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Last Occurrence Dating of the Puerto Rican Mammal Fauna


    Donald A. McFarlane 

 The late Quaternary endemic mammal fauna of Puerto Rico as currently recognized consists of 15 species of bats and 5 terrestrial genera representing 3 different orders. Of these, 100 % of the terrestrial taxa have been extinct since at least since the early historic period, defined here as beginning in AD 1500. 

Although these extinctions have been widely discussed (Morgan and Woods, 1985; MacPhee and Marx, 1997), the catastrophic loss of one ground sloth, three native rodents, and an insectivore had not until recently been evaluated radiometrically and thus could not hitherto be reasonably assigned to a cause or causes. New last-occurrence dates I have reported (McFarlane, in press) are the first attempts at establishing the necessary radiometric framework.

    It is an axiom of paleontology that the fossil record is unlikely to yield the last individuals of a lineage, and that extinction dates must be inferred from ‘last occurrence’ dates. Where a sequence of independent dates is available, it may be possible to estimate the statistical confidence limits around an inferred extinction date (McFarlane, 1999), but in no single case is the West Indian mammal record currently adequate for statistical treatment (Table 1). This project represents the first serious attempt to generate a statistically useful assemblage of ‘terminal’ or ‘last occurrence’ dates for the very recently extinct Puerto Rican terrestrial mammal fauna, to search for an extinction ‘pulse’, and to correlate these extinctions with narrowly constrained environmental and anthropogenic impacts. The result is expected to be a better understanding of the ecological principles underlying and defining the vulnerability of extant insular mammal faunas, which have borne more than 70% of all terrestrial mammalian extinctions Worldwide since AD 1500 (MacPhee and Flemming, 1997). All extant West Indian endemic terrestrial mammals are now considered endangered or highly threatened, so that a better understanding of the recent history of their congeners is a matter of urgency.


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