“This work will be a standard reference for the islands of the Pacific for any herpetologist.”

Aaron M. Bauer, Villanova University

“This book fills a longstanding gap in knowledge. It presents a wealth of unpublished and primary data in a synthetic way that will provide a better understanding of Pacific Basin biodiversity.”

Robert Fisher, USGS Western Ecological Research Center

George R. Zug is an emeritus research scientist of reptiles and amphibians at the National Museum of Natural History, Smithsonian Institution.

Reptiles and Amphibians of the Pacific Islands

A Comprehensive Guide

By George R. Zug

UNIVERSITY OF CALIFORNIA PRESS

Copyright © 2013 The Regents of the University of California
All rights reserved.
ISBN: 978-0-520-27495-2

Contents

Preface, ix,
INTRODUCTION, 1,
Pacific Geography and Geology, 1,
The Contemporary Pacific, 3,
Human History in the Pacific, 4,
ISLAND AND ISLAND GROUP HERPETOFAUNAS, 9,
North Pacific, 11,
West- and North-Central Pacific: Micronesia, 17,
Equatorial Pacific, 24,
Southwest Pacific, 30,
South-Central Pacific: Polynesia, 39,
Eastern Pacific, 44,
Selected References, 48,
RECOGNIZING SPECIES, 51,
Identifying Amphibians and Reptiles, 51,
Frogs, 55,
Lizards, 79,
Snakes, 213,
Turtles, 239,
Crocodiles, 267,
Acknowledgments, 271,
Checklist of Pacific Island Amphibians and Reptiles, 277,
Appendix: Sources for Illustrations, 287,
Index of Common English Names, 299,
Index of Scientific Names, 303,

INTRODUCTION

PACIFIC GEOGRAPHY AND GEOLOGY

The Pacific Ocean is a remnant of the once great sea that surrounded the supercontinent Pangaea. As Pangaea broke up and its fragments began to move apart, the Indian and the Atlantic Oceans developed. Although the Pacific Ocean is only a shadow of its former self, it remains the largest of our present oceans and covers about a third of the Earth’s surface, roughly 180 million square kilometers (about 70 million square miles).

The floor of the Pacific Ocean lies at an average depth of 4,000 meters, with its deepest spot—more than 11 kilometers (36,198 ft)—found in the Mariana Trench in the western Pacific. The ocean floor is neither smooth nor a gently sloping basin. Thousands of seamounts are scattered throughout; some of these extend above the sea’s surface as islands or groups of islands. The ocean floor also contains plateaus, ridges, and trenches. All these features derive from tectonic activity within and at edges of the oceanic plates.

The Earth’s crust is comprised of oceanic and continental plates abutting one another, with no gaps between. Each plate consists of the lithosphere and upper ductile portion of the Earth’s mantle and floats on the deeper, more solid portion of the mantle. Continental plates are thicker (30–70 km) but lighter and float higher than the more dense oceanic plates (which are 3–7 km thick). The plates move because one or more of their edges is a growth zone. Growth results from a constant upwelling of molten material from the underlying mantle. As the upwelling adds new material to the edges of the abutting plates, the older portions of the plates move away from the growth zone. Because the molten material is hotter than the older portion of the plates, it is less dense and rises above the ocean floor, creating oceanic ridges or rises. These oceanic ridges are divergent zones, because the adjacent plates are slowly growing and moving away from one another. The opposite edge of each plate, where it abuts against another plate, is called the “convergent zone.” The heavier oceanic plate pushes beneath the thicker, but lighter, continental plate or, if two oceanic plates collide, both move downward. At these convergent zones the oceanic plate margins subduct (move downward) into the mantle.

On one side of a subduction zone, volcanic activity and plate uplift usually create either mountain chains (if the zone is on the edge of a continental plate) or island archipelagos (if the zone is on an oceanic plate). Islands also arise within oceanic plates where a plume of mantle pushes through the plate and erupts as a volcano on the plate’s surface. These submarine volcanoes commonly persist for centuries. Their periodic lava outflows gradually build a mound that eventually rises above the sea’s surface to form an island. These mantle hotspots are relatively stationary within the lower mantle; as the plate continues to move, the volcano is eventually cut off from the mantle plume and loses its magma source. Soon, geologically speaking, another volcano arises and begins to build toward the surface of the sea. The weathering of the extinct volcano and the cooling and subsiding of the adjacent plate slowly erode and drown the island, which becomes a seamount.

The plate’s movement over a hotspot creates a linear chain or arc of islands. The oldest islands in the chain are the most distant from the hotspot and also the smallest, because they have undergone the longest period of erosion. The Hawaiian Islands, for example, comprise an archipelago of hotspot islands on the Pacific Plate; the Island of Hawai’i is still over the hotspot and continuing to grow; in the distant northwest of the archipelago, the French Frigate Shoals are sinking below sea level and becoming seamounts. To take another example, the Galápagos Islands are formed from a hotspot on the Nazca Plate. Other islands and island chains form along the convergent zones. Intense interactions between subducting plates and the mantle often result in strings of volcanoes beside the deep abyssal trenches; the Mariana Archipelago was created in this manner. Subduction zones and rises also shift. These geological changes have occurred regularly within the Southwest Pacific; the Tongan and Fijian islands were created along such convergent zones that are no longer active.

Pacific islands have repeatedly formed from the processes outlined above, although in a much more complex manner than described here. The islands and island chains that we see today have been around only relatively briefly—generally no more than 40 million years. During that short interval, islands have grown and disappeared; island chains have rotated, changing their positions relative to nearby chains. The arrival and colonization of these islands by reptiles began soon after plants arrived and established a protective and nourishing cover for animal life. Exactly when the present lineages arrived on each island group is only beginning to be discovered. The complex timing and sequence of arrival varies greatly across the great expanse of the Pacific. We can expect a variety of evolutionary scenarios. One scenario is seen in the Galápagos, where the oldest island dates to about 4–5 million years ago, yet data from molecular genetics indicate that some lineages of Galápagos organisms began diverging from their mainland ancestors 8–10 million years ago and apparently arrived on a hotspot island that is now only a seamount.

THE CONTEMPORARY PACIFIC

The Pacific is bound on the north by the Bering Straits; on the east by the Americas; on the west by the continents of Asia, Australia, and the islands on the platform between them; and on the south it merges without a clear surface demarcation into the Antarctic Ocean. This enormous area encompasses numerous nations and island groups containing an estimate of over 24,000 separate islands.

What is and is not part of the Pacific—particularly the western Pacific—is variously delimited. Some authorities have the Pacific and the Indian Oceans abutting the western edge of the Lesser and Greater Sunda Islands. Other authorities set the western edge at the eastern edge of this Sundan platform. A majority viewpoint accepts the landmasses of Japan, Taiwan, the Philippines, New Guinea, and eastern Australia, which face the open waters of the Pacific, as its western edge.

A broad array of regions, islands, island groups, and nations are found within the Pacific. The simplest grouping to describe is the distinction between continental and oceanic islands. Continental islands have had a subaerial (above water or sea level) connection to a continental landmass. They lie on the shallower portions of the continental shelf and are largely found in the western Pacific because the shelf in the eastern Pacific is nearly nonexistent and the continental slope of the Americas is extremely steep. Only a few islands lie on this narrow eastern Pacific shelf; they are very close to the American mainland and include the Mexican Tres Marías, the California Channel Islands, the Queen Charlotte Islands, and the Aleutian Islands. In contrast, the western Pacific Rim islands of Japan, the Ryukyu Islands, Taiwan, the Philippines, New Guinea, and the Great Barrier Reef islands are all continental islands.

Some additional regional terms apply largely to oceanic islands. The most obvious one is “Oceania.” A standard definition of Oceania includes Australia, Papua New Guinea, the Solomon Islands, New Caledonia, and New Zealand and the oceanic islands of Polynesia, Micronesia, and Melanesia. This definition of Oceania excludes the Philippines, Japan, eastern Pacific islands (e.g., the Galápagos Islands, Clipperton Island), and even the Hawaiian Islands. My preferred usage stresses the oceanic part of Oceania and includes all the islands of Micronesia and Polynesia as well as the oceanic part of Melanesia westward into the eastern Solomon Islands. The Australopapuan landmass is continental. New Caledonia and New Zealand are excluded because they are fragments of the supercontinent Pangaea.

HUMAN HISTORY IN THE PACIFIC

Melanesia, Micronesia, and Polynesia are ethnographic regions defined by the cultures and origins of their human inhabitants. These are well-established, useful geographic terms. “Melanesia” is comprised of New Guinea and the groups of islands west of it to Fiji. “Micronesia” lies north of the equator and includes the widely scattered islands from the Palau-Marianas axis to the International Dateline. “Polynesia” covers a vast area of the Central Pacific east of the International Dateline from the Hawaiian Islands southward to Rapa Nui (Easter Island). A westward tongue of Polynesia extends diagonally across the Dateline from Tonga to Nauru.

Melanesia was the first area settled by humans among the Pacific islands, with people arriving in New Guinea at least by 40,000 BCE. These people, who became the Papuans, were largely hunters and gathers, dependent on the plants and animals of the forest and nearshore marine environments. They were able to cross narrow water gaps with crude canoes and rafts. Presumably they attempted a crossing only when they were able to see the land mass of their destination. The multiplicity of Papuan languages attests to multiple invasions of New Guinea by peoples of many different cultures and at different times.

A diaspora of people from Taiwan and adjacent mainland China began about 3000 BCE. These people, now known as “Austronesians,” were the colonizers of Oceania. Austronesians were horticulturalists. They carried domesticated plants (e.g., yams, taro) and animals (e.g., pigs, dogs, chickens) in their settlement of new lands. Their double-outrigger canoes allowed them to transport more people and cargo, and permitted travel to more distant lands that were beyond their sight-horizon. The latter ability suggests the possession of elementary navigation skills and the identification of suitable settlement sites by previous exploration.

The Austronesians spread southward into the Philippines, which they settled, displacing the earlier arriving Negritos populations. Their dispersal continued, with groups moving westward into the Sunda Islands, southward to northern New Guinea and the Bismarck Archipelago, and from there eastward into southern Oceania and eastward into the Palau and Mariana Archipelagos, eventually populating most of western Micronesia.

The Austronesians moving along New Guinea were coastal inhabitants, mostly living in stilted villages over water. They certainly interacted with the Papuan populations, introducing the latter to their domesticated crops and animals, tools, and ceramics. This Austronesian culture became known as the “Lapita.” The Lapita continued to move eastward, reaching easternmost Solomon Islands by about 1300 BCE, Fiji by about 1100 BCE, and the Tongan and Samoan islands by about 900 BCE. Migration paused, although interchange among the peoples of these two latter island groups continued and slowly the new Polynesian culture evolved. In the middle of the first millennium AD, apparently a new major phase of dispersal resulted in the population of the remainder of Oceania. This time, large numbers of individuals (40 to 60) and their cargo were able to travel to other islands in large double-hulled canoes. These canoes were a major development of the proto-Polynesian culture. The Cook Islands, the Marquesas and Society Islands, and the Hawaiian Islands were settled by this method by 800 AD. New Zealand was the last major island reached by the Polynesians, who settled there in the 1200s AD.

Plants and animals had been scattered throughout the Pacific long before humans arrived. Plants, quickly followed by animals, arrived soon after land rose above the sea. Biological communities that developed over many millennia were drastically disrupted, their component species decimated, and many driven extinct with arrival of the Austronesians. Present day island floras and faunas are vastly different from the prehuman ones. In many instances, the floras and faunas are now dominated by alien species whose prehistoric presence has made them appear as though they are natives. This guide addresses only the reptiles and amphibians inhabiting the oceanic Pacific islands today; the origin and dispersal of the Pacific island herpetofaunas are not addressed.

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