Islands

Perhaps a dozen extinct species of dwarf megalonychid sloths weighing roughly 5 to 70 kilograms (10 to 150 pounds), considerably less than their fossil relatives from North, Central, and South America and in some

*I define megaherbivores as plant-eating mammals exceeding a metric ton, or 1,000 kilograms (2,200 pounds).

cases equal to living tree sloths, are known from the fossil record of islands in the Caribbean, especially from Cuba and Hispaniola (White and MacPhee 2001).

According to Jennifer White and Ross MacPhee, "All mainland mega-lonychids . . . are thought to have become extinct by the end of the Pleistocene; Antillean taxa held on until the middle-late Holocene (at least on some islands), but all were gone well before European arrival" (White and MacPhee 2001). Eight taxa occurred in Cuba, six on the island of Hispaniola, two genera in Puerto Rico and one each in Grenada and Curacao. A few specimens have been radiocarbon dated; the early returns indicate that the dwarf species lasted thousands of years longer than their massive continental relatives, their extinction coincidental with human colonization of the West Indies. Recent dating of ground sloth extinction on the American mainland and in the West Indies offers a critical test of the overkill model; the sloths on Haiti outlast those of the mainland.

Madagascar, an island the size of Texas that remained far enough east of the coast of Africa to have evolved numerous endemic species, saw the loss of Plesiorycteropus, long thought to be a relative of the African aardvarks. Its relationship to the aardvark family (Orycteropidae) is so remote, however, that mammalogist Ross MacPhee of the American Museum has placed it in an order of its own (Bibymalagasia). The larger of two described species is estimated to have weighed up to 18 kilograms (40 pounds); the smaller weighed 6 to 10 kilograms (13 to 22 pounds). Both were apparently better adapted for climbing than African aardvarks.

Beginning about 2,400 years ago, the big losers were primates: 16 species (6 genera) of lemurs, all larger than 10 kilograms (22 pounds) and the largest, Archaeoindris, approximating a gorilla in size (see figure 8). Species of Megaladapis, sometimes called the "koala lemur," are known from the last full glacial. Madagascar also lost hippos, giant tortoises, and Aepyornis, the elephant bird, the largest flightless bird of near time. Its eggs had a fluid capacity exceeding a gallon. In some coastal regions, Aepyornis eggshells litter the ground like the wrack of clamshells. Shrinkage of large herbivore biomass is reflected in large spore counts of Sporormiella, which decline with the extinctions of hippos and other large vertebrates and recover with the introduction of cattle (Burney and others 2004). Based on two radiocarbon dates, David Burney's group believes Hippopotamus survived on the east coast until only two centuries ago.

Around 500 years ago, New Zealand saw the extinction of 10 (or fewer) species of moa, flightless birds ranging in size from kiwis to larger

Figure 8. Extinct genera of lemurs of Madagascar. One of the largest living lemurs, Indri, shown for scale. i. Palaeopropithecus; 2. Megaladapis; 3. Babakotia; 4. Archaeolemur; 5. Hadropithecus; 6. Archaeoindris. Reprinted from Simons 1997.

Figure 8. Extinct genera of lemurs of Madagascar. One of the largest living lemurs, Indri, shown for scale. i. Palaeopropithecus; 2. Megaladapis; 3. Babakotia; 4. Archaeolemur; 5. Hadropithecus; 6. Archaeoindris. Reprinted from Simons 1997.

than ostriches. Unlike ostriches and emus, the moas presumably moved with their heads down for easier travel through dense forests.

Hawaii saw the near-time extinctions of many birds, including a flightless gooselike duck, Thambetochen, and a flightless ibis, Apteribis, both named by Storrs Olson and Alexander Wetmore of the Smithsonian Institution. Other islands in the remote Pacific lost endemic parrots, pigeons, doves, megapodes or bush turkeys (Megapodius), and especially flightless rails (Gallirallus), as well as large invertebrates such as land snails.

Figure 9. Moa extinction in New Zealand. Adapted from Anderson and McGlone 1992. Fossil moa are most numerous in the cross-hatched areas. A. Anomlopteryx; D. Dinornis; Em. Emeus; E. Euryapteryx; M. Mega-lapteryx; P. Pachyornis. According to Worthy and Holdaway 2002, the period of extinction was breathtakingly short.

Figure 9. Moa extinction in New Zealand. Adapted from Anderson and McGlone 1992. Fossil moa are most numerous in the cross-hatched areas. A. Anomlopteryx; D. Dinornis; Em. Emeus; E. Euryapteryx; M. Mega-lapteryx; P. Pachyornis. According to Worthy and Holdaway 2002, the period of extinction was breathtakingly short.

Many rodents that reached oceanic islands such as the West Indies and the Mediterranean Islands and evolved into endemic genera did not survive human arrival along with the introduction of domestic rats (Rat-tus). In some cases the rats appear to have colonized first.

In the case of insectivores, tiny fossorial mammals like moles and shrews, anthropogenic extinction in near time would not be expected. Exceptions can occur on oceanic islands, perhaps as the result of the introduction of human commensals such as rats. The list of near-time extinctions is astounding in itself. Even more astounding, I was to discover, was the apparent reason for them. That reason was taking shape for me in 1956 and is hotly debated 50 years later. I have spent many of those years searching for resolution, as the next chapters will indicate. I believe the evidence points overwhelmingly to one disturbing conclusion.

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