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the last has unusually slender wing bones and an extra-stout
bill. The small species in the Cookilaria group, Chatham Petrel
{P. axillaris), Cook's Petrel {P. cookii), and Pycroft's Petrel {P.
pycrofti), are smaller than the small taxon and are biogeographically
improbable. Similarly, Stejneger's Petrel {P. longirostris)
and Gould's Petrel {P. leucoptera) are subtropical or tropical
Pacific species and thus are unlikely candidates for the
small Amsterdam species.
Pterodroma macroptera
All Pterodroma long bones within the larger size range indicated
above are referred to P. macroptera for the following reasons.
Among similar-sized species, P. cervicalis is a tropical
Pacific species, so it was discounted, and P. externa from the
eastern Pacific has a much stouter bill and a different cranial
shape. Pterodroma magentae is smaller and breeds on the
Chatham Islands, and limited evidence suggests that it ranges
across the eastern Pacific. Its crania differ from those of P
macroptera, particularly in the form of the os lacrimale, as follows:
the nasal process is deeper; the exterior surface of the
ventral processes are subparallel rather than convergent on
each other; the lacrimal foramen is markedly bigger; and the
ventral border of the os ectethmoidale has a marked lump in it
rather than being straight. The fossils from Amsterdam were
the same size as those of P. solandri and those of the nominate
race of P. macroptera from Eclipse Island, Western Australia,
but are significantly smaller than those of P. macroptera gouldi
from the New Zealand region. The fossils are the same shape
as bones of P. macroptera, however, and they differ from those
of P. solandri in that (1) the cranium is less inflated posterior to
the orbit so that in dorsal view the crista temporalis is nearly
straight (posterolaterally curved in P. solandri), (2) the extension
of the crista temporalis on the processus postorbitalis is
more laterally directed (more anteriorly directed in P. solandri),
(3) the prominentia cerebellaris is compressed (rounded in
P. solandri), (4) the os palatium in P. macroptera is flat ventrally
(curved ventrally in P. solandri), (5) the foramen bound
by the lacrimal, jugal, and premaxilla is relatively shorter in P
macroptera than in P. solandri, (6) the width between the temporal
fossae is narrower in P. macroptera, (7) the lacrimals at
the point of maximum width are more angled in P. macroptera
(more rounded in P. solandri), and (8) the premaxilla has a
steep, straight posterior end in P. macroptera, but the posterior
end is shallower and notched in the relatively narrower premaxilla
of P. solandri. Pterodroma solandri is a winter breeder
on Lord Howe Island in the Tasman Sea and migrates to the
North Pacific in the southern summer, making it further unlikely
to be the Amsterdam petrel. Pterodroma macroptera is regularly
seen offshore around Amsterdam (Roux and Martinez,
1987) and as already noted, it is the only large Pterodroma
still nesting in the Amsterdam / St. Paul area.
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
Pterodroma mollis
Bones of the smaller species of Pterodroma are identical to
those of P. mollis, which has a remnant population still surviving
on Amsterdam Island (Roux and Martinez, 1987; Micol,
1995). Other similar-sized species of Pterodroma can be discounted:
P. brevirostris has an unmistakably shorter, stouter
bill; P. nigripennis is a tropical to subtropical Pacific species;
and P. inexpectata, although ranging to the Antarctic, migrates
to the North Pacific in the nonbreeding season. The size range
of the Amsterdam population is shown by the upper and lower
points of the apparently normally distributed length data (Figure
8). The smallest individuals from Amsterdam are considerably
smaller than the few available recent specimens from
Gough Island and New Zealand beaches, and they probably
represent the lower end of the size variation in a population that
is only slightly smaller than the nominate race of P. mollis
from Gough Island. Birds from the Antipodes in the New
Zealand region are most similar to the nominate race. Although
the Indian Ocean birds have been referred to a distinct subspecies,
P. mollis dubia, on the basis of color, there is much variation
in coloration, which also alters with wear (see discussion
in Marchant and Higgins, 1990).
Pterodroma arminjoniana
A few Pterodroma bones are intermediate in size between
those referred herein to P. mollis or to P. macroptera and are
similar in size to those of the Kermadec Petrel (P. neglecta),
Phoenix Petrel (P. alba), Barau's Petrel (P. baraui), and Herald
Petrel (P. arminjoniana). Pterodroma alba and P. neglecta are
primarily subtropical to tropical Pacific species (Marchant and
Higgins, 1990) and so are considered unlikely candidates; however,
P neglecta has been found recently at Round Island,
Mauritius (A. Tennyson, Museum of New Zealand, pers.
comm., May 1996). Both P. baraui and P. arminjoniana breed
in the Indian Ocean. A premaxilla in this size range from site
18, where wing bones of the intermediate-sized Pterodroma
also were found, is 33.3 mm long, 15 mm wide, and 8.1 mm
high at mid-nares, so it is much shorter and wider than either P.
neglecta or P baraui but is very similar to P. arminjoniana
(MNZ 22140) from Trindade Island in the South Atlantic.
Thus, this premaxilla and the intermediate-sized Pterodroma
wing bones from site 18 are referred to P. arminjoniana.
Pterodroma baraui
Intermediate-sized bones of Pterodroma included crania at
sites 8.3 and 8.11, two premaxillae at site 8.4 and one at site
8.6, and a fragmentary premaxilla at site 8.8. These premaxillae
are narrower and are not as deep as those of P. macroptera
from Amsterdam Island. They are narrower and more elongate
than those of P. arminjoniana but are similar to P. baraui. The
two fossil crania also are identified as P. baraui because although
they are of similar size to crania of P. arminjoniana as