Avian Premaxilla and Tarsometatarsus from The
762 ShortCommunications andCommentaries [Auk,Vol. 112 The Auk 112(3):762-767, 1995 Avian Premaxilla and Tarsometatarsusfrom the Uppermost Cretaceous of Montana ANDRZEJ ELZANOWSKIa AND MICHAEL K. BRETT-$URMAN2 •Departmentof VertebrateZoology, National Museum of NaturalHistory, SmithsonianInstitution, Washington, D.C. 20560, USA; and 2Departmentof Geology,George Washington University, Washington, D.C. 20052,USA Despitea variety of fragmentary,apparently neog- is rounded and smooth,and the sidesare very steep. nathousavian fossilsknown from the uppermostCre- The largest among the neurovascularforamina scat- taceousdeposits (Brodkorb 1963, Olson 1985, Olson tered on each side are two elongatedorsal foramina: and Parris 1987),we still lack even an approximate the vessel from the rostral one coursed rostrad, whereas idea of how many neognathouslineages survived be- the vesselfrom the caudalone apparentlybifurcated yond the Cretaceous/Tertiaryboundary. Most of the into a smaller rostral and a larger caudal branch. In Maastrichtian avian bones reveal a charadriiform or addition, a number of smaller openingsperforates transitional charadriiform-gruiform morphology, eachside of the symphysis. which may be plesiomorphicfor most (Olson 1985) The ventral surfaceof the premaxillarysymphysis but probably not all of the neognaths(Elzanowski is strongly concave(Fig. lc, d). There are no distinct 1995). Other than that, there is some fossil evidence neurovascularforamina on the ventral (palatal) sur- for the existence of loons in the Cretaceous(Olson face,with the possibleexception of one small opening 1992)and mostly indirect evidencefor the pre-Ter- on the left side. The palatal shelvesof the premaxilla tiary origins of the relict pelecaniforms(Phaethon- begin from the symphysialtip and graduallybroaden tidae and Fregatidae) and procellariiforms (Elza- caudally where each of them occupiesone-third of nowski and Gaiton 1991).
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