Early dinosaurs showed rapid evolutionary rates, which were sustained on the line leading to birds. Maintenance of evolvability in key lineages might explain the uneven distribution of trait diversity among groups of animal species.

The fossil record of crocodylians and their relatives (pseudosuchians) reveals a rich evolutionary history, prompting questions about causes of long-term decline to their present-day low biodiversity. We analyse climatic drivers of subsampled pseudosuchian biodiversity over their 250 million year history, using a comprehensive new data set. Biodiversity and environmental changes correlate strongly, with long-term decline of terrestrial taxa driven by decreasing temperatures in northern temperate regions, and biodiversity decreases at lower latitudes matching patterns of increasing aridification. However, there is no relationship between temperature and biodiversity for marine pseudosuchians, with sea-level change and post-extinction opportunism demonstrated to be more important drivers. A ‘modern-type' latitudinal biodiversity gradient might have existed throughout pseudosuchian history, and range expansion towards the poles occurred during warm intervals. Although their fossil record suggests that current global warming might promote long-term increases in crocodylian biodiversity and geographic range, the 'balancing forces' of anthropogenic environmental degradation complicate future predictions.

Today, biodiversity decreases from equatorial to polar regions. This is a fundamental pattern governing the distribution of extant organisms, the understanding of which is critical to predicting climatically driven biodiversity loss. However, its causes remain unresolved. The fossil record offers a unique perspective on the evolution of this latitudinal biodiversity gradient (LBG), providing a dynamic system in which to explore spatiotemporal diversity fluctuations. Deep-time studies indicate that a tropical peak and poleward decline in species diversity has not been a persistent pattern throughout the Phanerozoic, but is restricted to intervals of the Palaeozoic and the past 30 million years. A tropical peak might characterise cold icehouse climatic regimes, whereas warmer greenhouse regimes display temperate diversity peaks or flattened gradients.

Titanosauriforms represent a diverse and globally distributed clade of neosauropod dinosaurs, but their inter‐relationships remain poorly understood. Here we redescribe Lusotitan atalaiensis from the Late Jurassic Lourinhã Formation of Portugal, a taxon previously referred to Brachiosaurus. The lectotype includes cervical, dorsal, and caudal vertebrae, and elements from the forelimb, hindlimb, and pelvic girdle. Lusotitan is a valid taxon and can be diagnosed by six autapomorphies, including the presence of elongate postzygapophyses that project well beyond the posterior margin of the neural arch in anterior‐to‐middle caudal vertebrae. A new phylogenetic analysis, focused on elucidating the evolutionary relationships of basal titanosauriforms, is presented, comprising 63 taxa scored for 279 characters. Many of these characters are heavily revised or novel to our study, and a number of ingroup taxa have never previously been incorporated into a phylogenetic analysis. We treated quantitative characters as discrete and continuous data in two parallel analyses, and explored the effect of implied weighting. Although we recovered monophyletic brachiosaurid and somphospondylan sister clades within Titanosauriformes, their compositions were affected by alternative treatments of quantitative data and, especially, by the weighting of such data. This suggests that the treatment of quantitative data is important and the wrong decisions might lead to incorrect tree topologies. In particular, the diversity of Titanosauria was greatly increased by the use of implied weights. Our results support the generic separation of the contemporaneous taxa Brachiosaurus, Giraffatitan, and Lusotitan, with the latter recovered as either a brachiosaurid or the sister taxon to Titanosauriformes. Although Janenschia was recovered as a basal macronarian, outside Titanosauria, the sympatric Australodocus provides body fossil evidence for the pre‐Cretaceous origin of titanosaurs. We recovered evidence for a sauropod with close affinities to the Chinese taxon Mamenchisaurus in the Late Jurassic Tendaguru beds of Africa, and present new information demonstrating the wider distribution of caudal pneumaticity within Titanosauria. The earliest known titanosauriform body fossils are from the late Oxfordian (Late Jurassic), although trackway evidence indicates a Middle Jurassic origin. Diversity increased throughout the Late Jurassic, and titanosauriforms did not undergo a severe extinction across the Jurassic/Cretaceous boundary, in contrast to diplodocids and non‐neosauropods. Titanosauriform diversity increased in the Barremian and Aptian–Albian as a result of radiations of derived somphospondylans and lithostrotians, respectively, but there was a severe drop (up to 40%) in species numbers at, or near, the Albian/Cenomanian boundary, representing a faunal turnover whereby basal titanosauriforms were replaced by derived titanosaurs, although this transition occurred in a spatiotemporally staggered fashion. © 2013 The Linnean Society of London

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Abstract.-Despite increasing concerns about the effect of sampling biases on our reading of the fossil record, few studies have considered the completeness of the fossil remains themselves, and those that have tend to apply non-quantitative measures of preservation quality. Here we outline two new types of metric for quantifying the completeness of the fossil remains of taxa through time, using sauropodomorph dinosaurs as a case study. The ''Skeletal Completeness Metric'' divides the skeleton up into percentages based on the amount of bone for each region, whereas the ''Character Completeness Metric'' is based on the number of characters that can be scored for each skeletal element in phylogenetic analyses. For both metrics we calculated the completeness of the most complete individual and of the type specimen. We also calculated how well the taxon as a whole is known from its remains. We then plotted these results against both geological and historical time, and compared curves of the former with fluctuations in sauropodomorph diversity, sea level, and sedimentary rock outcrop area. Completeness through the Mesozoic shows a number of peaks and troughs; the Early Jurassic (Hettangian-Sinemurian) is the interval with highest completeness, whereas the mid-to-Late Cretaceous has completeness levels that are consistently lower than the rest of the Mesozoic. Completeness shows no relationship to rock outcrop area, but it is negatively correlated with sea level during the Jurassic-Early Cretaceous and correlated with diversity in the Cretaceous. Completeness of sauropodomorph type specimens has improved from 1830 to the present, supporting the conclusions of other recent studies. However, when this time interval is partitioned, we find no trend for an increase in completeness from the 1990s onward. Moreover, the 2000s represent one of the poorest decades in terms of average type specimen completeness. These results highlight the need for quantitative methods when assessing fossil record quality through geological time or when drawing conclusions about historical trends in the completeness of taxa. The new metrics may also prove useful as sampling proxies in diversity studies.

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The accurate reconstruction of palaeobiodiversity patterns is central to a detailed understanding of the macroevolutionary history of a group of organisms. However, there is increasing evidence that diversity patterns observed directly from the fossil record are strongly influenced by fluctuations in the quality of our sampling of the rock record; thus, any patterns we see may reflect sampling biases, rather than genuine biological signals. Previous dinosaur diversity studies have suggested that fluctuations in sauropodomorph palaeobiodiversity reflect genuine biological signals, in comparison to theropods and ornithischians whose diversity seems to be largely controlled by the rock record. Most previous diversity analyses that have attempted to take into account the effects of sampling biases have used only a single method or proxy: here we use a number of techniques in order to elucidate diversity. A global database of all known sauropodomorph body fossil occurrences (2024) was constructed. A taxic diversity curve for all valid sauropodomorph genera was extracted from this database and compared statistically with several sampling proxies (rock outcrop area and dinosaur-bearing formations and collections), each of which captures a different aspect of fossil record sampling. Phylogenetic diversity estimates, residuals and sample-based rarefaction (including the first attempt to capture 'cryptic' diversity in dinosaurs) were implemented to investigate further the effects of sampling. After 'removal' of biases, sauropodomorph diversity appears to be genuinely high in the Norian, Pliensbachian-Toarcian, Bathonian-Callovian and Kimmeridgian-Tithonian (with a small peak in the Aptian), whereas low diversity levels are recorded for the Oxfordian and Berriasian-Barremian, with the Jurassic/Cretaceous boundary seemingly representing a real diversity trough. Observed diversity in the remaining Triassic-Jurassic stages appears to be largely driven by sampling effort. Late Cretaceous diversity is difficult to elucidate and it is possible that this interval remains relatively under-sampled. Despite its distortion by sampling biases, much of sauropodomorph palaeobiodiversity can be interpreted as a reflection of genuine biological signals, and fluctuations in sea level may account for some of these diversity patterns.