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Both the evolution of tooth morphology and the relationship between dental features and diet in toothed birds have long been studied. Here we quantify variation in tooth crown shape in 28 key Mesozoic bird species, and examine differences in dental morphology among birds belonging to different taxonomic groupings and inferred to have had different diets. Using geometric morphometric methods (GMM) and phylogenetic comparative methods (PCM), we found few clear differences in tooth crown shape between different taxonomic and ecological categories, and our analysis provides little support for many dietary inferences drawn in previous studies. However, the Solnhofen Archaeopteryx, Jeholornis, Protopteryx, Pengornis, Longipteryx, Tianyuornis, Mengciusornis, Ichthyornis and Hesperornis all were found to possess relatively specialized tooth crown shapes, perhaps reflecting specialized diets such as insectivory, granivory, piscivory and consumption of soft-shelled arthropods. Similarity in tooth crown shape across many Mesozoic birds may indicate the lack of dietary specialization, and the association between tooth form and diet may have been weakened in any case by ‘functional replacement’ of the dentition by a horny beak and, in many cases, gastroliths.

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.

Here we describe a new hesperornithiform specimen from the Upper Cretaceous Kanguk Formation of Devon Island, Nunavut, Canada. This specimen (NUVF 286) is referred to cf. Hesperornis sp. based on size and shape of femora and teeth preserved with other skeletal elements. Previous osteohistologic analyses indicate a subadult ontogenetic stage at the time of death. This new cf. Hesperornis specimen includes the first teeth associated with a high-latitude hesperornithiform, allowing for comments on the trophic behavior of these birds. Paleoecological reconstructions based on current knowledge of polar assemblages and comparisons to modern birds suggest that high-latitude hesperornithiform birds may have had more varied diets than previously assumed.

Evidence from the Pierre Shale (Late Cretaceous) of South Dakota is presented for an attack on a juvenile Hesperornis by a polycotylid plesiosaur. The wound healed and the Hesperornis grew to maturity. Evidence of survival provides our best information about predator prey interactions in the fossil record but are rare for birds where survival is an unlikely outcome.

A historical collection of hesperornithiform fossils from the Gammon Ferruginous, Pembina, and Millwood members of the Pierre Shale (Campanian, Upper Cretaceous) in southern Manitoba, Canada, was examined to revise their taxonomy. Only two species of Hesperornis have been recognized in previous studies on the Pierre Shale in Manitoba, but our study recognizes six species of two genera, including H. lumgairi sp. nov. H. regalis is the most common species but absent in the uppermost unit within the studied sequence. The result of this study supports the paleobiogeographic subdivision of the Campanian vertebrate fauna within the Western Interior Seaway, but not the faunal boundary that distinguishes the avian fauna of Manitoba from that of South Dakota and Kansas.

This article uses the example of Hesperornis regalis, an ancient toothed bird discovered in Kansas during the 1870s, to discuss a practice that became extremely widespread in late-nineteenth-century paleontology: the use of plaster cast replicas to circulate especially noteworthy discoveries. Building upon a growing literature at the intersection of book history and the history of science, I argue that paleontologists developed plaster casts as a compromise medium that combined some features of print with others from original natural history specimens. For example, because plaster casts were mechanical reproductions, they could be fabricated in fairly large numbers at a relatively modest price. This allowed them to circulate more readily than original fossils. At the same time, however, paleontologists treated casts as a material trace of prehistory, much like an original fossil itself. As a result, they were seen as especially authoritative and trustworthy objects of knowledge. Insofar as they combined features of print and prehistory, I argue that casts functioned as a genuine mode of publication in late-nineteenth-century paleontology, but one that foregrounded its own materiality.

The Late Cretaceous Hesperornithiformes constitute a geographically expansive order of early birds, spanning the Northern Hemisphere from Asia to North America. Within North America, hesperornithiforms have been reported from as far north as Ellesmere Island in the Arctic to the Gulf Coastal Plain of southwest Arkansas, a distribution spanning the entire Western Interior Seaway. This paper presents two new specimens of Hesperornis from the middle to late Campanian of Arkansas: an isolated phalanx from the third toe and a section of the shaft of a tibiotarsus. These are the second and third occurrences of Hesperornis from the southeastern-most portion of the range in North America. An expanded description of the only other hesperornithiform material from Arkansas, an isolated partial tarsometatarsus, is also provided. Morphometric comparisons with other hesperornithiforms show that these specimens are some of the largest known individuals of Hesperornis.

Despite extensive discoveries across the globe over the past two centuries, little phylogenetic work has been done on the Hesperornithiformes. Spanning the late Early to Late Cretaceous, hesperornithiforms are one of the most diverse groups of Mesozoic birds in terms of both their geographical distribution and the wide differences in body size and diving specializations. This study presents the first phylogenetic analysis of the Hesperornithiformes that includes a majority of the described taxa, enabling the first detailed look at evolutionary relationships within the clade. The results of this study support the monophyly of the Hesperornithiformes, which is recovered as the sister clade to the avian crown group, Neornithes. Within the Hesperornithiformes, the Brodavidae and Hesperornithidae are monophyletic while the Baptornithidae are polyphyletic. Little evidence of species-level taxonomic differentiation is found within Hesperornis, with many species indistinguishable from Hesperornis regalis. Evoluti...

Reconstruction of the soft tissues (i.e., collateral ligaments, Lig. anticum, menisci, tendon of the M. fibularis brevis) involved in the mechanism of intertarsal joint stabilization in two species of extinct birds, Hesperornis regalis and Emeus crassus, allowed insights into their locomotion. The foot-propelled diving of Hesperornis included loon-like movement of the tarsometatarsus and grebe-like movement of the toes. Movement of the tarsometatarsus in Emeus was restricted to the parasagittal plane, thus resembling those of other Ratites and most highly cursorial birds.

Background The dentitions of extinct organisms can provide pivotal information regarding their phylogenetic position, as well as paleobiology, diet, development, and growth. Extant birds are edentulous (toothless), but their closest relatives among stem birds, the Cretaceous Hesperornithiformes and Ichthyornithiformes, retained teeth. Despite their significant phylogenetic position immediately outside the avian crown group, the dentitions of these taxa have never been studied in detail. To obtain new insight into the biology of these ‘last’ toothed birds, we use cutting-edge visualisation techniques to describe their dentitions at unprecedented levels of detail, in particular propagation phase contrast x-ray synchrotron microtomography at high-resolution. Results Among other characteristics of tooth shape, growth, attachment, implantation, replacement, and dental tissue microstructures, revealed by these analyses, we find that tooth morphology and ornamentation differ greatly between the Hesperornithiformes and Ichthyornithiformes. We also highlight the first Old World, and youngest record of the major Mesozoic clade Ichthyornithiformes. Both taxa exhibit extremely thin and simple enamel. The extension rate of Hesperornis tooth dentine appears relatively high compared to non-avian dinosaurs. Root attachment is found for the first time to be fully thecodont via gomphosis in both taxa, but in Hesperornis secondary evolution led to teeth implantation in a groove, at least locally without a periodontal ligament. Dental replacement is shown to be lingual via a resorption pit in the root, in both taxa. Conclusions Our results allow comparison with other archosaurs and also mammals, with implications regarding dental character evolution across amniotes. Some dental features of the ‘last’ toothed birds can be interpreted as functional adaptations related to diet and mode of predation, while others appear to be products of their peculiar phylogenetic heritage. The autapomorphic Hesperornis groove might have favoured firmer root attachment. These observations highlight complexity in the evolutionary history of tooth reduction in the avian lineage and also clarify alleged avian dental characteristics in the frame of a long-standing debate on bird origins. Finally, new hypotheses emerge that will possibly be tested by further analyses of avian teeth, for instance regarding dental replacement rates, or simplification and thinning of enamel throughout the course of early avian evolution. Electronic supplementary material The online version of this article (doi:10.1186/s12862-016-0753-6) contains supplementary material, which is available to authorized users.

The type specimen of a large, flightless marine bird, Hesperornis regalis, was collected by O.C. Marsh in 1871. Due to the practices of the time, and the lack of accurate maps, the type locality was initially recorded by Marsh in a letter simply as the “upper Cretaceous of Western Kansas,” and then later reported as “the gray shale near the Smoky Hill River in Western Kansas.” Since the Smoky Hill Chalk Member of the Niobrara Formation is exposed along the Smoky Hill River in present day Wallace, Logan and Gove counties over a distance of more than 75 miles, this vague locality information encompasses about 5 million years of depositional history. An 1880 account by Marsh narrows the locality down to the south bank of the Smoky Hill River about 20 miles east of Fort Wallace in Logan County. The results of a recent field investigation of the eastward route traveled by Marsh's 1871 Yale College Scientific Expedition sheds light on the probable locality of both the type specimen (YPM 1200) of Hesperornis reg...

Partial reconstruction of hindlimb myology and syndesmology of Hesperornis regalis, based on fossil and extant comparative anatomical material, is provided. Possessing a combination of morphological features characteristic of modern loons and grebes, H. regalis was somewhat closer to loons in overall hindlimb anatomy. The acetabular foramen indicates that the femoral head of Hesperornis had a more restricted excursion in the acetabulum compared with modern Aves. The development of femoral retractors m. iliofemoralis and m. caudofemoralis exceeded that of modern foot-propelled diving birds, showing greater protractive forces applied to the femur during the propulsive stroke. The origin of intermediate and lateral portions of m. gastrocnemius reached its maximum in Hesperornis, extending proximally beyond the greater trochanter and migrating onto the cranial surface of the femur. Ligaments of the knee joint, which show typical avian morphology, allowed a high degree of inward–outward rotation of the tibiota...

We show that the topology of separate elements in avian compound rhamphothecae are strongly similar among different clades, not only in external appearance but in how these elements conform to underlying structures. We conducted a morphological survey of 81 extant bird species and tested superficial similarities in external beak morphology for substantive similarity in associated skeletal structures and nerve courses. A revised set of morphological characters for compound rhamphothecae was optimized onto three recent phylogenetic trees to assess the relationships of homology and homoplasy in rhamphothecal morphology. Osteological correlates of rhamphothecae from the extinct basal ornithurine birds Hesperornis and Ichthyornis show that compound rhamphothecae are the primitive state for the clade including extant birds (Neornithes). Simple rhamphothecae are the result of the loss of softer keratinous grooves between rhamphothecal components, and there are many examples of transitional forms betwee...

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

Many studies on avian microanatomy have established a relationship between high bone compactness (i.e., higher degree of osteosclerosis) and diving behavior. Greatest degrees of compactness have been observed in the femora and humeri of penguins, femur of Hesperornis Marsh, 1872, and of Polarornis gregorii Chatterjee, 2002, and to a somewhat lesser degree, in the humeri of flightless Pan-Alcidae. Within Anatidae, humeral and femoral compactness among diving species is greater than among non-diving species, whereas flightless diving species have a greater degree of compactness than their flying close relatives. In Cayaoa bruneti Tonni, 1979, an extinct flightless foot-propelled, diving anatid with extreme forelimb reduction, osteosclerosis is as great as that of penguins. Although osteosclerosis in the humerus of wing-propelled divers could be part of adaptations to flightlessness, osteosclerosis in the femur of both foot- and wing-propelled divers could be part of the consequences of flightlessness and which is a result of selection to counter buoyancy. Múltiples estudios en microanatomía aviana han establecido una relación entre una alta compactación ósea (es decir, un grado considerable de osteosclerosis) y el comportamiento buceador. Los mayores grados de compactación han sido observados en fémures y húmeros de pingüinos actuales y fósiles, fémures de Hesperornis Marsh, y de Polarornis gregorii Chaterjee, y en un grado algo menor, en húmeros de Pan-Alcidae no voladores. Dentro de los Anatidae, la compactación humeral y femoral es mayor entre las especies buceadoras que entre las no buceadoras, mientras que las especies buceadoras no-voladoras presentan un grado de compactación mayor que sus parientes cercanos voladores. En Cayaoa bruneti Tonni, un anatido extinto no volador, buceador propulsado por las patas, con una reducción extrema de los miembros anteriores, la osteosclerosis en el fémur es tan alta como la de pingüinos. La osteosclerosis en el fémur de los buceadores propulsados por las patas y los propulsados por las alas puede ser parte de las consecuencias de la pérdida de vuelo, seleccionada positivamente para contrarrestar la flotabilidad. Fil: de Mendoza, Ricardo Santiago. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico de Paleontología de Vertebrados; Argentina Fil: Tambussi, Claudia Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

Testing models of macroevolution, and especially the sufficiency of microevolutionary processes, requires good collaboration between molecular biologists and paleontologists. We report such a test for events around the Late Cretaceous by describing the earliest penguin fossils, analyzing complete mitochondrial genomes from an albatross, a petrel, and a loon, and describe the gradual decline of pterosaurs at the same time modern birds radiate. The penguin fossils comprise four naturally associated skeletons from the New Zealand Waipara Greensand, a Paleocene (early Tertiary) formation just above a well-known Cretaceous/Tertiary boundary site. The fossils, in a new genus (Waimanu), provide a lower estimate of 61-62 Ma for the divergence between penguins and other birds and thus establish a reliable calibration point for avian evolution. Combining fossil calibration points, DNA sequences, maximum likelihood, and Bayesian analysis, the penguin calibrations imply a radiation of modern (crown group) birds in the Late Cretaceous. This includes a conservative estimate that modern sea and shorebird lineages diverged at least by the Late Cretaceous about 74 +/- 3 Ma (Campanian). It is clear that modern birds from at least the latest Cretaceous lived at the same time as archaic birds including Hesperornis, Ichthyornis, and the diverse Enantiornithiformes. Pterosaurs, which also coexisted with early crown birds, show notable changes through the Late Cretaceous. There was a decrease in taxonomic diversity, and small- to medium-sized species disappeared well before the end of the Cretaceous. A simple reading of the fossil record might suggest competitive interactions with birds, but much more needs to be understood about pterosaur life histories. Additional fossils and molecular data are still required to help understand the role of biotic interactions in the evolution of Late Cretaceous birds and thus to test that the mechanisms of microevolution are sufficient to explain macroevolution.

New materials of Hesperornis rossicus Nessov et Yarkov, 1993 (one complete and one fragmentary tarsometatarsus) from the lower Campanian Karyakino locality in Saratov Province, Russia, show for the first time distal tarsometatarsal morphology for this species and allow reconsideration of its diagnosis. H. rossicus is the most derived species of the genus, having the greatest size for the genus and strongly reduced inner fingers, with undivided trochlea on tarsometatarsus for digits II and III and condyle for digit II completely behind that of digit III. Previous records of Hesperornis sp. from Rychkovo and Hesperornithidae indet. from Bereslavka (both Volgograd Province, Russia) are referred here to H. rossicus.

Consensus is elusive regarding the phylogenetic relationships among neornithine (crown clade) birds. The ongoing debate over their deep divergences is despite recent increases in available molecular sequence data and the publication of several larger morphological data sets. In the present study, the phylogenetic relationships among 43 neornithine higher taxa are addressed using a data set of 148 osteological and soft tissue characters, which is one of the largest to date. The Mesozoic non-neornithine birds Apsaravis, Hesperornis, and Ichthyornis are used as outgroup taxa for this analysis. Thus, for the first time, a broad array of morphological characters (including both cranial and postcranial characters) are analyzed for an ingroup densely sampling Neornithes, with crown clade outgroups used to polarize these characters. The strict consensus cladogram of two most parsimonious trees resultant from 1000 replicate heuristic searches (random stepwise addition, tree-bisection-reconnection) recovered several previously identified clades; the at-one-time contentious clades Galloanseres (waterfowl, fowl, and allies) and Palaeognathae were supported. Most notably, our analysis recovered monophyly of Neoaves, i.e., all neognathous birds to the exclusion of the Galloanseres, although this clade was weakly supported. The recently proposed sister taxon relationship between Steatornithidae (oilbird) and Trogonidae (trogons) was recovered. The traditional taxon “Falconiformes” (Cathartidae, Sagittariidae, Accipitridae, and Falconidae) was not found to be monophyletic, as Strigiformes (owls) are placed as the sister taxon of (Falconidae + Accipitridae). Monophyly of the traditional “Gruiformes” (cranes and allies) and ”Ciconiiformes” (storks and allies) was also not recovered. The primary analysis resulted in support for a sister group relationship between Gaviidae (loons) and Podicipedidae (grebes)—foot-propelled diving birds that share many features of the pelvis and hind limb. Exclusion of Gaviidae and reanalysis of the data set, however, recovered the sister group relationship between Phoenicopteridae (flamingos) and grebes recently proposed from molecular sequence data.

The Smoky Hill Chalk Member of the Niobrara Chalk was deposited in the Western Interior Sea during a span of about five million years extending from the upper Coniacian through the lower Campanian. Coincidentally, this period also encompasses much of the early evolution and radiation of the family Mosasauridae. Thousands of mosasaur specimens have been collected from the Smoky Hill Chalk Member of western Kansas since the first Yale College Scientific Expedition in 1870. Early workers viewed the entire Smoky Hill Chalk Member as the “Pteranodon beds” and were not able to provide accurate stratigraphic information. Even though mosasaurs are represented by numerous complete and well preserved specimens, the ranges of the various species could not be defined further without better stratigraphic data. In 1898, S. W. Williston first described the general distribution of mosasaurs within the Rudistes and Hesperornis beds of the Smoky Hill Chalk Member. Seventy years later, D. A. Russell grouped mosasau...

The new reconstructions of the Archaeopteryx skull in lateral view and its bony palate reflect the new data obtained from the Munich (7 th ) and Eichstdtt (5 th ) specimens (ELZANOWSKI & WELLNHOFER, 1996). The lateral view shows a unique conformation of the temporal region, which is intermediate between that of theropods and modern birds, and lacks any indication of the articulation between the postorbital and the jugal bar. The bony palate combines the theropod hooked ectopterygoid and the maniraptoran pterygopalatine fenestra with pronouncedly avian features of the palatine and pterygoid. The palate easily compares to that of Gobiptefyx, fills the gap between the theropods and Hesperornis, and shows several palaeognathous similarities.

A tarsometatarsus of Hesperornis from the Kanguk Formation on Ellesmere Island is described and illustrated and constitutes the northernmost occurrence of the genus. Palynological evidence and stratigraphic position indicate that Canadian occurrences of Hesperornis are Campanian in age except the specimen from the Mason River Formation which might be as young as early Maastrichtian. Paleogeographic reconstructions indicate that all specimens are from a seaway extending along the western interior of North America.

We report on the bone microstructure of the Cretaceous birdsHesperornis regalisandIchthyornis victor. Thin sections of representative elements of both these ornithurine birds show a rapid, sustained bone deposition without any pauses or interruptions in bone formation. This growth pattern contrasts sharply with the cyclical pattern of bone deposition previously reported for the Cretaceous non-ornithurine birdsPatagopteryxand representatives of the enantiornithines. These findings suggest physiological advancement in Cretaceous ornithurine birds. The bone microstructure of the divingHesperornisshows similarities to the bone structure of modern penguins, and to that of a loon from the Cretaceous of Antarctica.

The braincase of the Early Cretaceous bird Enaliornis is indicative of a primitive avian brain with a relatively large medulla oblongata, a small cerebellum, small cerebral hemispheres broadly separated from the labyrinth, and a strong basilordotic bend of the whole brain, the latter being characteristic of an airencephalic skull. The reduction of the dorsal pneumatic recess, the large size of the auricular fossa, and possibly the lack of interfoliar ridges on the roof of the cerebellar fossa suggest diving habits and thus support the association of the braincases with the type tarsometatarsus of Enaliornis. The braincase of Enaliornis is most similar to those of Hesperornis, Phaethon, Diomedeidae and Fregata. Most of the similarities to these taxa are primitive for birds.

Birds are characterized by pneumatization of their skeletons by epithelial diverticula from larger, air—filled cavities. The diverticula—or ‘air sacs’—that invade the postcranium result from outgrowths of the lungs; postcranial pneumaticity has been very well studied. Much more poorly understood are the air sacs that pneumatize the skull. Study of craniofacial pneumaticity in modern birds (Neornithes) indicates the presence of two separate systems: nasal pneumaticity and tympanic pneumaticity. The lacrimal and maxillary bones are pneumatized by diverticula of the main paranasal cavity, the antorbital sinus. There are five tympanic diverticula in neornithines that pneumatic the quadrate, articulare and the bones of the braincase. The pneumatic features of the following six genera of Mesozoic birds are examined: Archaeopteryx, Enaliornis, Baptornis, Parahesperornis, Hesperornis and Ichthyornis. Despite the ‘archaic’ aspect of most of these birds, many of the pneumatic features of neornithines are found in Mesozoic birds and are considered primitive for Aves. The phylogenetic levels at which most of the avian pneumatic features arose within Archosauria are uncertain. Until the phylogenetic levels at which homologous pneumatic features arose are determined, it is unwise to use most pneumatic characters in the discussion of avian origins. Within avian phylogeny, Ornithurae and Neornithes are well–supported by pneumatic synapomorphies. There is a trend towards reduction of craniofacial pneumaticity within Hesperornithiformes. Within Neornithes, four derived pneumatic characters suggest that the Palaeognathae (ratites and tinamous) is monophyletic.

Fossils preserving traces of soft anatomy are rare in the fossil record; even rarer is evidence bearing on the size and shape of sense organs that provide us with insights into mode of life. Here, we describe unique fossil preservation of an avian brain from the Volgograd region of European Russia. The brain of this Melovatka bird is similar in shape and morphology to those of known fossil ornithurines (the lineage that includes living birds), such as the marine diving birds Hesperornis and Enaliornis, but documents a new stage in avian sensory evolution: acute nocturnal vision coupled with well-developed hearing and smell, developed by the Late Cretaceous (ca 90 Myr ago). This fossil also provides insights into previous ‘bird-like’ brain reconstructions for the most basal avian Archaeopteryx—reduction of olfactory lobes (sense of smell) and enlargement of the hindbrain (cerebellum) occurred subsequent to Archaeopteryx in avian evolution, closer to the ornithurine lineage that comprises living birds. The Melovatka bird also suggests that brain enlargement in early avians was not correlated with the evolution of powered flight.

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.

Morphological variation in the avian palatal skeleton (palatum osseum) was publicized by Huxley (1867) and expanded upon subsequently by many authors, but variation in the included nominal element, the palatinum (os palatinum), is less well known. Here we describe, illustrate, and name variable features of the avian palatinum that we judge to be potentially important for phylogenetic inference. To standardize anatomical nomenclature, we introduce formal names (per ICAAN) and revise others for palatal features provisionally considered to be homologous among modern birds (Neornithes). The palatinum can be divided topographically into four parts—pars maxillaris, pars choanalis, pars lateralis, and pars pterygoideus—each having variation in organization, function, and phylogenetic corollaries that facilitate comparisons within Neornithes and with Mesozoic allies. Emphasis on study of juvenile specimens of modern birds in which intact sutures are discernible revealed details in the structure of arcus pterygopalatinus and arcus pterygovomeralis that facilitated diagnosis of both palaeognathous and neognathous birds, and (within the latter) the Galloanserae and its sister-group, Neoaves. Articulatio vomeroparasphenoidalis may represent a synapomorphy of palaeognathous birds (ratites and tinamous). Although articulatio intrapterygoidea commonly is thought to provide the flexibility within arcus ptery-gopalatinus required for cranial kinesis in neognathous birds, we found that six patterns of articulations and flexible zones (zonae flexoriae) serve that function; these patterns are probably apomorphous, sometimes convergently, within Aves. Hesperornis apparently displays homoplasious flexibility within arcus pterygopalatinus. We found developmental evidence against paedomorphosis (“neoteny”) as an explanation of certain distinguishing features of palaeognathous palates, and comparison with palatal remnants of Archaeopteryx, Gobipteryx, Hesperornis, and several nonavian theropods suggest plesiomorphy of other palaeognathous features. Reconsideration of “palaeognathous” characters found in adults of some neognathous taxa, previously explained as evolutionary reversals, led us to a variety of alternative hypotheses. We believe that analysis of individual characters within the avian palatinum and palatal skeleton holds significantly greater promise for phylogenetic and functional inferences than the continued use of the classical, composite palatal types—palaeognathous, schizognathous, desmognathous, and aegithognathous—for phylogenetic reconstructions.

An occurrence of the Cretaceous toothed bird Hesperornis Marsh is recorded from a tarsometatarsus found in the middle Campanian Foremost Formation, Alberta. The discovery may be the geologically youngest record of Hesperornis known and provides the only well documented nonmarine occurrence of the genus.

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.

Additional preparation of a specimen found a century ago permits complete reconstruction of the skull of the Cretaceous bird Hesperornis. This skull provides new evidence on the evolution of the avian palate and the origin of avian cranial kinesis, and further substantiates the evolution of birds from theropod dinosaurs.

EARLY in November, 1914, MN\r. Charles W. Gilmore, who has charge of the fossil birds and reptiles in the Division of Paleontology of the United States National Museum, Washington, D.C., sent me a fossil vertebra, which was collected when he was associated with Dr. T. W. Stanton on an expedition in Montana during the early autumn of 1914. This vertebra, when received by me, was labeled thus: "Coniornis altus Marsh, Lumbar vertebra, Dog Creek, 1 mi. above its mouth, Fergus County, Montana. Cretaceous Clagget formation (upper yellowish sandstone) September 26, 1914." T. W. Stanton, C. W. Gilmore. All. No." There being no proper material in the collections of the U. S. National Museum wherewith to compare this vertebra, I studied it as best I could through comparing the fossil bone with the figures given by Marsh in his Odontornithes. This comparison convinced me of the fact that the vertebra belonged to some medium-sized Hesperornis; further, that it more closely resembled the 23d vertebra of the spinal column of Hesperornis regalis than it did any other vertebra, and I was therefore led to believe that it was the corresponding vertebra of some species of Hesperornis, smaller than H. regalis, probably of a species heretofore undescribed. As I knew that Doctor Richard S. Lull, of the Peabody Museum, was engaged upon a study of the Hesperornithidc, at the time this bone came to me for study, I determined to refer it to him for an opinion. This I did with a letter dated at Washington, D. C., the 10th of November, 1914. Doctor Lull very kindly made an exhaustive study of this fossil vertebra, and returned it to me with a letter of transmittal, dated November 20, 1914. At the close of his comnmunication on the subject, he says: "I will lend you a cast of the 23d vertebra of

(1872). XXXII.—Description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. Annals and Magazine of Natural History: Vol. 10, No. 57, pp. 212-217.

In 1872, O. C. Marsh described a new Cretaceous bird Ichthyornis dispar based on a posteranial skeleton (Marsh 1872a). Later in the same year, he described a new reptilian genus Colonosaurus for two toothed jaws found associated with the type specimen of Ichthyornis dispar (Marsh 1872b). In the following year, Marsh referred the toothed "Colonosaurus" jaws to Ichthyornis dispar stating that: "On subsequently removing the surrounding shale, the skull and additional portions of both jaws were brought to light, so that there cannot now be a reasonable doubt that all are parts of the same bird" (Marsh 1873). This assignment was accepted until 1952 when J. T. Gregory compared the jaws of Icthyornis dispar to those of mosasaurs. Gregory (1952) concluded that the toothed jaws assigned to Ichthyornis by Marsh were actually the jaws of a small mosasaur which had accidently been deposited together with the skeleton of a bird. The recent classifications of fossil birds by Storer (1960), Romer (1966, 1968), and Brodkorb (1967) all follow Gregory and removed Ichthyornis from the toothed birds. After careful study of the toothed jaws associated with the type specimen of Ichthyornis dispar (Yale Peabody Museum [YPM] 1450) M. V. Walker (1967) recently stated his opinion that until further proof is available the toothed jaws should be considered to belong to Ichthyornis. Fortunately, Walker has since found a second partial skeleton of Icthyornis, again with associated toothed jaws. The jaws associated with Walker's partial skeleton consist only of portions of the toothed dentaries; the quadrate articulations of both jaws are unfortunately missing (Walker, unpubl.). I recently discovered an additional mandibular fragment of Ichthyornis (I. cf. dispar) which was catalogued together with bones of a specimen of the much larger Cretaceous bird Hesperornis (YPM 1478) in the Yale Peabody Museum collection. This new mandibular fragment of Ichthyornis is the only known

The evolution of the avian palate has been a subject of great interest for over a century. Recently the primitive - derived sequences (i.e., character polarities) of the relevant features have become confused. Outgroup comparisons with theropod dinosaurs, crocodiles and other archosaurian reptiles suggest a number of palatal features that may be ancestral for birds. Ratites and tinamous exhibit a large number of these primitive features. Having polarized various palatal characters, we tested these polarities by examining the palates of Mesozoic birds. Archaeopteryx, Gobipteryx, and the hesperornithids were analysed. Although Archaeopteryx is too poorly known to reconstruct the palate, it shows a number of primitive features ; the identification of one of the bones as an ectopterygoid is questioned. Gobipteryx also exhibits many plesiomorphies and retains the elongate pterygoids of non-avian archosaurs. The palate of hesperornithid birds is reconstructed and shown to be widely divergent morphologically from other archosaurs ; it retains a few primitive features while showing several clear autapomorphies., Depuis plus d'un siècle l'évolution du palais avien a été un problème d'un grand intérêt. Récemment les séquences «primitif-dérivé», c'est-à-dire la polarisation des caractères pour les caractères pertinents, sont devenues confuses. Les comparaisons extra-groupes (outgroup comparisons) avec certains dinosaures théropodes, les crocodiles et d'autres reptiles archosauriens suggèrent un certain nombre de caractères palatins pouvant être ancestraux pour les oiseaux. Les Ratites et les Tinamous possèdent plusieurs de ces caractères primitifs. Ayant établi la polarité de plusieurs caractères palatins, nous avons testé ces polarités en examinant le palais d'oiseaux mésozoïques. Les conditions retrouvées chez Archaeopteryx, Gobipteryx et les Hesperornithiformes ont été analysées. Bien que le palais d'Archaeopteryx soit trop peu connu pour permettre sa reconstitution, il possède toutefois un certain nombre de caractères primitifs ; l'identification d'un des os comme étant un ectoptérygoïde est remise en question. Gobipteryx présente aussi plusieurs plésiomorphies et conserve les ptérygoïdes allongés retrouvés chez les Archosaures non-aviens. Le palais des Hesperornithiformes est reconstruit et montre une grande divergence morphologique par rapport à celui d'autres Archosaures ; il conserve quelques caractères primitifs mais présente en même temps plusieurs autapomorphies distinctes., Witmer Lawrence M., Martin Larry D. The primitive features of the avian palate, with special reference to 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. 21-40.

Both Hesperornis and Ichthyornis are toothed birds; they and Archaeopteryx share broad flattened teeth with highly expanded roots. The teeth of Ichthyornis have been reported to have been set in sockets as were those of Archaeopteryx , but new specimens of Ichthyornis show the teeth set in a groove as in Hesperornis . These new fossils are from an adult but not old bird; thus, the presence or absence of tooth sockets in birds may be dependent on age.

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.

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