4 October 1994 PROC. BIOL. SOC. WASH. 107(3), 1994, pp. 429-435 A GIANT PRESBYORNIS {AVES: ANSERIFORMES) AND OTHER BIRDS FROM THE PALEOCENE AQUIA FORMATION OF MARYLAND AND VIRGINIA Storrs L. Olson Abstract.•Presbyornis isoni, new species, is described from a humérus and an alar phalanx from marine sediments of the late Paleocene Aquia Formation in Maryland. About the size of the smallest living species of crane (Gruidae), it was much larger than any previously known member of the Presbyomithidae. Other fragmentary bird remains from the Aquia Formation are noted, several of which may be referable to the suborder Phaethontes of the Pelecaniformes. Additional Paleocene birds from eastern North America occur in the Hor- nerstown Formation of New Jersey, which is now considered to be Danian (early Paleocene) in age, rather than late Cretaceous. The marine sediments of the Aquia For- Genus Presbyornis Wetmore, 1926 mation crop out in the Chesapeake Bay area Presbyornis isoni, new species of Maryland and Virginia. They are of late Figs. 1, 2 Paleocene (Landenian) age and overlie the Holotype. ~l^ñ humérus lacking proxi- Brightseat Formation (Danian), between mal third, collections of the Department of which there is a disconformity representing Paleobiology, National Museum of Natural about 3.6 million years, a period of time History, Smithsonian Institution, USNM approximately equivalent to that of the ex- 294116. Collected in March 1993 by Ron- posed Aquia Formation (Hazel 1969). The ald M. A. Ison. Aquia is divided into an upper Paspotansa Type locality. • Maryland, Charles Coun- Member and a lower Piscataway Member, ty, east bank of the Potomac River, from the latter having sometimes been designat- the area designated as Bluebanks, south of ed in earlier literature as the Piscataway Liverpool Point and north of Douglas Point Formation or Piscataway Indurated Marl (Widewater Quadrangle, USGS 7.5 minute Member of the "early Eocene." These sed- series). iments accumulated in a pelagic environ- Horizon and age.•Nea.T the base of the ment, well offshore, and are reasonably pro- Upper Paleocene (Landenian), Aquia For- ductive of vertebrate fossils, e.g., turtles mation, Piscataway Member. The specimen (Weems 1988), but so far have yielded very came from near the base of the blufFexposed few bird remains. A recently collected hu- at the type locality, which is probably upper mérus is the largest and most diagnostic avi- nannoplankton zone NP5, but possibly low- an fossil yet discovered in the Aquia For- er NP6 (Laurel M. Bybell, USGS, pers. mation, As it merits description, I have comm.). On the scale of Berggren et al. taken the opportunity to review the few oth- (1985), the age would be somewhere be- er avian fossils found so far in the same tween 61 and 62 million years. strata. Measurements ofholotype (mm).•Distal width, 23.3; depth through radial condyle, Class Aves 12.9; greatest diameter of brachial depres- Order Anseriformes sion, 8.8; width and depth of shaft at ap- Family Presbyomithidae Wetmore, 1926 proximate midpoint, 10.8 X 8.2. 430 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON B C Fig. I. Hiimeri in palmar view (A-C) and phalanx 1 of major alar digit (D-E) of Presbyomithidae: A, Presbyornis isoni new species, holotype (USNM 294116); B, Telmabates antiquus (AMNH 3170); C, Presbyornis pervetus (cast, USNM 483163); D, Presbyornis isoni new species, paratype (USNM 294117); E, Presbyornis pervetus (cast, USNM 483164). All figures natural size. Paratype.•Left phalanx 1 of major alar size, there are no discernable diflerences be- digit, abraded along the posterior edge, tween P. isoni and P. pervetus, save that the USNM 294117. Collected in June 1984 by olecranal fossa appears less distinct in the Eugene Hartstein at the same locality as the former, which may be a size-related factor. holotype. Discussion. •Presbyornis is a remarkable Measurements of paratype (mm).• bird that exemplifies an early stage in the Length, 40.6; greatest diameter of proximal evolution of the Anseriformes, combining articulation, 9.5. a long-legged, shorebird-like body with the Etymology. •Named in honor of the col- head of a duck (Olson & Feduccia 1980). lector, Ronald M. A. Ison, an enthusiastic Presbyornis pervetus occurs abundantly in amateur paleontologist. lacustrine deposits of the early Eocene Green Diagnosis.•Much larger than Presbyor- River Formation of Wyoming, Colorado, nis pervetus Wetmore, 1926, or any other and Utah, and a slightly smaller form is known members of the family. Apart from found in the Paleocene of Utah and Mon- -^••'•..U: VOLUME 107, NUMBER 3 431 Fig. 2. Left humeri oí Presbyornis: (A, C, E) P. isoni new species, holotype (USNM 294116); (B, D, F) P. pervetus (part of UCMP 136541). A-B, palmar view; C-D, anconal view; E-F, distal view. Specimens coated with ammonium chloride. 1.5 x. golia (Olson 1985a: 171). The contempora- Stockholm, pers. comm.). The type species, neous genus Telmabates, from Patagonia, is T. antiquus, was considerably larger than very similar to Presbyornis and was syn- Presbyornis pervetus. onymized with that genus by Feduccia & Presbyornis isoni was much larger than McGrew (1974). Further study, however, either. To put the relative differences in has shown that the limb proportions of Tel- terms of modem analogs for size, Presbyor- mabates differ sufficiently from Presbyornis nis pervetus would have been about the size to merit retention of the genus (Per Ericson, of the largest species of Burhinus, the Bush Swedish Museum of Natural History, Stone-curlew, B. magnirostris, of Australia. 432 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Telmabates antiquus was about the size of vergent of the Pelecaniformes, relegated to a Limpkin, Aramus guarauna, whereas a separate suborder Phaethontes. The first Presbyornis isoni would have been the size fossil assigned to the family was Prophae- of a Demoiselle Crane, Anthropoides virgo. thon shrubsolei Andrews (1899), known It is possible, given its much larger size, from a skull, mandible, and partial postcra- that the feeding adaptations oí P. isoni may nial skeleton from the early Eocene (Ypre- have been difierent from those of/*, perve- sian) London Clay of England. Harrison & tus, and that were the entire skeleton avail- Walker (1976) restudied the specimen and able it might be assigned to a different genus. created a new order and family for it, only As it is, however, there is no distinction the latter being justified, however (Olson whatever to be made between these taxa 1985a). The only other fossil member of the except on size. Phaethontes is Heliadornis ashbyi Olson The considerable assemblage of birds (1985b), known from three associated bones known from the Homerstown Formation of from the Middle Miocene (Langhian) Cal- New Jersey (Olson & Parris 1987) are now vert Formation of Maryland, which was re- believed to be Danian (early Paleocene) ferred to the Phaethontidae. rather than latest Cretaceous in age (see be- low), and are older than P. isoni. Most of Family Prophaethontidae these birds were referred to the "form fam- Harrison & Walker, 1976 ily" Graculavidae, which shares similarities Genus Prophaethon Andrews, 1899 with the Presbyomithidae. Presbyornis isoni Prophaethonl sp. was larger than any of these species except Material examined.•T>\%idl end of right Laornis edvardsianus, which was much larg- humérus, USNM 483158. Collected 1 m er than P. isoni. The species in the Hor- from top of chalky shell band of Aquia For- nerstown most similar to P. isoni is Ana- mation at Capital Beltway and Central Av- talavis rex, which was a much smaller bird enue, Prince Georges, County, Maryland in which the brachial depression is longer, (Lanham Quadrangle, USGS 7.5 minute se- narrower, and not as deep, and in which the ries), by Calvin F. Allison, Jr. in 1973. Dis- shaft appears to have been relatively shorter tal width, 7.6 mm. and more curved. Right coracoid lacking part of the acro- Although the alar phalanx referred to P. coracoid and the lateral process of the ster- isoni is not a particularly diagnostic ele- nal end, USNM 483159. Collected by T. B. ment, its size and overall similarity to the Ruhoffat a road cut on Indian Head High- same element in Presbyornis makes it highly way, about 200 m north of Piscataway Creek, unlikely that it would belong to some other Prince Georges County, Maryland (Piscata- family altogether. That two elements of this way Quadrangle, USGS 7,5 minute series). presumed land bird were discovered at the "About 10-12 feet above road." This is ev- same site, the sediments of which were de- idently the same as the type locality of the posited well offshore and where bird bones fossil turtle Catapleura ruhoßi (Weems are scarce, suggests that they may have come 1988). Length to internal distal angle 28.5 from the same individual, despite having mm. been collected years apart. Remarks.•The humérus is extremely similar to that in modem tropicbirds of the Order Pelecaniformes Sharpe genus Phaethon, practically the only notice- Suborder Phaethontes able difference being the indistinctness of The modem tropicbirds (Phaethontidae, the external tricipital groove, but this may Phaethon), are the most primitive and di- be an artifact as the specimen is consider- VOLUME 107, NUMBER 3 433 ably worn in this area. It comes from a bird Abraded distal end of left tibiotarsus lack- much smaller than any living tropicbird, ing internal condyle, USNM 294118. Col- about the size of a Common Tern, Sterna lected from "Top Gully" of Aquia For- hirundo, and thus much smaller than Pro- mation at the Hampton Mall Site, Central phaethon shrubsolei or Heliadornis ashbyi, Avenue near Capital Beltway, Prince although the distal end of the humérus is Georges County, Maryland (Lanham Quad- unknown in either of those species.