Medicine Formation Of Montana Research Articles

The first report of Champsosaurus lindoei (Choristodera: Champsosauridae) from the Campanian of the United States: anatomical, phylogenetic, and palaeoecological significance

Abstract Although the neochoristodere Champsosaurus is well documented in Campanian deposits of western North America, species-diagnostic remains from these strata are restricted to the Dinosaur Park Formation of Alberta, Canada. Here, we describe an exceptionally well-preserved specimen of Champsosaurus lindoei from the Two Medicine Formation of Montana, USA—one of the few occurrences of the genus within the formation, and the first confirmed occurrence of C. lindoei outside of Dinosaur Provincial Park and its vicinity. This specimen preserves previously unknown aspects of this species, including the pes, tail, and integument, allowing for the first detailed postcranial description in this taxon. The integumentary impressions preserved on the ventral surface are the largest described thus far for Champsosaurus, supporting previous suggestions that Champsosaurus scales increase in size ventrally. We also conducted the first species-level phylogeny for Champsosaurus, where we recovered a pectinate tree topology with Palaeocene species as the sister taxa to older Maastrichtian and Campanian species, and provide further evidence for at least three lineages of Champsosaurus surviving the Cretaceous-Palaeogene (K-Pg) extinction. Finally, the recovery of the specimen from the semi-arid upland deposits of the Two Medicine Formation suggests that Champsosaurus may have been better able to withstand drier environments than previously thought.

PROBABLE JUVENILE FRONTAL OF DASPLETOSAURUS HORNERI (DINOSAURIA: THEROPODA) FROM THE TWO MEDICINE FORMATION OF MONTANA, WITH IMPLICATIONS FOR TYRANNOSAURID ONTOGENY

A partial left frontal (UCM 55499) of a small tyrannosaurid theropod from the Campanian Two Medicine Formation of Montana is described, and is considered to probably represent a juvenile of Daspletosaurus horneri. UCM 55499 compares favorably with the frontals of other young juvenile tyrannosaurid specimens, and its diminutive size suggests that the element comes from a small juvenile individual. Differences (including width of the nasal process, and degree of expansion of the postorbital buttress and the caudal shelf) between it and frontals of the larger individuals of Daspletosaurus horneri are similar to those between juveniles and adults of other tyrannosaurids such as Tyrannosaurus rex, suggesting that overall ontogenetic trends in the frontal bone of Daspletosaurus horneri are largely consistent with the patterns seen in other tyrannosaurids.

Palm fronds from western Canada are the northernmost palms from the Late Cretaceous of North America and may include the oldest Arecaceae

Palm leaf fossils are common from Late Cretaceous floras in the United States, but Late Cretaceous Canadian palm records are limited largely to Nanaimo Group strata of British Columbia, with only anecdotal records from east of the Rocky Mountains. Here we report Late Cretaceous leaf fossils from Alberta and Saskatchewan, Canada. Segment angles with the rachis or costa are investigated as an additional character to distinguish costapalmate from pinnate and entire-pinnate palm leaves. The leaf fossils from Alberta and Saskatchewan represent costapalmate-palms (Sabalites), in contrast to the relatively common entire-pinnate palm fossils known from the Coniacian–early Campanian lower Nanaimo Group of British Columbia (e.g., Geonomites imperialis; potentially the oldest known North American palm) and the Campanian Two Medicine Formation of Montana (cf. Phoenicites). The presence of fossil palms in the Campanian to Maastrichtian of Alberta and Saskatchewan constrains climate reconstructions for the Late Cretaceous high mid-latitudes of North America (c. 55° N) to exclude significant freezing episodes. Additionally, we update the nomenclature for G. imperialis, renaming it as a species of Phoenicites, and briefly consider its value to understanding the evolution of pinnate palms. Further, we challenge the interpretation of Sabalites magothiensis as a costapalmate species and reassess the age of S. carolinensis as late Campanian.

Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America1

Tyrannosaurids were the apex predators of Late Cretaceous Laurasia and their status as dominant carnivores has garnered considerable interest since their discovery, both in the popular and scientific realms. As a result, they are well studied and much is known of their anatomy, diversity, growth, and evolution. In contrast, little is known of the earliest stages of tyrannosaurid development. Tyrannosaurid eggs and embryos remain elusive, and juvenile specimens — although known — are rare. Perinatal tyrannosaurid bones and teeth from the Campanian–Maastrichtian of western North America provide the first window into this critical period of the life of a tyrannosaurid. An embryonic dentary (cf. Daspletosaurus) from the Two Medicine Formation of Montana, measuring just 3 cm long, already exhibits distinctive tyrannosaurine characters like a “chin” and a deep Meckelian groove, and reveals the earliest stages of tooth development. When considered together with a remarkably large embryonic ungual from the Horseshoe Canyon Formation of Alberta, minimum hatchling size of tyrannosaurids can be roughly estimated. A perinatal premaxillary tooth from the Horseshoe Canyon Formation likely pertains to Albertosaurus sarcophagus and it shows small denticles on the carinae. This tooth shows that the hallmark characters that distinguish tyrannosaurids from other theropods were present early in life and raises questions about the ontogenetic variability of serrations in premaxillary teeth. Sedimentary and taphonomic similarities in the sites that produced the embryonic bones provide clues to the nesting habits of tyrannosaurids and may help to refine the prospecting search image in the continued quest to discover baby tyrannosaurids.

Ontogeny and variation in the skull roof and braincase of Maiasaura peeblesorum from the Two Medicine Formation of Montana, U.S.A.

Ontogeny and variation in the skull roof and braincase of Maiasaura peeblesorum from the Two Medicine Formation of Montana, U.S.A.

The easternmost occurrence of Saurornitholestes from the Judith River Formation, Montana, indicates broad biogeographic distribution of Saurornitholestes in the Western Interior of North America

ABSTRACT Small-bodied dromaeosaurid and troodontid theropod dinosaurs are present in most of the terrestrial Late Cretaceous formations of the North American Western Interior, but are represented predominantly by shed teeth and more rarely by isolated skeletal elements and associated skeletons. The eudromaeosaurian dromaeosaurid Saurornitholestes is among the most commonly recovered small theropods from North America, known from abundant shed teeth, isolated cranial and postcranial elements, and several partial or near-complete skeletons from the Campanian aged Two Medicine Formation of Montana and the Dinosaur Park Formation of Alberta. Conversely, few Saurornitholestes specimens beyond shed teeth have been recovered from temporally equivalent units of the Judith River Formation of Montana. This study reports the first cranial material, a near-complete frontal, referable to Saurornitholestes from the Judith River Formation of Montana. This specimen is the easternmost occurrence of this taxon and was recovered approximately 400 km east of the localities which have produced referred Saurornitholestes specimens in the Two Medicine Formation, proximal to the Cordilleran thrust front. As such, this new specimen indicates that Saurornitholestes was biogeographically widespread and occupied both inland and coastal environments across the northern portions of the Late Cretaceous Western Interior of North America.

Insect trace fossils elucidate depositional environments and sedimentation at a dinosaur nesting site from the Cretaceous (Campanian) Two Medicine Formation of Montana

We describe the diversity and abundance of insect (specifically hymenopterans and coleopterans) pupation structures in the Upper Cretaceous (Campanian) Two Medicine Formation at the Egg Mountain locality, western Montana, U.S.A., an important dinosaur nesting site. The study interval comprises a massive calcareous siltstone and indurated silty limestone horizons interpreted as the product of cumulative paleosols. A 7 m by 11 m area was quarried with a jackhammer at intervals of 12.5 cm thickness for a 1.5 m thick stratigraphic section. The ichnoassemblage comprises four morphotypes (small, medium, large, and wide) assigned to Fictovichnus sciuttoi, of which three represent wasp (hymenopteran) cocoons while the fourth (wide) type potentially was produced by a coleopteran. Medium and small F. sciuttoi are dominant while large and wide Fictovichnus are less common and absent in some sample intervals. Other probable insect traces include partial perforations in cocoons (Tombownichnus), isolated burrows, and an enigmatic hemispherical trace. Material is representative of a depauperate Celliforma ichnofacies. Pervasive cocoons and other traces throughout the sequence suggest persistent soil conditions suitable for insect nesting and pupation, and suggest an absence of sediment pulses of sufficient thickness to prohibit thorough colonization. Peaks in pupation chamber abundance may reflect episodes of reduced sedimentation rates otherwise unseen in the absence of primary bedding structures. Well-drained and friable soil conditions favorable for insect nesting also may help explain the abundance of dinosaur nests and other vertebrate nesting events in associated strata as well as the presence of small terrestrial forms.

Fossil eggshell cuticle elucidates dinosaur nesting ecology.

The cuticle layer consisting mainly of lipids and hydroxyapatite (HAp) atop the mineralized avian eggshell is a protective structure that prevents the egg from dehydration and microbial invasions. Previous ornithological studies have revealed that the cuticle layer is also involved in modulating the reflectance of eggshells in addition to pigments (protoporphyrin and biliverdin). Thus, the cuticle layer represents a crucial trait that delivers ecological signals. While present in most modern birds, direct evidence for cuticle preservation in stem birds and non-avian dinosaurs is yet missing. Here we present the first direct and chemical evidence for the preservation of the cuticle layer on dinosaur eggshells. We analyze several theropod eggshells from various localities, including oviraptorid Macroolithus yaotunensis eggshells from the Late Cretaceous deposits of Henan, Jiangxi, and Guangdong in China and alvarezsaurid Triprismatoolithus eggshell from the Two Medicine Formation of Montana, United States, with the scanning electron microscope (SEM), electron probe micro-analysis (EPMA), and Raman spectroscopy (RS). The elemental analysis with EPMA shows high concentration of phosphorus at the boundary between the eggshell and sediment, representing the hydroxyapatitic cuticle layer (HAp). Depletion of phosphorus in sediment excludes the allochthonous origin of the phosphorus in these eggshells. The chemometric analysis of Raman spectra collected from fossil and extant eggs provides further supportive evidence for the cuticle preservation in oviraptorid and probable alvarezsaurid eggshells. In accordance with our previous discovery of pigments preserved in Cretaceous oviraptorid dinosaur eggshells, we validate the cuticle preservation on dinosaur eggshells through deep time and offer a yet unexplored resource for chemical studies targeting the evolution of dinosaur nesting ecology. Our study also suggests that the cuticle structure can be traced far back to maniraptoran dinosaurs and enhance their reproductive success in a warm and mesic habitat such as Montana and southern China during the Late Cretaceous.

Fossil egg and eggshells from the Upper Cretaceous Hell Creek Formation, Montana

ABSTRACTDespite over a hundred years of intense paleontological exploration, the terrestrial rocks of the Upper Cretaceous (Maastrichtian) Hell Creek Formation of eastern Montana are remarkable for the absence of fossil eggs. Here, we describe the first fossil egg and additional eggshell fragments from the formation. The two-layered structure of the smooth 1600-µm-thick eggshell of Belonoolithus garbani, oogen. et oosp. nov., permits assignment of the 6 cm × 8 cm egg to Theropoda. Additional theropod eggshells, Dimorphoolithus bennetti, oogen. et oosp. nov., closely resemble Tubercuoolithus choteauensis (incertae sedis) from the Campanian Two Medicine Formation of Montana, differing only in ornamentation. Therefore, we establish Tubercuoolithidae, oofam. nov., to accommodate both eggshell types. Other eggshell types include two varieties of Spheroolithus, as well as Testudoolithus and Krokolithes. Whereas B. garbani and D. bennetti are unique to the Hell Creek Formation, the other three oogenera also occur in the stratigraphically older Two Medicine and Judith River formations of Montana, and the Oldman Formation of southern Alberta, Canada.Citation for this article: Jackson, F. D., and D. J. Varricchio. 2016. Fossil egg and eggshells from the Upper Cretaceous Hell Creek Formation, Montana. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1185432.

A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana.

BackgroundBrachylophosaurini is a clade of hadrosaurine dinosaurs currently known from the Campanian (Late Cretaceous) of North America. Its members include: Acristavus gagslarsoni, which lacks a nasal crest; Brachylophosaurus canadensis, which possesses a flat paddle-shaped nasal crest projecting posteriorly over the dorsal skull roof; and Maiasaura peeblesorum, which possesses a dorsally-projecting nasofrontal crest. Acristavus, from the lower Two Medicine Formation of Montana (~81–80 Ma), is hypothesized to be the ancestral member of the clade. Brachylophosaurus specimens are from the middle Oldman Formation of Alberta and equivalent beds in the Judith River Formation of Montana; the upper Oldman Formation is dated 77.8 Ma.Methodology/Principal FindingsA new brachylophosaurin hadrosaur, Probrachylophosaurus bergei (gen. et sp. nov.) is described and phylogenetically analyzed based on the skull and postcranium of a large individual from the Judith River Formation of northcentral Montana (79.8–79.5 Ma); the horizon is equivalent to the lower Oldman Formation of Alberta. Cranial morphology of Probrachylophosaurus, most notably the nasal crest, is intermediate between Acristavus and Brachylophosaurus. In Brachylophosaurus, the nasal crest lengthens and flattens ontogenetically, covering the supratemporal fenestrae in large adults. The smaller nasal crest of Probrachylophosaurus is strongly triangular in cross section and only minimally overhangs the supratemporal fenestrae, similar to an ontogenetically earlier stage of Brachylophosaurus. Sutural fusion and tibial osteohistology reveal that the holotype of Probrachylophosaurus was relatively more mature than a similarly large Brachylophosaurus specimen; thus, Probrachylophosaurus is not simply an immature Brachylophosaurus.Conclusions/SignificanceThe small triangular posteriorly oriented nasal crest of Probrachylophosaurus is proposed to represent a transitional nasal morphology between that of a non-crested ancestor such as Acristavus and the large flat posteriorly oriented nasal crest of adult Brachylophosaurus. Because Probrachylophosaurus is stratigraphically and morphologically intermediate between these taxa, Probrachylophosaurus is hypothesized to be an intermediate member of the Acristavus-Brachylophosaurus evolutionary lineage.

Lay, brood, repeat: nest reuse and site fidelity in ecologic time for two Cretaceous troodontid dinosaurs

ABSTRACT—Whereas ‘biological site fidelity’ refers to the regular reuse of a favored locale (e.g., breeding ground or nest) by an individual animal, ‘paleontological site fidelity’ typically refers to repeated use of a nesting locality by a herd or species over geologic time scales. Two new Cretaceous specimens from the Two Medicine Formation of Montana, U.S.A., and the Liantoutang Formation of Zhejiang, China, each preserve two closely superimposed clutches of the egg form Prismatoolithus. These eggs belong to the Troodontidae, small theropod dinosaurs sharing a close ancestry with Aves. In both specimens, eggs of a lower clutch are truncated at a level below what would normally preserve in an undisturbed hatched clutch. These traces differ from past examples of dinosaur site fidelity in (1) the close or cross-cutting relationship of the clutches, (2) the precise overlay of clutch atop clutch, and (3) the implication of nest reuse and, thus, site fidelity on an ecologic rather than geologic scale and at approximately the individual rather than species level. Given the likely extended occupation of troodontid nesting sites by attending adults, factors such as nesting success and territoriality may, in addition to favorable substrates, have influenced the behaviors recorded by these specimens. The arrangements of eggs as clutches within the geologic record represent trace fossils. Thus, they record past in situ behavior, providing important insight into dinosaur nesting. In addition, they can serve as independent indicators of substrate conditions and sedimentary history, potentially refining our understanding of paleoenvironments.

Euoplocephalus tutus and the Diversity of Ankylosaurid Dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA

Few ankylosaurs are known from more than a single specimen, but the ankylosaurid Euoplocephalus tutus (from the Late Cretaceous of Alberta, Canada and Montana, USA) is represented by dozens of skulls and partial skeletons, and is therefore an important taxon for understanding intraspecific variation in ankylosaurs. Euoplocephalus is unusual compared to other dinosaurs from the Late Cretaceous of Alberta because it is recognized from the Dinosaur Park, Horseshoe Canyon, and Two Medicine formations. A comprehensive review of material attributed to Euoplocephalus finds support for the resurrection of its purported synonyms Anodontosaurus lambei and Scolosaurus cutleri, and the previously resurrected Dyoplosaurus acutosquameus. Anodontosaurus is found primarily in the Horseshoe Canyon Formation of Alberta and is characterized by ornamentation posterior to the orbits and on the first cervical half ring, and wide, triangular knob osteoderms. Euoplocephalus is primarily found in Megaherbivore Assemblage Zone 1 in the Dinosaur Park Formation of Alberta and is characterized by the absence of ornamentation posterior to the orbits and on the first cervical half ring, and keeled medial osteoderms on the first cervical half ring. Scolosaurus is found primarily in the Two Medicine Formation of Montana (although the holotype is from Dinosaur Provincial Park), and is characterized by long, back-swept squamosal horns, ornamentation posterior to the orbit, and low medial osteoderms on the first cervical half ring; Oohkotokia horneri is morphologically indistinguishable from Scolosaurus cutleri. Dyoplosaurus was previously differentiated from Euoplocephalus sensu lato by the morphology of the pelvis and pes, and these features also differentiate Dyoplosaurus from Anodontosaurus and Scolosaurus; a narrow tail club knob is probably also characteristic for Dyoplosaurus.

A new ankylosaurid from the late Cretaceous Two Medicine Formation of Montana, USA

Oohkotokia horneri gen. et sp. nov. is described based on a specimen in the collections of the Museum of the Rockies, Montana, USA. Oohkotokia exhibits a unique combination of characters not seen in other late Campanian North American ankylosaurids: prominent, horn-like, trihedral squamosal bosses, a small, undistinguished median nasal plate on the dorsal surface of the rostrum, a relatively small occipital condyle, a smooth, finely pitted osteoderm external texture, and triangular lateral osteoderms. Other specimens from the Two Medicine Formation are referable to Oohkotokia. O. horneri, Euoplocephalus tutus, Dyoplosaurus acutosquameus, and Scolosaurus cutleri separate stratigraphically.

‘Glishades ericksoni’, an indeterminate juvenile hadrosaurid from the Two Medicine Formation of Montana: implications for hadrosauroid diversity in the latest Cretaceous (Campanian-Maastrichtian) of western North America

Glishades ericksoni was named on the basis of partial paired premaxillae collected from the Late Campanian Two Medicine Formation of Montana, and was described as a non-hadrosaurid hadrosauroid. This interpretation of G. ericksoni has significant implications for hadrosauroid diversity and distribution because it represents the first occurrence of a non-hadrosaurid hadrosauroid in the Late Campanian of North America, and therefore implies either a prolonged period of sympatry between these forms and hadrosaurids or a biotic interchange with Asia. Given its small size, and therefore potential juvenile status, the taxonomic identity of G. ericksoni is re-evaluated here. Comparison with similarly-sized, taxonomically determinate, and coeval hadrosaurid specimens from the Two Medicine Formation (Prosaurolophus, Gryposaurus, and Maiasaura) suggest that the combination of characters used to distinguish G. ericksoni as a non-hadrosaurid hadrosauroid are more widely distributed or individually variable in hadrosaurids, or can be explained as the result of ontogenetic variation. In particular, the unique combination of characters used to diagnose G. ericksoni is also found in juvenile individuals of Prosaurolophus, Gryposaurus, and Maiasaura. Inclusion of juveniles of these taxa, scored on the basis of comparable anatomy, in the original phylogenetic analysis recovers the juvenile hadrosaurid specimens outside Hadrosauridae. Consequently, G. ericksoni cannot be confidently differentiated from a juvenile saurolophine, which are common in the upper and middle sections of the Two Medicine Formation, and is thus considered a nomen dubium. Given their absence in well-sampled Late Campanian and Maastrichtian deposits, non-hadrosaurid hadrosauroids appear to have been completely replaced by hadrosaurids in western North America by the Late Campanian.

The skull and appendicular skeleton of Gryposaurus latidens, a saurolophine hadrosaurid (Dinosauria: Ornithopoda) from the early Campanian (Cretaceous) of Montana, USA

The osteology of the holotype and referred specimens of the saurolophine hadrosaurid, Gryposaurus latidens , from the lower Two Medicine Formation of Montana (USA), is described in detail. With an estimated early Campanian (Late Cretaceous) age, this dinosaur is one of the oldest known hadrosaurids. Gryposaurus latidens shows several autapomorphies, including dentary tooth crowns, with an apicobasal length/mesiodistal width ratio of 1.7–2.2, a single median carina, and large marginal denticles in sections of the dental battery; deep and oval depression on the posteroventral premaxillary surface; and, in the context of Hadrosauridae, a shallow lacrimal process of the rostral process of the jugal. Furthermore, G. latidens differs from G. notabilis and G. monumentensis in having a broadly arcuate anterolateral oral margin of the premaxilla, a posterior margin of the narial fenestra that is wider than the dorsoventral depth of the proximal region of the narial bar, with a nasal crest that rises above the level of the frontals (in adults) and is located above the posterior margin of the narial fenestra, and wide and shallow posteroventral margin of the rostral process of the jugal, among other characters. This study confirmed a previous hypothesis supporting G. latidens as the sister taxon to a clade composed of the other species of Gryposaurus .

A Subadult Specimen of Rubeosaurus ovatus (Dinosauria: Ceratopsidae), with Observations on Other Ceratopsids from the Two Medicine Formation

BackgroundCentrosaurine ceratopsids are well known from the middle Campanian Upper Two Medicine Formation of Montana. Four taxa have been named: Brachyceratops montanensis, Rubeosaurus ovatus, Einiosaurus procurvicornis, and Achelousaurus horneri. Rubeosaurus has been historically the most enigmatic of these taxa; only two specimens, the holotype caudal parietal bar and a referred incomplete skull, have been assigned to Rubeosaurus.Methodology/Principal FindingsA revised interpretation of the parietal processes of USNM 14765, the partial skeleton of a subadult centrosaurine formerly referred to Brachyceratops, indicates that it shares a P5 spike with the holotype of Rubeosaurus ovatus and should therefore be referred to that taxon. Brachyceratops is considered a nomen dubium.Conclusions/SignificanceUSNM 14765 provides additional anatomical information for Rubeosaurus ovatus. These new data are incorporated into a recent phylogenetic analysis of centrosaurine relationships; Rubeosaurus appears as the sister taxon of a clade composed of Einiosaurus, Achelousaurus, and Pachyrhinosaurus.

Glishades ericksoni, a new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous of North America

A new genus and species of hadrosauroid dinosaur, Glishades ericksoni, is described based on paired partial premaxillae collected from the Upper Cretaceous Two Medicine Formation of Montana, in the Western Interior of the United States of America. This taxon is diagnosed on the basis of a unique combination of characters: absence of everted oral margin, arcuate oral margin with wide and straight, obliquely oriented, and undeflected anterolateral corner, grooved transversal thickening on ventral surface of premaxilla posterior to denticulate oral margin, and foramina on anteromedial surface above oral edge and adjacent to proximal end of narial bar. Maximum parsimony analysis positioned G. ericksoni as a derived hadrosauroid. Exclusion of G. ericksoni from Hadrosauridae was unambiguously supported by the lack in AMNH 27414 of a dorsomedially reflected premaxillary oral margin. Furthermore, the maximum agreement subtree positioned G. ericksoni as the sister taxon to Bactrosaurus johnsoni. This position was unambiguously supported by posteroventral thickening on the ventral surface of the premaxilla (independently derived in saurolophid hadrosaurids and Ouranosaurus nigeriensis) and having foramina on each premaxilla on the anterior surface, adjacent to the parasagittal plane of the rostrum (reconstructed as independently derived in Brachylophosaurus canadensis, Maiasaura peeblesorum, and Edmontosaurus annectens).

UNIQUE MANIRAPTORAN EGG CLUTCH FROM THE UPPER CRETACEOUS TWO MEDICINE FORMATION OF MONTANA REVEALS THEROPOD NESTING BEHAVIOUR

Abstract:  Egg clutches of non‐avian maniraptoran theropods (Dinosauria) are rare, particularly in North America where those of Troodon formosus are the only maniraptoran clutches known. Here we describe a new partial maniraptoran clutch and nesting trace referred to Montanoolithus strongorum oogen. et oosp. nov. (Montanoolithidae oofam. nov.), from the Upper Cretaceous Two Medicine Formation of Montana. Based on a cladistic analysis of reproductive traits, we infer that this clutch belonged either to a caenagnathid or to a dromaeosaurid, which makes it the first clutch known of either taxon. This specimen preserves impressions and eggshell fragments of at least five eggs on a nest structure. The eggs are asymmetrical, paired, and lay radially in a ring configuration on the sloped sides of a bioturbated, flat‐topped sandstone mound. Geology of the locality indicates the female nested in a poorly‐vegetated area of freshly deposited sand, possibly near an active river channel. This clutch reveals that the egg‐layer of Montanoolithus strongorum had a unique suite of reproductive characteristics and nesting behaviours among maniraptorans.

Opportunistic exploitation of dinosaur dung: fossil snails in coprolites from the Upper Cretaceous Two Medicine Formation of Montana

Multiple associations of fossil snails with dinosaur coprolites demonstrate that snails and dinosaurs not only shared ancient habitats but were trophically linked via dinosaur dung. Over 130 fossil snails representing at least seven different taxa have been found on or within herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana. The terrestrial snail Megomphix is the most common taxon, but three other terrestrial taxa (Prograngerella, Hendersonia and Polygyrella) and three aquatic snails (Lioplacodes, ?Viviparus and a physid) also occur in coprolites. At least 46% of the shells in the faeces are whole or nearly so, indicating that most (if not all) of the snails were not ingested by dinosaurs, but were post-depositional visitors to the dung pats. The sizeable, moist and microbially enriched dinosaur faeces would have provided both food and roosting sites for the ancient snails, and the large number of snail–coprolite associations reflect recurring, opportunistic exploitation of dung. The terrestrial taxa in the coprolites suggest that this Late Cretaceous locality included sufficiently moist detrital or vegetative cover for snails when dinosaur dung was not present. The aquatic snails probably entered the faeces during flood events. Dinosaur dung would have provided an abundant but patchy influx of resources that was probably seasonally available in the ancient environment.

A revision of the late campanian centrosaurine ceratopsid genus Styracosaurus from the Western Interior of North America

ABSTRACT The centrosaurine ceratopsid genus Styracosaurus is known from multiple specimens and a multigeneric bone bed in the upper 30 m of the Late Cretaceous Dinosaur Park Formation of southern Alberta, and a single specimen (S. ovatus) from approximately time equivalent sediments of the Two Medicine Formation of Montana. Key cranial elements (nasals and postorbitals) of Styracosaurus appear to undergo similar ontogenetic changes as documented in Centrosaurus. Although all adult-sized centrosaurines except Centrosaurus apertus are known to possess spike-like parietal ornamentation at the P3 position on the parietal, only Styracosaurus has the P4 ornamentation expressed as a well-developed spike. Styracosaurus shows intraspecific variation in the shape of the more anteriorly placed P5–P7 ornamentation that are either the typical unmodified crest-shaped epoccipitals of other centrosaurines or are developed as short spikes. S ovatus from Montana is retained as a valid species based on the autapomorphic convergence of the P3 spikes toward the midline.