Fossil Lizards from the Late Quaternary of 'Eua, Tonga!
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Pacific Science (1993), vol. 47, no. 2: 101-114 © 1993 by University of Hawaii Press. All rights reserved Fossil Lizards from the Late Quaternary of 'Eua, Tonga! GREGORY K. PREGILL 2 ABSTRACT: The lizard fauna ofPolynesia consists mainly ofskinks and geckos that are believed to have reached many ofthe islands by way ofhuman assistance beginning with the early Polynesian voyagers. Documenting the natural versus human-assisted origins of lizards in the Pacific would be greatly enhanced by a fossil record, but that record for lizards has been limited to a few archaeological and noncultural sites that postdate human arrival. This study reports fossil remains of eight, possibly nine, species of lizards screened from cave sediments on 'Eua, Tonga. One ofthese deposits is precultural, the deepest layers ofwhich were excavated from below a calcite lens dated at ca. 60,000 to 80,000 yr B.P. Fossils from the precultural strata include a gecko referred to Perochirus sp., a genus known today no nearer than Vanuatu; a skink representing either an undescribed species of Emoia or Emoia trossula Brown & Gibbons; and remains of the widespread Emoia cyanura (Lesson). A single bone of an unidentified large (> 150 mm snout-ventlength) skink (cf. Emoia, Eugongylus) was recovered from deposits ofpost-human arrival age, but no such large skinks are currently known from the island. Additional cave sites yielded essentially contemporane ous remains ofspecies extant on 'Eua: Gehyra oceanica (Lesson), Lepidodactylus cf. lugubris (Dumeril & Bibron), Nactus pelagicus (Girard), Cryptoblepharus poecilopleurus (Wiegmann), and Lipinia noctua (Lesson). No fossil evidence was found of the Crested Iguana, Brachylophus fasciatus (Brongniart), whose presence on 'Eua never has been verified by specimens. THE FOSSIL RECORD for lizards in Polynesia site on Lifuka, Ha'apai Group, Tonga (Pregill is brief. In all instances the few specimens and Dye 1989). from archaeological excavations or noncul- This paper describes fossils of eight, possi tural sites are younger.than the earliest human bly nine, species of lizards from Late Quater occupation. For example, seven lizard species nary cave deposits on the island of 'Eua in are known from the Kuakini archaeological southern Tonga (Figure I). Bones of three of site near Kona, Hawaii (Pregill 1984). On these species were recovered from precultural Aitutaki and Atiu, Cook Island Group, exca- sediment. Lizard bones from eight other caves vations ofcultural and noncultural sites have were also found, all of which are referable to yielded remains of vertebrates including liz- species extant on 'Eua. ards, but only the birds have been identified I visited 'Eua from 20 November to 3 (Steadman 1991). Perhaps the most unusual December 1987 to collect and study resident lizard fossils from Piili:nesia are theJ.emains~zaJ:d-populatiQns-and-t0-seareh-for-f --1 ~f-extinct giant iguanas (Brachylophus spp.) deposits in caves and other erosional features unearthed at the Tongoleleka archaeological in the island's limestone cliffs. I dug test pits and screened sediment in three sites that were noted briefly by Steadman (1989). Parties led I Manuscript accepted 30 June 1992. by David Steadman visited the island from 24 2 Department ofHerpetology, San Diego Natural His tory Museum, P.O. Box 1390, San Diego, California November to 17 December 1988 and from 22 92112. November to 16 December 1989 to continue 101 PACIFIC SCIENCE, Volume 47, April 1993 102 I I I Niuafo'ou .Tafahi Niuatoputapu \J - KINGDOM OF TONGA t>Fonualei - • Toku VAVA'U GROUP Vava'u Huoga ~ ~~ Pangalmotu o Noapapu' Kapa Late Ovaka - I- HA'APAI GROUP Ha'ano ':Foa ,J Lifuka Uiha"/? Uoleva I- 20' Nomuka-p Falcon Mango·· . Huoga Hunga Ha'apai' Tonga - I- TONGATAPU TOngata~~~;~k~ GROUP Kalau' " I-- 22' ~Ata o 20 40 mi o 20 40 60 80 km 176' 174' I I I FIGURE I. The Kingdom ofTonga, showing the location of 'Eua in the Tongatapu Group. Fossil Lizards of 'Eua,Tonga-PREGILL 103 these excavations and search for additional is composed of bedded volcanics capped fossil-bearing sites. by thick deposits of Miocene and younger limestone. Hoffmeister's (1932) six physiographic General Description of 'Eua provinces remain useful descriptions of the 2 island. From east to west these are as follows: 'Eua is a small island (87 km ) oriented on (1) eastern terraces and coast region, (2) east a north-south axis. It has a maximum length ern ridge (including several subprovinces), (3) of about 19 km and nar,rows sharply at its western slope of the eastern ridge, (4) central northern and southern ends (Figure 2). The valley, (5) western ridge summit, and (6) widest part ofthe island, about 7 km, is across western slope terraces and coast region. The the east-west midsection. 'Eua's geology and eastern ridge is 'Eua's most prominent physio physiography were described by Hoffmeister graphic feature, dominating the east coast of (1932), and there are also recent descriptions the island for nearly its entire length (Figure of'Eua's limestone and caves by Cunningham 2). The central portion of the ridge reaches a and Anscombe (1985) and Lowe and Gunn maximum elevation of 312 m; the highest (1986). Like most of southern Tonga, 'Eua point on the island. The windward (east) side ofthe ridge is defined by a series ofsteep cliffs, broken occasionally by terraces of forest and small gardens. A To the west of the eastern ridge the terrain slopes gently toward the large central valley, 3km defined on the west by a gentler ridge that more or less follows the contour of the west coast. The western ridge summit meets the central valley at about the IOO-m contour. A narrow fringing reef surrounds most of the island. Rich volcanic soils have washed into the central valley, and, where not cleared for settlements or plantations, there are scattered stands of second-growth forest and fallow gardens of coconut and citrus. Much of the island is or has been under cultivation and grazing for many generations. Plantations of from one to many hectares form a patchwork over the island, even in seemingly inaccessible terrain such as the terraces seaward of the eastern ridge. This narrow stretch of the island, however, still supports the most exten sive stands ofundisturbed forest. The western slope of the eastern ridge maintains some II fairl¥_luxurious_decidu0us-and-eveFgreenl woodlands, although numerous small planta- tions encroach up from the central valley. 'Eua's fertile soil and good climate have brought increasingly heavy agricultural de- mands. In fact, much of the harvest of yams, FIGURE 2. 'Eua, Tonga, showing principal localities and physiographic features discussed in text. Most of taro, bananas, manioc, sweet potatoes, and the fossiliferous caves are located on the windward papayas is exported to Tongatapu. Undoubt- (eastern) cliffs of the eastern ridge. edly, this transformed landscape has affected 104 PACIFIC SCIENCE, Volume 47, April 1993 the density and distribution of the island's of relatively organic, charcoal-rich sediment lizard populations. that represents roughly the past 3000 yr, based on the represented fauna and 14C dates of 570 ± 70 yr B.P. at 20 em and another of 2710 ± 70 yr B.P. at 36 em. Many ofthe bones MATERIALS AND METHODS in layer I, other than those of rats, are from Cave Sites domestic animals such as chickens, pigs, and dogs that were brought to 'Eua by early The limestone ofthe eastern ridge is deeply people. Layers II and III comprise about 100 weathered along the windward (eastern) side, em of calcareous sediment lacking cultural leaving numerous caves and other erosional artifacts (charcoal) or remains of domestic features exposed in the forested cliffs. Re animals. These layers predate human arrival mains ofnative vertebrate species were found and contain partially mineralized bones of in the sediment of 12 caves scattered along the native lizards (three, probably four, species length of the windward side of the eastern described herein), birds (27 species of land ridge. The bones, all recovered by screening birds, of which 21 no longer occur on 'Eua sediment through 6-mm (1/4") and 3-mm [Steadman in press]), and bats (at least five (1/8") mesh, mainly represent ancient prey species, of which three no longer occur on remains brought into the caves by Barn Owls 'Eua, under study by K. F. Koopman). Be (Tyto spp.). The most important ofthese sites tween layers II and III is a 3- to 4-cm layer of are That Cave, Tupou Cave, Collapse Cave, calcite flowstone having Dr/Th dates ranging and 'Anatu. That Cave and Tupou Cave are from 60.0 ± 3.0 to 78.8 ± 2.7 kyrB.p. (Stead located near the northeastern coast, just be man in press). The deposits of layer III are, low Anokula. The abundance of rat (Rattus therefore, at least ofan age that makes 'Anatu spp.) bones in the sediments ofThat Cave and by far the oldest fossil site in all of Polynesia Tupou Cave indicate that the fossil deposits outside of Hawaii and New Zealand. postdate the arrival ofpeople to 'Eua and are less than 3000 yr old. Collapse Cave is located 2 km east of Kolomaile village. No excava- Systematic Paleontology tions were conducted in Collapse Cave, but bones of birds and bats were found scattered Fossils were identified with the aid ofcom on the surface, the age of which is unknown parative skeletons, most of which were made because ofthe lack ofcultural or sedimentary from specimens collected in the field on 'Eua contexts, but most probably they are also and deposited in the collections of the San latest Holocene. Similarly, Paul's Cave practi- Diego Natural History Museum (SDSNH). Es cally lacks sediment altogether.