A hesperornithiform limb bone from the Basal Greenhorn Formation (Late Cretaceous; Middle Cenomanian) of North Central Kansas

Department of Earth Sciences, University of Southern California, Los Angeles,California 90007 U.S.A., abell@nhm.org.The vast majority of bird remains from the Late Cretaceous ofNorth America are members of the extinct Hesperornithiformes,a group of highly specialized, foot-propelled diving birds. Thefirst known hesperornithiform bird (Hesperornis regalis) fromNorth America was described by Marsh (1872) on the basis of apartial specimen that he discovered in 1871 in the NiobraraChalk of western Kansas. Marsh (1876) described two otherspecies of Hesperornis (H. crassipes and H. gracilis) as well as amember of a new family of hesperornithiform, Baptornisadvenus (1877), from the Niobrara of Kansas. At about the sametime, Seely (1876) described the oldest known hesperornithiformbirds (Enaliornis sedgwicki and E. barretti) from the Late Creta-ceous (Early Cenomanian) Cambridge Greensand of England.Williston (1898) summarized the original discoveries of toothedbirds in Kansas reported by Marsh and discussed additionalspecimens subsequently acquired by the University of Kansas.More recently, Martin (1984) described Parahesperornis alexifrom the upper Smoky Hill Chalk (Upper Santonian-LowerCampanian) of Kansas, and a Middle Cenomanian hesperor-nithiform fauna was described from Saskatchewan (Tokaryket al. 1997; Cumbaa et al., 2006).While the Hesperornithiformes have a global distributionfrom the Early Cenomanian (Galton and Martin, 2002) to theMaastrichtian (Hou, 1999; Dyke et al., 2006), all previouslyknown hesperornithiform specimens from Kansas are Santonianto Early Campanian in age (Martin and Bonner, 1977). Al-though most hesperornithiform specimens from Kansas havelittle or no reliable contextual information, it appears that theoldest remains are from the Smoky Hill Chalk member of theNiobrara Chalk (Santonian). The oldest known North Americanhesperornithiform remains were reported by Tokaryk et al.(1997, see also Cumbaa et al., 2006) from Middle Cenomanianbone beds along the Carrot River near the Pasquia Hills ineastern Saskatchewan, Canada. A new genus, Pasquiaornis, be-longing to the Baptornithidae has been described from thesedeposits and two species, P. hardiei and P. tankei, have beenidentified thus far (Tokaryk et al., 1997). Interestingly, none ofthe better known hesperornithiforms from lower latitudes havebeen found in these older deposits.Here we describe a specimen belonging to a new taxon ofhesperornithiform from the basal Lincoln Limestone memberof the Greenhorn Formation (Cenomanian) of Kansas. This oc-currence pushes back the fossil record of hesperornithiforms inthe United States to a point comparable to the earliest knownrecords from Canada. The specimen described here, FHSM VP-6318, was collected by R. Zakrzewski in 1979 while on a fieldtrip with students (pers. comm., 2008) and is now housed in theSternberg Museum in Fort Hays, Kansas (FHSM). While Martin(1983:313) mentioned the specimen as “an Enaliornis-like tarso-metatarsus from the Cenomanian, Greenhorn Formation, Kan-sas, in the Sternberg Museum,” he did not cite or otherwisedescribe it. Tokaryk, et al. (1997, p. 174) and Rees and Lindgren(2005, p.1326) cited Martin’s remarks, but, other than a briefcomparison of FHSM VP-6318 to Pasquiaornis (Tokaryk et al.,1997), no further information has been published. Therefore,this paper presents the first detailed description with figures ofthe specimen.LOCALITY/STRATIGRAPHIC OCCURRENCEFHSM VP-6318 was surface collected from the basal portionof the Lincoln Member of the Greenhorn Limestone on June 21,1979 about 2.5 km east of the town of Fairport, Kansas in west-ern Russell County, Kansas. The exact locality is on record atthe Sternberg Museum of Natural History, Fort Hays State Uni-versity, Hays, Kansas. Stratigraphically, the specimen had erod-ed from a limestone ledge less than 1 m above the contact of theLincoln Member and the underlying Graneros Shale (Zakr-zewski, pers. comm., 2008). The basal Lincoln Member is char-acterized by skeletal limestones composed of a well cementedmatrix containing abundant inoceramid prisms, valves and frag-ments, as well as other invertebrates and vertebrate remainsincluding numerous fish bones, scales, and teeth (Hattin, 1975;Liggett, et al., 2005). FHSM VP-6318 is considered to be upperMiddle Cenomanian in age.Liggett, et al. (2005) described a mixed marine and terrestrialfauna, including sharks, bony fish, a pliosaur (Brachaucheniuslucasi), a lizard (Coniasaurus cf. crassidens) and the earliestknown Kansas pterosaur, from a lag deposit at the contact be-tween the Lincoln Member of the Greenhorn Limestone and theGraneros Shale at the same locality where FHSM VP-6318 wascollected. Liggett, et al. (2005) noted that an