Background Extended neoteny and late stage allometric growth increase morphological disparity between stages in at least some dinosaurs. Coupled with relatively low dinosaur density the Upper Cretaceous of North America, ontogenetic transformational representatives are often difficult to distinguish. For example, many hadrosaurids previously reported represent small lambeosaurine species were demonstrated be juveniles larger taxa. Marginocephalians (pachycephalosaurids + ceratopsids) undergo...

Background A dinosaur census recorded during the Hell Creek Project (1999–2009) incorporates multiple lines of evidence from geography, taphohistory, stratigraphy, phylogeny and ontogeny to investigate relative abundance large dinosaurs preserved in Upper Cretaceous Formation northeastern Montana, USA. Overall, skeletal assemblages (excluding lag-influenced records) consist primarily subadult or small adult size individuals. Small juveniles adults are both extremely rare, whereas individuals...

The persistence of original soft tissues in Mesozoic fossil bone is not explained by current chemical degradation models. We identified iron particles (goethite-αFeO(OH)) associated with recovered from two dinosaurs, using transmission electron microscopy, energy loss spectroscopy, micro-X-ray diffraction and Fe absorption near-edge structure. Iron chelators increased tissue immunoreactivity to multiple antibodies dramatically, suggesting a role for both preserving masking proteins tissues....

Abstract The idea that original soft tissue structures and the native structural proteins comprising them can persist across geological time is controversial, in part because rigorous testable mechanisms occur under natural conditions, resulting such preservation, have not been well defined. Here, we evaluate two non-enzymatic protein crosslinking mechanisms, Fenton chemistry glycation, for their possible contribution to preservation of blood vessel recovered from cortical bone a...

A Rietveld method is described which extracts information on crystal structure, texture and microstructure directly from two-dimensional synchrotron diffraction images. This advantageous over conventional analysis that relies individual peaks, particularly for low-symmetry materials with many overlapping peaks images a poor peak-to-background ratio. The applied to two mineralized biological samples hydroxylapatite fabrics: an ossified pachycephalosaurid dinosaur tendon Atlantic salmon scale....

This is the first cranial ontogenetic assessment of Triceratops, well-known Late Cretaceous dinosaur distinguished by three horns and a massive parietal-squamosal frill. Our analysis based on growth series 10 skulls, ranging from 38 cm long baby skull to about 2 m adult skulls. Four stages correspond suite characters expressed in postorbital horns, frill, nasal, epinasal horn epoccipitals. Postorbital are straight stubs early ontogeny, curve posteriorly juveniles, straighten subadults...

The placement of over 50 skulls the well-known horned dinosaur Triceratops within a stratigraphic framework for Upper Cretaceous Hell Creek Formation (HCF) Montana reveals evolutionary transformation this genus. Specimens referable to two recognized morphospecies Triceratops, T. horridus and prorsus, are stratigraphically separated HCF with prorsus morphology recovered in upper third formation found lower formation. Hypotheses that these represent sexual or ontogenetic variation single...

Modern histological techniques allow paleontologists to investigate the internal microstructure of bone tissue.We apply high resolution images thin sections from an ontogenetic series (not conspecific) pachycephalosaurid frontoparietal domes test hypothesis that these Late Cretaceous dinosaurs used their heads as battering rams, analogous behavior bighorn sheep, Ovis canadensis, or a thermoregulatory device.Our analysis reveals structure pachycephalosaur dome is dynamic tissue reflects...

A new isotopic age of ca. 78 Ma was obtained by the conventional K–Ar method and laser-fusion 40 Ar/ 39 Ar analysis biotite sanidine crystals from two bentonites in Judith River Formation Kennedy Coulee, Hill County, Montana. The analyses yielded weighted mean ages 78.2 ± 0.2 (biotite) (sanidine) for sample 84MG8-3-4, 79.5 78.5 85MG7-16-1. These are first determinations Formation. dated Coulee bracket significant Judithian "age" mammal localities, UCMP V77083 V81234.The radioisotopic County...

Historically, studies of pachycephalosaurs have recognized plesiomorphically flat-headed taxa and apomorphically domed taxa. More recently, it has been suggested that the expression frontoparietal dome is ontogenetic derived from a juvenile morphology. However, strong evidence to support this hypothesis lacking. Here we test in large, stratigraphically constrained sample specimens assigned Stegoceras validum, best known pachycephalosaur, using multiple independent lines including conserved...

ABSTRACT The discovery of the smallest Triceratops skull (UCMP 154452) provides a new ontogenetic end member for earliest stage ceratopsid (Centrosaurinae plus Chasmosaurinae) cranial development. lack co-ossification among parietal, squamosals, postorbitals, quadratojugal arch, and braincase preserves sutural contacts bone surfaces that later become obscured in adults. ability to document early development morphology horns frill allows reevaluation their functional roles. UCMP 154452 shows...

ABSTRACT Historically, the scarcity of non-adult Triceratops fossils collected from Upper Cretaceous sediments North America limited our understanding and promoted controversy with regard to morphology, presence or absence cranial epi-ossifications in this widely known horned dinosaur. The recent discovery several exceptionally well preserved juvenile subadult skulls numerous juvenile, subadult, adult elements, Hell Creek Formation eastern Montana, confirms ontogeny morphology study. We...

Abstract In the Cretaceous of North America, environmental sensitivity and habitat specialization have been hypothesized to explain surprisingly restricted geographic ranges many large-bodied dinosaurs. Understanding drivers behind this are key determining broader trends dinosaur species community response climate change under greenhouse conditions. However, previous studies question commonly examined only small components paleo-ecosystem or operated without comparison similar modern systems...

ABSTRACT The East African Rift separates the northwestern and southeastern Ethiopian high plateaus, which are capped by massive Cenozoic volcanics overlying thick deposits of marine nonmarine Mesozoic sediments. During geological mapping projects 1920s–1930s, a few vertebrate fossils were found on plateau. In contrast, beginning in 1976, then from 1993 to present, paleontological field work Abay (Blue Nile) River gorge along eastern edge plateau resulted discovery fossil chondrichthyans...

New end-stage juvenile specimens of Pachycephalosaurus from the Upper Cretaceous Hell Creek Formation, Montana, confirm earliest expression squamosal nodes, parietal ornamentation, and jugal morphology in smallest presumably youngest individuals yet known. High-resolution computed tomography slightly thickened, undomed reveals a dense cortex, highly cancellous interior irregularly shaped erosion cavities, bony trabeculae indicative primary, fast growing bone. The parietal, with its...

ABSTRACT A new skull of Stygimoloch spinifer (MPM 8111) from the Upper Cretaceous Hell Creek Formation North Dakota is most complete specimen discovered to date. It allows much and braincase this unusual pachycephalosaurid be described for first time confirms a suite diagnostic characters species. The long with vaulted, transversely narrow frontoparietal dome robust squamosal forming prominent posterior shelf. shelf ornamented by three four large, low-angle horns multiple clusters smaller...

ABSTRACT Colepiocephale lambei from the Foremost Formation of Alberta is a problematic pachycephalosaurid that has recently been hypothesized as (1) synonymous with Stegoceras validum, (2) distinct species within clade, and (3) an unusual taxon more derived than Stegoceras. Conflict among these hypotheses arises different interpretations parietosquamosal region dome. Re-evaluation morphology C. based on all known material indicates posteromedial extension parietal broken off at its base in...

The Hell Creek Formation preserves one of the most intensely studied late Cretaceous terrestrial fossil units. Over 22 dinosaur genera are currently recognized from this unit, but record juvenile individuals is surprisingly limited. Here, we document a nestling hadrosaur that represents first occurrence an articulated skeleton latest (late Maastrichtian) North America. specimen (UCMP 128181) partial scapula, nearly complete rib cage, vertebral series shoulder to mid-tail, large portion...

Abstract The ontogeny and taxonomy of the dome-headed pachycephalosaurs are topics continued debate. Pachycephalosaurid diversity in Maastrichtian North America is particularly controversial, validity composition within genus Sphaerotholus remains unresolved. While type species, S. goodwini, generally considered valid, debate has centred around buchholtzae edmontonensis. Here we employ morphometrics, histology phylogenetic analysis to resolve these issues. An ontogenetic assessment (N...

Stable isotopes are powerful tools for elucidating ecological trends in extant vertebrate communities, though their application to Mesozoic ecosystems is complicated by a lack of isotope data from comparable environments/ecosystems (e.g. coastal floodplain forest environments, lacking significant C 4 plant components). We sampled 20 taxa across broad phylogenetic, body size, and physiological scope the Atchafalaya River Basin Louisiana as an environmental analogue Late Cretaceous floodplains...