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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.

In the accompanying Comment, Choi et al. dispute morphological, histological, geochemical and biomechanical evidence for a soft-shelled egg in Mussaurus, an Early Jurassic sauropodomorph, based on three main assertions, namely that: (1) the carbonate signal associated with Mussaurus eggshell could represent original biomineral, despite its chemical and petrographic resemblance to the limy sediment matrix; (2) the endogenous N-, O- and S-heterocyclic polymers, which generate the Mussaurus egg morphology and encode the biomineralization signal, might represent sedimentary kerogen (refuted in figure 2a of ref.) or graphitic carbon, which cannot possibly form under the pressure and temperature conditions in question; (3) birefringence, which would indicate eggshell calcite, may be obscured in the thin section by organic matter (contra the previous claim suggesting only graphite might be preserved). Choi et al. disagree with our analyses of the Mussaurus eggshell while ignoring the biomechanical evidence and compound maps presented in Norell et al. and accepting identical analyses for the Protoceratops eggshell. Choi et al. did not perform new analyses, but scored the Mussaurus eggshell as hard on the basis of comparisons with hard-shelled but unrelated non-dinosaurian eggshell (Aenigmaoolithus) from a dissimilar age, region and volcanic setting. They re-ran our ancestral state reconstruction without time scaling and obtained an ambiguous 52% probability of hard-shelled eggs in the ancestral dinosaur, in contrast to our inference of an ancestrally soft egg.

The terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.

Dale Russell described the osteology, morphology, and ecology of the small theropod “Stenonychosaurus inequalis” in two papers, speculating on its life habits, brain power, vision, movement, feeding, and hand capabilities. Russell even pondered a tool-using dinosauroid, the hypothetical troodontid descendant if the lineage had survived the Cretaceous–Paleogene extinction event. We revisit the life habits of the North American troodontids Troodon formosus and Latenivenatrix mcmasterae in part by reviewing various trace fossils of T. formosus discovered in Montana. These fossils include egg clutches, a nest, and recently discovered regurgitalites. We also contemplate the possibility of dinosaur tool use. Troodon likely constructed earthen nests in the same way that ratites and other birds did to create their nesting scrapes through backward hindlimb kicks. The more complex clutch architecture suggests dexterous movement of the eggs, potentially requiring manual manipulation. Functionally, reproductive traces support elevated body temperatures and a metabolic output that approach but do not equal that of modern birds. Brooding would require very high energy investment from the adult. The regurgitalites largely contain multi-individual aggregations of the marsupialiform Alphadon and support Russell’s hypotheses of troodontids as crepuscular to nocturnal, intelligent, small game hunters with elevated metabolism and enhanced vision. Tool use in a few crocodilians and widely among extant birds suggests a reasonable possibility of this behavior in nonavian dinosaurs. Whether an avian-comparable encephalization quotient and freed forelimbs would make North American troodontids good candidates for exhibiting such behavior remains an open and speculative question. However, given the minimal modification made to tools by modern archosaurs, recognition of fossil tools poses a challenging problem.

When sociality evolved and in which groups remain open questions in mammalian evolution, largely due to the fragmentary Mesozoic mammal fossil record. Nevertheless, exceptionally preserved fossils collected in well-constrained geologic and spatial frameworks can provide glimpses into these more fleeting aspects of early mammalian behaviour. Here we report on exceptional specimens of a multituberculate, Filikomys primaevus gen. nov., from the Late Cretaceous of Montana, primarily occurring as multi-individual, monospecific aggregates of semi-articulated skulls and skeletons within a narrow stratigraphic (~9 cm thick) and geographic (

Troodon formosus, a theropod from the Late Cretaceous, is one of the few species of dinosaurs with multiple nest sites uncovered. It has been consistently demonstrated that eggs within these nests would have been partially buried in life—an exceedingly rare state in modern vertebrates. There has been debate over Troodon's capacity to engage in thermoregulatory contact incubation, especially regarding an adult's ability to efficiently supply partially buried eggs with energy. An actualistic investigation was undertaken to determine the thermodynamic efficiency of contact incubating partially buried eggs. An efficient system would keep eggs at temperatures closer to the surrogate parent than the ambient, without prohibitively high energy input. For the experiment, a surrogate dinosaur was created and used in both indoor controlled ambient temperature trials and in an outdoor variant. Even with ambient temperatures that were likely cooler than Cretaceous averages, the results showed that contact incubating partially buried eggs did seem to confer an energetic advantage; egg temperatures remained closer to the surrogate than ambient in both indoor and outdoor tests. Still, critics of contact incubating partially buried eggs are correct in that there is a depth at which adult energy would fail to make much of an impact—perhaps more relevant to buried eggs, as partially buried eggs would be in contact with an adult and likely above the thermal input threshold. Additionally, results from this experiment provide evidence for a possible evolutionary path from guarding behavior to thermoregulatory contact incubation.

Calcified eggshell protect developing embryos against environmental stress and contributes toreproductive success. Since modern crocodilians and birds lay hard-shelled eggs, this eggshelltype has also been inferred for nonavian dinosaurs. Known dinosaur eggshell is characterized byan innermost membrane, an overlying protein matrix containing calcite, and an outermost waxycuticle. The calcitic eggshell consists of one or more ultrastructural layers that, along withrespiratory pore configurations, differs drastically across the three major dinosaur clades. Whileonly hadrosaurid, derived sauropod, and tetanuran eggshells have been discovered to date,missing fossil eggshells covering the phylogenetic gaps between these taxa challenge efforts tohomologize eggshell across all dinosaurs. We present mineralogical, organochemical, andultrastructural evidence for an originally non-biomineralized, soft-shelled nature of exceptionallypreserved ornithischian Protoceratops and basal sauropodomorph Mussaurus eggs. Statisticalevaluation of in situ organic phase Raman spectra obtained for a representative set of hard- andsoft-shelled, fossil and extant diapsid eggshells, clusters the originally organic, but secondarilyphosphatized Protoceratops and the carbonaceous Mussaurus eggshells with soft eggshells.Histology corroborates the organic composition of these two soft-shelled dinosaur eggs,revealing a stratified arrangement resembling soft turtle eggshell. An ancestral statereconstruction of composition and ultrastructure compared eggshells from Protoceratops andMussaurus to those from other archosaurs, and revealed that the first dinosaur egg was softshelled.The calcified dinosaur egg evolved at least three times independently throughout theMesozoic, explaining the bias towards eggshells of highly derived dinosaurs in the fossil record. Fil: Norell, Mark A.. American Museum of Natural History; Estados Unidos Fil: Weimann, Jasmina. University of Yale; Estados Unidos Fil: Fabbri, Matteo. University of Yale; Estados Unidos Fil: Yu, Congyu. American Museum of Natural History; Estados Unidos Fil: Marsicano, Claudia Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Moore Nall, Anita. State University of Montana; Estados Unidos Fil: Varricchio, David J.. State University of Montana; Estados Unidos Fil: Pol, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentina Fil: Zelenitsky, Darla K.. University of Calgary; Canadá

A locality in the Upper Cretaceous Two Medicine Formation of Montana preserves abundant and variable horseshoe crab tracks and trails of the ichnotaxon Kouphichnium isp. These specimens span six morphologies differing in track form and trail configuration. These differences likely reflect variations in track-maker locomotion and behavior, substrate consistency, epichnial versus hypichnial preservation, and undertrack versus true tracks. Several tracks preserve the first clear appendage impressions for an extinct horseshoe crab. This discovery adds new information to the fossil horseshoe crab diversity in the Cretaceous Period. Trackway dimensions, such as the external width across the pusher legs or of the prosomal drag mark, provide information on the track-maker size. Most trackways correspond with crabs 9–14 cm wide; the abundance but limited size range of the traces suggests the large assemblage corresponds to a mating aggregation. The trace fossil record of xiphosurids indicates that throughout their history, horseshoe crabs inhabited both marine and nonmarine settings. They were definitively present in freshwater habitats from the lower Carboniferous through at least the Paleogene. Horseshoe crab trace abundance is highest from the upper Carboniferous through the Jurassic and likely reflects two factors: true upper Carboniferous taxonomic diversity and a preponderance of suitable sites for trackway preservation in the Late Triassic and Jurassic. Cretaceous traces are uncommon, and this Two Medicine locality is the first occurrence of horseshoe crab traces in the Late Cretaceous worldwide. Overall, track abundance and diversity would seem to correspond well with the reported horseshoe crab body fossil record.

A new trace fossil, Feoichnus martini new ichnospecies, from the Two Medicine Formation is here described. This ichnotaxon is reported from the upper Campanian deposits of the Egg Mountain locality (Montana) and consists of a hemispherical to hemiellipsoidal structure with a truncated upper edge, and a regular, rounded lower edge marked by a lined border composed of stained layers. The trace maker likely impregnated the border using organic fluids. The simple lined wall observed in F. martini n. isp. suggests that the structure was produced by an invertebrate soil-dwelling organism, likely an insect. Specimens are preserved as casts in calcitic Inseptisols alongside an abundant vertebrate fossil record composed by dinosaurian and nondinosaurian fossil remains, dinosaur eggs and nest structures, and pervasive insect bioturbation. Feoichnus martini n. isp. represents an additional, minor component of the impoverished Celliforma ichnofacies reported at Egg Mountain and expands the paleogeographical distribution of the ichnogenus Feoichnus Krause et al., 2008 to the Upper Cretaceous deposits of Montana, USA.UUID: http://zoobank.org/7c1a5026-7f27-4f12-a9fb-1eb8daa93baf

Fossils from the Jehol Group (Early Cretaceous, Liaoning Province, China) are integral to our understanding of Paraves, the clade of dinosaurs grouping dromaeosaurids, troodontids, and avialians, including living birds. However, many taxa are represented by specimens of unclear ontogenetic age. Without a more thorough understanding of ontogeny, evolutionary relationships and significance of character states within paravian dinosaurs may be obscured and our ability to infer their biology restricted. We describe a complete specimen of a new microraptorine dromaeosaur, Wulong bohaiensis gen. et sp. nov., from the geologically young Jiufotang Formation (Aptian) that helps solve this problem. Phylogenetic analysis recovers the specimen within a monophyletic Microraptorinae. Preserved in articulation on a single slab, the type specimen is small and exhibits osteological markers of immaturity identified in other archosaurs, such as bone texture and lack of fusion. To contextualize this signal, we histologically sampled the tibia, fibula, and humerus and compared them with new samples from the closely related and osteologically mature Sinornithosaurus. Histology shows both specimens to be young and still growing at death, indicating an age for the new dinosaur of about 1 year. The holotype possesses several feather types, including filamentous feathers, pennaceous primaries, and long rectrices, establishing that their growth preceded skeletal maturity and full adult size in some dromaeosaurids. Comparison of histology in the new taxon and Sinornithosaurus indicates that macroscopic signs of maturity developed after the first year, but before cessation of growth, demonstrating that nonhistological indicators of adulthood may be misleading when applied to dromaeosaurids. Anat Rec, 303:963-987, 2020. © 2020 American Association for Anatomy.

Vertebrate assemblages from the mid-Cretaceous (Albian-Cenomanian) Wayan Formation of Idaho and Vaughn Member of the Blackleaf Formation of Montana are dominated by the small burrowing dinosaur, Oryctodromeus cubicularis. Specimens can be assigned to three distinct taphofacies dependent on degrees of skeletal articulation and associated lithofacies. Taphofacies A comprises mostly to fully articulated specimens in bioturbated sandstones. Taphofacies B comprises partially articulated to associated collections of skeletal elements in pedogenic mudstones, siltstones, and fine-grained sandstones. Taphofacies C comprises isolated skeletal elements within the debris-flow deposit of the Robison Bonebed. Except for one associated nodosaur skeleton, Oryctodromeus is the only vertebrate represented by significant associations of skeletal elements or portions of articulated skeletal elements within the Wayan Formation/Vaughn Member units, and occurrences represent a paleocommunity dominated by a small cursorial and fossorial vertebrate. The co-occurrence of multiple individuals, representing presumed juvenile and adult growth stages, reinforce previous suggestions of parental care in this species. In addition, newly reported Oryctodromeus burrows compare in overall morphology and size with the burrow containing the holotype of Oryctodromeus. These data suggest the possibility that evidence for additional fossil taxa having had a communal and fossorial lifestyle may be discerned through further focused taphonomic investigations.

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 ...

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.

Among amniotes, turtles are the only clade that lay aragonitic eggs. Because aragonite is a metastable mineral, unequivocal preservation of aragonite in fossil turtle eggs has only been reported from Pliocene deposits. Here, we report in situ preservation of aragonite in a turtle egg from the Judith River Formation (Campanian) of Montana, USA. We utilized electron backscatter diffraction (EBSD) and Raman spectroscopy to explore the carbonate mineral polymorphs in the eggshell. The EBSD maps show the presence of both aragonite and calcite with the former preserved as needle-like crystal, a feature of all turtle eggshells. The presence of aragonite is independently validated by Raman maps. This dual approach provides direct, unambiguous evidence that the record of aragonitic turtle eggshell dates back at least to the Campanian (ca. 76 Ma) and supports the hypothesis that aragonitic eggshell is a synapomorphy of all turtles. The presence of pristine aragonite also indicates minimal taphonomic alteration at the fossil locality. Consequently, diverse invertebrate or vertebrate fossils from localities with aragonitic turtle eggs may provide high quality, unaltered palaeoenvironmental information.

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.

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...

Two closely associated egg types occur at the same locality in the Upper Cretaceous (Maastrichtian) St. Mary River Formation in north central Montana. These specimens represent the first fossil eggs described from this formation. At least fifteen small ovoid eggs or egg portions are scattered through a 25 cm interval of rock. Five significantly larger, round eggs overlie these smaller eggs and are in close proximity to one another on a single bedding plane. The best preserved egg of the smaller size measures 36 mm × 62 mm and exhibits the prismatic, two-layered eggshell structure of a theropod egg. The dispersed distribution and inconsistent angles of these small eggs likely resulted from disturbance by subsequent nesting activity and/or possibly nest predation. At least twelve additional small prismatic eggs also occur at this site. We assign the small eggs as a new oogenus and oospecies, Tetonoolithus nelsoni , within the Prismatoolithidae. The large round eggs measure 130 mm in diameter and the eggshell displays substantial diagenetic alteration. These eggs likely belonged to a hadrosaur due to their similarity in egg size, shape, and eggshell thickness to Maiasaura eggs from the stratigraphically lower Two Medicine Formation. Eggs at different stratigraphic levels at this site indicate that conditions favorable to both dinosaur species persisted for an extended period of time. However, determining whether these dinosaurs occupied the nesting site at the same or different years remains beyond the resolution of the rock record.

Nesting behaviors of extant vertebrates can serve as taphonomic models for interpreting extinct archosaurian reproduction. Past studies have examined birds with open nests and nest-bound young and tortoises with buried nests and precocial young. Here we taphonomically describe nesting sites of two crocodylians, American crocodile (Crocodylus acutus) at Turkey Point, Florida and broad-snouted caiman (Caiman latirostris) from Santa Fe and Chaco provinces, Argentina. Surveys focused on eggshell abundance, orientation, and distribution and nest modification of successfully hatched nests. American crocodiles excavate triangular or semi-circular depressions into their nest during hatching. Maximum depths of these parent-assisted hatching traces ranged from 20–45 cm, with a breadth of 50–80 cm. Eggshell orientations outside these excavated pits favored concave down (53.1–80.0%). Broad-snouted caiman constructed mound nests of predominantly plant debris in forested areas with organic rich soil or on vegetation islands. Nests ranged in diameter from 1.2–1.6 m with a height of 0.3–0.6 m. Eggshell orientations within opened egg chambers favored concave up (61.8%), whereas fragments outside the chamber were nearly evenly distributed (51.8% concave-up). Eggshell distribution and orientation at these nesting sites result from adult females assisting and transporting eggs and young during hatching. Observed eggshell orientations in and around the egg chamber in caiman nests are similar to the 60:40 up:down hatching ratio reported in both bird and tortoise nests, whereas crocodile nests are more similar to a 40:60 ratio of trampled shell. Documentation of these nest characteristics and eggshell orientations may facilitate interpretations of parental assistance in the fossil record. Fil: Ferguson, Ashley L.. State University of Montana; Estados Unidos Fil: Varrichio, David J.. State University of Montana; Estados Unidos Fil: Piña, Carlos Ignacio. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina Fil: Jackson, Frankie D.. State University of Montana; Estados Unidos

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 large-bodied carnivores including at least four large-bodied non-avian theropods (an abelisaurid,Spinosaurus,Carcharodontosaurus, andDeltadromeus), 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.

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.

The reproductive biology of living birds differs dramatically from that of other extant vertebrates. Although some attributes of modern avian reproduction had their origin within theropod dinosaurs like oviraptors and troodontids, even the most derived non-avian theropods lack key features of modern birds. We review the current knowledge of reproduction in Mesozoic birds and 3 lines of evidence that contribute to our understanding of the evolution of the modern avian reproductive mode: (1) efforts to define the ancestral reproductive condition on the basis of extant birds, (2) the fossil record of non-avian theropod dinosaurs, and (3) the fossil record of reproduction in primitive Mesozoic birds (e.g., Enantiornithes). The fossil evidence from Mesozoic birds and non-avian theropods suggests that reproduction passed through 5 stages from basal theropods to neornithines: (1) pre-maniraptoran theropods, (2) oviraptor-grade maniraptorans, (3) troodontid-grade paravians, (4) Enantiornithes, and (5) ba...

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 repo...

An incomplete specimen assigned to the genus Neurankylus sp. was collected from Coniacian deposits of the Frontier Formation of Montana (USA). The material consists of anterior plastron, a costal plate and neural plate fragment, and several undetermined skeletal elements. The identification is based on the relatively large size of the specimens, scute elements joining along the mid-line of the plastron with the intergulars reaching the humerals, and complete fusion of the sutures. The specimen represents the first baenid turtle reported from non-marine Frontier Formation deposits and is particularly relevant for understanding stratigraphical and paleogeographical distribution of the Family Baenide. This will have important implications for phylogenetic studies and paleoenvironmental interpretation of non-marine Frontier Formation deposits of south-western Montana.

The interpretation of fossil eggshells can be problematic because eggshells may be transported by hydraulic flow in floodplains, making it difficult to interpret the reproductive behavior and ecology of parent animals. A series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. We investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell height and volume, and the size of clastic sediment expected to be associated with transported eggshells. Goose, emu, and ostrich eggshell fragments were released in a flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinyl chloride). At eggshell deposition, eggshell orientation and flow depths were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition, tested relative to eggshell height and volume, and used to estimate the size of hydraulically equivalent particles. The probability of concave-down orientation after transport was > 85% regardless of eggshell type or substrate. The bed shear stress at eggshell deposition reflected the eggshell height and volume. The estimated size of hydraulically equivalent particles was coarse sand or larger. A high proportion of concave-down eggshells in a fossil assemblage may indicate transport. In addition, eggshells may be sorted according to their height and volume. Coarse sand or larger particles observed in a matrix of fossil eggshells may suggest eggshell transport.

A nesting trace preserved in alluvial floodplain deposits in the Upper Cretaceous Two Medicine Formation at the Willow Creek anticline in north-central Montana contains four crushed theropod eggs referable to the oospecies Continuoolithus canadensis. These eggs immediately overlie the lower surface of a 35-cm-long × 7-cm-thick, dark-green mudstone lens, surrounded by reddish-purple mudstone. The long axes of three eggs are parallel to one another and to the lower boundary of the lens, whereas the fourth egg lies at a 30° angle to the others. A thin, 1-cm-thick organic horizon overlies the eggs, suggesting they were buried with some vegetation. Geometric modeling of the slightly asymmetrical C. canadensis eggs yields a volume and mass of approximately 194 cm3 and 205 g for each egg. This method provides a more accurate estimation for the surface area than allometric equations that are based on modern bird eggs because of the elongate shape of many non-avian theropod eggs. Pore density and water vapor conductance (GH2O) calculated from one egg in the trace and five additional C. canadensis eggs from the Willow Creek anticline vary across three regions. High, moderate, and very low GH2O characterize the equatorial zone, blunt, and tapering poles, respectively. The average GH2O for all eggs exceeds that of an avian egg of similar mass by 3.9×, thus supporting sedimentologic evidence of substrate burial during incubation.

Dinosaur reproductive biology is often inferred from the biology of extant taxa; however, taphonomic studies of modern nest sites have focused exclusively on avian, rather than reptilian species. We documented eight Agassiz's desert tortoise (Gopherus agassizii) nests and ten loggerhead sea turtle (Caretta caretta) nests. Gopherus agassizii excavated burrows up to 70 cm long and laid rigid-shelled eggs 10-12 cm below the burrow floor. The 19 cm 3 12 cm depressions consisted of hard consolidated sand surrounded by a 3-4-cm-high rim and contained 2-5 hatched eggs in a single layer. These hatched egg bottoms represent , 25% of the original egg, and five of 27 contained fully developed dead neonates. Desiccated membrane separated from the egg interior forming pockets that filled with eggshell and sand. Of 106 and 79 eggshell fragments in the hatched egg and surrounding sand, 48% and 23% occurred concave up, respectively. However, the combined numbers of eggshell fragments inside the eggs and in the immediately surrounding sand approximates the 60:40 ratios at in situ avian nests. Therefore, this ratio may provide reliable evidence for hatching sites regardless of the incubation strategy employed by the adult. Caretta caretta nests differed from those of tortoises in their greater depth ( , 50 cm) and occurrence in moist, cohesive sand. Clutches contained over 100 pliable-shelled eggs that tore and collapsed upon hatching, without brittle fracture. Failed eggs in two clutches showed five development stages, indicating that the deaths occurred over an extended time period. With the exception of predation, the G. agassizii and C. caretta nests showed no significant eggshell or hatched eggs above the egg chamber.

D. horneri sp. nov. Etymology Horneri, Latinized form of Horner, in honor of Jack Horner, in recognition of his successful field program in the Two Medicine Formation that has recovered many new species of dinosaurs that are critical for our understanding of the palaeobiology of dinosaurs in Laramidia, support in the preparation and curation of these specimens, and to acknowledge that his mentoring efforts have launched many professional scientific careers. Holotype MOR (Museum of the Rockies, Bozeman) 590, a complete skull, partial pectoral limb, and nearly complete hindlimb (Fig.1, see Supplementary Tables S1–S3). Paratypes MOR 1130, an incomplete skull, partial axial series, and partial pelvic girdle and hindlimb. MOR 553S/7.19.0.97, a nearly complete dentary of a small juvenile, based on four features shared with the holotype and the other paratype: 17 dental alveoli, first three alveoli form a rostromedially extending arcade, laterally bowed dentary, rostroventral corner of bone is below the level of the septum between alveoli three and four. Referred material AMNH FARB (American Museum of Natural History, Fossil Amphibians, Reptiles, and Birds, New York) 5477, a maxilla, partial postorbital, and parietal; MOR 3068, a partial mandibular ramus; MOR 553D.9.19.91, left ectopterygoid; MOR 553E.7.6.91.196, right ectopterygoid. Horizon and localities Glacier County (Co.), Lewis and Clark Co., and Teton Co., Montana, USA; Upper Cretaceous upper Two Medicine Formation. Stratigraphic Distribution The type and paratype specimens all come from the upper portion of the Two Medicine Formation 32, 33 (TMF); MOR 590 occurs 65 m below a dated bentonite horizon (TM-4) 7, and the MOR 553 specimens sit at least 10 m above this same bentonite. TM-4 occurs 480m above the base of the ~545 m–thick TMF 32, and recalibration of legacy standards on 40 Ar/ 39 Ar ages from the TMF 32 indicates that the TM-4 tuff is older than previously considered, yielding a recalibrated age of 75.03 Ma +/− 0.72 Ma 34. The fourth skeleton (MOR 1130) comes from within the disturbed belt on the eastern flank of the Rocky Mountains where folding and faulting make determining exact stratigraphic positions difficult. However, the MOR 1130 specimen sits 5.9 m above a newly dated bentonite, reported here to be 74.38 +/− 0.72 Ma (U-Pb zircon weighted mean age (1 σ; MSWD = 0.55); see Supplementary Fig.S1, Discussion S1, Table S4; for bentonite locality information see ref. 35), indicating that it is slightly younger than the other specimens. Diagnosis Can be distinguished from all other derived tyrannosauroids, including Daspletosaurus torosus, by the presence of: a wide dental arcade at the front of the snout, where the maxillary and dentary tooth rows extend distinctly rostromedially and the first interdental plate of the maxilla is narrow, which resembles those of the premaxilla where the tooth row is mediolaterally oriented; dentary distinctly bowed (convex) laterally; promaxillary sinus stopping between alveoli 3 and 4, as observed in medial view of the completely prepared pneumatic chamber; rostral end of the choana on the maxilla above alveolus 7; inflated dorsal surface of the lacrimal not reaching the medial edge of the bone; medial pneumatic recess of the lacrimal tall and narrow slot; concave upper half of orbital margin of the lacrimal; entire circumference of the pneumatic recess of the squamosal is undercut and clearly defined; sinuous rostral edge in dorsal view of the dorsotemporal fossa on the frontal; joint surface for the squamosal on the parietal covers the base of the caudolateral process; and the tympanic ridge extends onto the prootic. Several autapomorphies were obtained by the cladistic analysis; autapomorphies were not included in the data matrix, but several characters were optimized on the terminal branch of D. horneri. These include a pneumatic foramen penetrating the lateral surface of the quadratojugal, shallow notch between the basal tubera, short epipophyses of the anterior cervicals, and the humerus is ~34% the length of the femur (for further comparisons see Supplementary Discussion S2 and Supplementary Fig.S2). Previous work The so-called Two Medicine tyrannosaurine has been included in several phylogenetic analyses 2 – 4, 8, 11, 36, with scorings based primarily on MOR 590. It has universally been recovered as a derived tyrannosaurine, but its specific relationships are unresolved, where it has been recovered as the sister species of D. torosus 2, 3, 8, 36 or closer to T. rex 4, 36. Description of the taxon has been limited to brief summaries of salient features (e.g., form of lacrimal horn) that distinguish it from D. torosus and to differentiate Daspletosaurus from other genera of tyrannosaurs 1, 37, but an extensive description of the taxon has not been made. Description and comparisons The D. horneri holoype is estimated to be ~9.0 m in total length and 2.2 m tall at the acetabulum (for additional measurements, see Supplementary Tables S1, S2 and S3). D. horneri differs from its sister species in that D. torosus has a rostral ramus of the lacrimal that is longer than the ventral ramus, indicating that D. horneri has a taller skull. The antorbital fossa of the lacrimal is separated by a deep concavity from the ventral ramus of the bone in D. torosus, whereas these surfaces are confluent in D. horneri. In D. torosus, the coronoid region of the surangular faces equally dorsally and laterally, whereas it faces more laterally than dorsally in D. horneri. Daspletosaurus is one of the best-supported tyrannosaurid clades, distinguished by a suite of unique, mostly cranial features (Fig.2) that suggests a relatively long evolutionary history. In particular, the cornual processes (‘horns’) of Daspletosaurus are enhanced: a new, secondary horn extends from the side of the large, triangular primary lacrimal horn that is expressed by most tyrannosaurids; and the postorbital horn, which nearly spans the rostrocaudal width of the postorbital bar, is the largest seen among tyrannosaurids. The primary cornual process of the lacrimal differs between the two Daspletosaurus species, being taller in D. torosus (ratio height of process to maximum height of rostral ramus: 69%) than in D. horneri (ratio: 53%). Results Phylogeny. The phylogenetic analysis (see Supplementary phylogenetic character list, Tables S5 and S6) recovered 18 most parsimonious trees, each having a tree length of 802 steps, a CI of 0.56, an HI of 0.44, and an RC of 0.45. The topology conforms to that of earlier works 3, 11, but the strict consensus tree and 50% majority rule tree shows that Aviatyrannis and Proceratosauridae and the lineage leading to more derived tyrannosauroids form an unresolved trichotomy (Fig.2 A; see Supplementary Fig.S3). Also, the tyrannosaurines Lythronax, Teratophoneus, and Nanuqsaurus form an unresolved trichotomy. Alioramus and Qianzhousaurus are recovered as sister species, and given that relationship we regard the genus Qianzhousaurus as a junior synonym of Alioramus (Fig.2 A). We follow the taxonomic practice in regarding sister species as congeneric, so this renaming does not constitute a phylogenetic rearrangement of alioramins. This convention is followed elsewhere in the tree (e.g., Albertosaurus, Daspletosaurus, Tyrannosaurus). Our results recover Timurlengia as more derived than Xiongguanlong and as the sister species of a new taxon from the Iren Dabasu Formation. The latter taxon (under study by TDC) is based on a partial individual (AMNH FARB 6556) that includes several teeth (premaxillary, lateral) and skull bones (lacrimal, jugal, pterygoid, ectopterygoid, quadratojugal) that was collected in 1923 under the auspices of the AMNH. The presence of D-shaped premaxillary teeth and the presence of a jugal pneumatic recess with a secondary fossa identifies it as a derived tyrannosauroid. The absence of hindlimb bones prevents comparison with the lectotype of Alectrosaurus olseni, and so it was treated as a separate taxon in our analysis (for a complete list of unambiguously resolved synapomorphies see Supplementary synapomorphy list). Importantly, Daspletosaurus horneri is recovered as the sister species of D. torosus; this relationship is supported by 11 unambiguously optimized synapomorphies (Fig.2 B–G), including the presence of a coarse subcutaneous surface of the maxilla, an accessory cornual process on the lacrimal, a partly concealed maxillary process of the lacrimal, a cornual process of the postorbital that closely approaches the laterotemporal fenestra, a rostral tip of the squamosal that stops caudal to the rostral margin of the laterotemporal fenestra, a ridge along the nasal process of the frontal, a deep ventral keel on the vomer, a caudal pneumatic recess of the palatine that is positioned caudal to the rostral margin of the dorsal process, a distinct mediolaterally oriented ridge on the dorsum of the laterosphenoid that extends toward the medial edge of the dorsotemporal fenestra, a ‘chin’ of the dentary (where the rostral and ventral margins of the dentary join) that is positioned below the third dentary tooth, and there are more than 13 maxillary teeth. Historical biogeography. The pattern of historical biogeography indicated by our parsimony analysis is consistent with the hypothesis of Brusatte and Carr 11, where North American taxa are not divided into northern and southern subclades 4. Our topology shows an Asian diversification intermediate-grade tyrannosauroids (Xiongguanlong baimoensis, Timurlengia euotica, Iren Dabasu taxon) during the mid- and early Late Cretaceous that preceded a dispersal event to North America, which was followed by subsequent and frequent exchange between the landmasses throughout the Late Cretaceous. Ontogeny. The growth series of D. horneri includes juveniles, subadults, and an adult (Fig.3). The smallest specimen, a dentary, has a tooth row that is 221.5 mm long, in contrast to the 423.0 mm tooth row of the adult, which has a 947.0 mm long skull. The length of the dentary tooth row has been shown by Currie 38 that in comparison with skull length, it shows a weak negative allometry. Therefore, the original skull length of the small specimen was greater than 496.0mm, slightly more than half the length of the adult skull. The parsimony analysis of morphological features (see Supplementary ontogenetic character list, Data S1) resulted in a single most parsimonious growth series of 168 steps, with a CI of 0.93, an HI of 0.07, an RI of 0.93, and an RC of 0.91 (Fig.3; see Supplementary Fig.S4). The transition from a gracile juvenile to a robust adult in D. horneri is similar to that seen in other tyrannosauroids 8, 26, 28. Soft tissues. The excellent quality of preservation of these specimens permits us to assess the type of soft tissue that covered the face (premaxilla, maxilla, nasal, lacrimal, jugal, postorbital, squamosal, dentary). In D. horneri, and in all derived tyrannosauroids, the subcutaneous texture is coarse and shows a hierarchy of textures (see Supplementary Discussion S3). In order to identify the soft tissue that produced this complex surface, we compared the condition of tyrannosaurids with that of crocodylians (Alligator mississippiensis) and birds (Struthio camelus, Anser sp., Anas sp., Cygnus sp., Meleagris gallopavo), and we followed several studies 29, 31, 39, 40 to identify osteological correlates imprinted on the cortical surface of facial bones to deduce their causal soft tissues. Although tyrannosaurids, crocodylians, and birds share neurovascular foramina that are densely clustered at the front of the jaws and form rows along the oral margin, the smooth texture of the snout in birds is sharply different from the hummocky texture of the facial bones of crocodylians and tyrannosaurids. The coarse surface of crocodylians is covered by many flat scales 29, whereas in birds the rhamphotheca (beak) covered the smooth surface of the snout and jaws. The coarse texture shared between tyrannosaurids and crocodylians indicates a primary covering of flat scales on the face of the nonavian dinosaurs (Fig.4). In archosaurs, a scaly integument appears to be correlated with the multiple rows of foramina seen in crocodylians and tyrannosaurids, whereas in birds the foramina deep to the beak are limited to the jaw tips, the caudal end of the maxilla, and in a row along the side of the lower jaw. A similar localization of foramina is seen in ornithischian dinosaurs, whose jaws and oral margins were sheathed by beaks ahead of the tooth row 39. Unlike crocodylians, the alveolar row of foramina in the dentary of derived tyrannosauroids and birds occurs in a common groove that extends for much of the length of the bone. This groove is not seen in crocodylians, although caudodorsally extending sulci extend from the foramina. In birds the groove is covered by the rhamphotheca, and the ventral branches of the rictal vessels and the external branch of the mandibular nerve lie in the groove 40. The groove in tyrannosauroids is shallowly inset, unlike the sharply inset condition that is seen in birds. The presence of the groove in tyrannosauroids indicates that the ventral branches of the rictal vessels evolved prior to, and might have been prerequisites for, the later appearance of the beak (in terms of the stepwise vascular changes leading from nonbeak to beak), at least on the lower jaw. The caudal end of the groove fades out in birds, a condition that is also seen in mature tyrannosauroids 41. Variation in the coarse zone of the face in tyrannosaurids indicates a variety of epidermal types, in addition to flat scales. The rostral surface of the premaxilla, dorsum of the nasals, dorsolateral surface of the lacrimal, cornual process of the jugal, and the rostroventrolatral surface of the dentary, bear small bony papillae, which indicate regions of armor-like skin 29 (Fig.4, see Supplementary Discussion S3). Finally, the coarse and rim-like edges of the postorbital horn, and its smooth central region, indicate a cornified sheath-like covering on its surface and part of the postorbital bar (Fig.4). Discussion Anagenesis. A hypothesis of anagenesis amongst tyrannosaurids (D. torosus -> D. horneri -> T. rex) is defensible if: (1) the taxa are sister species or a phylogenetically successive series of species, (2) the species are stratigraphically sequential, (3) the phylogenetic relationships do not conflict with their stratigraphic sequence, and the taxa (4) are from the same landmass or adjacent landmasses that had connections that do not conflict with their chronological sequence. Our new phylogeny (Fig.2 A) shows that D. torosus and D. horneri are sister species, whereas T. rex is nested in a separate clade. This topology is different from the phylogenetic arrangement of previous workers 1, where D. torosus is the sister species of a clade composed of D. horneri and T. rex. In our phylogeny, T. rex is separated from the Daspletosaurus clade by two phylogenetically- and almost certainly stratigraphically-successive 4 sister species, Zhuchengtyrannus magnus and T. bataar. Chronostratigraphic and lithostratigraphic correlation between the TMF and Dinosaur Park Formation (DPF) suggests that the DPF correlates with the upper 220 m of the TMF 42 – 45. In-progress high-precision U-Pb dating of the four ash beds spanning the top of the Oldman Formation, the DPF and the lower part of the Bearpaw Formation (BPF) indicates an age range between 76.69 Ma–74.26 Ma (internal error D. torosus specimens are restricted to the lower two-thirds of the DPF (~76.7–75.2 Ma), and D. horneri specimens are limited to the uppermost part of the TMF 45 (~75.1–74.4 Ma) there appears to be little or no stratigraphic overlap between Daspletosaurus specimens from these two field areas. New high-precision CA-TIMS U-Pb dating is underway and promises to better resolve stratigraphic uncertainties. Therefore, D. torosus and D. horneri meet the primary criteria for anagenesis: They are sister species, stratigraphically successive, and are from the Northern Rocky Mountain Region. In contrast, the divergence between the Daspletosaurus clade on the one hand, and the Z. magnus + Tyrannosaurus clade on the other, was the result of a cladogenetic (lineage-splitting) event, since they do not form a continuous series of stratigraphically sequential taxa. Therefore, T. rex was not a continuation of the anagenetic Daspletosaurus lineage 1. The Z. magnus + Tyrannosaurus clade consists of a pair of sister species (T. bataar + T. rex) and a sister taxon that extends from the preceding node (Z. magnus). This topology is consistent with a hypothesis of anagenesis: Z. magnus lived no less than 73.5 Ma 47, and T. rex lived between 66.0 and ~67.2–67.4 Ma 48. The age of the Nemegt Formation, from which T. bataar has been collected, is less than 75.0 Ma based on radiometric dating of the underlying Barun Goyot Formation 49. Therefore, if T. bataar is intermediate in age between Z. magnus and T. rex, then the chronological sequence of these tyrannosaurs is also consistent with anagenesis. The time gap (~6.1– 6.3 Myrs) that separates Z. magnus and T. rex greatly exceeds that between D. torosus and D. horneri; therefore, the hypothesis of anagenesis from Z. magnus to T. rex will be tested as new tyrannosaur specimens are collected from that interval in Asia and included in new phylogenetic analyses. This is also the case for the two sister species of Albertosaurus, which are stratigraphically successive and from the same geographic region, in northern Laramidia 37, 50. If the Asian sister species Alioramus remotus and A. sinensis are shown to be stratigraphically successive (the taxa are widely separated geographically, and neither is constrained by radiometric dates 5, 10), then they meet the criteria as well, but in the absence of those data the decision between anagenesis and cladogenesis is equivocal. Based on this approach, the evidence for anagenesis might be widespread among other dinosaur lineages with high-quality fossil records. If so, then anagenesis was an important contributor towards the generation of species diversity, in addition to cladogenes

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.

During the mid-Cretaceous, multituberculate mammal communities were restructured, as ‘plagiaulacidan’ multituberculates, common from the Middle Jurassic through Early Cretaceous, began to be replac...

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,...

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 infe...