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The Hesperornithiformes constitute the first known avian lineage to secondarily lose flight in exchange for the evolution of a highly derived foot-propelled diving lifestyle, thus representing the first lineage of truly aquatic birds. First unearthed in the 19th century, and today known from numerous Late Cretaceous (Cenomanian-Maastrichtian) sites distributed across the northern hemisphere, these toothed birds have become icons of early avian evolution. Initially erected as a taxon in 1984 by L. D. Martin, Parahesperornis alexi is known from the two most complete hesperornithiform specimens discovered to date and has yet to be fully described. P. alexi thus contributes significantly to our understanding of hesperornithiform birds, despite often being neglected in favor of the iconic Hesperornis. Here, we present a full anatomical description of P. alexi based upon the two nearly complete specimens in the collections of the University of Kansas Natural History Museum, as well as an extensive comparison to other hesperornithiform taxa. This study reveals P. alexi to possess a mosaic of basal and derived traits found among other hesperornithiform taxa, indicating a transitional form in the evolution of these foot-propelled diving birds. This study describes broad evolutionary patterns within the Hesperornithiformes, highlighting the significance of these birds as not only an incredible example of the evolution of ecological specializations, but also for understanding modern bird evolution, as they are the last known divergence of pre-modern bird diversification.

New remains of Hesperornithidae are described from several Late Cretaceous (Campanian) localities of the Lower Volga Region (European Russia). New specimens from Rychkovo and Karaykino localities cannot be referred to as Hesperornis rossicus Nessov et Yarkov, 1993 and likely represent a new undescribed species. Bones from Rychkovo belonged to immature individuals with an incompletely formed tarsometatarsus, which is comparable in size to those of adults known from Karyakino. A tarsometatarsus from the Malaya Rybka locality belongs to a smaller hesperornithiform species and represents the first avian record in this locality. An even smaller hesperornithiform from the Bereslavka locality resembles Asiahesperornis bazhanovi Nessov et Prizemlin, 1991. We discuss the systematics of Eurasian hesperornithiforms. We adhere to the validity of Hesperornis rossicus and doubt of the assignment to this species of Swedish materials. Asiahesperornis bazhanovi is undoubtedly a separate valid taxon of hesperornithiforms, but the generic name Asiahesperornis Nessov et Prizemlin, 1991 may be a junior synonym of Parahesperornis Martin, 1984.

A new hesperornithiform bird specimen from Devon Island in the Canadian High Arctic is represented by three cervical vertebrae and is assigned to Canadaga arctica. The new specimen is only the second occurrence of C. arctica and corresponds in morphology and size to the type specimen from Bylot Island, also in the High Arctic. This new fossil adds to the record of North American hesperornithiforms, which had a well-documented Arctic presence. Body size comparisons of all North American specimens from the Campanian reveal that the largest known hesperornithiforms were from high latitudes, but otherwise no clear correlation between body size and latitude is apparent. The largest hesperornithiforms (Canadaga arctica and Heperornis regalis) are found at the highest latitudes, while the smallest forms (Baptornis advenus and Parahesperornis alexi) are found at the southern extent of the birds’ range. Coniornis (a medium body-sized genus) is only found in the middle of the range. No size trends are discernable w...

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

Despite the abundance of hesperornithiform fossils from the Western Interior of North America, particularly the Niobrara Chalk of Kansas, few specimens are known of Parahesperornis, a toothed, foot-propelled diving bird somewhat smaller than Hesperornis. Numerous specimens of three species of Hesperornis as well as those of Baptornis advenus are known from the Smoky Hill Chalk of western Kansas, but only two specimens of Parahesperornis have been collected to date. This paper presents a new specimen of Parahesperornis and a detailed description of the tarsometatarsus of this genus. Minor differences in morphology of the isolated tarsometatarsus presented here prevent its inclusion in Parahesperornis alexi, however these differences are not sufficient to warrant the designation of a new taxon at this time.

A recently discovered skull of the Cretaceous toothed diving bird Hesperornis permits evaluation of previous descriptions of the skull, analysis of cranial kinesis in hesperornithid birds, and discussion of the evolution of avian cranial kinesis. We found no evidence in hesperornithids for mesokinesis, a system that in lizards involves relative movement of the frontals and parietals. "Maxillokinesis," the fore-aft movements of the palatomaxillary arcade, was also rejected. Evidence for cranial kinesis in hesperornithid birds involves the presence of a streptostylic quadrate bone of virtually modern morphology, three types of flexion zones at the posterior end of the upper jaw, and a hiatus in the nasalinterorbital septum. Among the forms of kinesis found in modern birds, prokinesis, in which the upper jaw moves as a unit, was the dominant type of cranial kinesis in hesperornithids as indicated by the rigid construction of the upper jaw, the position of the holorhinal nostril, and the anteriorly truncate mesethmoid bone; rhynchokinesis and amphikinesis were not possible. Prokinesis is considered primitive for at least the group including Hesperornithiformes and later birds. Discovery of prokinesis in Hesperornis represents the first time all of the morphological correlates of prokinesis have been identified in a bird plesiomorphically lacking pterygoid segmentation. Received 23 April 1987, accepted 5 October 1987. THE skulls of birds have long been recognized as being capable of intracranial mobility (Herissant 1748). After Nitzsch's (1816-1817) analysis, study of avian cranial kinesis received little attention until the beginning of the 20th century (Versluys 1910, 1912). The general patterns of avian kinesis, prokinesis and rhynchokinesis, have been described for modern birds (e.g. Hofer 1949, Bock 1964, Biihler 1981, Zusi 1984). The analyses of the evolution of cranial kinesis in birds, however, have been largely theoretical. In part this is due to lack of sufficient fossil data on the early stages of avian cranial anatomy. A newly discovered fossil bird from the Triassic of Texas was examined by two of us (LDM and LMW) and, although streptostylic, was found to lack the morphological features characteristic of modern avian cranial kinesis. Before the discovery of Triassic birds, the late Jurassic bird Archaeopteryx was the oldest and most primitive known member of the Aves. The anatomy of Archaeopteryx has been the focus of previous studies involving the evolution of cra3 Present address: Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205 USA. nial kinesis in birds (Bock 1964, Wellnhofer 1974, Whetstone 1983, Biihler 1985). Unfortunately, only three specimens of Archaeopteryx preserve cranial material, and all have important details obscured by crushing. Thus, interpretation of the osteological features associated with kinesis is difficult. One aspect of cranial kinesis in Archaeopteryx, namely mesokinesis, can be assessed because of new preparation of the "London" cranium (Whybrow 1982). These findings are discussed below. Although preservational problems prevent detailed analysis of kinesis in Archaeopteryx, one group of Mesozoic birds, the Hesperornithiformes, has sufficiently preserved fossil material. Marsh (1880) described the nominative form Hesperornis. Fossils of hesperornithiform birds are currently restricted to Cretaceous strata. These birds had lost the capacity for flight and became such highly specialized foot-propelled divers that they could not bring their legs under their bodies and stand upright (despite Marsh's oft-repeated restoration; Heilmann 1926, Martin 1980). Teeth are associated with all of the cranial specimens, some of which have teeth still implanted in the jaws. There are four described genera of Hesperornithiformes and others as yet undescribed (Martin MS). Presently, three families are rec111 The Auk 105: 111-122. January 1988 This content downloaded from 157.55.39.255 on Wed, 25 May 2016 06:05:03 UTC All use subject to http://about.jstor.org/terms 112 BUJHLER, MARTIN, AND WITMER [Auk, Vol. 105 ognized: the early Cretaceous Enaliornithidae, including only Enaliornis (Seeley 1876); the late Cretaceous Baptornithidae, including only Baptornis (Marsh 1880, Martin and Tate 1976); and the late Cretaceous Hesperornithidae, including Hesperornis and Parahesperornis (Marsh 1880, Martin 1984). Cranial materials of Baptornis and Enaliornis are fragmentary and are insufficient to address kinesis. Thus, we restrict the following discussion of cranial kinesis to data derived from the hesperornithids Parahesperornis and, in particular, Hesperornis. Kinematics of the hesperornithid skull were ignored by Marsh (1880). Shufeldt (1915) and Heilmann (1926) did not study the original specimens but restored the palate of Hesperornis as being similar to that of a loon. These reconstructions are inaccurate, however, and the hesperornithid palate is unique (Witmer and Martin 1987). Gingerich (1973, 1976) studied the actual fossils described by Marsh (1880), provided a reconstruction (in reality a composite of Hesperornis and Parahesperornis), and discussed cranial kinesis. Our investigations of hesperornithid birds provide detailed positive evidence for prokinesis in a Mesozoic bird and give insight into the evolution of cranial kinesis in birds.

Both Archaeopteryx and the hesperornithids (Hesperornis and Parahesperornis) have open sutures between the different skull bones. These sutures are growing zones and in adult modern birds they are usually lost because modern birds have a restricted growing phase. The suture between the frontals and parietals is - contrary to statements in the literature - neither in Archaeopteryx nor in Hesperornis or Parahesperornis developed as an intracranial articulation, i.e. these early birds had no mesokinesis. The suture between the maxilla and premaxilla did not allow gliding movements, i.e. no maxillokinesis. In Archaeopteryx probably a primitive type of prokinesis had been developed. In Hesperornis and Parahesperornis a prokinetic mechanism had been developed which was very similar to the kinematical condition of the upper jaw of modern prokinetic birds., Archaeopteryx, de même que les Hesperornithides (Hesperornis et Parahesperornis), a des sutures ouvertes entre les différents os du crâne. Ces sutures sont des zones de croissance et chez les oiseaux modernes adultes elles sont généralement perdues parce que les oiseaux modernes ont une phase de croissance de durée réduite. Contrairement aux affirmations trouvées dans la littérature, ni chez Archaeopteryx, ni chez Hesperornis ou Parahesperornis, la suture entre les frontaux et les pariétaux n'est développée en une articulation intracrânienne, c'est-à-dire que ces premiers oiseaux n'avaient pas un crâne mésocinétique. La suture entre le maxillaire et le prémaxillaire ne permettait pas de mouvements de glissement, c'est-à-dire pas de maxillocinétique. Chez Archaeopteryx devait exister un type primitif de procinétique. Chez Hesperornis et Parahesperornis s'est développé un mécanisme très semblable à celui qui existe dans la mâchoire supérieure des oiseaux procinétiques actuels., Bühler Paul. On the mobility of the upper jaw and the segments of the braincase in the mesozoic birds. In: Documents des Laboratoires de Géologie, Lyon, n°99, 1987. L'évolution des oiseaux d'après le témoignage des fossiles. Table ronde internationale du CNRS, Lyon-Villeurbanne, 18-21 septembre 1985. pp. 41-48.