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Presbyornis isoni and Other Late Paleocene Birds
from North Dakota
ABSTRACT
Paleocene fossil birds from North Dakota in the collections of
the Science Museum of Minnesota range in age from Tiffanian 3
to Tiffanian 4 and seem to represent five taxa. A humems is
referred to the anseriform Presbyornis isoni Olson, previously
known from a less complete humerus from the late Paleocene of
Maryland. All known specimens of Dakotornis cooperi Erickson,
referable to the extinct charadriiform form-family Graculavidae,
are reviewed. A cervical vertebra and a tarsometatarsal fragment,
both within the probable body-size range of Dakotornis cooperi
but probably representing different taxa, are referred to the Graculavidae.
Another distal end of a tarsometatarsus, from perhaps the
smallest currently known Paleocene bird, also is referred to the
Graculavidae. These two tarsometatarsi exhibit a mosaic of
charadriiform characters. Together with the tarsometatarsus of Telmatomis
priscus Marsh, three size classes of North American
Paleocene graculavid tarsometatarsi are now known.
Introduction
A new Paleocene species of the fossil anseriform genus
Presbyornis, P. isoni, was established by Olson (1994) on the
basis of two bones, an incomplete humems and a manual phalanx
1 of the major digit, discovered in Maryland. This is the
largest known presbyornithid. The purpose of this paper is to
describe an additional, more complete humems of P. isoni as
well as other avian fossils from three late Paleocene sites in
North Dakota: the Wannagan Creek Quarry, the Judson Locality,
and the Brisbane Locality.
The Wannagan Creek Quarry of western North Dakota occurs
in the Bullion Creek (formerly "Tongue River") Formation,
consisting of riverine and lacustrine deposits. The Wannagan
Creek fossil flora and fauna indicate a subtropical swamp
environment: the most abundant large vertebrate is the 15-ft
(4.5-m) crocodile Leidyosuchus formidabilis Erickson; the flo-
Richard D. Benson
RichardD. Benson, J.F. Bell Museum, and 100 Ecology Building, University
of Minnesota, St. Paul, Minnesota 55108, United States.
253
ra is dominated by bald cypress {Taxodium olriki (Heer)
Brown), fig {Ficus spp.), magnolia {Magnolia spp.), and sycamore
{Platanus spp.) (Erickson, 1991). About 110 mi (175
km) east of the Wannagan Creek Quarry, the Judson Locality
also occurs in the Bullion Creek Formation, in deltaic sediments
(Holtzman, 1978). The Brisbane Locality occurs in the
underlying Slope Formation (Kihm, 1993) near the contemporary
marine Cannonball Formation. The paleontology of these
two near-shore localities indicates warm-temperate cedar
swamps, the faunas of which also included crocodilians (Holtzman,
1978). Fossil footprints of probable shorebirds have been
reported from another late Paleocene site (Locality L6421)
near Wannagan Creek Quarry (Kihm and Hartman, 1995).
Nomenclature for species' binomials and English names of
modem birds follows Sibley and Monroe (1990).
AGE AND CORRELATION.—The age of the avian fossils from
Maryland reported by Olson (1994:429) is "near the base of the
Upper Paleocene (Landenian), Aquia Formation, Piscataway
Member... probably upper nannoplankton zone NP5, but possibly
lower NP6. ...On the scale of Berggren et al. (1985), the
age would be somewhere between 61 and 62 million years."
This falls within the Tiffanian North American Land Mammal
Age, the Landenian of Europe being more or less coterminous
with the Tiffanian of North America (Berggren et al., 1985).
The Wannagan Creek Quarry dates to early Tiffanian 4
{=Plesiadapis churchilli zone), within the earlier half of paleomagnetic
chron 25 Reversed (Sloan, 1987), whereas the Maryland
locality that yielded the type specimens of P. isoni dates to
the middle of chron 26 Reversed (Berggren et al., 1985), seemingly
to Tiffanian 1. The Wannagan Creek beds of North Dakota
would correlate, in the notation used in Olson (1994), to nannoplankton
zone NP7 or NP8, with an age of about 60 million
years according to the scales of both Berggren et al. (1985) and
Meehan and Martin (1994). The Judson Locality is within the
later half of paleomagnetic chron 26 Normal, in early Tiffanian
4 (Kihm, 1993, and pers. comm., 1996), probably less than
100,000 years earlier than Wannagan Creek. The Brisbane Locality
dates to early Tiffanian 3A {=Plesiadapis rex zone: Neo-