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A Marine Hesperornithiform (Avialae: Ornithuromorpha) from the Maastrichtian of Japan: Implications for the Paleoecological Diversity of the Earliest Diving Birds in the End of the Cretaceous
Abstract
Asian hesperornithiforms are extremely rare in contrast to North American records; thus, their diversity in Asia during the Cretaceous is unclear. Maastrichtian hesperornithiform materials have been reported from both fluvial and marine deposits in North America but only from fluvial deposits in Asia. Asian hesperornithiforms from Maastrichtian deposits have been considered as freshwater taxa because of their occurrence from fluvial sediments and their histological features. Here, we report the first hesperornithiform record from marine Maastrichtian deposits in Asia. It is represented by an isolated left tibiotarsus from the inter-arc basin deposit of the Kita-ama Formation (lower Maastrichtian), Izumi Group of southwest Japan. It has a shallow tibial incision, fibular crest extending to the mid shaft, and laterally angled lateral articular surface. Although its phylogenetic position within Hesperornithiformes is ambiguous, these characters are similar to non-hesperornithid hesperornithiforms. Unossified proximal and distal epiphyses indicate that this individual was immature. A remarkably thick cortical area of the tibiotarsus suggests that this hesperornithiform was a sea-dwelling bird and that the habitat of this group during the Maastrichtian extended to both terrestrial and marine environments in Asia and North America.
The Hesperornithiformes (sometimes referred to as Hesperornithes) are the first known birds to have adapted to a fully aquatic lifestyle, appearing in the fossil record as flightless, foot-propelled divers in the early Late Cretaceous. Their known fossil record—broadly distributed across the Northern Hemisphere—shows a relatively rapid diversification into a wide range of body sizes and degrees of adaptation to the water, from the small Enaliornis and Pasquiaornis with lesser degrees of diving specialization to the large Hesperornis with extreme morphological specializations. Paleontologists have been studying these birds for over 150 years, dating back to the “Bone Wars” between Marsh and Cope, and as such have a long history of naming, and renaming, taxa. More recent work has focused to varying degrees on the evolutionary relationships, functional morphology, and histology of the group, but there are many opportunities remaining for better understanding these birds. Broad-scale taxonomic evaluations of the more than 20 known species, additional histological work, and the incorporation of digital visualization tools such as computed tomography scans can all add significantly to our understanding of these birds.
Here we describe a partial hadrosaurid skeleton from the marine Maastrichtian Kita-ama Formation in Japan as a new taxon, Yamatosaurus izanagii gen. et sp. nov., based on unique characters in the dentition. Our phylogenetic analysis demonstrates Yamatosaurus izanagii belongs to Hadrosauridae, composed of Hadrosaurus foulkii + (Yamatosaurus izanagii + (Saurolophinae + Lambeosaurinae)). The coracoid lacks a biceps tubercle as in non-hadrosaurid hadrosauroids, suggesting its presence is a key feature for the clade of Saurolophinae and Lambeosaurinae. The evolutionary rates analysis further supports that shoulder and forelimb features, which are likely to have been involved in locomotion, were important for the early evolution of Hadrosauridae. Our biogeographic analyses show that basal hadrosaurids were widely distributed in Asia and Appalachia, that the clade of Saurolophinae and Lambeosaurinae originated in Asia, and that eastern Asia may have served as a refugium of relict hadrosauroid taxa such as Plesiohadros djadokhtaensis, Tanius sinensis, and Yamatosaurus izanagii during the Late Cretaceous. The contemporaneous occurrence of basal (Yamatosaurus izanagii) and derived (Kamuysaurus japonicus) hadrosaurids during the Maastrichtian in Japan is the first record in Asia. Because of the long geographical distance between these localities, they likely did not co-exist, but instead demonstrate some level of provinciality.
Here we describe a partial hadrosaurid skeleton from the marine Maastrichtian Kita-ama Formation of the Izumi Group in Japan as a new taxon, Yamatosaurus izanagii gen. et sp. nov. Our phylogenetic analysis demonstrates it belongs to the Hadrosauridae, composed of Hadrosaurus foulkii + ( Yamatosaurus izanagii + (Saurolophinae + Lambeosaurinae). Yamatosaurus izanagii is unique in having only one functional tooth/row in the middle of the dentary dental battery and complete absence of the branched ridges on the occlusal surfaces. The coracoid lacks a biceps tubercle as in non-hadrosaurid hadrosauroids, suggesting its presence is a key feature for the clade of Saurolophinae and Lambeosaurinae. The evolutionary rate analysis further supports that shoulder and forelimb features, which are likely to be involved in locomotion, are important for the early evolution of Hadrosauridae. Our biogeographic analyses show that the basal Hadrosauridae was widely distributed in Asia and Appalachia, and the clade of Saurolophinae and Lambeosaurinae originated in Asia. The contemporaneous occurrence of basal ( Yamatosaurus izanagii ) and derived ( Kamuysaurus japonicus ) hadrosaurids during the Maastrichtian in Japan is the first record in Asia. Because of a long geographical distance between these localities, they may not co-exist but show some level of provinciality.
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.
Seven species of decapods are described from the Izumi Group (Upper Cretaceous: Campanian–Maastrichtian) of Hyogo and Osaka Prefectures, central Japan. Archaeopidae, a new family of Retroplumoidea embraces the monotypic Late Cretaceous genus Archaeopus. Hinecaris simplex, a new genus and species is the first record for the axiidean family Axiidae from the Cretaceous rocks of Japan. “Callianassa” (s.l.) masanorii Karasawa, 1998, is re-described and is moved from Callianassidae to Gourretiidae. A re-description is given for Linuparus japonicus Nagao, 1931, and Archaeopus ezoensis (Nagao, 1941). The lectotype for Linuparus japonicus Nagao, 1931, is herein designated.
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.
The Smoky Hill Member of the Niobrara Chalk in Kansas (USA) has yielded the remains of numerous members of the Hesperornithiformes, toothed diving birds from the late Early to Late Cretaceous. This study presents a new taxon of hesperornithiform from the Smoky Hill Member, Fumicollis hoffmani, the holotype of which is among the more complete hesperornithiform skeletons. Fumicollis has a unique combination of primitive (e.g. proximal and distal ends of femur not expanded, elongate pre-acetabular ilium, small and pyramidal patella) and derived (e.g. dorsal ridge on metatarsal IV, plantarly-projected curve in the distal shaft of phalanx III:1) hesperornithiform characters, suggesting it was more specialized than small hesperornithiforms like Baptornis advenus but not as highly derived as the larger Hesperornis regalis. The identification of Fumicollis highlights once again the significant diversity of hesperornithiforms that existed in the Late Cretaceous Western Interior Seaway. This diversity points to the existence of a complex ecosystem, perhaps with a high degree of niche partitioning, as indicated by the varying degrees of diving specializations among these birds.
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. Evolution within the Hesperornithiformes provides a fascinating example of progressive development of specialized diving adaptations in birds. The acquisition of these diving specializations appears to be uncorrelated to the independent evolution of multiple large increases in body size.
Many studies on avian microanatomy have established a relationship between high bone compactness (i.e., considerable degree of osteosclerosis) and diving behavior. Greatest degrees of compactness have been observed in the femora and humeri of fossil and extant penguins, femora of Hesperornis Marsh, and Polarornis gregorii Chatterjee, 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 ones, whereas flightless diving species have a greater degree of compactness than their volant close relatives. In Cayaoa bruneti Tonni, an extinct flightless foot-propelled, diving anatid with extreme forelimb reduction, femoral osteosclerosis is as great as that of penguins. Osteosclerosis in the femur of both foot- and wing-propelled divers could be part of the consequences of flightlessness and a result of selection to counter buoyancy.
The broad biogeographic distribution of Hesperornis fossils in Late Cretaceous Western Interior Seaway deposits has prompted questions about whether they endured polar winters or migrated between mid- and high latitudes. Here, we compare microstructures of hesperornithiform long bones from Kansas and the Arctic to investigate whether migration or Late Cretaceous polar climate affected bone growth. We also examine modern penguin bones to determine how migration and climate may influence bone growth in birds with known behaviours. Histological analysis of hesperornithiform samples reveals continuous bone deposition throughout the cortex, plus an outer circumferential layer in adults. No cyclic growth marks, zonation or differences in vasculature are apparent in the Hesperornis specimens. Comparatively, migratory Adélie and chinstrap penguin bones show no zonation or changes in microstructure, suggesting that migration is not necessarily recorded in avian bone microstructure. Non-migratory gentoos show evidence of rapid bone growth possibly associated with increased chick growth rates in high-latitude populations and large body size. The absence of histological evidence for migration in extinct Hesperornis and extant pygoscelid penguins may reflect that these birds reached skeletal maturity before migration or overwintering. This underscores the challenges of using bone microstructure to infer the effects of behaviour and climate on avian growth.
The Cretaceous stratigraphy and main palaeogeographic features of the North-Eastern Peri-Tethys are briefly summarised on the base of new data. The study is mainly focused on the time-slices that were chosen for the recently published Peri-Tethys Atlas: Early Hauterivian, Early Aptian, Late Cenomanian, Early Campanian and Late Maastrichtian. Two main epochs in the development of this area are recognised. The Early Cretaceous is characterised by the prevalence of the terrigenous sedimentation and the existence of a large longitudinal strait through the Russian Platform, which controlled the Boreal/Tethyan connection. The southward Boreal water movement prevailed during the Neocomian. The strongest Boreal transgression took place in the Late Hauterivian, when cool water reached the Crimea basin. The Aptian–Albian time was characterised by a northward Tethyan water movement, interrupted by the Early Albian Boreal transgression. Tectonic rebuilding of the region took place in the Albian–Cenomanian. It resulted in the disappearance of the sea-strait through the Russian Platform and in the opening of another sea-strait in the Turgai area in the Turonian. This strait connected the Peri-Tethyan seas, the Western Siberia Boreal basin and joined with the Western Interior Seaway in the other side of the Hemisphere. The Northern Hemisphere Megastrait appeared. During this time mainly carbonate sedimentation prevailed, but the existence of a new longitudinal strait determined a two-way water and faunal exchange. Tethyan water moved up to the south and the south-east parts of the Western Siberian basin, while the cold Boreal water influence can be recognised along the northern margin of the Russian Platform basin.
Although studies of osteological morphology, gross myology, myological histology, neuroanatomy, and wing-scaling have all documented anatomical modifications associated with wing-propelled diving, the osteohistological study of this highly derived method of locomotion has been limited to penguins. Herein we present the first osteohistological study of the derived forelimbs and hind limbs of wing-propelled diving Pan-Alcidae (Aves, Charadriiformes). In addition to detailing differences between wing-propelled diving charadriiforms and nondiving charadriiforms, microstructural modifications to the humeri, ulnae and femora of extinct flightless pan-alcids are contrasted with those of volant alcids. Histological thin-sections of four species of pan-alcids (Alca torda, †Alca grandis, †Pinguinus impennis, †Mancalla cedrosensis) and one outgroup charadriiform (Stercorarius longicaudus) were compared. The forelimb bones of wing-propelled diving charadriiforms were found to have significantly thicker (∼22%) cortical bone walls. Additionally, as in penguins, the forelimbs of flightless pan-alcids are found to be osteosclerotic. However, unlike the pattern documented in penguins that display thickened cortices in both forelimbs and hind limbs, the forelimb and hind limb elements of pan-alcids display contrasting microstructural morphologies with thickened forelimb cortices and relatively thinner femoral cortices. Additionally, the identification of medullary bone in the sampled †Pinguinus impennis specimen suggests that further osteohistological investigation could provide an answer to longstanding questions regarding sexual dimorphism of Great Auks. Finally, these results suggest that it is possible to discern volant from flightless wing-propelled divers from fragmentary fossil remains. Anat Rec, 297:188-199, 2014. © 2013 Wiley Periodicals, Inc.
Eustatic sea-level changes of the Cretaceous are reevaluated based on a synthesis of global stratigraphic data. A new terminology for local/regional or relative sea-level changes (eurybatic shifts) is proposed to distinguish them from global (eustatic) sea-level changes, with the observation that all measures of sea-level change in any given location are eurybatic, even when they include a strong global signal. Solid-earth factors that influence inherited regional topography and thus modify physical measures of amplitude of the sea-level rises and falls locally are reviewed. One of these factors, dynamic topography (surface expression of mass flow in the upper mantle on land- and seascapes), is considered most pertinent in altering local measures of amplitude of sea-level events on third-order time scales (0.5-3.0 Myr). Insights gained from these models have led to the reconciliation of variance between amplitude estimates of eurybatic shifts in any given region and global measures of eustatic changes. Global estimates of third-order events can only be guesstimated at best by averaging the eurybatic data from widely distributed time-synchronous events. Revised curves for both long-term and short-term sea-level variations are presented for the Cretaceous Period. The curve representing the long-term envelope shows that average sea levels throughout the Cretaceous remained higher than the present day mean sea level (75–250 m above PDMSL). Sea level reached a trough in mid Valanginian (~ 75 m above PDMSL), followed by two high points, the first in early Barremian (~ 160-170 m above PDMSL) and the second, the highest peak of the Cretaceous, in earliest Turonian (~ 240-250 m above PDMSL). The curve also displays two ~ 20 Myr-long periods of relatively high and stable sea levels (Aptian through early Albian and Coniacian through Campanian). The short-term curve identifies 57 third-order eustatic events in the Cretaceous, most have been documented in several basins, while a smaller number are included provisionally as eustatic, awaiting confirmation. The amplitude of sea-level falls varies from a minimum of ~ 20 m to a maximum of just over 100 m and the duration varies between 0.5 and 3 Myr. The causes for these relatively rapid, and at times large amplitude, sea-level falls in the Cretaceous remain unresolved, although based mainly on oxygen-isotopic data, the presence of transient ice cover on Antarctica as the driver remains in vogue as an explanation. This idea has, however, suffered a recent setback following the discovery of pristine foraminiferal tests in the Turonian of Tanzania whose oxygen- isotopic values show little variation, implying absence of glacioeustasy at least in the Turonian. The prevalence of 4th-order (~ 400 Kyr) cyclicity through most of the Cretaceous (and elsewhere in the Paleozoic and Cenozoic) strongly implies that the periodicity on this time scale, presumably driven by long-term orbital eccentricity, may be a fundamental feature of depositional sequences throughout the Phanerozoic.
Five taxa of fossil birds comprising at least 17 individuals have been discovered in a Cenomanian (early Late Cretaceous) nearshore marine deposit along the Carrot River, near the Pasquia Hills of Saskatchewan, Canada. More than a hundred fossils, all from a single locality, constitute the oldest and most diverse avifauna from the Cretaceous of North America. Four species represent the earliest known North American Ornithurae, two of them new species of the baptornithid Pasquiaornis, n. gen. (Hesperornithiformes), and the other two referred to the ichthyornithid Ichthyornis (Ichthyornithiformes). Pasquiaornis is more primitive than Baptornis, and its humérus and femur show resemblances to those of flying birds. A presumed enantiornithine is also present.
Femoral osteology and soft tissues evolved in a stepwise pattern in archosauromorph reptiles on the line to crown group birds. Crocodylia retains most ancestral archosaurian traits, whereas Dinosauromorpha (including birds) acquired many more derived traits. The complex sequence of changes included major shifts of several thigh muscle insertions. Medial rotation of the proximal femur (e.g. the femoral head) in archosaurs moved the greater trochanter laterally, bringing along the insertion of M. pubo-ischio-femoralis externus. Within Dinosauromorpha, the lesser trochanter moved proximally away from the trochanteric shelf. Presumably the lesser trochanter indicates the insertion of M. iliotrochantericus caudalis whereas the trochanteric shelf indicates the insertion of M. iliofemoralis externus. An accessory trochanter at the base of the lesser trochanter marks the insertion of M. pubo-ischio-femoralis internus 2 in tetanuran theropods. I propose hypotheses for the homologies of several intermuscular lines and other features on the femoral shaft. On the line to Neornithes, most changes of femoral morphology predated Aves and the origin of flight; few femoral features are unique to birds. Overall, the pattern of morphological evolution is consistent with stepwise functional evolution of the hindlimb within Dinosauromorpha on the line to Neornithes. The clade Ornithurae evolved the last few hindlimb apomorphies that characterize extant birds, in conjunction with more flexed hip and knee joints.
Field surveys of the Upper Cretaceous Hell Creek Formation in southwestern North Dakota since 1986 have produced a total of 10 124 specimens from 42 vertebrate microsites and an additional 41 dinosaur skulls or partial skeletons or skulls from separate sites representing 61 taxa of vertebrates dominated by fish, dinosaurs, turtles, and crocodilians. Common elements of this diverse fauna occur to within 2.37 m of the Cretaceous-Tertiary (K-T) boundary. The stratigraphically highest fossil in the study is a partial ceratopsian skeleton 1.77 m below the K-T boundary in the basal Fort Union Formation. All dinosaurs that occur at more than two sites also occur at the highest level that yielded more than 500 specimens (8.40 m below the K-T boundary). The fine-grained uppermost 2 m of the Hell Creek is nearly devoid of all fossils, including taxa known to occur in the overlying formation. The absence of channel deposits in this part of the formation may be the reason for the absence of fossil localities. The presence of marine-tolerant taxa suggests that the study area may have been adjacent to a previously unidentified seaway of latest Cretaceous age. Rarefac-tion analysis indicates no evidence for a decline in vertebrate diversity through the formation or dinosaurian diversity in the 3 m below the K-T boundary. Our results are not compatible with gradual vertebrate extinction at the end of the Cretaceous.
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 within the genus Hesperornis or within the species H. regalis. The presence of large hesperornithiforms at high latitudes may indicate that either strong seasonal distribution of resources contributed to larger body sizes at higher latitudes, or Campanian thermal gradients along the Western Interior Seaway were significant enough to affect body size for thermoregulatory reasons (sensu Bergmann's rule). The absence of body size trends within mid-latitude Hesperornis specimens suggests that the climatic gradient in the southern portion of the Seaway was not strong enough to force morphological evolutionary responses, or that character displacement, migration and/or other factors affected body size. Sample size and the inherent problems of an incomplete fossil record must also be considered.
A ∼42 m section of Late Cretaceous Upper Campanian sediments in Saskatchewan Landing Provincial Park, southwestern Saskatchewan, Canada, represents the easternmost outcrop of the Dinosaur Park Formation in the Western Interior Basin. Herein we document a new microvertebrate locality from the upper part of this formation that shows high diversity in a mixed coastal and marine assemblage. Palynology, ichnology, sedimentology, and vertebrate palaeontology are integrated to determine paleoenvironmental and paleoecological conditions in the region. The site is interpreted as having been deposited under marginal-marine conditions near a shoreline undergoing transgression by the encroaching Bearpaw Sea. Though well studied and sampled in Alberta, the Dinosaur Park Formation is poorly exposed with little known associated vertebrate assemblages in Saskatchewan. These discoveries from the new microvertebrate site offer new insights into Late Cretaceous ecosystems near paleocoastlines, allowing for future studies of spatial diversity patterns relative to Albertan faunas. Herein is also presented the first published occurrences of several Late Campanian vertebrate taxa in Saskatchewan.
The Cretaceous Hesperornithiformes are an extinct group of aquatic birds long recognized to have practiced foot-propelled diving. This specialization is seen today in a number of modern avian families (loons, grebes, cormorants, and some ducks) that have convergently derived a diving lifestyle. Historically, hesperornithiforms have usually been compared to modern loons and grebes as analogues. However, these comparisons are based on qualitative observations of skeletal morphology and have never been tested using morphometric data. Studying the morphological details underlying this functional convergence provides an opportunity to better understand the lifestyle of the extinct Hesperornithiformes, particularly in regard to adaptations for foot-propelled diving and ecological niches these birds may have occupied.
This study presents a morphometric analysis of the hindlimb of hesperornithiforms and modern foot-propelled diving birds. Measurements were collected from the tarsometatarsus, tibiotarsus, and femur of eight genera of modern birds and six genera of hesperornithiforms. In order to explore variation within the data, a number of different combinations of measurements (for example, tarsometatarsus and tibiotarsus, or tibiotarsus and femur) were subjected to principal components analyses (PCA). The primary reason for investigating the data in different subsets was to increase taxonomic inclusion among the fossil specimens, where missing data was the largest impediment to the study.
Results of this study show that hesperornithiforms rarely shared morphospace with loons or grebes, but more often did share morphospace with cormorants and diving ducks. Therefore, loons and grebes may not serve as the most appropriate analogue for the Hesperornithiformes. Use of these sorts of analyses, in conjunction with detailed morphological work, may enhance our understanding of the evolution of complex ecological strategies and niche partitioning among birds and other organisms.
Allow yourself to be taken back into deep geologic time when strange creatures roamed the Earth and Western North America looked completely unlike the modern landscape. Volcanic islands stretched from Mexico to Alaska, most of the Pacific Rim didn’t exist yet, at least not as widespread dry land; terranes drifted from across the Pacific to dock on Western Americas’ shores creating mountains and more volcanic activity. Landscapes were transposed north or south by thousands of kilometers along huge fault systems. Follow these events through paleogeographic maps that look like satellite views of ancient Earth. Accompanying text takes the reader into the science behind these maps and the geologic history that they portray. The maps and text unfold the complex geologic history of the region as never seen before.
Despite its importance in various disciplines, a general method to assess ontogenetic ages of skeletal and fossil specimens has been lacking for birds. Although the textural ageing method was formulated to assess relative ontogenetic ages of specimens from inspection of bone surface textures, the exact correspondence of surface textures to ontogenetic stages has not yet been clear. In this study, bone surface textures of six major limb bones (humerus, ulna, carpometacarpus, femur, tibiotarsus, and tarsometatarsus) were described in postnatal ontogenies of four species of modern birds (Calonectris leucomelas, Phalacrocorax capillatus, Larus crassirostris, and Cerorhinca monocerata) from 14–28 individuals of known ontogenetic stages for each species. Consistently with the previous postulation, it was found that bones of chicks were characterized by rough surface textures with numerous grooves/depressions that host minute foramina. Bones of fledglings/juveniles, which are generally as large as those of adults but more slender, were characterized by the occasional presence of depressions and foramina. Histological observations confirmed that these rough surface textures were underlain by fibrolamellar bone tissue which is associated with active periosteal ossification. These results indicate that the smooth surface texture in adults is formed after the cessation of circumferential bone growth, which probably takes place between fledging and the attainment of sexual maturity. The available evidence suggests that the textural ageing is probably applicable to the entire Neognathae, a clade containing most crown-group birds.
Asian hesperornithiforms are extremely rare in contrast to the much more abundant record from North America. In Asia, these fossil birds are only known from fragmentary materials from Mongolia. Here we describe the skeletal remains of a new hesperornithiform Chupkaornis keraorum gen. et sp. nov. from the Upper Cretaceous Kashima Formation (Coniacian to Santonian) of the Yezo Group in Mikasa City, Hokkaido, Japan. This is the best-preserved hesperornithiform material from Asia and it is the first report of hesperornithiforms from the eastern margin of the Eurasian continent. Chupkaornis has a unique combination of characters: finger-like projected tibiofibular crest of femur, deep, emarginated lateral excavation with a sharply defined edge of the ventral margin of the thoracic vertebrae, and the heterocoelous articular surface of the thoracic vertebrae. Our new phylogenetic analysis revises the phylogenetic relationships of Hesperornithiformes. In contrast to previous studies, Enaliornis is assigned as the most basal taxon and Baptornis is positioned as more derived than Brodavis. Chupkaornis is a sister taxon to the clade of Brodavis and higher taxa. Parahesperornis and Hesperornis are positioned within Hesperornithidae, the derived Hesperornithiformes. Many of the skeletal character changes are concentrated at the base of Hesperornithidae (Parahesperornis and more derived taxa), and involve the modification of the pelvic girdle and hind limb morphology (e.g. dorsal directed antitrochanter of pelvis, short and sprawled femur, including probable lobe-toed feet suggested by the specialized distal articular surface of first digit of fourth toe, and predominantly robust digit IV phalanges). These skeletal modifications are likely adaptations for foot-propelled diving behaviour. http://zoobank.org/urn:lsid:zoobank.org:pub:FB783237-E565-4B74-9386-EADF8E12DFD4 © The Trustees of the Natural History Museum, London 2017. All rights reserved.
A vertebra from the Judith River Formation (Campanian) of Saskatchewan, found with other Upper Cretaceous vertebrate remains, is referred to the loon-like hesperornithiform Baptornis , and is the first recorded occurrence of this genus from continental deposits. It is also the first bird described from the Judith River Formation of western Canada.
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.
Fossil birds are relatively rare in Cretaceous deposits of the Northern Great Plains, so the discovery of a large, new diving bird was unexpected. From marine deposits of the Niobrara Formation in Kansas a small diversity of birds was known, but until now the large diving bird, Hesperornis, was the only bird taxon known from the Pierre Shale Group of South Dakota. The new discovery, a partial skeleton of another diving bird, Baptornis, was secured from the Sharon Springs Formation (lower middle Campanian) of the Pierre Shale Group in Fall River County, South Dakota. The specimen is represented by vertebrae, pelvic fragments, and lower leg elements that are similar to but much more robust than Baptornis advenus from the subjacent Niobrara Formation. The new taxon is nearly twice the size of the Niobrara species, principally in robustness rather than in length of elements. Overall, the specimen represents the first occurrence of Baptornis from the Pierre Shale Group, represents a new species, and indicates a greater diversity of birds from the Pierre Shale Group than was previously known.
Palaeontology, the scientific study of fossils, has developed from a descriptive science to an analytical science used to interpret relationships between earth and life history. This book provides a comprehensive and thematic treatment of applied palaeontology, covering the use of fossils in the ordering of rocks in time and in space, in biostratigraphy, palaeobiology and sequence stratigraphy. Robert Wynn Jones presents a practical workflow for applied palaeontology, including sample acquisition, preparation and analysis, and interpretation and integration. He then presents numerous case studies that demonstrate the applicability and value of the subject to areas such as petroleum, mineral and coal exploration and exploitation, engineering geology and environmental science. Specialist applications outside of the geosciences (including archaeology, forensic science, medical palynology, entomopalynology and melissopalynology) are also addressed. Abundantly illustrated and referenced, Applications of Palaeontology provides a user-friendly reference for academic researchers and professionals across a range of disciplines and industry settings.
Substantial changes in bone histology accompany the secondary adaptation to life in the water. This transition is well documented in several lineages of mammals and non-avian reptiles, but has received relatively little attention in birds. This study presents new observations on the long bone microstructure of penguins, based on histological sections from two extant taxa (Spheniscus and Aptenodytes) and eight fossil specimens belonging to stem lineages (†Palaeospheniscus and several indeterminate Eocene taxa). High bone density in penguins results from compaction of the internal cortical tissues, and thus penguin bones are best considered osteosclerotic rather than pachyostotic. Although the oldest specimens sampled in this study represent stages of penguin evolution that occurred at least 25 million years after the loss of flight, major differences in humeral structure were observed between these Eocene stem taxa and extant taxa. This indicates that the modification of flipper bone microstructure continued long after the initial loss of flight in penguins. It is proposed that two key transitions occurred during the shift from the typical hollow avian humerus to the dense osteosclerotic humerus in penguins. First, a reduction of the medullary cavity occurred due to a decrease in the amount of perimedullary osteoclastic activity. Second, a more solid cortex was achieved by compaction. In extant penguins and †Palaeospheniscus, most of the inner cortex is formed by rapid osteogenesis, resulting an initial latticework of woven-fibered bone. Subsequently, open spaces are filled by slower, centripetal deposition of parallel-fibered bone. Eocene stem penguins formed the initial latticework, but the subsequent round of compaction was less complete, and thus open spaces remained in the adult bone. In contrast to the humerus, hindlimb bones from Eocene stem penguins had smaller medullary cavities and thus higher compactness values compared with extant taxa. Although cortical lines of arrested growth have been observed in extant penguins, none was observed in any of the current sampled specimens. Therefore, it is likely that even these 'giant' penguin taxa completed their growth cycle without a major pause in bone deposition, implying that they did not undergo a prolonged fasting interval before reaching adult size.
One of the most important avian fossils is a nearly complete skeleton of a hesperornithid from the late Cretaceous Niobrara Chalk Formation of western Kansas found by H. T. Martin in 1894. Williston assigned it to Hesperornis gracilis, a form named by Marsh but never really diagnosed or illustrated. Because of the size and apparent completeness of Marsh's monumental work on the Mesozoic birds of North America, these birds have been largely ignored since its publication. This has largely been the fate of H. T. Martin's exceptional specimen, parts of which have been figured under both Hesperornis gracilis, and H. regalis. This specimen can now be shown to be a previously undescribed genus of hesperornithiform bird, that provides the basis for a re-evaluation of the relationships of the Hesperornithiformes to other Mesozoic birds. Archaeopteryx is a member of a side-branch of avian evolution, the subclass Sauriurae, which became extinct at the end of the Mesozoic. The hesperornithiform Enaliornis is the earliest bird which can be shown to belong to the subclass Ornithurae to which all modern birds belong.
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.
Revised, updated, and expanded with the latest interpretations and fossil discoveries, the second edition of Oceans of Kansas adds new twists to the fascinating story of the vast inland sea that engulfed central North America during the Age of Dinosaurs. Giant sharks, marine reptiles called mosasaurs, pteranodons, and birds with teeth all flourished in and around these shallow waters. Their abundant and well-preserved remains were sources of great excitement in the scientific community when first discovered in the 1860s and continue to yield exciting discoveries 150 years later. Michael J. Everhart vividly captures the history of these startling finds over the decades and re-creates in unforgettable detail these animals from our distant past and the world in which they lived-above, within, and on the shores of America's ancient inland sea.
The Upper Cretaceous Izumi basin extends almost 300 km from northwestern Shikoku to western Kii Peninsula along the Median Tectonic Line in Southwest Japan. The strata are folded into a syncline, dipping 30° to 50° to the east. A magnetostratigraphic study was carried out in the succession of strata from the lowest horizons in northwestern Shikoku to the upper horizons in Awaji Island 170 km to the east. Despite the unique and complicated structure of the basin, the thick sedimentary pile provides a continuous record of geomagnetic polarity changes. The pattern of magnetic polarity zones matches a geomagnetic polarity change during the early Campanian to earliest Maastrichtian in accord with previous biostratigraphic studies. Sedimentation rates based on the polarity zonation are 0.7 to 2 cm per year. -from English summary
A new family, Brodavidae, with one new genus and four species, is described from the Late Cretaceous (Maastrichtian) of Asia and North America. These include the first freshwater occurrences and latest records of the order Hesperornithiformes, an extinct group of diving birds whose marine members had probably lost their powers of flight by the end of the Early Cretaceous. Minimal pachyostosis in the freshwater form suggests the possibility of volant abilities.
Taxonomy and stratigraphic distribution of the Upper Cretaceous marine reptiles from Japan are reviewed. Remains of the Chelonioidea (sea turtles), Mosasauridae, and Plesiosauria are known in various parts of Japan, including the holotypes of the dermochelyid Mesodermochelys undulatus, mosasaurine Mosasaurus hobetsuensis and M. prismaticus, tylosaurine Taniwhasaurus mikasaensis, and elasmosaurid Futabasaurus suzukii. Less diagnostic materials of other groups such as protostegiids, plioplatecarpines, polycotylids, pliosauroids, were also collected. Mesodermochelys dominates the chelonioid fauna, and in comparison with European and North American faunas, suggests a rather restricted geographical distribution of chelonioid species during the Late Cretaceous. The mosasaurid records support the world-wide trend of increasingly mosasaurine-dominated post-Santonian assemblages, and demonstrate suprageneric-level compositional changes in the northwestern Pacific through time. Elasmosaurid fossils are known from all stages of the Upper Cretaceous in Japan and indicate their continuous presence in the northwestern Pacific. Polycotylid remains are fewer in number and limited to the lower Upper Cretaceous. Pliosauroid specimens are even rarer but raise the upper limit of the stratigraphic range of the group in Northern Pacific to the Turonian.
History.
The oldest remains of British fossil birds are recorded by Sir Charles Lyell as having been first found in 1858, in the Cambridge Upper Greensand. This stratum still continues the only member of the British Secondary deposits in which the bones of birds have been identified by morphological characters; for though the Rev. Mr. Dennis had previously asserted the occurrence of birds in the Stonesfield Slate, on the evidence of the microscopic structure of osseous tissue, it is safer, in the absence of recognizable bones, to believe that the ornithic structure he detected was found in an ornithosaurian rather than in a true bird. The discovery of bird-bones in the Cambridge Greensand was made by Mr. Lucas Barrett, F.G.S., then Assistant Naturalist to the late Professor Sedgwick in the Woodwardian Museum of the University of Cambridge; but I am not aware that Mr. Barrett ever published any account of his discovery. The bones are mentioned by Lyell as “the remains of a bird which was rather larger than the common Pigeon, and probably of the order Natatores, and which, like most of the Gull tribe, had well-developed wings. Portions of the metacarpus, metatarsus, tibia, and femur have been detected; and the determinations of Mr. Barrett have been confirmed by Professor Owen.” What became of Mr. Barrett's specimens I was never able to find out. They were not in the Woodwardian Museum when I succeeded to Mr. Barrett's duties in 1859; and the whole of the remains to which I
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.
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.
Vertebrate remains have been recovered from two horizons in late Cretaceous strata along the east bank of the Anderson River at latitude 69 °N. The lower horizon has produced a fauna very similar to that of the Niobrara Chalk in western Kansas, including mosasaurs, plesiosaurs, and abundant toothed birds. The upper horizon has yielded a moderately short-necked plesiosaur of cimoliasaurian affinities. These vertebrates lived in or near a strait linking the Arctic Ocean with the interior sea in very late Cretaceous time.
The vertebrate fauna from the Upper Cretaceous of Manitoba is described. Of the 18 genera, 13 have not been recorded previously from this province. The vertebrate assemblage resembles that of the Niobrara Formation of western Kansas, but is noteworthy for the relative abundance of toothed birds.
Charles Darwin commented that Ichthyornis, as one of the “toothed birds” from the Late Cretaceous of Kansas, offered some of “the best support to the theory of evolution” (in litt., C. Darwin to O.C. Marsh, August 31, 1880). Ichthyornis figures no less prominently today. It is one of the closest outgroups to crown clade Aves, and remains one of the only Mesozoic avialans known from more than a handful of specimens. As such, Ichthyornis is an essential taxon for analyses of deep divergences within Aves because of its influence in determining the morphologies ancestral to the crown clade. Ichthyornis, however, has languished in need of new anatomical description and taxonomic revision. Many of the best Ichthyornis specimens were largely inaccessible, plastered into Yale Peabody Museum (YPM) exhibit mounts for nearly a century. The focus of this study was the entire YPM Ichthyornis collection, the largest at any institution. The elements removed from the mounts were identified to the specimens with which they were originally associated. Detailed morphological study of the 81 YPM specimens yielded the following results: (1) there is evidence for only one species of Ichthyornis, rather than the eight previously proposed; (2) 78 specimens are part of this species, Ichthyornis dispar; (3) two previously identified species are not part of Ichthyornis; and (4) one new species is identified. This analysis also provided a case study in the application of phylogenetic nomenclature at the species level. The morphology of Ichthyornis dispar is described in detail from the holotype and referred specimens. Phylogenetic analyses of 202 morphological characters, scored for 24 terminal taxa, evaluated the relationships among Mesozoic ornithurines including Ichthyornis dispar and the newly identified taxa. Analysis of 23 core taxa produced two most parsimonious trees (L: 384, CI: 0.66). Marsh's “Ichthyornithiformes” is not monophyletic: Two previously named species of Ichthyornis as well as Apatornis celer are placed as more closely related to or as part of Aves. The results of the phylogenetic analyses have implications for previous hypotheses of the timing and pattern of the origin of Aves.
The avialan taxon Apsaravis ukhaana from the Late Cretaceous of southern Mongolia is completely described and its phylogenetic position is evaluated. Apsaravis ukhaana is from continental sandstones exposed at the locality of Ukhaa Tolgod, Omnogov Aimag, Mongolia. The holotype specimen consists of the nearly complete, articulated skeleton of a small volant avialan. Apsaravis ukhaana is unambiguously differentiated from other avialans based on the presence of several unique morphologies: a strong tubercle on the proximal humerus, a hypertrophied trochanteric crest on the femur, and extremely well-projected posterior wings of a surface of the distal tibiotarsus that in Aves articulates with the tibial cartilage. Ten other homoplastic characters optimize as autapomorphies of Apsaravis ukhaana in the phylogenetic analysis. They are as follows: ossified mandibular symphysis; dentary strongly forked posteriorly; hooked acromion process on scapula; highly angled dorsal condyle of humerus; humeral condyles weakly defined; distal edge of humerus angling strongly ventrally; humerus flared dorsoventrally at its distal terminus; lateral condyle of tibiotarsus wider than medial one; neither condyle of tibiotarsus tapering toward the midline; and metatarsal II trochlea rounded rather than ginglymoid. Phylogenetic placement of Apsaravis ukhaana as the sister taxon of Hesperornithes + Aves resulted from analysis of 202 characters scored for 17 avialan ingroup taxa. The implications of Apsaravis ukhaana, and the results of the phylogenetic analysis, for the evolution of flight after its origin and character support for enantiornithine monophyly are extensively discussed.