Museum of the Rockies

Many animals produce alarm signals when they detect a potential predator, but we still know little about the information contained in these signals. Using presentations of 15 species of live predators, we show that acoustic features of the mobbing calls of black-capped chickadees (Poecile atricapilla) vary with the size of the predator. Companion playback experiments revealed that chickadees detect this information and that the intensity of mobbing behavior is related to the size and threat of the potential predator. This study demonstrates an unsuspected level of complexity and sophistication in avian alarm calls.

With the rapid evolution of microplastic research over several decades, there is an urgent need to compare methodologies for quantifying microplastic in aquatic environments.

ABSTRACT Ontogenetic changes in the bone histology of Maiasaura peeblesorum are revealed by six relatively distinct but gradational growth stages: early and late nestling, early and late juvenile, sub-adult, and adult. These stages are distinguished not only by relative size but by changes in the histological patterns of bones at each stage. In general, the earliest stages are marked by spongy bone matrix with large vascular canals. Through growth, the cortical bone differentiates into fibro-lamellar tissue that tends to become more regularly layered in the outer cortex. By the sub-adult stage, lines of arrested growth (LAGs) begin to appear regularly. Resorption lines and substantial Haversian substitution in many long bones also begin to appear at this stage, and the external cortex has a lamellar-zonal structure in some bones that indicates imminent cessation of growth. Judging by the rates of apposition of similar bone tissues in living amniotes, and by the number and placement of LAGs, these patterns suggest that young Maiasaura nestlings grew at very high rates, and at high and moderately high rates during later nestling, juvenile, and sub-adult stages, slowing to low and very low growth rates in adults (7–9 m total length). The nesting period would have lasted one to two months, late juvenile size (3.5 meters) would have been reached in one or two years, and adult size in six to eight years, depending on the basis for extrapolating bone growth rates. The histological tissues, patterns, and inferred growth rates of the bones of Maiasaura are completely different from those of living non-avian reptiles, generally similar to those of most other dinosaurs and pterosaurs for which data are available, and much like those of extant birds and mammals. No living reptiles (except birds) grow to adult size at these rates, nor do they show these histological patterns. We conclude that Maiasaura did not grow at all like living non-avian reptiles, which cannot be considered informative models for most aspects of dinosaurian growth (or physiology, to the extent that growth rates reflect metabolism). The use of lines of arrested growth (LAGs) to infer dinosaurian physiology has never been tested and is not supported by independent lines of evidence; their use in calculating age is also more complex than previously suggested and should not be based on single bones.

Fossilized bones from extinct taxa harbor the potential for obtaining protein or DNA sequences that could reveal evolutionary links to extant species. We used mass spectrometry to obtain protein sequences from bones of a 160,000- to 600,000-year-old extinct mastodon (Mammut americanum) and a 68-million-year-old dinosaur (Tyrannosaurus rex). The presence of T. rex sequences indicates that their peptide bonds were remarkably stable. Mass spectrometry can thus be used to determine unique sequences from ancient organisms from peptide fragmentation patterns, a valuable tool to study the evolution and adaptation of ancient taxa from which genomic sequences are unlikely to be obtained.

Lower Cretaceous fossils from central Niger document the succession of sauropod dinosaurs on Africa as it drifted into geographic isolation. A new broad-toothed genus of Neocomian age ( approximately 135 million years ago) shows few of the specializations of other Cretaceous sauropods. A new small-bodied sauropod of Aptian-Albian age ( approximately 110 million years ago), in contrast, reveals the highly modified cranial form of rebbachisaurid diplodocoids. Rates of skeletal change in sauropods and other major groups of dinosaurs are estimated quantitatively and shown to be highly variable.

Twelve different bones from the skeleton of the holotype specimen of the hadrosaurian dinosaur Hypacrosaurus stebingeri were thin-sectioned to evaluate the significance of lines of arrested growth (LAGs) in age assessments. The presence of an external fundamental system (EFS) at the external surface of the cortex and mature epiphyses indicate that the Hypacrosaurus specimen had reached adulthood and growth had slowed considerably from earlier stages. The number of LAGs varied from none in the pedal phalanx to as many as eight in the tibia and femur. Most elements had experienced considerable Haversian reconstruction that had most likely obliterated many LAGs. The tibia was found to have experienced the least amount of reconstruction, but was still not optimal for skeletochronology because the LAGs were difficult to count near the periosteal surface. Additionally, the numbers of LAGs within the EFS vary considerably around the circumference of a single element and among elements. Counting LAGs from a single bone to assess skeletochronology appears to be unreliable, particularly when a fundamental system exists. Because LAGs are plesiomorphic for tetrapods, and because they are present in over a dozen orders of mammals, they have no particular physiological meaning that can be generalized to particular amniote groups without independent physiological evidence. Descriptions of dinosaur physiology as “intermediate” between the physiology of living reptiles and that of living birds and mammals may or may not be valid, but cannot be based reliably on the presence of LAGs.

Current and future cost and performance data for electricity generating technologies, including both renewable and conventional technologies.

Molecular preservation in non-avian dinosaurs is controversial. We present multiple lines of evidence that endogenous proteinaceous material is preserved in bone fragments and soft tissues from an 80-million-year-old Campanian hadrosaur, Brachylophosaurus canadensis [Museum of the Rockies (MOR) 2598]. Microstructural and immunological data are consistent with preservation of multiple bone matrix and vessel proteins, and phylogenetic analyses of Brachylophosaurus collagen sequenced by mass spectrometry robustly support the bird-dinosaur clade, consistent with an endogenous source for these collagen peptides. These data complement earlier results from Tyrannosaurus rex (MOR 1125) and confirm that molecular preservation in Cretaceous dinosaurs is not a unique event.

ABSTRACT Histological evidence of the bones of pterosaurs and dinosaurs indicates that the typically large forms of these groups grew at rates more comparable to those of birds and mammals than to those of other living reptiles. However, Scutellosaurus, a small, bipedal, basal thyreophoran ornithischian dinosaur of the Early Jurassic, shows histological features in its skeletal tissues that suggest relatively lower growth rates than in those of larger dinosaurs. In these respects Scutellosaurus, like other small dinosaurs such as Orodromeus and some basal birds, is more like young, rapidly growing crocodiles than larger, more derived ornithischians (hadrosaurs) and all saurischians (sauropods and theropods). Similar patterns can be seen in small, mostly basal pterosaurs such as Eudimorphodon and Rhamphorhynchus. However, superficial similarities to crocodile bone growth belie some important differences, which are most usefully interpreted in phylogenetic and ontogenetic contexts. Large size evolved secondarily in several dinosaurian and pterosaurian lineages. We hypothesize that this larger size was made possible by rapid growth strategies that are reflected by characteristic highly vascularized fibro-lamellar bone tissues that comprise most of the cortex. Dinosaurs and pterosaurs, like other tetrapodes, generally grew more quickly in early stages and more slowly as growth neared completion. As in other vertebrate groups, taxa of small adult size may have grown at lower rates or for shorter durations than larger taxa did. Phylogenetic patterns suggest that by themselves, the low vascularity and inferred low growth rates seen in small dinosaurs and pterosaurs are not good indicators of thermometabolic regime, because they are correlated so strongly with size. They may reflect mechanical exigencies of small size rather than especially lower growth rates, tied to the process of deposition of particular kinds of bone tissues. The evolution of life history strategies in dinosaurs and pterosaurs, as they relate to rates of growth and adult body sizes, will be better understood as more complete histological studies place these data into phylogenetic and ontogenetic contexts.

We performed multiple analyses of Tyrannosaurus rex (specimen MOR 1125) fibrous cortical and medullary tissues remaining after demineralization. The results indicate that collagen I, the main organic component of bone, has been preserved in low concentrations in these tissues. The findings were independently confirmed by mass spectrometry. We propose a possible chemical pathway that may contribute to this preservation. The presence of endogenous protein in dinosaur bone may validate hypotheses about evolutionary relationships, rates, and patterns of molecular change and degradation, as well as the chemical stability of molecules over time.

Histologic studies of embryonic and perinatal longbones of living birds, non-avian dinosaurs, and other reptiles show a strong phylogenetic signal in the distribution of tissues and patterns of vascularization in both the shafts and the bone ends. The embryonic bones of basal archosaurs and other reptiles have thin-walled cortices and large marrow cavities that are sometimes subdivided by erosion rooms in early stages of growth. The cortices of basal reptiles are poorly vascularized, and osteocyte lacunae are common but randomly organized. Additionally, there is no evidence of fibrolamellar tissue organization around the vascular spaces. Compared with turtles, basal archosaurs show an increase in vascularization, better organized osteocytes, and some fibrolamellar tissue organization. In dinosaurs, including birds, vascularization is greater than in basal archosaurs, as is cortical thickness, and the osteocyte lacunae are more abundant and less randomly organized. Fibrolamellar tissues are evident around vascular canals and form organized primary osteons in older perinates and juveniles. Metaphyseal (“epiphyseal”) morphology varies with the acquisition of new features in derived groups. The cartilage cone, persistent through the Reptilia (crown-group reptiles, including birds), is completely calcified in ornithischian dinosaurs before it is eroded by marrow processes; cartilage canals, absent in basal archosaurs, are present in Dinosauria; a thickened calcified hypertrophy zone in Dinosauria indicates an acceleration of longitudinal bone growth. Variations in this set of histological synapomorphies overlap between birds and non-avian dinosaurs. In birds, these variations are strongly correlated with life-history strategies. This overlap, plus independent evidence from nesting sites, reinforces the hypothesis that variations in bone growth strategies in Mesozoic dinosaurs reflect different life-history strategies, including nesting behavior of neonates and parental care.

Most biological nitrogen fixation (BNF) results from the activity of the molybdenum nitrogenase (Mo-nitrogenase, Nif), an oxygen-sensitive metalloenzyme complex found in all known diazotrophs. Two alternative forms of nitrogenase, the vanadium nitrogenase (V-nitrogenase, Vnf) and the iron-only nitrogenase (Fe-only nitrogenase, Anf) have also been identified in the genome of some organisms that encode for Nif. It has been suggested that alternative nitrogenases were responsible for N2-fixation on early Earth because oceans were depleted of bioavailable Mo. Results of recent phylogenetic- and structure-based studies suggest, however, that such an evolutionary path is unlikely, and favor a new model for a stepwise evolution of nitrogenase where the V-nitrogenase and the Fe-only nitrogenase are not the ancestor of the Mo-nitrogenase. Rather, Mo-nitrogenase emerged within the methanogenic archaea and then gave rise to the alternative forms suggesting they arose later in response to the availability of fixed N2 and local environmental factors that influenced metal availability. This review summarizes the current state of knowledge on (1) the biochemistry of these complex systems highlighting the common and specific structural features and catalytic activities of the enzymes, (2) the recent progress in defining the discrete set of genes associated to N2-fixation and the regulatory features that coordinate the differential expression of genes in response to metal availability, and (3) the diverse taxonomic and phylogenic distribution of nitrogenase enzymes and the evolutionary history of BNF from the perspective of metal content and metal availability.

BACKGROUND: Extended neoteny and late stage allometric growth increase morphological disparity between growth stages in at least some dinosaurs. Coupled with relatively low dinosaur density in the Upper Cretaceous of North America, ontogenetic transformational representatives are often difficult to distinguish. For example, many hadrosaurids previously reported to represent relatively small lambeosaurine species were demonstrated to be juveniles of the larger taxa. Marginocephalians (pachycephalosaurids + ceratopsids) undergo comparable and extreme cranial morphological change during ontogeny. METHODOLOGY/PRINCIPAL FINDINGS: Cranial histology, morphology and computer tomography reveal patterns of internal skull development that show the purported diagnostic characters for the pachycephalosaurids Dracorex hogwartsia and Stygimoloch spinifer are ontogenetically derived features. Coronal histological sections of the frontoparietal dome of an adult Pachycephalosaurus wyomingensis reveal a dense structure composed of metaplastic bone with a variety of extremely fibrous and acellular tissue. Coronal histological sections and computer tomography of a skull and frontoparietal dome of Stygimoloch spinifer reveal an open intrafrontal suture indicative of a subadult stage of development. These dinosaurs employed metaplasia to rapidly grow and change the size and shape of their horns, cranial ornaments and frontoparietal domes, resulting in extreme cranial alterations during late stages of growth. We propose that Dracorex hogwartsia, Stygimoloch spinifer and Pachycephalosaurus wyomingensis are the same taxon and represent an ontogenetic series united by shared morphology and increasing skull length. CONCLUSIONS/SIGNIFICANCE: Dracorex hogwartsia (juvenile) and Stygimoloch spinifer (subadult) are reinterpreted as younger growth stages of Pachycephalosaurus wyomingensis (adult). This synonymy reduces the number of pachycephalosaurid taxa from the Upper Cretaceous of North America and demonstrates the importance of cranial ontogeny in evaluating dinosaur diversity and taxonomy. These growth stages reflect a continuum rather than specific developmental steps defined by "known" terminal morphologies.

![Figure][1] Deccan plateau basalts. Lava from Deccan volcanism formed distinct layering. CREDIT: GSFC/NASA In the Review “The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene boundary” (P. Schulte et al. , 5 March, p. [1214][2]), the terminal Cretaceous

Soft tissues are preserved within hindlimb elements of Tyrannosaurus rex (Museum of the Rockies specimen 1125). Removal of the mineral phase reveals transparent, flexible, hollow blood vessels containing small round microstructures that can be expressed from the vessels into solution. Some regions of the demineralized bone matrix are highly fibrous, and the matrix possesses elasticity and resilience. Three populations of microstructures have cell-like morphology. Thus, some dinosaurian soft tissues may retain some of their original flexibility, elasticity, and resilience.

An external fundamental system (EFS) is a form of bone microstructure present in the outermost cortex of long bones in animals that have attained skeletal maturity. It indicates an effective cessation of any significant periosteal growth (i.e., growth in circumference or girth). Although an EFS has been noted in several reptile taxa, the idea that reptiles grow continually throughout their lives remains popular. Examination of femoral bone microstructure from captive American Alligators (Alligator mississippiensis) reveals parallel-fibered tissue terminating periosteally in an EFS, thus confirming determinate growth in another reptile taxon. The results of this study have several important implications for both modern and fossil tetrapods: first, because many birds, nonavian dinosaurs, pterosaurs, and basal pseudosuchians all produce an EFS, it can be concluded that determinate growth is a shared characteristic of Archosauria; second, because the captive alligators were not senescent, an EFS should not be associated with “old age” when interpreting growth histories of extinct animals; third, if no EFS is present, this should not immediately suggest indeterminate growth but rather that skeletal maturity was not attained prior to death. In addition, this study highlights the need for more osteohistological studies to establish exactly how widespread determinate growth is within both extinct and extant members of Sauropsida, because this form of growth may be the rule rather than the exception.

Tyrannosaurus rex is the most commonly found North American latest Cretaceous theropod, but until the 1980s only five specimens had been discovered, and no more than six have received a full description. Consequently there has been little information on how old Tyrannosaurus specimens were at maturity or death. Histological analysis of seven individuals provided, for the first time, an opportunity to assess the age represented by the bone cortex, to estimate the average individual age of these skeletons, to determine whether they represented fully grown individuals, and to predict their individual longevity. Though a range of ages (15-25 years) was found for the specimens studied, the seven individuals demonstrate that T. rex reached effectively full size in less than 20 years. The growth rate of T. rex was comparable to that of the African elephant, which has a similar mass and time to maturity. Some of the known specimens of T. rex did not quite reach full size; others do not seem to have survived long after achieving it.

Photophysical investigations of the canonical nucleobases that make up DNA and RNA during the past 15 years have revealed that excited states formed by the absorption of UV radiation decay with subpicosecond lifetimes (i.e., <10(-12) s). Ultrashort lifetimes are a general property of absorbing sunscreen molecules, suggesting that the nucleobases are molecular survivors of a harsh UV environment. Encoding the genome using photostable building blocks is an elegant solution to the threat of photochemical damage. Ultrafast excited-state deactivation strongly supports the hypothesis that UV radiation played a major role in shaping molecular inventories on the early Earth before the emergence of life and the subsequent development of a protective ozone shield. Here, we review the general physical and chemical principles that underlie the photostability, or "UV hardiness", of modern nucleic acids and discuss the possible implications of these findings for prebiotic chemical evolution. In RNA and DNA strands, much longer-lived excited states are observed, which at first glance appear to increase the risk of photochemistry. It is proposed that the dramatically different photoproperties that emerge from assemblies of photostable building blocks may explain the transition from a world of molecular survival to a world in which energy-rich excited electronic states were eventually tamed for biological purposes such as energy transduction, signaling, and repair of the genetic machinery.

Unambiguous indicators of gender in dinosaurs are usually lost during fossilization, along with other aspects of soft tissue anatomy. We report the presence of endosteally derived bone tissues lining the interior marrow cavities of portions of Tyrannosaurus rex (Museum of the Rockies specimen number 1125) hindlimb elements, and we hypothesize that these tissues are homologous to specialized avian tissues known as medullary bone. Because medullary bone is unique to female birds, its discovery in extinct dinosaurs solidifies the link between dinosaurs and birds, suggests similar reproductive strategies, and provides an objective means of gender differentiation in dinosaurs.

Abstract Elongate and asymmetric eggs of the oospecies Prismatoolithus levis occur regularly in the Upper Cretaceous Two Medicine Formation of western Montana. These eggs had previously been assigned to the ornithischian Orodromeus makelai, for both juvenile and adult remains are typically associated with these eggs. Reexamination of the embryos shows them to exhibit at least 24 apomorphies of the clades Dinosauria, Theropoda and Paraves. The embryos also display a pneumatic quadrate, closely placed basal tubera, a high tooth count, a metatarsal II much narrower than IV and a strongly constricted metatarsal III, all possible synapomorphies of the Troodontidae. Presence of large basal tubera and a broadly rounded anterior border of the maxillary fenestra permit assignment to Troodon formosus. Most but not all bones appear ossified, suggesting a developmental level comparable to stages 35–38 of avian embryos and a time approaching hatching. Embryos show a consistent level of development from one egg to another indicating synchronous hatching of the clutch. Embryonic Troodon exhibit long distal segments and radically different hindlimb proportions in comparison to adults. Orodromeus and other small vertebrate remains associated with Troodon egg horizons may represent prey of the adults during egg-laying and brooding. Troodon eggs show several aspects either shared or convergent with some birds, and further demonstrate the close relationship of Troodontidae and Aves. These features include: asymmetric egg form, non-branching angusticanaliculate pores, distinct structural differentiation of the mammillary and overlying prismatic layer, barrel-shaped mammillary cones with a blocky calcite cleavage, and prismatic structure visible throughout the second structural layer.