Pregill4 Abstract: Ana Pe'ape'a is a small cave on the southern shore ofTutuila, Amer­ ican Samoa. Excavations at Ana Pe'ape'a yielded 13,600+ bones of small verte­ brates, dominated (>95%) by the nonnative Pacific Rat, Rattus exulans. Represented in the owl-derived bone deposit are two species that no longer oc­ cur on Tutuila, the Pacific Boa (Candoia bibroni) and the Sooty Crake (Porzana tabuensis). Based on bone counts, C. bibroni was the second most common species at the site. The third most common, the Sheath-tailed Bat (Emballonura semi­ caudata), is extremely rare on Tutuila today. Compared with bone records in nearby Tonga, we believe that the deposit at Ana Pe'ape'a, with a radiocarbon date of A.D. 445 to 640, is at least 1,000 yr too young to be dominated by extinct species. THE WEST POLYNESIAN faunal region com­ and Turner 1985]). Independent (formerly prises Fiji, Tonga, Samoa, and the outlying Western) Samoa comprises the very large is­ islands of Rotuma, 'Uvea, Futuna, 'Alofi, and lands of Upolu and Savai'i and their small Niue (Steadman 1993a, Steadman et al. offshore islands. American Samoa comprises 2000). Raised limestone islands in Fiji, Ton­ Tutuila, its offshore island of Aunu'u, the ga, and Niue have yielded rich deposits of Manu'a group (Ta'u, Ofu, Olosega), and the prehistoric bones in caves and rockshelters outlying atolls of Swains and Rose. that represent many extinct species or pop­ The wet volcanic soils of Samoa are well ulations of lizards, birds, and bats (Pregill suited for sustaining forests (Whistler 1980, 1993, Koopman and Steadman 1995, Pregill 1992, Elmqvist et al. 1994) but are not favor­ and Worthy 2003, Steadman in press). By able for bone preservation. Lava tubes have contrast, information on prehistoric verte­ produced extensive prehistoric bone records brates is very sparse in nearby Samoa (Figure in the Hawaiian Islands (James et al. 1987, 1), which lacks limestone and instead consists James and Olson 1991, Olson and James mainly of young basalt-rich volcanic rocks 1991) and the Galapagos Islands (Steadman with radiometric (4OK_ 40Ar) ages no older 1986, Steadman and DeLeon 1999), but Sa­ than ca. 2.8 ± 0.20 million yr (from Upolu moan lava tubes are poorly suited for bone [Simkin et al. 1981, Keating 1985, Natland deposition and preservation because of flow­ ing water, wet soils, and stagnant air saturated with humidity (Thomson 1921, Kear and Wood 1959, Hoch and Asche 1988). Archae­ 1 Financial support came from the National Science ological excavations even at the relatively dry Foundation (grant EAR-9714819 to D.W.S.). Manu­ entrances of the Falemauga Caves on Upolu script accepted 26 January 2004. are not known to have yielded bones (Free­ 2 Florida Museum of Natural History, University of man 1944). Florida, Gainesville, Florida 32611. 3 Corresponding author (phone: 352-392-1721 x261; Thus, on 21 April 1999, it was a nice sur­ fax: 352-846-0287; e-mail: [email protected]). prise to discover a small but dry accumulation 4 Department of Biology, University of San Diego, of bone-rich sediment in a cave on Tutuila. 2 San Diego, California 92110. At 141.97 km , Tutuila is the largest island in American Samoa but still about an order of Pacific Science (2004), vol. 58, no. 4:615-624 magnitude smaller than Upolu or Savai'i. © 2004 by University of Hawai'i Press Here we describe the results of this discovery, All rights reserved which represents Tutuila's only evidence of 615 616 PACIFIC SCIENCE· October 2004 25 0 25 50 km INDEPENDENT SAMOA , ',1,',',1 I I 10 0 ~ ~'~POIU AMERICAN SAMOA /" Apolima .;.---• Nu'utele Ofu Olosega 170":WW ~ ~~tuila VJ Ta'u J MANU'A ISLANDS TUTUILA 15'5 170"5O"W FIGURE 1. The location ofAna Pe'ape'a, Tutuila, American Samoa, in a regional and local context. prehistoric vertebrates. Our findings also Unit 4 (100 by 100 by 8-10 em deep) was on generate a limited discussion of the historic a ledge on the cave's northeastern wall. Each biogeography of Samoan reptiles and birds. Excavation Unit reached the basaltic bedrock of the cave. All excavation was by trowel. Levels are arbitrary vertical designations, MATERIALS AND METHODS whereas Layers reflect natural stratigraphic Ana Pe'ape'a (140 18' 24/1 S, 1700 41' 00/1 W) changes. During the excavations, on 22-23 is a small (ca. 24 m 2 of horizontal passage), April 1999, all sediment was dry-sieved in the seaward-facing cave of erosional origin at Ana field with screens of 12.5-,6.4-, 3.2-, and 1.6­ Pe'ape'a Point (alternative name Mata'ae mm mesh, thereby assuring recovery of the Point) on the south-central coast of rugged smallest identifiable specimens. Tutuila (Figure 1). It lies 200 m SSW of The bones are mostly dark reddish brown Matu'u Village and is visible from the coastal but vary in color from yellow to orange to highway (Figure 2). Only ca. 25 m inland black. In the field they were stored dry, sealed from and ca. 10 m above the sea, Ana Pe'ape'a in plastic bags (Whirl-pac, Nasco), and then presumably formed through wave action at a shipped to the Florida Museum of Natural time when the basalt escarpment was lower History (UF) to be cleaned, identified, and relative to sea level. curated. Identification of the bones was based The bones in Ana Pe'ape'a are mostly on comparisons with modern skeletons in UF from Excavation Units 1 and 2 (166 em long and the National Museum of Natural His­ by 30-80 cm wide by 18-40 cm deep), in tory, Smithsonian Institution (USNM), sup­ a small deposit of dry sediment on a ledge plemented for reptiles by specimens from along the cave's northern wall. Excavation the San Diego Natural History Museum Unit 3 (100 by 100 by 33-56 cm deep) was on (SDNHM). Although D.W.S. sorted all of the the main, central floor ofthe cave. Excavation non-Rattus bones from Ana Pe'ape'a, he did Prehistoric Vertebrate Assemblage from Tutuila . Steadman and Pregill 617 FIGURE 2. The entrance (upper right) of Ana Pe'ape'a, Tutuila, 22 April 1999. Jeffrey Sailer is walking in the left foreground. not pick out every bone ofRattus exulans from some wood charcoal and a single fragmentary the concentrated sediment matrix. Thus the premolar of a pig (Sus scrofa) in the top of numbers of bones in Table 1 are accurate for Layer II in Unit 3, and a calcaneum of a dog every species except R. exulans, for which at (Canis familiaris) in Unit 4. least several thousand additional bones were Based on the radiocarbon C4C) chro­ recovered but not counted. nology of human arrival in the Fiji-Tonga­ Samoa region (Kirch and Hunt 1993, Ander­ son and Clark 1999, Burley et al. 1999, RESULTS Steadman et al. 2002), the presence of bones of the nonnative Rattus exulans throughout Stratigraphy and Chronology the deposit at Ana Pe'ape'a should indicate The sediment at Ana Pe'ape'a consists of an age of less than 2,900-2,800 cal B.P. An poorly stratified, pebbly, cobbly silt. In Exca­ accelerator-mass spectrometer (AMS) 14C vation Units 1 and 2, it is loose, light reddish date (Beta-134572 [Figure 3]) is 1,505 to brown to dark brown, whereas in Excavation 1,310 cal B.P. (cal A.D. 445 to 640), based Unit 3 it is compacted and grayish brown in on purified collagen (acid-alkali pretreatment, Layer I, becoming less indurated and variably followed by ultrafiltration) from the femur more reddish in Layer II. The sediment in of a juvenile chicken (Gallus gallus). This Excavation Unit 4 is light to dark yellowish age is reasonable in light of the 19 taxa of brown. We found no artifacts or other cul­ vertebrates identified at Ana Pe'ape'a, which tural evidence, with the possible exception of include at least four that are introduced 618 PACIFIC SCIENCE· October 2004 Atmospheric data from Stuiver et al. (1998);OxCal v3.5 Bronk Ramsey (2003); cub r:4 sd:12 prob usp [chron] 1800 BP 1500±40 BP c: 68.2% probability .Q .... 1700 BP 1415 BP (66.2%) 1330 BP III c: 1320 BP (2.0%) 1310 BP 'E... 1600 BP 95.4% probability ~ 1520 BP (95.4%) 1300 BP '"0 c: 1500 BP o ..0... B 1400 BP o ~ a::III 1300 BP 1200 BP 1800CalBP 1600 CalBP 1400CalBP 1200 CalBP Calibrated date FIGURE 3. Calibration curve for the radiocarbon date (Beta-134572) from purified collagen of a chicken (Gallus gallus) femur from Ana Pe'ape'a, Tutuila. (chicken, rat, dog, and pig), none that is ex­ Of the three bones referred to Emoia spp., tinct, and only two with populations that are the largest (a maxilla) came from a medium­ extirpated on Tutuila (a snake and bird; see large skink with an estimated snout-vent next section). length (SVL) of 110 mm. Three species of Emoia in that size range now inhabit Ameri­ Vertebrate Fauna can Samoa: Emoia lawesii, E. nigra, and E. sa­ moensis (Brown 1991). The last two occur All lizard taxa identified from Ana Pe'ape'a today on Tutuila. Our skeletal material of probably occur today on Tutuila. The gekko these three skinks is limited to E. nigra, which Gehyra oceanica is common in American Sa­ corresponds in general morphology with the moa and has been recorded from all islands.