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NUMBER 89 263
10mm
FIGURE 1.—Proximal end of the left humerus of Graculavus augustus, new species (holotype, AMNH 25223): a,
cranial view; b, caudal view; c, medial view.
base of ventral tubercle, 28.5 mm; internal width of tricipital
fossa through base of ventral tubercle and distal border of impression
for M. scapulohumeralis caudalis, 9.5 mm; distance
from capital incisure to dorsal tubercle, 17.3 mm
ETYMOLOGY.—From the Latin augustus, majestic, for the
large size of the bird, as well as the month of collection.
DIAGNOSIS.—Derived characters of the Neornithes: moderate
enlargement of the articular head of the humems. Derived
characters within the Neornithes: very large bicipital crest and
prominence; thin, erect ventral tubercle; large dorsal tubercle;
and well-defined caudal margin of the humems.
The diagnosis of Graculavus is based on the differential diagnosis
for Graculavus velox (Shufeldt, 1915; Olson and Parris,
1987). Graculavus augustus is very similar to G. velox but
is about one-third larger, and the area between the ventral and
dorsal tubercles is relatively wider and flatter.
DESCRIPTION.—The new specimen comes from a very large
bird with the proximal end of the humems in the size range of
the largest gulls or geese. Surface preservation is excellent. The
tips of the dorsal and ventral tubercles are missing, but the
shape of the remaining base of each is consistent with the morphology
of Graculavus velox. The pectoral crest is missing (as
it is in G. velox). The bicipital crest is broken off just distal to
the impression for M. scapulohumeralis caudalis. The shaft is
broken off slightly distal to the tricipital fossa.
The bone is delicately sculpted. The proximal end of the humems
is very flat and broad. The articular head is small. On the
cranial surface of the humerus, the bicipital prominence is
large, slightly raised, and rounded. The sulcus for the trans­
verse ligament is deep and well defined but short, extending
from the border of the bicipital crest only as far as the ventral
tubercle. The impression for M. coracobrachialis cranialis is
shallow and indistinct. In caudal view, the preserved base of
the dorsal tubercle shows that it was moderately large and
strongly protmdent from the shaft and was very far from the articular
head. The head of the humems does not overhang the
capital incisure, which is deep and well defined. The caudal
end of the incisure is excavated into a sulcus continuous with
the deep sulcus undercutting the articular head. Distally this
sulcus is bordered by a large, well-defined transverse scar extending
from the base of the ventral tubercle diagonally toward
the articular head. Evidently the dorsal tubercle also was deeply
undercut, but breakage obscures detail.
The bicipital crest is broad and appears to have been rounded
rather than sharply angular. The impression for M. scapulohumeralis
caudalis is extremely large and well defined. The
ventral tubercle is slender and erect, but breakage prevents seeing
its total length. The tricipital fossa is very large and wide
and is without a pneumatic foramen. There is a central tumescence
in the fossa, separating it into proximal and distal basins.
The tumescence is the obverse side of the deep sulcus for the
transverse ligament, visible because the cranial wall of the fossa
is very thin, and the fossa lacks the bony stmts and velum
usually associated with pneumaticity. The more proximal of
the two resulting basins is small in Graculavus.
The surface of the fossa distal to the tumescence shows a series
of narrow, shallow transverse ridges and sulci that appear
to be impressions of parallel muscle fibers. The striations ter-