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SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
FIGURE 7.—Skeletal elements of P'achyanas chathamica (MNZ S29475, PRM sample #92/91) from Te Ana a
Moe Cave, Te Whanga Lagoon, Chatham Island. Total length of cranium+premaxilla is 113.8 mm.
ing over water. In the absence, however, of any fossil record
of birds on the Chathams beyond the last 7000 years, one can
only speculate on the numbers and variety that may have
reached the Chathams in earlier times and subsequently died
out, leaving no trace of their passing. Possibly through extinction
of early colonists, but more likely as a consequence of the
serendipitous nature of transoceanic colonization ("sweepstakes
dispersal"), some significant avian groups are absent
from the known avifauna of the Chathams, including ratites
(moas and kiwis), Podicipedidae, Coturnix, Strigidae, Alcedinidae,
Acanthisittidae, Callaeidae, and Turnagra. No native
frogs, tuatara, or geckos are known, fossil or living, from the
Chathams. The one extant species of skink is possibly a geologically
relatively recent arrival.
Both extant and extinct Chatham birds are presumably derived
from the same ancestral stocks as are comparable species
on the New Zealand mainland. They have, however, evolved in
isolation and exhibit many of the same evolutionary features
found in bird faunas on other small, isolated, oceanic islands,
such as New Caledonia (Balouet and Olson, 1989), the Hawaiian
Islands (Olson and James, 1982, 1991; James and Olson,
1991), and many other islands of Australasia and the southwest
Pacific (van Tets et al., 1981; Meredith, 1991; Steadman,
1995). Typically, on oceanic islands such as these, which prior
to human colonization lacked mammalian predators, birds exhibit
increased body size and may lose their powers of flight
(McNab, 1994). The evolutionary history of Chatham Islands
birds has followed this same path. Most of the Chatham Islands
land birds and waterfowl tend to be larger than their mainland