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In the lead-up to the Cretaceous/Paleogene mass extinction, dinosaur diversity is argued to have been either in long-term decline, or thriving until their sudden demise. The latest Cretaceous (Campanian–Maastrichtian [83–66 Ma]) of North America provides the best record to address this debate, but even here diversity reconstructions are biased by uneven sampling. Here we combine fossil occurrences with climatic and environmental modelling to quantify latest Cretaceous North American dinosaur habitat. Ecological niche modelling shows a Campanian-to-Maastrichtian habitability decrease in areas with present-day rock-outcrop. However, a continent-wide projection demonstrates habitat stability, or even a Campanian-to-Maastrichtian increase, that is not preserved. This reduction of the spatial sampling window resulted from formation of the proto-Rocky Mountains and sea-level regression. We suggest that Maastrichtian North American dinosaur diversity is therefore likely to be underestimated, with the apparent decline a product of sampling bias, and not due to a climatically-driven decrease in habitability as previously hypothesised.
The Late Jurassic to Early Cretaceous interval represents a time of environmental upheaval and cataclysmic events, combined with disruptions to terrestrial and marine ecosystems. Historically, the Jurassic/Cretaceous (J/K) boundary was classified as one of eight mass extinctions. However, more recent research has largely overturned this view, revealing a much more complex pattern of biotic and abiotic dynamics than has previously been appreciated. Here, we present a synthesis of our current knowledge of Late Jurassic–Early Cretaceous events, focusing particularly on events closest to the J/K boundary. We find evidence for a combination of short-term catastrophic events, large-scale tectonic processes and environmental perturbations, and major clade interactions that led to a seemingly dramatic faunal and ecological turnover in both the marine and terrestrial realms. This is coupled with a great reduction in global biodiversity which might in part be explained by poor sampling. Very few groups appear to have been entirely resilient to this J/K boundary ‘event’, which hints at a ‘cascade model’ of ecosystem changes driving faunal dynamics. Within terrestrial ecosystems, larger, more-specialised organisms, such as saurischian dinosaurs, appear to have suffered the most. Medium-sized tetanuran theropods declined, and were replaced by larger-bodied groups, and basal eusauropods were replaced by neosauropod faunas. The ascent of paravian theropods is emphasised by escalated competition with contemporary pterosaur groups, culminating in the explosive radiation of birds, although the timing of this is obfuscated by biases in sampling. Smaller, more ecologically diverse terrestrial non-archosaurs, such as lissamphibians and mammaliaforms, were comparatively resilient to extinctions, instead documenting the origination of many extant groups around the J/K boundary. In the marine realm, extinctions were focused on low-latitude, shallow marine shel
Although Stegosaurus is one of the most iconic dinosaurs, well-preservedfossils are rare and as a consequence there is still much that remains unknownabout the taxon. A new, exceptionally complete individual affords theopportunity to describe the anatomy of Stegosaurus in detail for the first time inover a century, and enables additional comparisons with other stegosauriandinosaurs. The new specimen is from the Red Canyon Ranch Quarry, near ShellWyoming, and appears to have been so well preserved because it was buriedrapidly in a pond or body of standing water immediately after death. The quarryis probably located in the middle part of the Morrison Formation, which isbelieved to be Tithonian in age in this area. The specimen is referable toStegosaurus stenops based on the possession of an edentulous anterior portion ofthe dentary and elevated postzygapophyses on the cervical vertebrae. Newinformation provided by the specimen concerns the morphology of thevertebrae, the iliosacral block and dermal armor. Several aspects of itsmorphology indicate the individual was not fully skeletally mature at the time ofdeath, corroborating a previous histological study.
In a number of recent studies we used computer modeling to investigate the evolution of muscle leverage (moment arms) and function in extant and extinct archosaur lineages (crocodilians, dinosaurs including birds and pterosaurs). These studies sought to quantify the level of disparity and convergence in muscle moment arms during the evolution of bipedal and quadrupedal posture in various independent archosaur lineages, and in doing so further our understanding of changes in anatomy, locomotion and ecology during the group's >250 million year evolutionary history. Subsequent work by others has led us to re-evaluate our models, which revealed a methodological error that impacted on the results obtained from the abduction-adduction and long-axis rotation moment arms in our published studies. In this paper we present corrected abduction-adduction and long axis rotation moment arms for all our models, and evaluate the impact of this new data on the conclusions of our previous studies. We find that, in general, our newly corrected data differed only slightly from that previously published, with very few qualitative changes in muscle moments (e.g., muscles originally identified as abductors remained abductors). As a result the majority of our previous conclusions regarding the functional evolution of key muscles in these archosaur groups are upheld.
The Blue Lias Formation at Lyme Regis (Dorset, UK) includes an exceptional pavement of abundant large ammonites that accumulated during a period of profound sedimentary condensation. Ammonites were originally composed of aragonite, an unstable polymorph of calcium carbonate, and such fossils are typically prone to dissolution; the occurrence of a rich association of aragonitic shells in a condensed bed is highly unusual. Aragonite dissolution occurs when pore-water pH is reduced by the oxidization of hydrogen sulphide close to the sediment-water interface. Evidence suggests that, in this case, the oxygen concentrations in the overlying water column were low during deposition. This inhibited the oxidation of sulphides and the associated lowering of pH, allowing aragonite to survive long enough for the shell to be neomorphosed to calcite. The loss of aragonite impacts upon estimates of past biodiversity and carbonate accumulation rates. The preservational model presented here implies that diagenetic loss of aragonite will be greatest in those areas where dysoxic-anoxic sediment lies beneath an oxic waterbody but least where the sediment and overlying water are oxygen depleted. Unfortunately, this implies that preservational bias through aragonite loss will be greatest in those biotopes which are typically most diverse and least where biodiversity is lowest due to oxygen restriction.
Exceptionally preserved organic remains are known throughout the vertebrate fossil record, and recently, evidence has emerged that such soft tissue might contain original components. We examined samples from eight Cretaceous dinosaur bones using nano-analytical techniques; the bones are not exceptionally preserved and show no external indication of soft tissue. In one sample, we observe structures consistent with endogenous collagen fibre remains displaying ~67 nm banding, indicating the possible preservation of the original quaternary structure. Using ToF-SIMS, we identify amino-acid fragments typical of collagen fibrils. Furthermore, we observe structures consistent with putative erythrocyte remains that exhibit mass spectra similar to emu whole blood. Using advanced material characterization approaches, we find that these putative biological structures can be well preserved over geological timescales, and their preservation is more common than previously thought. The preservation of protein over geological timescales offers the opportunity to investigate relationships, physiology and behaviour of long extinct animals.
Estimates of body mass often represent the founding assumption on which biomechanicaland macroevolutionary hypotheses are based. Recently, a scalingequation was applied to a newly discovered titanosaurian sauropod dinosaur(Dreadnoughtus), yielding a 59 300 kg body mass estimate for this animal.Herein, we use a modelling approach to examine the plausibility of this massestimate for Dreadnoughtus. We find that 59 300 kg for Dreadnoughtus ishighly implausible and demonstrate that masses above 40 000 kg requirehigh body densities and expansions of soft tissue volume outside the skeletonseveral times greater than found in living quadrupedal mammals. Similarresults from a small sample of other archosaurs suggests that lower-end massestimates derived from scaling equations are most plausible for Dreadnoughtus,based on existing volumetric and density data from extant animals. Althoughvolumetric models appear to more tightly constrain dinosaur body mass, thereremains a clear need to further support these models with more exhaustive datafrom living animals. The relative and absolute discrepancies in mass predictionsbetween volumetric models and scaling equations also indicate aneed to systematically compare predictions across a wide size and taxonomicrange to better inform studies of dinosaur body size.
Pentastomids (tongue worms) are worm-like arthropods known today from ∼140 species . All but four are parasitic on vertebrates. Their life cycle typically involves larval development in an intermediate host followed by maturation in the respiratory tract of a definitive terrestrial host. Fossil pentastomids are exceedingly rare and are known only from isolated juveniles [2-6]. The identity of the possible hosts of fossil pentastomids and the origin of their lifestyle have generated much debate. A new, exceptionally preserved species, described based on adults from 425-million-year-old marine rocks, is the only known fossil pentastomid associated with a host, in this case a species of ostracod crustacean. The pentastomids are preserved near eggs within the ostracod and also, uniquely for any fossil or living pentastomid, are attached externally to the host. This discovery affirms the origin of pentastomids as ectoparasitic on marine invertebrates. The terrestrialization of pentastomids may have occurred in parallel with the vertebrate invasion of land.
Body mass is a key biological variable, but difficult to assess from fossils.Various techniques exist for estimating body mass from skeletal parameters,but few studies have compared outputs from different methods. Here, weapply several mass estimation methods to an exceptionally complete skeletonof the dinosaur Stegosaurus. Applying a volumetric convex-hullingtechnique to a digital model of Stegosaurus, we estimate a mass of 1560 kg(95% prediction interval 1082–2256 kg) for this individual. By contrast,bivariate equations based on limb dimensions predict values between 2355and 3751 kg and require implausible amounts of soft tissue and/or highbody densities. When corrected for ontogenetic scaling, however, volumetricand linear equations are brought into close agreement. Our results raise concernsregarding the application of predictive equations to extinct taxa withno living analogues in terms of overall morphology and highlight the sensitivityof bivariate predictive equations to the ontogenetic status of thespecimen. We emphasize the significance of rare, complete fossil skeletonsin validating widely applied mass estimation equations based on incompleteskeletal material and stress the importance of accurately determiningspecimen age prior to further analyses.
Large-scale extraction of power from tidal streams within the Pentland Firth is expected to be underway in the near future. The Inner Sound of Stroma in particular has attracted significant commercial interest. To understand potential environmental impacts of the installation of a tidal turbine array a case study based upon the Inner Sound is considered. A numerical computational fluid dynamics model, Fluidity, is used to conduct a series of depth-averaged simulations to investigate velocity and bed shear stress changes due to the presence of idealised tidal turbine arrays. The number of turbines is increased from zero to 400. It is found that arrays in excess of 85 turbines have the potential to affect bed shear stress distributions in such a way that the most favourable sites for sediment accumulation migrate from the edges of the Inner Sound towards its centre. Deposits of fine gravel and coarse sand are indicated to occur within arrays of greater than 240 turbines with removal of existing deposits in the shallower channel margins also possible. The effects of the turbine array may be seen several kilometres from the site which has implications not only on sediment accumulation, but also on the benthic fauna.
The exceptionally rare transition to quadrupedalismfrom bipedal ancestors occurred on three independent occasionsin ornithischian dinosaurs. The possible driving forcesbehind these transitions remain elusive, but several hypotheses—includingthe development of dermal armour and theexpansion of head size and cranial ornamentation—have beenproposed to account for this major shift in stance. Wemodelled the position of the centre of mass (CoM) in severalexemplar ornithischian taxa and demonstrate that the anteriorshifts in CoM position associated with the development of anenlarged skull ornamented with horns and frills for display/defence may have been one of the drivers promoting ceratopsianquadrupedality. A posterior shift in CoM position coincidentwith the development of extensive dermal armour inthyreophorans demonstrates this cannot have been a primarycausative mechanism for quadrupedality in this clade.Quadrupedalism developed in response to different selectivepressures in each ornithischian lineage, indicating differentevolutionary pathways to convergent quadrupedalmorphology.
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