Paul Upchurch

Cranial design and function in a large theropod dinosaur

Finite element analysis (FEA) is used by industrial designers and biomechanicists to estimate the performance of engineered structures or human skeletal and soft tissues subjected to varying regimes of stress and strain. FEA is rarely applied to problems of biomechanical design in animals, despite its potential to inform structure–function analysis. Non-invasive techniques such as computed tomography scans can be used to generate accurate three-dimensional images of structures, such as skulls, which can form the basis of an accurate finite element model. Here we have applied this technique to the long skull of the large carnivorous theropod dinosaur Allosaurus fragilis. We have generated the most geometrically complete and complex FEA model of the skull of any extinct or extant organism and used this to test its mechanical properties and examine, in a quantitative way, long-held hypotheses concerning overall shape and function. The combination of a weak muscle-driven bite force, a very ‘light’ and ‘open’ skull architecture and unusually high cranial strength, suggests a very specific feeding behaviour for this animal. These results demonstrate simply the inherent potential of FEA for testing mechanical behaviour in fossils in ways that, until now, have been impossible.

An analysis of dinosaurian biogeography: evidence for the existence of vicariance and dispersal patterns caused by geological events

As the supercontinent Pangaea fragmented during the Mesozoic era, dinosaur faunas were divided into isolated populations living on separate continents. It has been predicted, therefore, that dinosaur distributions should display a branching (‘vicariance’) pattern that corresponds with the sequence and timing of continental break‐up. Several recent studies, however, minimize the importance of plate tectonics and instead suggest that dispersal and regional extinction were the main controls on dinosaur biogeography. Here, in order to test the vicariance hypothesis, we apply a cladistic biogeographical method to a large dataset on dinosaur relationships and distributions. We also introduce a methodological refinement termed ‘time‐slicing’, which is shown to be a key step in the detection of ancient biogeographical patterns. These analyses reveal biogeographical patterns that closely correlate with palaeogeography. The results provide the first statistically robust evidence that, from Middle Jurassic to mid‐Cretaceous times, tectonic events had a major role in determining where and when particular dinosaur groups flourished. The fact that evolutionary trees for extinct organisms preserve such distribution patterns opens up a new and fruitful direction for palaeobiogeographical research.

A revision of titanosaurus lydekker (dinosauria - sauropoda), the first dinosaur genus with a ‘gondwanan’ distribution

Synopsis Titanosaurs represent approximately one‐third of sauropod diversity and were geographically widespread throughout the Cretaceous, especially on southern continents. Titanosaurs evolved numerous appendicular synapomorphies that account for their specialised ‘wide‐gauge’ limb posture, which can be recognised in their trackways. The macronarian origin of titanosaurs is only recently agreed upon and aspects of their inter‐relationships remain poorly understood. Titanosauria is named for the poorly known genus Titanosaurus, which was coined by Lydekker in 1877 on the basis of a partial femur and two incomplete caudal vertebrae. Fourteen species have since been referred to Titanosaurus, which distribute the genus across Argentina, Europe, Madagascar, India and Laos, and throughout 60 million years of the Cretaceous. Despite its centrality to titanosaur systematics and biogeography, the genus Titanosaurus has never been revised. A re‐evaluation of all Titanosaurus species recognises as diagnostic only five. The type species T. indicus is invalid because it is based on ‘obsolescent’ characters ‐ once diagnostic features that have gained a broadertaxonomic distribution over time. Consequently, the genus Titanosaurus and its co‐ordinated rank‐taxa (e.g. Titanosaurinae, Titanosauridae, Titanosauroidea) must be abandoned. The unranked taxon Titanosauria, however, remains valid. A new phylogenetic taxonomy is proposed for Titanosauria that utilises nodes that have been judged stable by the most recent cladistic analyses. The early appearance of titanosaur ichnofossils (Middle Jurassic) and body fossils (Late Jurassic) precludes a vicariant origin for the group, but such a pattern cannot yet be ruled out for lower‐level taxa within Titanosauria.

Testing the effect of the rock record on diversity: a multidisciplinary approach to elucidating the generic richness of sauropodomorph dinosaurs through time

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.

Redescription and reassessment of the phylogenetic affinities of euhelopus zdanskyi (Dinosauria: Sauropoda) from the early cretaceous of China

Synopsis Euhelopus zdanskyi was the first dinosaur described from China. Both traditional and modern cladistic assessments have found support for an endemic clade of Chinese sauropods (Eu‐helopodidae) that originated during an interval of geographic isolation, but the monophyly of this clade has remained controversial. The phylogenetic affinity of the eponymous genus Euhelopus is central to this controversy, yet its anatomy has not been completely restudied since the original German‐language monograph in 1929. We jointly re‐examined the cranial and postcranial anatomy of the holotypic and referred materials of Euhelopus to provide a new diagnosis for the genus and to explore its phylogenetic affinities. Diagnostic features of Euhelopus include: postaxial cervical vertebrae that have variably developed epipophyses and more subtle “pre‐epipopophyses” below the prezygapophyses; cervical neural arches with an epipophyseal‐prezygapophyseal lamina separating two pneumatocoels; anterior cervical vertebrae with three costal spurs on the tuberculum and capitulum; divided middle presacral neural spines, which in anterior dorsal vertebrae bear a median tubercle that is as large or larger than the metapophyses; middle and posterior dorsal parapophyseal and diapophyseal laminae arranged in a “K” configuration; and presacral pneumaticity that extends into the ilium. Following this morphological study, we rescored Euhelopus for the two most comprehensive sauropod data matrices (Wilson 2002; Upchurch etal. 2004a), which previously yielded vastly different hypotheses for its relationships. Both matrices decisively demonstrate that Euhelopus is closely related to Titanosauria; traditional and cladistic claims that Euhelopus, Omeisaurus, Mamenchisaurus and Shunosaurus formed a monophyletic “Euhelopodidae” endemic to East Asia are not supported. These results suggest that there were at least two clades of very long‐necked sauropods in East Asia, occurring in the Middle Jurassic (i.e. Omeisaurus + Mamenchisaurus) and Early Cretaceous (e.g. Euhelopus, Erketu), with the latter group perhaps also occurring in Europe (Canudo et al. 2002). It is probable that the Euhelopus + Erketu lineage invaded East Asia from another part of Pangaea when isolation ended in the Early Cretaceous. The large number of basal titanosauriforms from East Asia has been interpreted to mean that this area may represent their centre of origin (You et al. 2003), but the titanosaur fossil record and phylogenetic studies indicate that the group probably originated prior to the Middle Jurassic and acquired a virtually global distribution before Pangaean fragmentation.

Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage

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.

Evolution of Herbivory in Terrestrial Vertebrates: The evolution of sauropod feeding mechanisms

Introduction Sauropods were gigantic, long-necked, herbivorous dinosaurs, which dominated many Jurassic and Cretaceous terrestrial faunas. First appearing in the fossil record during the Early Jurassic, they rapidly achieved a nearly global distribution, with apparent peaks in diversity and abundance in the Kimmeridgian, Hauterivian–Barremian, and Campanian–Maastrichtian (McIntosh 1990; Weishampel 1990; Hunt et al. 1994; Barrett 1998). Early discoveries of poorly preserved sauropod material were interpreted as the remains of marine crocodiles (Owen 1841, 1842). Better preserved specimens ( Cetiosaurus ) from the Middle Jurassic of Oxfordshire, however, allowed Phillips (1871:294) to recognize that these animals were terrestrial dinosaurs which probably ate plants. This discovery was soon overshadowed by spectacular material from the western United States (Cope 1877a, b; Marsh 1877a, b, 1878, 1879), prompting Marsh (1878) to create the new dinosaurian subgroup Sauropoda. The retracted nostrils in the skull of Diplodocus (Marsh 1884), and the gigantic size of these animals, led many workers to conclude that sauropods must have been aquatic (Cope 1878; Marsh 1883; Hatcher 1901; Hay 1908). This ‘aquatic’ hypothesis had an important effect on interpretations of sauropod feeding habits and mechanisms. If such gigantic animals were restricted to food available in or near bodies of water, they probably ate soft aquatic vegetation or invertebrates (Hay 1908; Holland 1924; Haas 1963). This view was seemingly supported by the ‘weak and inefficient’ masticatory apparatus of most sauropods, especially the ‘tooth-comb’ of Diplodocus , which could have been used for straining items from the water.

Estimating the effects of sampling biases on pterosaur diversity patterns: implications for hypotheses of bird/pterosaur competitive replacement

Abstract Pterosaurs were the first flying vertebrates and formed important components of terrestrial and marginal marine ecosystems during the Mesozoic. They became extinct during the latest Cretaceous (latest Maastrichtian), at, or near, the Cretaceous/Paleogene boundary, following an apparent decline in diversity in the Late Cretaceous. This reduction in species richness has been linked to the ecological radiation of birds in the Early Cretaceous and the proposal that birds competitively excluded pterosaurs from many key niches. However, although competition is often posited as a causal mechanism for many of the clade-clade replacements observed in the fossil record, these hypotheses are rarely tested. Here we present a detailed examination of pterosaur diversity through time, including both taxic and phylogenetically corrected diversity estimates and comparison of these estimates with a model describing temporal variation in the number of pterosaur-bearing formations (a proxy for rock availability). Both taxic and phylogenetic diversity curves are strongly correlated with numbers of pterosaur-bearing formations, suggesting that a significant part of the signal contained within pterosaur diversity patterns may be controlled by geological and taphonomic megabiases rather than macroevolutionary processes. There is no evidence for a long-term decline in pterosaur diversity through the Cretaceous, although a reduction in morphological, ecological, and phylogenetic diversity does appear to have occurred in the latest Cretaceous. Competitive replacement of pterosaurs by birds is difficult to support on the basis of diversity patterns.

THE ANATOMY AND TAXONOMY OF CETIOSAURUS (SAURISCHIA, SAUROPODA) FROM THE MIDDLE JURASSIC OF ENGLAND

Abstract The Middle Jurassic sauropod Cetiosaurus is significant both historically and in terms of its potential phylogenetic relationships. The anatomy and taxonomy of this form are poorly understood because inadequate diagnoses have allowed the proliferation of species names and the referral of very fragmentary specimens. A review of Cetiosaurus species indicates that all, except C. oxoniensis, are unavailable or nomina dubia. The current type species, C. medius, can no longer be regarded as a valid taxon. Previous suggestions that Cardiodon is a senior subjective synonym of Cetiosaurus cannot be sustained because the two forms do not share any autapomorphies. It is proposed that the generic name Cetiosaurus be retained, with C. oxoniensis as the new type species. The most complete specimen of C. oxoniensis (a partial skeleton from Bletchingdon Station, Oxfordshire) is redescribed and compared with other sauropods. Cetiosaurus is rediagnosed on the basis of autapomorphies, including: (1) ‘pyramid’-shaped neural spines in posterior cervical and anterior dorsal vertebrae; (2) loss of the spinodiapophyseal lamina on all dorsal vertebrae; (3) anterior chevrons with anteroposteriorly compressed distal shafts; (4) distal caudal centra have a ‘tongue’-like projection at the dorsal midline of their articular ends; and (5) a distinct triangular hollow on the lateral surface of the ilium at the base of the pubic process.

Sea level, dinosaur diversity and sampling biases: investigating the 'common cause' hypothesis in the terrestrial realm

The fossil record is our primary window onto the diversification of ancient life, but there are widespread concerns that sampling biases may distort observed palaeodiversity counts. Such concerns have been reinforced by numerous studies that found correlations between measures of sampling intensity and observed diversity. However, correlation does not necessarily mean that sampling controls observed diversity: an alternative view is that both sampling and diversity may be driven by some common factor (e.g. variation in continental flooding driven by sea level). The latter is known as the ‘common cause’ hypothesis. Here, we present quantitative analyses of the relationships between dinosaur diversity, sampling of the dinosaur fossil record, and changes in continental flooding and sea level, providing new insights into terrestrial common cause. Although raw data show significant correlations between continental flooding/sea level and both observed diversity and sampling, these correlations do not survive detrending or removal of short-term autocorrelation. By contrast, the strong correlation between diversity and sampling is robust to various data transformations. Correlations between continental flooding/sea level and taxic diversity/sampling result from a shared upward trend in all data series, and short-term changes in continental flooding/sea level and diversity/sampling do not correlate. The hypothesis that global dinosaur diversity is tied to sea-level fluctuations is poorly supported, and terrestrial common cause is unsubstantiated as currently conceived. Instead, we consider variation in sampling to be the preferred null hypothesis for short-term diversity variation in the Mesozoic terrestrial realm.