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Hadrosauriformes is a group of ornithopod dinosaurs with a rich and extensive Cretaceous track record. However, their rear foot (pes) anatomy is rather conservative. Thus, distinguishing different putative track producers from morphological differences is often impeded unless their identification is corroborated by stratigraphic and geographic distribution. On the contrary, the forefoot (manus) anatomy of hadrosauriform taxa reflects distinctive characters that, when preserved in tracks, may be critical for identifying their trackmakers. In this study, we examined three manus tracks preserved as sandstone casts, collected from Coniacian deposits of the Frontier Formation, southwestern Montana, USA. Tracks are assigned to Hadrosauriformes according to their steeply inclined morphology, functionally tridactyl condition, presence of hoof-like impressions and crescentic cross-sectional shape. Track preservation suggests that digit II could be extended medially, whereas movements for digits III and IV were limited. The dorsally curved digit II and III impressions indicate that these digits could be hyperextended. One track shows a short, spade-like ungual II impression, suggesting a closer affinity of its producer to hadrosauroid or hadrosaurid ornithopods. Osteological characters of the manus combined with track morphology can help with discerning different hadrosauriform producers, providing important implication for palaeoecological and palaeogeographical reconstructions. [ABSTRACT FROM AUTHOR]

The Coniacian-Santonian stages in western North America are characterized by a sparse fossil record. We present here the first account of dinosaur tracks from nine sites in the Frontier Formation (Coniacian-Santonian) of southwestern Montana. Tracks are largely preserved in distal alluvial facies as sandstone casts, with a single example of shallow epirelief impression interpreted as undertrack. Sandstone casts show significant relief, kinematic features (i.e., scale marks), and variable morphologies, arguing for a strong substrate control on their preservation. Putative producers are assigned to ornithopod, ankylosaurian, and theropod dinosaurs in decreasing order of abundance. This record reflects a composition similar to those of other middle Cretaceous formations in North America. Moreover, ankylosaurian tracks of the Frontier Formation represent the first known from Coniacian strata in North America. The incorporation of body and trace fossils yielded by the Frontier Formation indicates the presence of a fauna with North American endemic elements. The establishment of Coniacian-Santonian dinosaurian palaeocommunities akin to those observed in Campanian and Maastrichtian formations may reflect the trend towards provincialism attested for the end of the Mesozoic in North America. [ABSTRACT FROM AUTHOR]

The vertebrate assemblages of the Albian to Cenomanian Wayan Formation of southeastern Idaho and southwestern Montana's coeval Vaughn Member of the Blackleaf Formation are dominated by the small, burrowing orodromine dinosaur Oryctodromeus cubicularis. Here, we describe in detail the osteology of Oryctodromeus based on new specimens from Idaho and Montana that add substantially to the preliminary description of the types from Montana, and provide a suite of additional diagnostic characters for the taxon: ilium with elongate preacetabular process; elongate cervical vertebra centra with an anteroposterior length 1.6 times the dorsoventral height; elongate dorsal vertebra centra with an anteroposterior length 1.4 times the dorsoventral height; more than 55 elongate caudal vertebrae enveloped in hypaxial and epaxial ossified tendons; and a femoral head on an elongate neck—similar to that of Koreanosaurus—projecting from the greater trochanter at about 35°. The tail, comprising two-thirds of the animal's roughly 3 meters length, and associated tendon sheaths in the axial column indicate greater flexibility than previously supposed for ossified tendons or, alternatively, suggest that the Oryctodromeus burrows had separate, or multiple entrances and exits. The elongated and angled femoral head likely facilitated digging via a braced splayed-leg posture. Our phylogenetic analysis incorporates new characteristics and supports the monophyly of Orodrominae, a clade of neornithischian dinosaurs from the middle to Late Cretaceous of Asia and western North America that utilized burrowing. [ABSTRACT FROM AUTHOR]

For most dinosaurs, clutches consisted of a single layer of spherical to sub-spherical, highly porous eggs that were probably fully buried. Both eggs and clutch form change drastically with pennaraptoran theropods, the clade that includes birds. Here, far less porous, more elongate eggs are arranged with additional complexity, and only partially buried. While partial egg burial seems to be effective for an extremely small group of modern birds, the behaviour's overall rarity complicates our understanding of Mesozoic analogies. Recent experimental examination of pennaraptoran nesting thermodynamics suggests that partial egg burial, combined with contact incubation, may be more efficacious than has been presumed. We propose that nest guarding behaviour by endothermic archosaurs may have led to an indirect form of contact incubation using metabolic energy to affect temperature change in a buried clutch through a barrier of sediment, which in turn may have selected for shallower clutch burial to increasingly benefit from adult-generated energy until partial egg exposure. Once partially exposed, continued selection pressure may have aided a transition to fully subaerial eggs. This hypothesis connects the presence of partially buried dinosaurian clutches with the transition from basal, crocodile-like nesting (buried clutches guarded by adults) to the dominant avian habit of contact incubating fully exposed eggs. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'. [ABSTRACT FROM AUTHOR]

The evolution of nest site use and nest architecture in the non-avian ancestors of birds remains poorly understood because nest structures do not preserve well as fossils. Nevertheless, the evidence suggests that the earliest dinosaurs probably buried eggs below ground and covered them with soil so that heat from the substrate fuelled embryo development, while some later dinosaurs laid partially exposed clutches where adults incubated them and protected them from predators and parasites. The nests of euornithine birds—the precursors to modern birds—were probably partially open and the neornithine birds—or modern birds—were probably the first to build fully exposed nests. The shift towards smaller, open cup nests has been accompanied by shifts in reproductive traits, with female birds having one functioning ovary in contrast to the two ovaries of crocodilians and many non-avian dinosaurs. The evolutionary trend among extant birds and their ancestors has been toward the evolution of greater cognitive abilities to construct in a wider diversity of sites and providing more care for significantly fewer, increasingly altricial, offspring. The highly derived passerines reflect this pattern with many species building small, architecturally complex nests in open sites and investing significant care into altricial young. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'. [ABSTRACT FROM AUTHOR]

Since their discovery in the 1920s, some asymmetric, elongated dinosaur eggs from the Upper Cretaceous of Mongolia have been interpreted as ceratopsian eggs. However, recent views support a maniraptoran affinity mainly based on macroscopic features. Technical advancements in palaeontology provide a novel approach to diagnose maniraptoran eggs, and the discovery of soft ceratopsian eggs makes the debate a timely issue worth revisiting. Here, we analysed Protoceratopsidovum eggshell from southern Mongolia with electron backscatter diffraction and the results were compared with East Asian and North American maniraptoran and ornithischian eggs. The microstructure and crystallography of Protoceratopsidovum confirms the maniraptoran hypothesis, given that it shows diagnostic features of the clade absent from ornithischian (e.g. hadrosaur) eggs. Additional characters, such as egg shape, ornamentation, egg pairing and clutch structure also support a maniraptoran affinity. Protoceratopsidovum has both elongatoolithid (oviraptorosaur egg) and prismatoolithid (troodontid egg) features, and it may bridge the morphological gap between the two established oofamilies. Considering the similarity between Protoceratopsidovum and potential dromaeosaur eggs, at least some Protoceratopsidovum may be deinonychosaur eggs. Fossil localities that yield both deinonychosaurs and Protoceratopsidovum may yield conclusive evidence for the true affinity of this ootaxon. Future discovery of the egg‐laying taxon of Protoceratopsidovum will not only improve our understanding of maniraptoran reproductive biology but also make Protoceratopsidovum a reliable indicator of the palaeobiogeography of that maniraptoran clade. [ABSTRACT FROM AUTHOR]

The Coniacian non-marine portion of the Frontier Formation in southwestern Montana has been primarily studied stratigraphically, whereas its trace fossil record and relative sedimentological significance have remained overlooked so far. We present the first description of a trace fossil assemblage reported from Frontier Formation deposits exposed in the western Centennial Mountains, Beaverhead County, Montana. Three main lithofacies groups with distinctive trace fossil assemblages have been recognised at the locality of Price Creek: (1) coarse-grained, thin and laterally extensive cross-bedded sandstone channel bodies characterised by rare vertical, passively filled burrows; (2) fine-grained overbank sandstones and siltstones, with abundant horizontal, meniscated, and unwalled burrows, sinusoidal trails, vertical burrows, and dinosaur tracks, and (3) fining-upward, planar cross-bedded silty sandstones, associated with carbonaceous plant material and bone fragments. The trace fossil assemblage is ascribed to the pre-desiccation suit of the Scoyenia ichnofacies. The occurrence of theropod, ornithopod, and thyreophoran dinosaur tracks, and invertebrate trace fossils suggests considerable diversity of terrestrial and aquatic fauna. Tracks described here represent the first dinosaurian record reported from Coniacian deposits in Montana and one of the few fossil records reported from non-marine Coniacian deposits in North America. [ABSTRACT FROM AUTHOR]

Reports on nesting debris generated by great blue heron (Ardea herodias), arboreal nesting birds with 'semi-altricial' young, are limited. In this study, surface and subsurface sampling were conducted in 2012 and 2013 in a heronry near the Missouri River in Montana, including bi-weekly collections in 2013 documenting accumulations over the breeding season. Disarticulated juvenile heron bones with lesser numbers of microvertebrates (fish and small mammals) and invertebrates (crayfish and snails) dominated the assemblage beneath the nests. Eggshell on the surface was present but uncommon (0.85 eggshells/m2) with eggshell orientation varying both by location and fragment size. Eggshell surveys differed with respect to sampled trees and sampling time, but generally favoured concave-up orientation whereas the early season small eggshell survey further from sampled trees favoured concave down. Shallow (10 cm deep) excavation revealed a subsurface assemblage very similar to that on the surface but favouring more resistant elements. Hence, the subsurface assemblage was nearly devoid of eggshell, with a lower representation of invertebrates and fragile bone, but an excess of heron hindlimbs. Our study demonstrates that arboreal nesting sites have the potential for long-term preservation and provides information useful for recognition and reconstruction of arboreal nesting sites from the fossil record. [ABSTRACT FROM AUTHOR]

Fossil gastric pellets (regurgitalites) have distinct taphonomic characteristics that facilitate inferences of behavioural ecology in deep time, despite their rarity in the fossil record. Using the taphonomic patterns of both extant and fossil small mammals from more recent geologic deposits as a guide, we assess the taphonomy of three unusual multi‐individual aggregates of mammal skeletons from palaeosols at Egg Mountain, a dinosaur nesting locality from the Upper Cretaceous Two Medicine Formation, Montana, USA. One aggregate consists of two individuals of the multituberculate Filikomysprimaevus. This specimen is characterized by brecciated crania, articulated postcrania, and an absence of digestive markings, all suggestive of a non‐predatory origin. Two additional aggregates consist of 3 and 11 individuals, respectively, primarily of the marsupialiform Alphadonhalleyi. High proportions of crania and indigestible elements (e.g. teeth), extensive disarticulation and breakage, digestive corrosion patterns, and the absence of a phosphatic ground mass are indicative of regurgitalites and align with features of extant prey in diurnal raptor gastric pellets. We interpret these specimens as the oldest known mammal‐bearing regurgitalites. The discrepancy in taphonomic features implies behavioural separation between the two mammalian taxa at the locality. Abundant shed teeth and nesting evidence at the locality favours the non‐avian theropod Troodonformosus as the predator responsible for the regurgitalites, congruent with previous inferences of a small‐bodied prey diet, manipulation of prey during feeding, heightened metabolic processes, and potential nocturnality for this taxon. [ABSTRACT FROM AUTHOR]

A new Cretaceous ootaxon (eggshell type) from the Kaiparowits Formation of Grand Staircase-Escalante National Monument is among a growing number of very small eggs described from the Mesozoic. Analyses of two partial eggs (~ 17.7 mm in diameter) and 29 eggshell fragments reveal that this new ootaxon exhibits nodose ornamentation with distinctive branching pore canals that open atop the nodes. Its two-layered microstructure consists of a mammillary layer and a continuous layer with rugged grain boundaries between calcite grains. Although the exact identity of the egg producer is unknown, the eggshell microstructure and small size is consistent with a small-bodied avian or non-avian theropod. The specific combination of small egg size, branching pores, two-layered microstructure, and dispersituberculate ornamentation preserved in this new ootaxon is unique among theropod eggs. This underscores that both eggshell and skeletal fossils of Cretaceous theropods can display a mosaic of transitional morphological and behavioural features characteristic of both avian and non-avian taxa. As such, this new ootaxon increases the diversity of Cretaceous eggs and informs our understanding of the evolution of theropod eggshell microstructure and morphology. [ABSTRACT FROM AUTHOR]

is a small-bodied ornithischian dinosaur from the mid-Cretaceous Blackleaf and Wayan Formations of Montana and Idaho, respectively, and is the only documented dinosaur with evidence of a burrowing ecology. The type locality, from the Blackleaf Formation of southwestern Montana, consisted of an infilled burrow structure containing the disarticulated skeletons of one adult and two juveniles and represents a rare association of body fossils and trace fossils of a single dinosaur taxon. While these fossils and their paleobiological implications were unprecedented, collection nevertheless necessitated removal of the burrow structure from its geological context and its destruction during body fossil preparation. Here we present the first photogrammetric models of the type locality burrow in its original geological context and three dimensional morphology, constructed from photos taken at three stages in excavation. Because the terminal extent of the burrow was collected prior to the burrow's complete exposure, the structure was never documented in its entirety. A composite model provides the only holistic documentation of the entire burrow morphology as originally preserved. These models supplement the original burrow description, serve as comparative tools for identifying and diagnosing future discoveries, and demonstrate the utility of pre-existing photographs for later photogrammetric reconstruction. [ABSTRACT FROM AUTHOR]

Nesting localities of extant birds and reptiles may provide taphonomic models for interpreting nesting sites of ancient archosaurs. Here we describe assemblages of nesting gulls (Larus delawarensis and L. californicus), American white pelicans (Pelecanus erythrorhynchos), and double-crested cormorants (Phalacrocorax auritus). Seventy nests yielded 2752 skeletal elements and 2308 eggshells. Most material was located inside the nest for gulls and consisted of osteologically mature gull bones and pelican eggshell. Pelican and cormorant nesting material were located outside the nest, with higher percentages of juvenile avian bone. Eggshell concave up and down ratios on the surface of gull nests compared closely to predated assemblages. Pelican and cormorant surface ratios were approximately 50:50, suggesting trampling by altricial young. Weathered bones in the subsurface of cormorant and pelican nests and layers of predated eggshell in gull nests suggest multi-year accumulations. The amount of material associated with the nests and the age of the nester's bones provides a means of distinguishing altricial and semi-precocial nesting sites. Nesting grounds for gulls with semi-precocial young yielded less skeletal material but a higher proportion of mature gull bones, whereas the large assemblages with altricial pelican and cormorant nests were dominated by prey items and their own young. [ABSTRACT FROM AUTHOR]

Calcified eggshells protect developing embryos against environmental stress and contribute to reproductive success1. As modern crocodilians and birds lay hard-shelled eggs, this eggshell type has been inferred for non-avian dinosaurs. Known dinosaur eggshells are characterized by an innermost membrane, an overlying protein matrix containing calcite, and an outermost waxy cuticle2–7. The calcitic eggshell consists of one or more ultrastructural layers that differ markedly among the three major dinosaur clades, as do the configurations of respiratory pores. So far, only hadrosaurid, a few sauropodomorph and tetanuran eggshells have been discovered; the paucity of the fossil record and the lack of intermediate eggshell types challenge efforts to homologize eggshell structures across all dinosaurs8–18. Here we present mineralogical, organochemical and ultrastructural evidence for an originally non-biomineralized, soft-shelled nature of exceptionally preserved ornithischian Protoceratops and basal sauropodomorph Mussaurus eggs. Statistical evaluation of in situ Raman spectra obtained for a representative set of hard- and soft-shelled, fossil and extant diapsid eggshells clusters the originally organic but secondarily phosphatized Protoceratops and the organic Mussaurus eggshells with soft, non-biomineralized eggshells. Histology corroborates the organic composition of these soft-shelled dinosaur eggs, revealing a stratified arrangement resembling turtle soft eggshell. Through an ancestral-state reconstruction of composition and ultrastructure, we compare eggshells from Protoceratops and Mussaurus with those from other diapsids, revealing that the first dinosaur egg was soft-shelled. The calcified, hard-shelled dinosaur egg evolved independently at least three times throughout the Mesozoic era, explaining the bias towards eggshells of derived dinosaurs in the fossil record. Molecular analyses of newly discovered, embryo-bearing ornithischian and sauropod dinosaur eggs suggest that the ancestral dinosaur egg was soft-shelled, and that hard-shelled eggs evolved independently at least three times in the major dinosaur lineages. [ABSTRACT FROM AUTHOR]

The geological and paleoenvironmental setting and the vertebrate taxonomy of the fossiliferous, Cenomanian- age deltaic sediments in eastern Morocco, generally referred to as the "Kem Kem beds", are reviewed. These strata are recognized here as the Kem Kem Group, which is composed of the lower Gara Sbaa and upper Douira formations. Both formations have yielded a similar fossil vertebrate assemblage of predominantly isolated elements pertaining to cartilaginous and bony fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, as well as invertebrate, plant, and trace fossils. These fossils, now in collections around the world, are reviewed and tabulated. The Kem Kem vertebrate fauna is biased toward largebodied carnivores including at least four large-bodied non-avian theropods (an abelisaurid, Spinosaurus, Carcharodontosaurus, and Deltadromeus), several large-bodied pterosaurs, and several large crocodyliforms. No comparable modern terrestrial ecosystem exists with similar bias toward large-bodied carnivores. The Kem Kem vertebrate assemblage, currently the best documented association just prior to the onset of the Cenomanian-Turonian marine transgression, captures the taxonomic diversity of a widespread northern African fauna better than any other contemporary assemblage from elsewhere in Africa. [ABSTRACT FROM AUTHOR]

With abundant well-preserved clutches and several adult-clutch associations, oviraptorids provide some of the most detailed information on reproduction for dinosaurs. Here, we describe an oviraptorosaur closely associated with two eggs from the Upper Cretaceous Nanxiong Formation of Jiangxi Province, China, and discuss its implications for various reproductive hypotheses. The specimen consists of a partial skeleton (gastralia, pelvis, portions of both hind limbs, and tail), with one egg within the pelvic canal and the other just posterior to it, ventral to the anterior caudal vertebrae. Several geopetal features indicate that the individual came to rest on its left side, with the eggs likely extruded during buildup of abdominal gases during decomposition. Similarity of pubis, caudal vertebrae, and pes dimensions to recently described material from the formation, e.g., Tongtianlong and Jiangxisaurus, suggests oviraptorid affinities. The specimen provides additional association of elongatoolithid eggs and the oogenus Macroolithus with oviraptorosaurs and further evidence for monoautochronic ovulation, i.e., iterative laying of two eggs at daily or greater intervals. With each egg 36–48% the size predicted for a modern bird of the same adult mass, total egg production would be slightly lower to similar between this non-avian maniraptoran and Neornithes. Histological tissues and open neurocentral sutures indicate that this reproductively active individual was several years old but still growing at the time of death, a pattern observed in other non-avian maniraptorans. The complete absence of medullary bone in this egg-bearing individual may challenge the identification of this tissue in other dinosaurs more distantly related to birds. [ABSTRACT FROM AUTHOR]

Analysis of ontogenetic changes in long bone microstructure aid in vertebrate life history reconstructions. Specifically, osteohistological examination of common fauna can be used to infer growth strategies of biologically uncommon, threatened, or extinct vertebrates. Although nine-banded armadillo biology has been studied extensively, work on growth history is limited. Here we describe long bone microstructure in tibiae and femora of a limited ontogenetic series of nine- banded armadillos (Dasypus novemcinctus) to elucidate patterns of bone growth. The cortex of the smallest individual is composed of compacted coarse cancellous bone (CCCB) and woven tissue. Extensive cortical drift is driven by periosteal erosion and further compaction of trabeculae resulting in an increase in the amount of CCCB. The cortex of the largest specimens is primarily CCCB with thickened endosteal bone and thin outer cortices of lamellar and parallel-fibered tissue. The outer cortices of the largest individuals are interpreted as an external fundamental system (EFS) indicating a cessation of appositional bone growth corresponding to skeletal maturity (i.e. asymptotic or adult size). The EFS forms in femora prior to tibiae, indicating femoral growth rates begin decreasing earlier than tibial in D. novemcinctus. Growth trends in common fauna like the nine-banded armadillo can be used as a foundation for understanding life histories of related, but uncommon or extinct, species of cingulates. [ABSTRACT FROM AUTHOR]

During the mid-Cretaceous, multituberculate mammal communities were restructured, as 'plagiaulacidan' multituberculates, common from the Middle Jurassic through Early Cretaceous, began to be replaced by the Cimolodonta, a clade that would come to be the most abundant and diverse group of mammals during the Late Cretaceous and early Paleocene. Although these broad strokes of multituberculate evolutionary history are well documented, the only fossil assemblage detailing this rise of the Cimolodonta during the Early–Late Cretaceous transition comes from the Mussentuchit Member of the Cedar Mountain Formation in central Utah. Here, we report on nine new multituberculate specimens from the Wayan Formation of southeastern Idaho, representing the second and northernmost record of multituberculate mammals from near the Early–Late Cretaceous boundary of North America. The Wayan assemblage consists of isolated cimolodontan premolars and molars representing at least four taxa, including one new species, Cimolodon akersteni. The presence of Cimolodon in the Wayan assemblage represents the earliest occurrence of this genus and the first appearance of a clade nested within Cimolodonta (the Cimolodontidae). Only two species are shared between the Wayan Formation and the Mussentuchit Member, cf. Paracimexomys perplexus and Bryceomys intermedius. All other specimens differ morphologically from any known mid-Cretaceous multituberculate species. The differences in the Wayan and Mussentuchit multituberculate local faunas could be due to differences in age, biogeography, paleoenvironment, sampling bias, or some combination of these factors. These new specimens reveal a greater diversity of mid-Cretaceous multituberculates than was previously recognized and provide new insights into the early evolution of Cimolodonta. [ABSTRACT FROM AUTHOR]

The first intact North American Macroelongatoolithus specimen was excavated from sediments in the Wayan Formation of southeastern Idaho and initially reported by Krumenacker et al. (2017, Historical Biology 29:170–186). Here, we present a description of the specimen, including a zonal analysis of microstructural variation and comparison with an egg pair from the Liangtoutang Formation of Zhejiang, China. We assign egg pair IMNH 2428\49608 from the Albian–Cenomanian Wayan Formation of Idaho and egg pair ZMNH M8705 from the Liangtoutang Formation of China to the oospecies Macroelongatoolithus carlylei. The eggs are 39.8–41.7 cm long and 10.8–14.3 cm wide, and the eggshell consists of two structural layers of calcite demarcated by a distinct, undulating boundary. Eggshell thickness is 1.01–2.17 mm, and the continuous layer to mammillary layer ratio (CL:ML) ranges from 2.05:1 to 7.68:1. Identification of intact Macroelongatoolithus specimens from North America supports synonymy of M. xixiaensis with M. carlylei, as proposed by Zelenitsky et al. (2002) on the basis of eggshell fragments. Due to the substantial microstructural variation of the specimens reported here, we also regard M. goseongensis and M. qiongensis as junior synonyms of M. carlylei. The degree of microstructural variation within the new specimens expands the expected range of variation typically used in diagnosing oospecies and has implications for the naming of new oospecies on the basis of fragments or egg portions alone. The discovery of Macroelongatoolithus eggs from the latest Early Cretaceous of Idaho confirms the presence of this extraordinary oogenus outside of Asia and provides nonskeletal evidence of a Gigantoraptor-sized oviraptorosaur in western North America. [ABSTRACT FROM AUTHOR]

The record of terrestrial vertebrates in the upper Albian to Cenomanian Wayan Formation of Idaho is sparse, with most fossils recovered belonging to the small orodromine neornithischian Oryctodromeus cubicularis and the maniraptoran ootaxon Macroelongatoolithus carlylei. Here we report on a diversity of theropod forms now recognised from various isolated teeth, vertebrae, eggs and eggshell. Theropods recognised from isolated teeth include a large possible tyrannosauroid, a small tyrannosauroid, dromaeosaurids, and indeterminate theropods. A possible neovenatorid and indeterminate theropods are recognised from isolated vertebrae. A giant oviraptorosaur is indicated by the presence of rare eggs and common eggshell accumulations referred to Macroelongatoolithus. While these remains are admittedly meager, their presence indicates that a substantial diversity of theropods existed in the Albian to Cenomanian environments of southeastern Idaho. The Wayan theropod assemblage is among the most diverse reported for this time period in North America, and represents a transitional assemblage resembling that of the later Late Cretaceous. [ABSTRACT FROM AUTHOR]

Iguanomorpha (stem + crown Iguania) is a diverse squamate clade with members that predominate many modern American lizard ecosystems. However, the temporal and palaeobiogeographic origins of its constituent crown clades (e.g. Pleurodonta (basilisks, iguanas, and their relatives)) are poorly constrained, mainly due to a meagre Mesozoic-age fossil record. Here, we report on two nearly complete skeletons from the Late Cretaceous (Campanian) of North America that represent a new and relatively large-bodied and possibly herbivorous iguanomorph that inhabited a semi-arid environment. The new taxon exhibits a mosaic of anatomical features traditionally used in diagnosing Iguania and non-iguanian squamates (i.e. Scleroglossa; e.g. parietal foramen at the frontoparietal suture, astragalocalcaneal notch in the tibia, respectively). Our cladistic analysis of Squamata revealed a phylogenetic link between Campanian-age North American and East Asian stem iguanomorphs (i.e. the new taxon + Temujiniidae). These results and our evaluation of the squamate fossil record suggest that crown pleurodontans were restricted to the low-latitude Neotropics prior to their early Palaeogene first appearances in the mid-latitudes of North America. [ABSTRACT FROM AUTHOR]

Diapsids show an extremely wide range of reproductive strategies. Offspring may receive no parental care, care from only one sex, care from both parents, or care under more complex regimes. Young may vary from independent, super-precocial hatchlings to altricial neonates needing much care before leaving the nest. Parents can invest heavily in a few young, or less so in a larger number. Here we examine the evolution of these traits across a composite phylogeny spanning the extant diapsids and including the limited number of extinct taxa for which reproductive strategies can be well constrained. Generalized estimating equation(GEE)-based phylogenetic comparative methods demonstrate the influences of body mass, parental care strategy and hatchling maturity on clutch volume across the diapsids. The influence of polygamous reproduction is not important despite a large sample size. Applying the results of these models to the dinosaurs supports the hypothesis of paternal care (male only) in derived non-avian theropods, previously suggested based on simpler analyses. These data also suggest that sauropodomorphs did not care for their young. The evolution of parental-care occurs in an almost linear series of transitions. Paternal care rarely gives rise to other care strategies. Where hatchling condition changes, diapsids show an almost unidirectional tendency of evolution towards increased altriciality. Transitions to social monogamy from the ancestral state in diapsids, where both sexes are polygamous, are common. In contrast, once evolved, polygyny and polyandry are very evolutionarily stable. Polygyny and maternal care correlate, as do polyandry and paternal care. Ancestral-character estimation (ACE) of these care strategies with the character transition likelihoods estimated from the original data gives good confidence at most important nodes. These analyses suggest that the basalmost diapsids had no parental care. Crocodilians independently evolved maternal care, paternal care evolved in the saurischian line, prior to derived theropod dinosaurs, and the most basal neognaths likely exhibited biparental care. Overall, the evolution of parental care among diapsids shows a persistent trend towards increased care of offspring, and more complex care strategies and behaviors with time. Reversions to reduced care are infrequent. [ABSTRACT FROM AUTHOR]

Embryonic remains within a small (4.75 by 2.23 cm) egg from the Late Cretaceous, Mongolia are here re-described. High-resolution X-ray computed tomography (HRCT) was used to digitally prepare and describe the enclosed embryonic bones. The egg, IGM (Mongolian Institute for Geology, Ulaanbaatar) 100/2010, with a three-part shell microstructure, was originally assigned to Neoceratopsia implying extensive homoplasy among eggshell characters across Dinosauria. Re-examination finds the forelimb significantly longer than the hindlimbs, proportions suggesting an avian identification. Additional, postcranial apomorphies (strut-like coracoid, cranially located humeral condyles, olecranon fossa, slender radius relative to the ulna, trochanteric crest on the femur, and ulna longer than the humerus) identify the embryo as avian. Presence of a dorsal coracoid fossa and a craniocaudally compressed distal humerus with a strongly angled distal margin support a diagnosis of IGM 100/2010 as an enantiornithine. Re-identification eliminates the implied homoplasy of this tri-laminate eggshell structure, and instead associates enantiornithine birds with eggshell microstructure composed of a mammillary, squamatic, and external zones. Posture of the embryo follows that of other theropods with fore- and hindlimbs folded parallel to the vertebral column and the elbow pointing caudally just dorsal to the knees. The size of the egg and embryo of IGM 100/2010 is similar to the two other Mongolian enantiornithine eggs. Well-ossified skeletons, as in this specimen, characterize all known enantiornithine embryos suggesting precocial hatchlings, comparing closely to late stage embryos of modern precocial birds that are both flight- and run-capable upon hatching. Extensive ossification in enantiornithine embryos may contribute to their relatively abundant representation in the fossil record. Neoceratopsian eggs remain unrecognized in the fossil record. [ABSTRACT FROM AUTHOR]

In 1991, Sabath described "larger avian eggs" from the Upper Cretaceous Barun Goyot and Djadokhta Formations of Mongolia. These were later included in the ootaxon Gobioolithus major. Here we recognize the larger avian eggs of Sabath as a distinct ootaxon, Styloolithus sabathi, oogen. et oosp. nov. These eggs differ from those of Gobioolithus in being larger (70 by 32 mm) and more elongate. Microscopically, the shell bears a third layer (possible external zone) thicker than the mammillary layer and nearly as thick as the second layer (possible squamatic zone); the continuous layer (including layers two and three) to mammillary layer thickness ratio is 3.1:1. Within the clutch, the tightly spaced eggs stand with their long axes steeply inclined. Adult remains are associated with two clutches, suggesting an incubation mode similar to that of troodontid maniraptorans, where adults sat atop largely buried eggs. S. sabathi provides evidence that relative egg size in Mesozoic non-ornithuromorph birds had increased markedly from the non-avian theropod condition in oviraptorids and troodontids, but had not yet reached the modern egg-adult proportions of Neornithes. Sediment-bound upright eggs appear common to Enantiornithes and more basal avians, suggesting that like non-avian theropods, these birds lacked chalazae, the chords of albumen allowing egg rotation in modern birds. Absence of this simple structure may have restricted these basal birds to ground nesting in areas with appropriate substrates and not permitted the type of nesting diversity found in Neornithes. Neornithes are the only Mesozoic clade of Dinosauria to nest completely free of sediment; this may have played a crucial role in their surviving the K-Pg mass extinction event. [ABSTRACT FROM AUTHOR]

Lack of stratigraphic context for dinosaur eggs inhibits understanding of dinosaur reproductive biology and the taphonomic processes of egg preservation. Past taphonomic work suggests two features, compression ridges (sharp edge of broken eggshell around egg circumference) and deformation asymmetry (proportion of crushed to rounded sides of the egg), as geopetal structures. We examined these features across a large sample ofSpheroolithuseggs from the Cretaceous of Zhejiang, China, to test their utility. On 103 isolated eggs, we determined asymmetry ratios (crushed side egg height divided by rounded side egg height) and observed an average asymmetry ratio of 0.71. Additional observations ofin situeggs demonstrate the stratigraphic downside as more rounded and less fractured, the stratigraphic upside as flatter with heavier fracturing and compression ridges as parallel to original bedding plane. Burial-caused fractures on the upper side of the egg allowed sediment to partially fill, subsequently supporting the bottom portion. Examining these features within 16 clutches allowed differentiation of biotic versus taphonomically altered arrangements. Three common clutch arrangements include planar (minimal egg overlap), offset (extreme overlap) and agglomerate (randomly arranged, closely packed). Analysis of egg strike and dip across clutches favours planar clutches as the principal configuration forSpheroolithusclutches. [ABSTRACT FROM PUBLISHER]

Mesozoic non-avian theropod dinosaurs displayed a diverse range of egg types and clutch forms, suggesting a variety of nesting behaviours, some of which may be shared with birds. More accurate inferences of these behaviours require taphonomic studies of modern nesting sites. Here, we document common tern (Sterna hirundo) nesting sites on Poplar Island in Chesapeake Bay, Maryland. Nests were surveyed on multiple occasions, documenting nest composition, density and distribution, as well as eggshell concentration and orientation. Three colonies yielded 79 tern nests with 193 eggs. Twelve nests hatched, 7 were predated, 30 failed and the fates of 30 remain unknown. Abundant eggshells occurred at the centre of the nests. Concave-up eggshell in or on the nest surface characterised hatched and predated nests, whereas eggshell forced into the subsurface seemed to favour concave-down orientation and may reflect post-hatching extended use of the nest. Eggs buried deep within the nest materials and/or substrate suggest adult abandonment. Quantitative data on eggshell orientation and observations regarding controls on nest distribution, egg predation and incorporation of intact eggs into the substrate at modern nesting sites provide physical guidelines for the improved interpretation of fossil nesting localities. [ABSTRACT FROM PUBLISHER]

Numerous discoveries in the Tiantai basin of Zhejiang Province, China, enrich our understanding of the parataxonomy, paleobiology and taphonomic histories of fossil eggs from a diverse array of Cretaceous oofamilies. We describe the most abundant of these egg types catalogued in the Zhejiang Museum of Natural History,Spheroolithuscf.zhangtoucaoensis(oofamily Spheroolithidae). Scanning electron microscopy, here utilised for the first time onSpheroolithuseggs from Tiantai, and petrographic microscopy reveal 0.81–1.37-mm thick eggshell composed of a single structural layer of calcite with slightly flaring shell units, irregular pores, horizontal accretion lines and a sweeping extinction pattern under crossed polars. This contradicts previous reports of the presence of two structural layers in TiantaiSpheroolithus. Clutches consist of 2–13 eggs arranged in an irregular, single-layered pattern. As these eggs are among the oldest Asian examples ofSpheroolithuscurrently known, they may shed light on the early evolution of this oogenus. This study establishes the definitive presence of the Spheroolithidae in the Tiantai basin,contrarecent reports, and provides the framework for ongoing examination of egg diversity and taphonomy in the Tiantai basin. [ABSTRACT FROM PUBLISHER]

We describe an extensive ichnofossil assemblage from the likely Cenomanian-age ‘lower’ and ‘upper’ units of the ‘Kem Kem beds’ in southeastern Morocco. In the lower unit, trace fossils include narrow vertical burrows in cross-bedded sandstones and borings in dinosaur bone, with the latter identified as the insect ichnotaxon Cubiculum ornatus. In the upper unit, several horizons preserve abundant footprints from theropod dinosaurs. Sauropod and ornithischian footprints are much rarer, similar to the record for fossil bone and teeth in the Kem Kem assemblage. The upper unit also preserves a variety of invertebrate traces including Conichnus (the resting trace of a sea-anemone), Scolicia (a gastropod trace), Beaconites (a probable annelid burrow), and subvertical burrows likely created by crabs for residence and detrital feeding on a tidal flat. The ichnofossil assemblage from the Upper Cretaceous Kem Kem beds contributes evidence for a transition from predominantly terrestrial to marine deposition. Body fossil and ichnofossil records together provide a detailed view of faunal diversity and local conditions within a fluvial and deltaic depositional setting on the northwestern coast of Africa toward the end of the Cretaceous. [ABSTRACT FROM AUTHOR]

A second nearly complete, articulated specimen of the basal troodontid Mei long (DNHM D2154) is reported from the Early Cretaceous (Hauterivian-Valanginian) lower Yixian Formation, Liaoning Province, China. New diagnostic features of Mei long are identified, including: a uniquely shaped maxilla, low with small, low maxillary fenestra; sacrum with an extremely wide caudal portion and elongate 4th and 5th sacral processes; and a large distal articular surface on the tibiotarsus which continues caudally on the tibia. A phylogenetic analysis including new data from the second specimen recovered Mei as a basal troodontid, in keeping with previous analyses. Although the skeleton exhibits several juvenile-like features including free cervical ribs, unfused frontals and nasals, and a short snouted skull, other attributes, full fusion of all neurocentral synostoses and the sacrum, and dense exteriors to cortical bone, suggest a small, mature individual. Microscopic examination of tibia and fibula histology confirms maturity and suggests an individual greater than two years old with slowed growth. Despite being one of the smallest dinosaurs, Mei long exhibits multi-year growth and cortical bone consisting largely of fibro-lamellar tissue marked by lines of arrested growth as in much larger and more basal theropods. This Mei long specimen lies in a similar but mirrored sleeping position to that of the holotype, strengthening the hypothesis that both specimens were preserved in a stereotypical life position. Like many Liaoning specimens, the new specimen also lacks extensive taphonomic and stratigraphic data, making further behavioral inference problematic. [ABSTRACT FROM AUTHOR]

The vertebrate fauna of the Cretaceous Blackleaf Formation of southwest Montana remains largely undocumented. A microsite (BL1) discovered in the Flood Member in the Lima Peaks area, Montana, consists of a green siltstone and yields taxa previously unreported from the formation, including several dinosaurs: a hypsilophodont, dromaeosaurid, tyrannosauroid, hadrosaurid and an ankylosaurian. Non-dinosaurian taxa include goniopholidid and Bernissartia crocodilians; Glyptops, cf. chelydrid and other turtles and at least two neopterygiian fish. This diversity corresponds well with the fluvial–deltaic–estuarine environment interpreted for the uppermost unit of the Flood Member. Taphonomic data and sedimentologic relationships suggest that this assemblage represents a floodplain depression accumulation. Comparisons with contemporaneous faunas from around the Western Interior of the USA suggest a remarkably consistent faunal makeup, at least at the family level, existed across western North America in the mid-Cretaceous. [ABSTRACT FROM AUTHOR]

Background: Troodontids are a predominantly small-bodied group of feathered theropod dinosaurs notable for their close evolutionary relationship with Avialae. Despite a diverse Asian representation with remarkable growth in recent years, the North American record of the clade remains poor, with only one controversial species--Troodon formosus--presently known from substantial skeletal remains. Methodology/Principal Findings: Here we report a gracile new troodontid theropod--Talos sampsoni gen. et sp. nov.-- from the Upper Cretaceous Kaiparowits Formation, Utah, USA, representing one of the most complete troodontid skeletons described from North America to date. Histological assessment of the holotype specimen indicates that the adult body size of Talos was notably smaller than that of the contemporary genus Troodon. Phylogenetic analysis recovers Talos as a member of a derived, latest Cretaceous subclade, minimally containing Troodon, Saurornithoides, and Zanabazar. MicroCT scans reveal extreme pathological remodeling on pedal phalanx II-1 of the holotype specimen likely resulting from physical trauma and subsequent infectious processes. Conclusion/Significance: Talos sampsoni adds to the singularity of the Kaiparowits Formation dinosaur fauna, which is represented by at least 10 previously unrecognized species including the recently named ceratopsids Utahceratops and Kosmoceratops, the hadrosaurine Gryposaurus monumentensis, the tyrannosaurid Teratophoneus, and the oviraptorosaurian Hagryphus. The presence of a distinct troodontid taxon in the Kaiparowits Formation supports the hypothesis that late Campanian dinosaurs of the Western Interior Basin exhibited restricted geographic ranges and suggests that the taxonomic diversity of Late Cretaceous troodontids from North America is currently underestimated. An apparent traumatic injury to the foot of Talos with evidence of subsequent healing sheds new light on the paleobiology of deinonychosaurians by bolstering functional interpretations of prey grappling and/or intraspecific combat for the second pedal digit, and supporting trackway evidence indicating a minimal role in weight bearing. [ABSTRACT FROM AUTHOR]

Insect trace fossils, such as burrows, pupation chambers and nests, can provide broad paleoecological insights by helping to define paleohydrology, effects of seasonality or conditions of associated paleosols. Insect traces adjacent to nesting sites of the dinosaur Troodon formosus in the Cretaceous (Campanian) Two Medicine Formation near Choteau, Montana, demonstrate such paleoecological utility. One outcrop in particular contains an abundance of insect burrows and pupation chambers in a calcareous paleosol. Most trace fossils are interpreted as apocritan (wasps and bees) burrows, brooding chambers and cocoons. Apocritans prefer to construct burrows and brooding chambers in well-drained soils during relatively dry conditions (avoiding wet seasons). Their trace fossils are consistent with previous inferences of semi-arid conditions and seasonality for the Two Medicine Formation. Moreover, apocritan nesting is likely to have occurred in the same places and conditions as dinosaur nests: well above the local water table and during dry seasons. Such trace fossils hold the potential for more precise definitions of paleoecological factors in dinosaur nest sites. For example, within the Two Medicine Formation, the Celliforma ichnofacies is commonly associated with eggs of T. formosus and Continuoolithus, but not with those of Maiasaura peeblesorum, perhaps indicative of subtle nesting site preferences. [ABSTRACT FROM AUTHOR]

Five factors, mobile terrestrial lifestyle, oviparity, parental care, multi-year maturation and juvenile sociality, contribute to a distinct life history for Mesozoic dinosaurs in comparison to extant archosaurs and mammals. Upright, para-sagittal gait reflects several synapomorphies of Dinosauria, and wide histological sampling suggests that multi-year maturation typified dinosaurs across a range of body sizes. Fossil support for juvenile sociality exceeds that for either oviparity or parental care. Implications of these factors include temporal segregation of adults for an extended, perhaps months-long reproductive cycle; spatial separation of adults and perhaps hatchlings to suitable nesting sites; increased likelihood for territoriality; reduced potential for long migrations; intraspecific niche segregation by age; population and community structure and macroevolutionary patterns. Fossil evidence for oviparity, parental care and juvenile sociality consists of combinations of adults, juveniles, embryos, eggs or traces and emphasises the importance of bonebeds and taphonomy in understanding dinosaur life-history strategies. Oviparity and parental care, predicted for dinosaurs by their extant phylogenetic bracket, have the least fossil support and cautions against overextending parsimonious interpretations to extinct taxa with the risk of obscuring novel or intermediate behaviours. Given the great diversity of Mesozoic dinosaurs, the proposed life history is hypothesised to represent only a general tendency. [ABSTRACT FROM AUTHOR]

Background: Tyrannosaurus rex and other tyrannosaurid fossils often display multiple, smooth-edged full-thickness erosive lesions on the mandible, either unilaterally or bilaterally. The cause of these lesions in the Tyrannosaurus rex specimen FMNH PR2081 (known informally by the name 'Sue') has previously been attributed to actinomycosis, a bacterial bone infection, or bite wounds from other tyrannosaurids. Methodology/Principal Findings: We conducted an extensive survey of tyrannosaurid specimens and identified ten individuals with full-thickness erosive lesions. These lesions were described, measured and photographed for comparison with one another. We also conducted an extensive survey of related archosaurs for similar lesions. We show here that these lesions are consistent with those caused by an avian parasitic infection called trichomonosis, which causes similar abnormalities on the mandible of modern birds, in particular raptors. Conclusions/Significance: This finding represents the first evidence for the ancient evolutionary origin of an avian transmissible disease in non-avian theropod dinosaurs. It also provides a valuable insight into the palaeobiology of these now extinct animals. Based on the frequency with which these lesions occur, we hypothesize that tyrannosaurids were commonly infected by a Trichomonas gallinae-like protozoan. For tyrannosaurid populations, the only non-avian dinosaur group that show trichomonosis-type lesions, it is likely that the disease became endemic and spread as a result of antagonistic intraspecific behavior, consumption of prey infected by a Trichomonas gallinae-like protozoan and possibly even cannibalism. The severity of trichomonosis-related lesions in specimens such as Tyrannosaurus rex FMNH PR2081 and Tyrannosaurus rex MOR 980, strongly suggests that these animals died as a direct result of this disease, mostly likely through starvation. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the anatomy of the early Cretaceous bird Rapaxanis pani originating from Liaoning Province, China. Researchers found six free caudal vertebrae, with the first two exposed in ventral view just down-slab to the left sacral process of S6. They observed that the caudal margin of the sternum features two very wide arcs of the lateral and median notches divided by an intermediate trabecula. They claimed that the elongate rostrum of Rapaxanis pani indicates that it is within Longipterygidae.

Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence. Methodology/Principal Findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia (''stomach ribs''), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax. Conclusions/Significance: We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds: (1) Phase I-Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (2) Phase II-Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation. (3) Phase III-Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic. (4) Phase IV-Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic. In addition, we conclude: (5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation. (6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flowthrough lung ventilation, locomotory balance, and/or thermal regulation. [ABSTRACT FROM AUTHOR]

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A partial humerus, ulna, and radius compose the type specimen of a new bird, Piksibarbarulna, new genus and species, from the Late Cretaceous (Campanian) Two Medicine Formation of western Montana. This ornithothoracine taxon differs from all other birds in having an enlarged dorsal epicondyle and a reduced ventral condyle on the humerus with corresponding modifications on the articular surface of the ulna. Among modern birds, Piksi is most similar to galliforms, but the paucity of unambiguous characters and its unusual morphology defy placement within any extant "order" and strongly questions any neornithine affinities. Instead, Piksi appears to have a fairly basal position within Ornithothoraces. Several morphologic features of Piksi occur in phylogenetically diverse but morphologically similar birds, such as galliforms, tinamous, and some columbiforms. The new bird comes from an inland, relatively dry paleo-environment. Atypical for a Cretaceous avian record dominated by waterfowl, Piksi appears to represents a heavy-bodied ground bird. Searching of inland depositional environments may yield new and ecologically distinct avian varieties.Une partie d'un humérus, d'un cubitus et d'un radius forment le spécimen type d'un nouvel oiseau, Piksi barbarulna, nouveau genre et nouvelle espèce, de la Formation de Two Medicine (Crétacé tardif - Campanien), de l'ouest du Montana. Ce taxon ornithothoracine diffère de tous les autres oiseaux car il a un épicondyle dorsal élargi et un condyle ventral réduit sur l'humérus ainsi que les modifications correspondantes sur la surface articulaire du cubitus. Parmi les oiseaux modernes, Piksi ressemble le plus aux Galliformes, mais la rareté de caractères non ambigus et sa morphologie inhabituelle empêchent de le placer dans un « ordre » existant quelconque et posent de sérieuses questions quant aux affinités néornithines. Au lieu, Piksi semble occuper une position assez à la base des Ornithothoraces. Plusieurs caractéristiques morphologiques de Piksi se retrouvent dans des oiseaux phylogénétiquement différents mais morphologiquement semblables, tels que les galliformes, les tinamous et quelques columbiformes. Le nouvel oiseau provient d'un paléo-environnement intérieur relativement sec. Ce qui est non typique pour les gisements fossilifères aviaires du Crétacé dominés par de la sauvagine, Piksi semble représenter un oiseau terrestre à forte corpulence. La recherche dans les environnements de déposition à l'intérieur des terres pourra donner des variétés aviaires nouvelles et écologiquement distinctes.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]