Genus Thambetochen Olson and Wetmore, 1976
Type species:Thambetochen chauliodous Olson and Wetmore, 1976; by original
designation.
Included species: T. chauliodous Olson and Wetmore, 1976; T. xanion, new
species.
Distribution: Oahu, .Molokai, and Maul
Emended diagnosis:M oa-nalos differing from Chelychelynechenin that the
rostrum is not greatly vaulted and widened, and the occlusal surfaces of the
dentaries are not flattened but are ridged and bear well developed "teeth." Nostril
comparatively large, longer than high. Mandibular symphysis straight, coronoid
area not greatly expanded, lateral protuberance of coronoid reduced and more
ventrally situated, retroarticular process long and narrow.
Compared with Ptaiochen, the nostrils are situated farther posteriorly, with the
rostral tip anterior to the nostril being longer; the midline groove on the palatal
surface of the rostrum is deeper and wider; the prefrontals (lacrimals) are much
smaller; the roof of the orbits is expanded laterally and contains deep impressions
for the salt glands on the ventral surface; the temporal fossae and the scars for
attachment of the dorsal neck musculature are much more extensive, whereas the
scar for M. depressor mandibulae has become more elongate and narrow; the
overall outline of the cranium in lateral view is more flattened dorsally and in
posterior view is squared. The coracoid is proportionately shorter, more robust,
and has the sternal end much more expanded (not differing greatly from Chelychelynechenin
this respect).T he head of the femur is not angled as much proximally
and is more nearly on a level with the trochanter, and the fibula lacks a
distinct, squared crest on the anterior margin. The syringeal bulla is smaller and
differs in several qualitative features.
Thambetochen chauliodous Olson and Wetmore, 1976
(Figs. 10B, D, 11A, C, E, G, 12A, C, D)
Thambetochen chauliodous Olson and Wetmore, 1976: 252.
"Maui Thambetochen sp. A" Olson and James, 1984:772.
"Thambetochen sp." James et al., 1987:2351.
Holotype:N early completea ssociateds keleton,B BM-X 146029.
Type locality: Site 1, Moomomi dunes, Molokai, Hawaiian Islands.
Distribution: Molokai: Moomomi dunes and Ilio Point. Maul: lava tubes on
the southern slope of Mt. Haleakala.
Emended diagnosis: Differs from T. xanion in larger size, shorter, more decurved
tip of rostrum, larger nostril, wider internarial bar and narrower lateral
nasal bar.
Remarks: The considerable amount of material of Thambetochen from the
duneso f Molokai palesb y comparisonw ith the hundredso f beautifullyp reserved
bones that are now available from the lava tubes of Maul. On Maui, Thambetochen
is less common at higher elevations than Ptaiochen, which in turn is much less
abundant in the lowlands.
Given the amount of variation in the populations from Maul and Molokai, we
have not been able to detect any certain differences between them. For the time
beingw e would refer the Maui populationt o T. chauliodousw, hich was originally
described from Molokai. There is one possible difference, however, that we are
unable to assessw ithout better-associatedin dividual skeletons,p articularly from
Molokai. The holotype of T. chauliodousw as a completea rticulated skeletonw ith
the pectoral girdle in place. The specimen was very carefully prepared, so that it
is certain that this individual did not possessa furcula. Nor have we encountered
any furculae or fragments thereof among the material of T. chauliodous from
Molokai. On the other hand, there are three distinct types of anafid furculae in
the Maul deposits that we assume to correspond with Branta and the two moanalos
found there. The furculae of the moa-nalos are weak, with widely divergent
rami, those belonging to Ptaiochen being markedly flattened antero-posteriorly.
Although it appears that the population of Thambetochen on Molokai may have
lacked the furcula and that the population on Maul retained it, it is also possible
that this condition varied individually.
Storrs L. Olson & Helen F. James,
Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part I. Non-Passeriformes
Ornithological Monographs 45 (1991)
The American Ornithologists' Union, Washington D.C.
elibrary.unm.edu/sora/om/om045.pdf
