It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.

Palaeobiodiversity analysis underpins macroevolutionary investigations, allowing identification of mass extinctions and adaptive radiations. However, recent large-scale studies on marine invertebrates indicate that geological factors play a central role in moulding the shape of diversity curves and imply that many features of such curves represent sampling artefacts, rather than genuine evolutionary events. In order to test whether similar biases affect diversity estimates for terrestrial taxa, we compiled genus-richness estimates for three Mesozoic dinosaur clades (Ornithischia, Sauropodomorpha and Theropoda). Linear models of expected genus richness were constructed for each clade, using the number of dinosaur-bearing formations available through time as a proxy for the amount of fossiliferous rock outcrop. Modelled diversity estimates were then compared with observed patterns. Strong statistically robust correlations demonstrate that almost all aspects of ornithischian and theropod diversity curves can be explained by geological megabiases, whereas the sauropodomorph record diverges from modelled predictions and may be a stronger contender for identifying evolutionary signals. In contrast to other recent studies, we identify a marked decline in dinosaur genus richness during the closing stages of the Cretaceous Period, indicating that the clade decreased in diversity for several million years prior to the final extinction of non-avian dinosaurs at the Cretaceous-Palaeocene boundary.

Palaeodiversity curves are constructed from counts of fossils collected at outcrop and thus potentially biased by variation in the rock record, specifically by the amount of sedimentary rock representative of different time intervals that has been preserved at outcrop. To investigate how much of a problem this poses we have compiled a highresolution record of marine rock outcrop area in Western Europe for the Phanerozoic and use this to generate a model that predicts the sampled diversity curve. We find that we can predict with high accuracy the variance of the marine genus diversity curve (itself dominated by European taxa) from rock outcrop data and a three-step model of diversity that tracks supercontinent fragmentation, coalescence and fragmentation. The size and position of two of the five major mass extinction spikes are largely predicted by rock outcrop data. We conclude that the long-term trends in taxonomic diversity and the end-Cretaceous extinction are not the result of rock area bias, but cannot rule out that rock outcrop area bias explains many of the short-term rises and falls in sampled diversity that palaeontologists have previously sought to explain biologically.

Introduction Cerebral small-vessel disease has been implicated in the development of Alzheimer's disease (AD). The retinal microvasculature enables the noninvasive visualization and evaluation of the systemic microcirculation. We evaluated retinal microvascular parameters in a case-control study of AD patients and cognitively normal controls. Methods Retinal images were computationally analyzed and quantitative retinal parameters (caliber, fractal dimension, tortuosity, and bifurcation) measured. Regression models were used to compute odds ratios (OR) and confidence intervals (CI) for AD with adjustment for confounders. Results Retinal images were available in 213 AD participants and 294 cognitively normal controls. Persons with lower venular fractal dimension (OR per standard deviation [SD] increase, 0.77 [CI: 0.62–0.97]) and lower arteriolar tortuosity (OR per SD increase, 0.78 [CI: 0.63–0.97]) were more likely to have AD after appropriate adjustment. Discussion Patients with AD have a sparser retinal microvascular network and retinal microvascular variation may represent similar pathophysiological events within the cerebral microvasculature of patients with AD.