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Author(s): Shi, Yaoran; Gu, Victoria W.; Farke, Andrew A. | Abstract: Isolated equid phalanges are relatively common finds in the Barstow Formation (Miocene, 19 to 13 million years ago, southern California), but anecdotal observations suggested that not all positions (proximal, middle, and distal/ungual) of the primary digit (digit III) are recovered with equal frequency. Our sample includes primarily surface-collected phalanges from the Barstow Formation, which we compare with phalanges of Pleistocene horses from Pit 3 and Pit 77 from Rancho La Brea (Los Angeles, California). The null hypothesis is that the three positions of phalanges should be equally common. Our Barstow sample includes 228 proximal, 151 middle, and 36 distal phalanges. A chi-square test (pl0.001) is consistent with preservation bias in phalangeal frequency for the full Barstow Formation sample, and this pattern generally holds within sub-samples by locality or depositional environment. Pit 3 of La Brea produced 163 proximal, 144 middle, and 103 distal phalanges. A chi-square test with correction for multiple comparisons suggests that proximal and middle phalanges are preserved with statistically equal frequency (p=0.278) whereas distal phalanges are less common (pl0.001). For Pit 77, there are 54 proximal, 55 middle, and 51 distal phalanges; the chi-square test finds that all three types are equally common (p=0.922). Overall, differences in physical properties between phalangeal positions, such as surface area, density, shape, and size, could influence preservation within each environment. The observed differences between Barstow and La Brea might be caused by variations in depositional environment that influence the surface exposure time of fossils and disarticulation pre-burial, as well as by differences in the size of the horses at each locality. We suggest that when permitted by sample size, it is desirable to distinguish unguals from other phalanges when analyzing taphonomic patterns in the fossil record.

The ankle in non-avian theropod dinosaurs consists of the astragalus and calcaneum proximally and a distal series of tarsal bones capping the metatarsals. Nearly all theropods have only two distal tarsals, identified as distal tarsal 3 and distal tarsal 4. Historically, the morphology and anatomical relationships of these distal tarsals is uncertain in ornithomimosaurs due to loss and/or disarticulation; even in articulated specimens, the bones can be difficult to access. A previously undescribed ornithomimid fossil from the Kaiparowits Formation (upper Campanian) of southern Utah, USA, provides unique views of the distal tarsals in articulation with their surrounding elements, allowing the most complete assessment yet of this region in an ornithomimid from North America. Distal tarsal 3 contacts both metatarsals II and III, whereas distal tarsal 4 contacts only metatarsal IV. Distal tarsal 4 also shows a tab-like process that projects laterally. Comparison of the new fossil with other ornithomimosaurs shows that distal tarsals in Ornithomimosauria can be generalized as: (i) paired as distal tarsals 3 and 4; (ii) not fused to one another or to the proximal metatarsus; and (iii) proximo-distally compressed. The distal tarsals of ornithomimosaurs vary in the antero-posterior positioning and extent to which they cover the proximal metatarsal surface.

Ceratopsians were herbivorous dinosaurs that dominated many of the terrestrial ecosystems in Asia and North America during the Cretaceous. The bizarre variety of skulls and lower jaw morphologies as well as the inferred ecological abundance of many species in this clade indicate that Ceratopsia was a successful group. Here we analyzed 126 lower jaws from 50 ceratopsian species, using two-dimensional geometric morphometrics and finite element analysis to investigate differences in shape and structural performance of this part of the feeding apparatus across Ceratopsia. Morphological differences in lower jaws across ceratopsian clades are said to originate from feeding adaptation. Our results show that the stress (physical loadings modeled in response to biting) in lower jaws was quite similar between “basal” and “derived” taxa, whereas major differences among clades occur for stress values associated with the coronoid process. The basal ceratopsians Hualianceratops and Yinlong had a highly stressed and primitive lower jaw, indicating that those animals may have fed on relatively soft foliage and fruits. A similar condition was found for basal neoceratopsians and protoceratopsids. Psittacosaurids possessed a well-integrated and compact lower jaw able to withstand high stress, at the cost of having a highly stressed coronoid process. Leptoceratopsids were characterized by the opposite condition. Taxa such as Leptoceratops, Prenoceratops, Zhuchengceratops and Cerasinops appear to have had a comparatively efficient feeding apparatus. Ceratopsidae represents the clade with the most efficient masticatory apparatus within Ceratopsia, even if the horizontal ramus of the lower jaw appears less able to withstand high levels of stress as compared with other ceratopsians. Additionally, we found the dentary and surangular–angular complex co-evolved to generate a masticatory apparatus able to withstand high stress, particularly in Protoceratopsidae and Triceratopsini. The major phenotypic evolutionary rate and morphological changes occurred during the mid- to Late Cretaceous, when intense climate change and angiosperm diversification could have affected the evolution of ecological diversity and feeding biomechanics in Ceratopsia. © 2017 Elsevier Ltd

A nearly complete, but isolated, femur of a small hadrosaurid from the Hell Creek Formation of Montana is tentatively referred to Edmontosaurus annectens . At 28 cm long, the element can be classified as that from an “early juvenile” individual, approximately 24 percent of the maximum known femur length for this species. Specimens from this size range and age class have not been described previously for E. annectens . Notable trends with increasing body size include increasingly distinct separation of the femoral head and greater trochanter, relative increase in the size of the cranial trochanter, a slight reduction in the relative breadth of the fourth trochanter, and a relative increase in the prominence of the cranial intercondylar groove. The gross profile of the femoral shaft is fairly consistent between the smallest and largest individuals. Although a n ontogenetic change from relatively symmetrical to an asymmetrical shape in the fourth trochanter has been suggested previously , the new juvenile specimen shows an asymmetric fourth trochanter. Thus, there may not be a consistent ontogenetic pattern in trochanteric morphology. An isometric relationship between femoral circumference and femoral length is confirmed for Edmontosaurus . Overall ontogenetic trends in the femur of Edmontosaurus are concordant with patterns seen in other Hadrosauridae, supporting a fairly conserved pattern of development for this element within the clade.

Pterosaurs were widespread during the Late Cretaceous, but their fossils are comparatively rare in terrestrial depositional environments. A large pterosaur bone from the Kaiparowits Formation (late Campanian, ~76–74 Ma) of southern Utah, USA, is tentatively identified as an ulna, although its phylogenetic placement cannot be precisely constrained beyond Pterosauria. The element measures over 36 cm in preserved maximum length, indicating a comparatively large individual with an estimated wingspan between 4.3 and 5.9 m, the largest pterosaur yet reported from the Kaiparowits Formation. This size estimate places the individual at approximately the same wingspan as the holotype forCryodrakon boreasfrom the penecontemporaneous Dinosaur Park Formation of Alberta. Thus, relatively large pterosaurs occurred in terrestrial ecosystems in both the northern and southern parts of Laramidia (western North America) during the late Campanian.

This paper is the first of a three-part series that investigates the architecture of cancellous (‘spongy’) bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion.On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling.

Ceratopsidae represents a group of quadrupedal herbivorous dinosaurs that inhabited western North America and eastern Asia during the Late Cretaceous. Although horns and frills of the cranium are highly variable across species, the lower jaw historically has been considered to be relatively conservative in morphology. Here, the lower jaws from 58 specimens representing 21 ceratopsoid taxa were sampled, using geometric morphometrics and 2D finite element analysis (FEA) to explore differences in morphology and mechanical performance across Ceratopsoidea (the clade including Ceratopsidae, Turanoceratops and Zuniceratops). Principal component analyses and non-parametric permuted MANOVAs highlight Triceratopsini as a morphologically distinct clade within the sample. A relatively robust and elongate dentary, a larger and more elongated coronoid process, and a small and dorso-ventrally compressed angular characterize this clade, as well as the absolutely larger size. By contrast, non-triceratopsin chasmosaurines, Centrosaurini and Pachyrhinosaurini have similar morphologies to each other. Zuniceratops and Avaceratops are distinct from other taxa. No differences in size between Pachyrhinosaurini and Centrosaurini are recovered using non-parametric permuted ANOVAs. Structural performance, as evaluated using a 2D FEA, is similar across all groups as measured by overall stress, with the exception of Triceratopsini. Shape, size and stress are phylogenetically constrained. A longer dentary as well as a long coronoid process result in a lower jaw that is reconstructed as relatively much more stressed in triceratopsins.

Ceratopsids (“horned dinosaurs”) are known from numerous specimens in western North America and Asia, a distribution reflecting the inferred subaerial link between the two landmasses during the Late Cretaceous. However, this clade was previously unknown from eastern North America, presumably due to limited outcrop of the appropriate age and depositional environment as well as the separation of eastern and western North America by the Western Interior Seaway during much of the Late Cretaceous. A dentary tooth from the Owl Creek Formation (late Maastrichtian) of Union County, Mississippi, represents the first reported occurrence of Ceratopsidae from eastern North America. This tooth shows a combination of features typical of Ceratopsidae, including a double root and a prominent, blade-like carina. Based on the age of the fossil, we hypothesize that it is consistent with a dispersal of ceratopsids into eastern North America during the very latest Cretaceous, after the two halves of North America were reunited following the retreat of the Western Interior Seaway.

Arrhinoceratops brachyops is a poorly understood chasmosaurine ceratopsid from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, previously described on the basis of only a single skull. Here, we report on a second specimen attributable to this species, including a relatively complete skull, syncervical, and partial left forelimb. This second specimen clarifies aspects of morphology not visible in the holotype, and also elucidates variation in A. brachyops. The species is distinguished by a square-shaped triangular process of the premaxilla, a steeply inclined triturating surface of the predentary, and a triangular nasal horncore in horizontal section. The dentary is also distinctive in bearing a bony lateral ridge similar to that of Anchiceratops ornatus, but more strongly developed. Phylogenetic analysis cannot resolve the relationships of Arrhinoceratops beyond the level of Chasmosaurinae, owing to both missing data and conflicting characters. However, we do find some support for a deep split within Chasmosaurinae, contrary to conventional topologies. We also report on other fragmentary specimens plausibly attributable to A. brachyops that suggest a minimum age range of approximately 750 ka for this species.

Ornithischia, a diverse clade of herbivorous dinosaurs, has numerous members with structures hypothesized to function in combat. These include the horned ceratopsids, dome-headed pachycephalosaurs, spike-thumbed iguanodonts, tail-clubbed ankylosaurs and spiked stegosaurs, among others. Three main lines of evidence support such inferences: (1) analogy with modern animals; (2) biomechanical analysis and simulation; and (3) paleopathology. The most solid inferences utilize multiple pieces of evidence, although this is hampered by a limited understanding of combat in modern animals.

An isolated coracoid represents the first described occurrence of an enantiornithine bird from the Kaiparowits Formation (Upper Cretaceous) of southern Utah, USA. The specimen is identified as enantiornithine by the convex scapular facet, approximate alignment of this facet with the humeral articular facet and acrocoracoid process, and the presence of an acrocoracoidal tubercle. This coracoid came from a comparatively large individual, consistent with previous reports of other large enantiornithines from strata of Campanian strata in North America, South America, and Europe. The occurrence of enantiornithines in the Kaiparowits Formation and their apparent absence in the well-sampled Dinosaur Park Formation of similar age in Alberta represents yet another faunal difference between the two areas, although this may be a result of environmental differences rather than the endemism proposed for non-avian dinosaurs.

Birds form the largest extant group of bipedal animals and occupy a broad range of body masses, from grams to hundreds of kilograms. Additionally, birds occupy distinct niches of locomotor behaviour, from totally flightless strong runners such as the ratites (moa, kiwi, ostrich) to birds that may walk, dabble on water or fly. We apply a whole-bone approach to investigate allometric scaling trends in the pelvic limb bones (femur, tibiotarsus, tarsometatarsus) from extant and recently extinct birds of greatly different size, and compare scaling between birds in four locomotor groups; flightless, burst-flying, dabbling and flying. We also compare scaling of birds’ femoral cross-sectional properties to data previously collected from cats. Scaling exponents were not significantly different between the different locomotor style groups, but elevations of the scaling relationships revealed that dabblers (ducks, geese, swans) have particularly short and slender femora compared with other birds of similar body mass. In common with cats, but less pronounced in birds, the proximal and distal extrema of the bones scaled more strongly than the diaphysis, and in larger birds the diaphysis occupied a smaller proportion of bone length than in smaller birds. Cats and birds have similar femoral cross-sectional area (CSA) for the same body mass, yet birds’ bone material is located further from the bone’s long axis, leading to higher second and polar moments of area and a greater inferred resistance to bending and twisting. The discrepancy in the relationship between outer diameter to CSA may underlie birds’ reputation for having ‘light’ bones.

In 1916, a centrosaurine dinosaur bonebed was excavated within the Campanian-aged deposits of what is now Dinosaur Provincial Park, Alberta, Canada. Specimens from this now-lost quarry, including two parietals, a squamosal, a skull missing the frill, and an incomplete dentary, were purchased by The Natural History Museum, London. The material was recently reprepared and identified herein as a previously unknown taxon, Spinops sternbergorum gen. et sp. nov. Based upon the available locality data and paleopalynology, the quarry lies in either the upper part of the Oldman Formation or the lower part of the Dinosaur Park Formation. The facial region of the partial skull is similar to putative mature specimens of Centrosaurus spp. and Styracosaurus albertensis, with short, rounded postorbital horncores and a large, erect nasal horncore. Parietal ornamentation is consistent on both known parietals and is unique among ceratopsids. Bilateral, procurved parietal hooks occupy the P1 (medial-most) position on the do...

The function and evolution of paranasal pneumaticity remains elusive, in part because of limited sampling and description. Here, the frontal sinuses from 62 species of bovids were investigated using X-ray computed tomography. This survey revealed hitherto undescribed diversity in the morphology of this sinus, and suggests that it was probably present in the common ancestor of Bovidae. Among extant bovids, the frontal sinuses were lost or reduced to recesses at least six different times. Quantitative analyses, when accounting for phylogeny using phylogenetically independent contrasts, did not find any link between the size or complexity of the frontal sinus and head-to-head ramming behaviour. Other analyses indicated that frontal sinus size was correlated most closely with the size of the frontal bone itself, rather than with the overall skull size or horn size. These results may be partially consistent with the hypothesis of sinuses being the result of ‘opportunistic pneumatization’, in which sinus size depends on the quantity of bone available for pneumatization as well as the mechanical demands placed on the skull. Additional evidence also indicates a strong phylogenetic correlation with sinus morphology, particularly with regard to the presence of paranasal diverticula, as well as the ability of sinuses to cross sutural boundaries. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 988–1014.

The results of Barnum Brown's 1937 expedition to the Almond Formation of Wyoming consisted of two unidentified ceratopsian skulls and a partial hadrosaurid specimen (AMNH 3651). The hadrosaurid is here attributed to the Maastrichtian genus Saurolophus , verifying previous biostratigraphic correlations of this formation using ammonite zones. Fossiliferous lower Maastrichtian formations occurring latitudinally between those of Alberta, Canada, and southwestern Texas, USA, such as the Almond Formation, are essential for testing the effects and duration of apparent hadrosaurid faunal segregation earlier in the Campanian, and indirectly aiding in the placement of faunal boundaries that are currently unknown for the late Campanian. The discovery of Saurolophus in Wyoming, a close relative of the Campanian genus Prosaurolophus , affirms that the segregation of hadrosaurid faunas established in the late Campanian (∼75 Ma) continued for at least 3 million years. Combining occurrences of Saurolophus from Mongolia and the Moreno Formation of California with those of Alberta, Canada, this genus appears to have had one of the largest geographic ranges of any equivalent clade of hadrosaurid dinosaur, although species level distributions are still uncertain.

SUMMARYFrontal sinuses in goats and other mammals have been hypothesized to function as shock absorbers, protecting the brain from blows during intraspecific combat. Furthermore, sinuses are thought to form through removal of `structurally unnecessary' bone. These hypotheses were tested using finite element modeling. Three-dimensional models of domesticated goat (Capra hircus) skulls were constructed, with variable frontal bone and frontal sinus morphology, and loaded to simulate various head-butting behaviors. In general, models with sinuses experienced higher strain energy values (a proxy for shock absorption) than did models with unvaulted frontal bones, and the latter often had higher magnitudes than models with solid vaulted frontal bones. Furthermore, vaulted frontal bones did not reduce magnitudes of principal strain on the surface of the endocranial cavity relative to models with unvaulted frontal bones under most loading conditions. Thus, these results were only partially consistent with sinuses, or the bone that walls the sinuses, acting as shock absorbers. It is hypothesized that the keratinous horn sheaths and cranial sutures are probably more important for absorbing blows to the head. Models with sinuses did exhibit a more `efficient'distribution of stresses, as visualized by histograms in which models with solid frontal bones had numerous unloaded elements. This is consistent with the hypothesis that sinuses result at least in part from the removal of mechanically unnecessary bone.

Recent collecting efforts (1993 to present) in the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar have yielded numerous specimens of the medium-sized abelisauroid theropod Majungasaurus crenatissimus (Deperet, 1896) Lavocat, 1955. Exquisite preservation, coupled with near-complete articulated or associated skeletons, has allowed an assessment of individual skeletal variation in this taxon, including a preliminary analysis of osteopathology in a non-tetanuran theropod. Importantly, Majungasaurus is the first abelisauroid theropod for which comprehensive pathology data are available. In a survey of 181 postcranial skeletal elements from a minimum of 21 individuals, abnormalities were identified in eight elements from a minimum of four individuals. These include a pedal phalanx with a mediolateral diaphyseal expansion of unknown etiology, a dorsal vertebra with a small exostosis, a caudal vertebra with probable idiopathic ossification of vertebral ligaments, and a pa...

Ceratopsids, horned herbivorous ornithischians from the Cretaceous of North America, are unique among dinosaurs in the form and expression of their cranial ornamentation. All ceratopsid genera possess a bony parieto-squamosal frill that projects over the neck region and some degree of development of nasal and orbital horns. These horns vary in form and location, from low bosses (e.g., Pachyrhinosaurus Sternberg, 1950) to long, conical horns (e.g., Triceratops Marsh, 1889 postorbital horns). Internal structural changes occurred along with these extreme external modifications of the skull (Forster, 1996). A frontal sinus complex occupies space variably involving the postorbital, frontal, parietal, supraoccipital, and exoccipital bones of the skull roof in ceratopsid dinosaurs (Fig. 1.1; Forster, 1996). These sinuses are relatively small, simple chambers in most members of the two ceratopsid clades Chasmosaurinae and Centrosaurinae (Lehman, 1990). However, the frontal sinuses reach large proportions in some species, with a portion of the sinuses extending into the base of the postorbital horncores (Forster, 1996; Sampson et al., 1997; Lehman, 1998). Forster (1996) termed this part of the sinus complex the “cornual” sinus, analogous to the cornual diverticulum of the frontal sinuses in bovid mammals (e.g., domesticated goats; Nickel et al., 1973). Marsh (1887) was the first to note cornual sinuses in a large chasmosaurine (USNM 1871, probably a specimen of Triceratops or Torosaurus Marsh, 1891; personal observation). Sampson et al. (1997) described small cornual sinuses in the centrosaurines Achelousaurus Sampson, 1995, Einiosaurus Sampson, 1995, and Pachyrhinosaurus . Other authors noted similar cornual sinuses in the chasmosaurines Pentaceratops Osborn, 1923, Torosaurus , and Triceratops , but cornual sinus morphology has not been described fully for any chasmosaurine (Hatcher et al., 1907; Forster, 1996; Lehman, 1998). This note describes chasmosaurine cornual sinuses in detail, using undescribed …

The 1937 American Museum of Natural History (AMNH)–Sinclair Oil Company joint expedition to the late Campanian and early Maastrichtian Almond Formation of the Rock Springs Uplift, southern Wyoming, recovered two ceratopsid cranial specimens. AMNH 3652, a partial skull lacking the frill, is characterized by elongate, procurving postorbital horns and a deep rostrum. Although the specimen cannot be identified to the generic or specific level, it appears to be closely related to the clade of chasmosaurine ceratopsids including Anchiceratops, Arrhinoceratops, Diceratops, Torosaurus , and Triceratops , exclusive of Pentaceratops and Chasmosaurus . AMNH 3656, a frill fragment, is characterized by large, triangular marginal processes and an average thickness in excess of 40 mm. This specimen is similar to previously reported frills from Anchiceratops . The ceratopsid specimens from the Almond Formation are significant because they represent two early occurrences of chasmosaurine ceratopsids as well as a unique occurrence in southern Wyoming. Present address: Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794, U.S.A. email: afarke{at}ic.sunysb.edu

The proximal end of a bird humerus recovered from the Paleocene Goler Formation of southern California is the oldest Cenozoic record of this clade from the west coast of North America. The fossil is characterized by a relatively large, dorsally-positioned head of the humerus and a subcircular opening to the pneumotricipital fossa, consistent with the Lithornithidae among known North American Paleocene birds, and is similar in size to Lithornis celetius. This specimen from the Tiffanian NALMA extends the known geographic range of lithornithids outside of the Rocky Mountains region in the United States. The inferred coastal depositional environment of the Goler Formation is consistent with a broad ecological niche of lithornithids. The age and geographic distribution of lithornithids in North America and Europe suggests these birds dispersed from North America to Europe in the Paleocene or by the early Eocene. During the Paleogene the intercontinental dispersal of lithornithids likely occurred alongside other known bird and mammalian movements that were facilitated by climatic and sea level changes.

Author(s): Farke, Andrew A.; Henn, Madison M.; Woodward, Samuel J.; Xu, Heendong A. | Abstract: Several crocodyliform lineages inhabited the Western Interior Basin of North America during the late Campanian (Late Cretaceous), with alligatoroids in the Kaiparowits Formation of southern Utah exhibiting exceptional diversity within this setting. A partial skeleton of a previously unknown alligatoroid taxon from the Kaiparowits Formation may represent the fifth alligatoroid and sixth crocodyliform lineage from this unit. The fossil includes the lower jaw, numerous osteoderms, vertebrae, ribs, and a humerus. The lower jaw is generally long and slender, and the dentary features 22 alveoli with conical, non-globidont teeth. The splenial contributes to the posterior quarter of the mandibular symphysis, which extends posteriorly to the level of alveolus 8, and the dorsal process of the surangular is forked around the terminal alveolus. Dorsal midline osteoderms are square. This combination of character states identifies the Kaiparowits taxon as the sister taxon of the early alligatoroid Leidyosuchus canadensis from the Late Cretaceous of Alberta, the first verified report of the Leidyosuchus (sensu stricto) lineage from the southern Western Interior Basin. This phylogenetic placement is consistent with at least occasional faunal exchanges between northern and southern parts of the Western Interior Basin during the late Campanian, as noted for other reptile clades.

BackgroundMonodominant bonebeds are a relatively common occurrence for non-avian dinosaurs, and have been used to infer associative, and potentially genuinely social, behavior. Previously known assemblages are characterized as either mixed size-classes (juvenile and adult-sized specimens together) or single size-classes of individuals (only juveniles or only adult-sized individuals within the assemblage). In the latter case, it is generally unknown if these kinds of size-segregated aggregations characterize only a particular size stage or represent aggregations that happened at all size stages. Ceratopsians ("horned dinosaurs") are known from both types of assemblages.Methods/principal findingsHere we describe a new specimen of the ceratopsian dinosaur Protoceratops andrewsi, Granger and Gregory 1923 from Mongolia representing an aggregation of four mid-sized juvenile animals. In conjunction with existing specimens of groups of P. andrewsi that includes size-clustered aggregations of young juveniles and adult-sized specimens, this new material provides evidence for some degree of size-clustered aggregation behaviour in Protoceratops throughout ontogeny. This continuity of size-segregated (and presumably age-clustered) aggregation is previously undocumented in non-avian dinosaurs.ConclusionsThe juvenile group fills a key gap in the available information on aggregations in younger ceratopsians. Although we support the general hypothesis that many non-avian dinosaurs were gregarious and even social animals, we caution that evidence for sociality has been overstated and advocate a more conservative interpretation of some data of 'sociality' in dinosaurs.

The Kirkwood Formation is the middle unit of the Uitenhage Group, a sequence of terrestrial and marine rocks that crops out in the Algoa Basin, Eastern Cape Province, South Africa. The Kirkwood Formation is divided into three members: the Swartkops Member, the Colchester Shale Member, and an unnamed, fossiliferous upper member consisting primarily of fluvial sandstones, red-brown and gray-green mudstones, and paleosols (McLachlan and McMillan, 1976; Shone, 1978). Recent dating of the Kirkwood Formation has placed it in the BerriasianValanginian ages near the onset of the Cretaceous (McMillan, 2003).

Paleopathology, the study of disease and injury in long-dead organisms, adds a unique dimension to paleobiological reconstructions. At the level of a single individual, paleopathology provides a partial life history. At the population level, paleopathology can offer information on environmental stresses and disease transmission. Finally, interspecific comparisons may help identify behavioral or functional differences between taxa. In some fortunate cases, large sample sizes allow the application of statistical methods to paleopathological data. These methods allow recognition of the real differences between populations and species and help to move paleopathology beyond collections of interesting anecdotes. Many diving animals are known to suffer from 'the bends' (also known as decompression syndrome or caisson disease), caused by buildup of nitrogen bubbles in the bloodstream during prolonged or especially deep dives, or sudden decompression. These nitrogen bubbles may lodge in small blood vessels supplying bone tissue, occluding the artery and resulting in tissue death, known as avascular necrosis (Rothschild and Storrs, 2003; Moore and Early, 2004). Among other osteological changes, the articular surfaces of limb bones or vertebrae may collapse (focal subsidence) in response to avascular necrosis. This focal subsidence is readily recognizable in the fossil record, and differences between taxa in the occurrence rates of this condition may be used to infer differences in diving behavior among extinct taxa. Rothschild and Storrs (2003) presented a comprehensive dataset of occurrences of focal subsidence in 576 humeri and 479

Ceratopsid (horned dinosaur) cranial material is relatively common in the Upper Cretaceous Naashoibito Member of the Kirtland Formation, San Juan Basin, New Mexico. However, the specimens are fragmentary, making identification problematic. Previously, it has been suggested that the Naashoibito specimens represent Torosaurus utahensis, a chasmosaurine taxon originally known from the North Horn Formation of Utah. This identification has been used to support a Lancian age for the Naashoibito Member and the Alamo Wash local fauna of the Kirtland Formation (e.g., Lehman, 1981; Lucas et al., 1987). Others (e.g., Lehman, 1990) have synonomized T. utahensis with Torosaurus latus, a taxon otherwise known only from the late Maastrichtian Lance and Hell Creek formations. Recent work has upheld the validity of T. utahensis (Sullivan et al., 2005). However, Sullivan and colleagues (2005) have also argued that no previously described ceratopsid specimens from the Naashoibito Member are identifiable beyond the level of Chasmosaurinae indeterminate and therefore are not useful for assessing biostratigraphic correlations and ceratopsid biogeography. Here we describe a partial chasmosaurine ceratopsid parietal from the Naashoibito Member of the Kirtland Formation. Although other fragmentary parietals have been recovered from this unit (e.g., Lehman, 1981; Lucas et al., 1987), the new specimen exhibits unusual morphology: an epoccipital element positioned along the midline. This feature has previously been reported only in Triceratops, a taxon not known from south of the Denver Basin. The occurrence of such a feature in a cera

Geophysical evidence strongly supports the complete isolation of India and Madagascar (Indo-Madagascar) by ∼100 million years ago, though sparse terrestrial fossil records from these regions prior to ∼70 million years ago have limited insights into their biogeographic history during the Cretaceous. A new theropod dinosaur, Dahalokely tokana, from Turonian-aged (∼90 million years old) strata of northernmost Madagascar is represented by a partial axial column. Autapomorphies include a prominently convex prezygoepipophyseal lamina on cervical vertebrae and a divided infraprezygapophyseal fossa through the mid-dorsal region, among others. Phylogenetic analysis definitively recovers the species as an abelisauroid theropod and weakly as a noasaurid. Dahalokely is the only known dinosaur from the interval during which Indo-Madagascar likely existed as a distinct landmass, but more complete material is needed to evaluate whether or not it is more closely related to later abelisauroids of Indo-Madagascar or those known elsewhere in Gondwana.

Ceratopsidae represents one of the last and best-known radiations of non-avian dinosaurs. Interspecific variation is well documented qualitatively with linear measurements, but little has been done to quantify shape differences in the frill that may indicate functional or evolutionary signals. In order to investigate shape change in the squamosal across Chasmosaurinae and Centrosaurinae, we applied geometric morphometrics to the outline of the squamosal for 155 specimens representing 27 ceratopsid species and Protoceratops spp. A Mantel test suggests that the shape of ceratopsid squamosals is highly constrained by phylogeny. MANOVA, ANOVA, and their phylogenetic versions suggest that an evolutionarily significant allometric signal exists between the two clades, but not within clades. Principal component analysis indicates that centrosaurines have a uniform squamosal shape, with the exceptions of Spinops and Diabloceratops. Even when accounting for phylogeny, the relationship between squamosal sha...

Identification of the ontogenetic status of an extinct organism is complex, and yet this underpins major areas of research, from taxonomy and systematics to ecology and evolution. In the case of the non-avialan dinosaurs, at least some were reproductively mature before they were skeletally mature, and a lack of consensus on how to define an ‘adult’ animal causes problems for even basic scientific investigations. Here we review the current methods available to determine the age of non-avialan dinosaurs, discuss the definitions of different ontogenetic stages, and summarize the implications of these disparate definitions for dinosaur palaeontology. Most critically, a growing body of evidence suggests that many dinosaurs that would be considered ‘adults’ in a modern-day field study are considered ‘juveniles’ or ‘subadults’ in palaeontological contexts.

BackgroundThe validity of Nedoceratops hatcheri, a chasmosaurine ceratopsid dinosaur known from a single skull recovered in the Lance Formation of eastern Wyoming, U.S.A., has been debated for over a century. Some have argued that the taxon is an aberrant Triceratops, and most recently it was proposed that N. hatcheri represents an intermediate ontogenetic stage between "young adult" and "old adult" forms of a single taxon previously split into Triceratops and Torosaurus.Methodology/principal findingsThe holotype skull of Nedoceratops hatcheri was reexamined in order to map reconstructed areas and compare the specimen with other ceratopsids. Although squamosal fenestrae are almost certainly not of taxonomic significance, some other features are unique to N. hatcheri. These include a nasal lacking a recognizable horn, nearly vertical postorbital horncores, and relatively small parietal fenestrae. Thus, N. hatcheri is tentatively considered valid, and closely related to Triceratops spp. The holotype of N. hatcheri probably represents an "old adult," based upon bone surface texture and the shape of the horns and epiossifications on the frill. In this study, Torosaurus is maintained as a genus distinct from Triceratops and Nedoceratops. Synonymy of the three genera as ontogenetic stages of a single taxon would require cranial changes otherwise unknown in ceratopsids, including additions of ossifications to the frill and repeated alternation of bone surface texture between juvenile and adult morphotypes.Conclusions/significanceTriceratops, Torosaurus, and likely Nedoceratops, are all distinct taxa, indicating that species richness for chasmosaurine ceratopsids in the Lance Formation just prior to the Cretaceous-Paleocene extinction was roughly equivalent to that earlier in the Cretaceous.

BackgroundDuring much of the Late Cretaceous, a shallow, epeiric sea divided North America into eastern and western landmasses. The western landmass, known as Laramidia, although diminutive in size, witnessed a major evolutionary radiation of dinosaurs. Other than hadrosaurs (duck-billed dinosaurs), the most common dinosaurs were ceratopsids (large-bodied horned dinosaurs), currently known only from Laramidia and Asia. Remarkably, previous studies have postulated the occurrence of latitudinally arrayed dinosaur "provinces," or "biomes," on Laramidia. Yet this hypothesis has been challenged on multiple fronts and has remained poorly tested.Methodology/principal findingsHere we describe two new, co-occurring ceratopsids from the Upper Cretaceous Kaiparowits Formation of Utah that provide the strongest support to date for the dinosaur provincialism hypothesis. Both pertain to the clade of ceratopsids known as Chasmosaurinae, dramatically increasing representation of this group from the southern portion of the Western Interior Basin of North America. Utahceratops gettyi gen. et sp. nov.-characterized by short, rounded, laterally projecting supraorbital horncores and an elongate frill with a deep median embayment-is recovered as the sister taxon to Pentaceratops sternbergii from the late Campanian of New Mexico. Kosmoceratops richardsoni gen. et sp. nov.-characterized by elongate, laterally projecting supraorbital horncores and a short, broad frill adorned with ten well developed hooks-has the most ornate skull of any known dinosaur and is closely allied to Chasmosaurus irvinensis from the late Campanian of Alberta.Conclusions/significanceConsidered in unison, the phylogenetic, stratigraphic, and biogeographic evidence documents distinct, co-occurring chasmosaurine taxa north and south on the diminutive landmass of Laramidia. The famous Triceratops and all other, more nested chasmosaurines are postulated as descendants of forms previously restricted to the southern portion of Laramidia. Results further suggest the presence of latitudinally arrayed evolutionary centers of endemism within chasmosaurine ceratopsids during the late Campanian, the first documented occurrence of intracontinental endemism within dinosaurs.