An Immature Specimen of Baptornis Advenus from the Cretaceous of Kansas

October 1977] General Notes 787

Egg weights were recordedfor 23 eggs,all but 2 of them infertile. The 2 fertile eggs,produced in 1963, weighed204.4 g and 199.7 g at 9 daysand at 13 daysprior to hatchingrespectively. The 21 infertile eggsfor which weights were obtained near the start of incubation varied from 199.0 to 258.0 g with a distribution as follows: 19%210 g (2 eggs),211-220 g (1), 221 230 g (2), 231-240 g (6), 241-250 g (4), 251-258 g (6). Sevenincubation periods have beenrecorded since 1963; 3 of 35 days, 2 of 36 days, 1 of 37 days, and 1 of 32 days. We thank Joseph Bell, Donald Bruning, Eric Edler, and Andrew Winnegar for observations and comments.--WILLIAM CONWAYAND ALLEGRAHAMER, New York Zoological Society, Bronx, New York 10460. Accepted 19 Aug. 76.

An immature specimen of Baptornis advenus from the Cretaceous of Kansas.--In 1962 Bonner discovereda partial skeletonof the Cretaceousdiving bird, Baptornis advenus, KansasUniversity Vertebrate Paleontology(KUVP) 16112, from the Smoky Hill (upper) member of the Niobrara Chalk. The specimenwas in KUVP LoganCounty collectinglocality 20, in the SE ¬, NW ¬, sec.13, T 15 S, R 34 W, Logan County, Kansas. This is the samelocality and horizon as the quarry that producedmany slabsof the floating crinoid, Uintacrinus socialis (Miller et al. 1957). The skeletonof Baptornis was fragmentary and from a young individual. Parts of the premaxilla, cervical, thoracic, and sacral vertebrae, pelvis, both femora, both tibiotarsi, both tarsometatarsiand somephalanges were recovered.Immature specimensof Mesozoicbirds occurinfrequently, although the proximal end of a tarsometatarsusassociated with the type of B. advenus is also from a very young individual. The adult skelton of Baptornis has recently been describedin detail by Martin and Tate (1976). In the presentspecimen, the fragment of premaxilla (Fig. 1, I) comesfrom a point just anterior to the external nares and indicatesa bill similar to that of Hesperornis.If teeth were present,they were restrictedto the maxillary as in Hesperornis. The cervical vertebrae include specimensthat seemto correspondto the 8th, 13th, and 14th cervicalsof Hesperornis,but appear to be shorterand more massivethan in that genus.The ventral border of the centrum correspondingto the 8th cervical is flat and hourglassshaped. The vertebrae correspondingto the 13th and 14th cervicalshave very short centraand long sublateralprocesses, which do not unite ventrally. Five vertebraebearing rib facetsare present.Two of thesehave narrow articulationsof the centra and narrow hypapophyses.Another vertebra correspondsto the 22nd vertebra in Hesperornis and has small hypapophyses.The two following vertebrae are also preserved.That correspondingto the 24th in Hesperornisdoes not bear a rib. It hasa shorttransverse process with a broad triangular area on its lateral margin for articulation with the ilium. A portion of the sacrum with three fused vertebrae is also present. Several of the dorsal vertebrae have small, shallow pits on the articular surface of the centrum although all are fully heterocoelous. The right femur (Fig. 1, A) is representedby fragmentsof both the proximal and distal ends,while the left femur is representedby a portionof the proximalend includingthe head. The femur seemsto have achieved mostof the adult proportions(Fig. 1, B). The tibiotarsiare representedby the distalend and part of the shaft of the right (Fig. 1, C) and the distal end of the left. The tarsalswere not fusedeither to the tibia or to the metatarsalsand thereforewere not recovered.The shaftof the tibiotarsusis very slender,flat and onlyabout 72% as wide as that of an adult. This specimenwas mistakenly identified as the proximal end of a large humerusby Walker (1967, p. 65). The three metatarsalsare not fusedin the proximal end of KUVP 16112, although the distal end was completely ossified. The metatarsals increase in size from the secondto the fourth. The tarsometatarsus(Fig. 1, F) is at least 10% smallerth an that of an adult (Fig. 1, G). Proximalends of two phalangesand the distal end of another are present. Descriptionsof immature fossilbirds are rare, althoughHoward (1945) publisheda very usefulpaper on the growthstages of the tarsometatarsiof the fossilturkeyParapavo californicus, from RanchoLa Brea. She recognized nine stages of development from newly hatched chicks to fully grown birds. The present specimensof Baptorniswould seemto fall into her "groupIV" which shecharacterized as having the "distal end nearly completelyformed exceptexternal foramen not entirely closedoff. Proximal end still spongy" (Howard 1945: 598). The proximal end (Fig. 1, H) associatedwith the holotypeof Baptornis advenusby Marsh (1880)would probablybelong in Howard's"group V" wherethe proximalend is lessporous and is flattened. It has a single small unfused tarsal which is roughly triangular in shapeand is situated between metatarsals II and IV. A partial skeletonin the collectionsof the Field Museum of Natural History (FMNH 395) hasthe tibiotarsi with someof the suturesfor the tarsals(Fig. 1, D) still visible.One largetarsal element covers the distalend. The astragalushas not fused and has a longdorsal process. It is completelyfused in the adult(Fig. 1, E) but the fusionappears to occurmuch later in the ontogenyof Baptornis than in modernbirds. 788 GeneralNotes [Auk, Vol. 94

Fig. 1. Comparisonof juveniles(A, C, D, F, H, I) and adults(B, E, G) ofBaptornis advenus:A, KUVP 16112, right femur, anterior view; B, UNSM 20030, right femur, anterior view; C, KUVP 16112, distal end of left tibia, anterior view (tarsals missing);D, FMNI-I 395, distal end of left tibiotarsus, anterior view {astragaulus not fully fused); E, UNSM 20030, distal end of tibiotarsus, anterior view (fully mature); F, KUVP 16122, left metatarsalsanterior view (tarsalsmissing); G, FMNI-I 395 left tarsometatarsus,anterior view; H, YPM 5768, anterior and posteriorviews of proximal end of left tarsometatarsus(tarsal not fully fused); I, KUVP 16112, dorsal and lateral views of premaxillary fragment, scale equals 2 cm. October 1977] GeneralNotes 789

The Hesperornithiformes are a primitive side branch of the early avian radiation that shares many characterswith Archaeopteryxand theropoddinosaurs (Martin and Tate, 1976). However the immature Baptornis material showsthat the major featuresof the mesotarsaljoint must have been fully established beforethe separationof the Hesperornithiformesfrom the main avian line. The fusionof the tarsalsnear the time of the termination of growth was also establishedbefore this split. It seemscertain that KUVP 16112is from a youngbird considerablysmaller than an adult and lackingthe developmentof many of the groovesand ossifiedarticular surfaces which assistthe functioningof the foot. One wondersif sucha youngbird would be likely to havetraveled long distances away from shoreor if the skeletonmay be interpreted as evidencethat Baptornis nestedin the vicinity of the find. Over one-third of the known specimensof Baptornis advenus have been from immature birds while Hesperornis, which is known from many more specimens,has not producedany comparablyyoung individuals.This suggeststhat the youngof Hesperornisdid not ventureso far out to seaas did thoseof Baptornis, or that Hesperornisnested in a different region. We are gratefulto M. Jenkinsonand M. A. Neuner for criticallyreading the manuscript.Special thanks are due to C. B. Schultz, University of Nebraska State Museum (UNSND, R. Zangerl, Field Museum (FMNH), andJohn Ostrom, Yale PeabodyMuseum (YPM) for the useof specimensin theircare. Marjorie Joseph prepared the illustrations.

LITERATURE CITED

HOWARD,H. 1945. Observationson young tarsometatarsiof the fossil turkey Parapavo californianus (Miller). Auk 62: 596-603. MARSH, O. C. 1880. Odontornithes,a monographof the extinct toothedbirds of North America. U.S. Geol. Expl. 40th Parallel, vol. 7: Washington,D.C., GPO. MARTIN,L. D., ANDJ. TATE,JR. 1976. The skeletonof Baptornisadvenus (Aves, Hesperornithiformes): in Collectedpapers in avianpaleontology honoring the 90thbirthday of Alexander Wetmore (Storrs L. Olson, Ed.), SmithsonianContributions to Paleobiology27: 35-66. MILLER, H. W., G. F. STERNBERG,AND m. g. WALKER. 1957. UintacrinusLocalities in the Niobrara Formation of Kansas. Trans. KansasAcad. Sci. 60(2): 163-166. WALKER,M. g. 1967. Revival of interestin the toothedbirds of Kansas.Trans. KansasAcad. Sci. 70(1): 60-66.

LARRYD. MARTIN AND ORVILLEBONNER, University of KansasMuseum of Natural History and Departmentof Systematicsand Ecology,Lawrence, Kansas 66045. Accepted19 Aug. 76.

Golden Eagle predation on pronghorn antelope.--The pronghornantelope (Antilocapra ameri- cana)and GoldenEagle (Aquila chrysaetos) coexist in many partsof the West, but direct observationsof goldeneagle predation on pronghorns are rare. Burns(1970, Canadian Field Naturalist 84:301) described in detail the killing of a femalefawn which had an estimatedweight of 31.7 kg. Lehti (1947, J. Wildl. Mgmt. 11: 348) reportedfinding a pronghorncarcass believed to have beenkilled by a Golden Eagle. Although predationby GoldenEagles has been reported for severalgame species and livestock, most studies show a predominanceof lagomorphsin Golden Eagle diets (McGahan 1968, Auk 86: 1). On 31 December1974, while censusing pronghorns in a winterconcentration ground along Interstate 80, 45 km west of Laramie, Wyoming,I saw a GoldenEagle attack a male pronghornfawn. The incident occurredat 0745hours. The fawn wasin a herdof 135pronghorns feeding midway up a smallhill. The eagle approachedover the top of the hill approximately10 m abovethe groundand struckthe fawn in the back, momentarilystunning it. Momentum carried the eagle to the ground. The herd ran off in the opposite directionand had traveled 400 m beforethe eagleagain becameairborne. The fawn followedthe herd, although far behind it. After thefawn hadrun abouta kilometerthe eagle again hit it in theback, injuring it severely.Both fell to the ground.The eaglecould not hold on to thefawn, whichgot up andran slowlyafter the herd.After the fawn had run 200m theeagle struck again and pulled the fawn to the groundwith its talonsembedded in the fawn'sback. After about30 sec,the fawn stoodup with theeagle on his back and charged around in a circle.