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256 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
ca, although Olson (1994) noted that the large-bodied P. isoni
might well be assignable to a different genus were more of its
skeleton known. The individual represented by SMM P96.9.2
was slightly larger than the one represented by the holotype of
Presbyornis isoni (see Table 1). Their relative difference in
size is not greater than that often seen within avian species
(pers. obs.), including Presbyornis pervetus (P.G.P. Ericson,
pers. comm., 1996).
Order CHARADRIIFORMES
Form-Family GRACULAVIDAE
Dakotornis cooperi Erickson, 1975
FIGURE 2
MATERIAL.—Holotype: A complete right humems, SMM
P74.24.106 (figured in Erickson, 1975), collected by Bmce R.
Erickson and field crew, July 1974. Referred Material: A
complete right humems, SMM P75.22.7 (Figure 2), collected
by Bmce R. Erickson, summer 1975; a mostly complete left tibiotarsus,
SMM P75.22.25 (not figured), collected by Tim Mc-
Cutcheon, 6 July 1975.
LOCALITY.—North Dakota, Billings County, -10 mi (16 km)
NW of Medora, Wannagan Creek Quarry. Field map quadrants:
holotype humems, G-5; other humems, G-2; tibiotarsus,
K-6 (quadrants are 5 ft (1.5 m) on a side).
HORIZON AND AGE.—Late Paleocene, early Tiffanian 4,
Bullion Creek Formation, Wannagan Creek Quarry, Bed 2 (lignitic
shale); absolute age, -60 Ma.
DISCUSSION.—Dakotornis cooperi Erickson is the only bird
from Wannagan Creek to have been previously published. It
was originally described as a "primitive ibis-like bird" representing
the extinct family Dakotomithidae within the suborder
Plataleae, although its resemblance to thick-knees was mentioned
(Erickson, 1975). Although the humems of Dakotornis
shares numerous characters with the Plataleidae (ibises), especially
in its stoutness and general outline, Dakotornis more
closely resembles the Graculavidae, as Olson and Parris (1987)
pointed out, and even some of the modem charadriiforms such
as Burhinidae (thick-knees), Haematopodidae (oystercatchers),
Recurvirostridae (avocets), Laridae (gulls), and Scolopacidae
(godwits, phalaropes, etc.). These charadriiforms resemble Dakotornis
in having a shallow proximal end of the humems that
is not pneumatic, a median crest at a nearly right angle to the
shaft, and a well-developed central ridge. In all of these characters
these modem charadriiforms and Dakotornis differ from
ibises. In two other characters of the humems—the proximally
produced external tuberosity and the lack of a typically
charadriiform ectepicondylar spur—Dakotornis is as similar to
thick-knees as to ibises. The rounded ectepicondylar prominence
of Dakotornis closely resembles that of Burhinus,
whereas in other charadriiforms a spur extends from the proximal
rim of this prominence. Dakotornis would thus seem to be
a good charadriiform. Peters
(1983) and Olson (1985) noted the
similarities between ibises and
charadriiforms (and gruiforms).
The two known humeri of Dakotornis
cooperi, holotype and referred,
discovered in different
field seasons, have until now been
separated from each other through
loans to different persons; I am
the first person to see both original
specimens side by side. The
referred humerus (Figure 2)
agrees in all characters with the
holotype. The only apparent difference
is that the external tuberosity
of the holotype (as figured in
Erickson, 1975) appears much
narrower and sharper than the
broad, rounded external tuberosity
of the referred humems. The apparent
narrowness of the tuberosity
in the holotype, however, is due
only to breakage. These two right
humeri of Dakotornis cooperi are
of nearly identical size; the holotype
is 87.1 mm long, and the other
is 89.0 mm long.
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:'/;•• 4
FIGURE 2.—Referred right
humerus of Dakotornis
cooperi, SMM P75.22.7
(x 1), anconal view.
The tibiotarsus (SMM P75.22.25) was tentatively assigned to
Dakotornis cooperi on the basis of size and provenance. Olson
and Parris (1987) have noted the graculavid nature of this spec-
GRACULAVIDAE, gen. et sp. probabiliter indescript.
MATERIAL.—A mostly complete third cervical vertebra, 18.5
mm long, -15 mm wide (both anteriorly and posteriorly),
SMM P77.7.159 (not figured); collected by Richard C. Holtzman,
summer 1977.
LOCALITY.—North Dakota, Morton County, -8 mi (13 km)
S of Judson; Judson Locality.
HORIZON AND AGE.—Late Paleocene, early Tiffanian 4,
Bullion Creek Formation, Judson Locality; absolute age, -60
Ma.
COMPARISONS.—This specimen is referred to the Graculavidae
due to its Paleocene age and its close resemblance to
modem charadriiform cervical vertebrae. This cervical vertebra
is identified as the third on the grounds of its caudally oriented,
long-bottomed cariniform hypapophysis, gracile neural spine,
and reduced pleurapophyses. The third cervical is typically a
short vertebra, unlike this specimen, which is 1.2 times longer
than its width, although this degree of elongation is common
among charadriiforms. In its general outline and proportions
between its parts, the specimen most closely resembles the cer-