Darren Naish

A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology

Azhdarchid pterosaurs were among the most widespread and successful of pterosaur clades, but their paleoecology remains controversial. Morphological features common to all azhdarchids include a long, shallow rostrum; elongate, cylindrical cervical vertebrae that formed a long and unusually inflexible neck; and proportionally short wings with an abbreviated fourth phalanx. While azhdarchids have been imagined as vulture-like scavengers, sediment probers, swimmers, waders, aerial predators, or stork-like generalists, most recent authors have regarded them as skim-feeders, trawling their lower jaws through water during flight and seizing aquatic prey from the waters surface. Although apparently widely accepted, the skim-feeding model lacks critical support from anatomy and functional morphology. Azhdarchids lack the many cranial specialisations exhibited by extant skim-feeding birds, most notably the laterally compressed lower jaw and shock absorbing apparatus required for this feeding style. Well-preserved azhdarchid skulls are rare, but their rostra and lower jaws appear to have been sub-triangular in cross-section, and thus dissimilar to those of skim-feeders and sediment probers. Taphonomic data indicates that azhdarchids predominately inhabited inland settings, and azhdarchid morphology indicates that they were poorly suited for all proposed lifestyles bar wading and terrestrial foraging. However, azhdarchid footprints show that their feet were relatively small, padded and slender, and thus not well suited for wading. We argue that azhdarchids were stork- or ground hornbill-like generalists, foraging in diverse environments for small animals and carrion. Proficient terrestrial abilities and a relatively inflexible neck are in agreement with this interpretation.

Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds

Turning large dinosaurs into small birds Most paleontologists agree that birds are descended from dinosaurs. How did such large terrestrial or aquatic animals evolve into small feathered fliers? Lee et al. used two large databases of theropod morphology to explore possible evolutionary patterns that may have driven this dramatic transformation (see the Perspective by Benton). They found no clear pattern of miniaturization across the entire clade of Theropoda. However, several lines of evidence suggested that the lineage leading to birds underwent sustained miniaturization. Within that lineage, body sizes decreased and species evolved faster. They also developed ecological and morphological innovations linked to smaller body sizes. Science, this issue p. 562; see also p. 508 Birds evolved from their dinosaurian ancestors through a period characterized by sustained and repeated decreases in size. [Also see Perspective by Benton] Recent discoveries have highlighted the dramatic evolutionary transformation of massive, ground-dwelling theropod dinosaurs into light, volant birds. Here, we apply Bayesian approaches (originally developed for inferring geographic spread and rates of molecular evolution in viruses) in a different context: to infer size changes and rates of anatomical innovation (across up to 1549 skeletal characters) in fossils. These approaches identify two drivers underlying the dinosaur-bird transition. The theropod lineage directly ancestral to birds undergoes sustained miniaturization across 50 million years and at least 12 consecutive branches (internodes) and evolves skeletal adaptations four times faster than other dinosaurs. The distinct, prolonged phase of miniaturization along the bird stem would have facilitated the evolution of many novelties associated with small body size, such as reorientation of body mass, increased aerial ability, and paedomorphic skulls with reduced snouts but enlarged eyes and brains.

New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary

Background Ichthyosauria is a diverse clade of marine amniotes that spanned most of the Mesozoic. Until recently, most authors interpreted the fossil record as showing that three major extinction events affected this group during its history: one during the latest Triassic, one at the Jurassic–Cretaceous boundary (JCB), and one (resulting in total extinction) at the Cenomanian-Turonian boundary. The JCB was believed to eradicate most of the peculiar morphotypes found in the Late Jurassic, in favor of apparently less specialized forms in the Cretaceous. However, the record of ichthyosaurs from the Berriasian–Barremian interval is extremely limited, and the effects of the end-Jurassic extinction event on ichthyosaurs remains poorly understood. Methodology/Principal Findings Based on new material from the Hauterivian of England and Germany and on abundant material from the Cambridge Greensand Formation, we name a new ophthalmosaurid, Acamptonectes densus gen. et sp. nov. This taxon shares numerous features with Ophthalmosaurus, a genus now restricted to the Callovian–Berriasian interval. Our phylogenetic analysis indicates that Ophthalmosauridae diverged early in its history into two markedly distinct clades, Ophthalmosaurinae and Platypterygiinae, both of which cross the JCB and persist to the late Albian at least. To evaluate the effect of the JCB extinction event on ichthyosaurs, we calculated cladogenesis, extinction, and survival rates for each stage of the Oxfordian–Barremian interval, under different scenarios. The extinction rate during the JCB never surpasses the background extinction rate for the Oxfordian–Barremian interval and the JCB records one of the highest survival rates of the interval. Conclusions/Significance There is currently no evidence that ichthyosaurs were affected by the JCB extinction event, in contrast to many other marine groups. Ophthalmosaurid ichthyosaurs remained diverse from their rapid radiation in the Middle Jurassic to their total extinction at the beginning of the Late Cretaceous.

Morphological Clocks in Paleontology, and a Mid-Cretaceous Origin of Crown Aves

Birds are among the most diverse and intensivelystudied vertebrate groups, but many aspects of theirhigher-level phylogeny and evolution still remaincontroversial. One contentious issue concerns theantiquity of modern birds (=crown Aves): the ageof the most recent common ancestor of all livingbirds (Gauthier 1986). Very few Mesozoic fossilsare attributable to modern birds (e.g., Clarke et al.2005; Dyke and Kaiser 2011; Brocklehurst et al. 2012;Ksepka and Boyd 2012) suggesting that they diversifiedlargely or entirely in the early Paleogene, perhaps in theecologicalvacuumcreatedbytheextinctionofnon-aviandinosaurs, pterosaurs, and many archaic (stem) birds(e.g.,Longrichetal.2011).Incontrast,molecularstudiesindicate that modern birds commenced radiating deepwithin the Mesozoic, for example ∼130Ma(Cooperand Penny 1997; Haddrath and Baker 2012)or∼113 Ma(Jetz et al. 2012), with ratites, galliforms, anseriforms,shorebirds, and even passerines surviving acrossthe KPg boundary (∼66 Ma). The oldest moleculardates further imply an extraordinarily rapid earlybird evolution, with the modern birds appearingonly 20 myr after

Ecology, Systematics and Biogeographical Relationships of Dinosaurs, Including a New Theropod, from the Santana Formation (?Albian, Early Cretaceous) of Brazil

Although rare, dinosaurs are well preserved in calcareous nodules of the Santana Formation (Early Cretaceous, ?Albian) of the Araripe Basin, in northeastern Brazil. So far, including only a spinosauroid and three coelurosaurs, the dinosaur fauna appears depauperate. High theropod diversity in assemblages where other dinosaurs are rare or absent is not unique to the Santana Formation. It is seen also in several other assemblages, including Solnhofen and the Maevarano Formation of Madagascar. We consider several factors, including the occurrence of intraguild predation, the possibility that small theropods could subsist in marginal environments, and reliance on coastal resources, that may have been responsible for this apparent ecological imbalance. A new coelurosaur from the Santana Formation, here formally named Mirischia asymmetrica, is shown to be distinct from Santanaraptor placidus [Kellner, A.W.A. (1999) “Short note on a new dinosaur (Theropoda, Coelurosauria) from the Santana Formation (Romualdo Member, Albian) northeastern Brazil”, Boletim do Museu Nacional, Nova Serie, Rio de Janeiro, Brasil 49, 1–8]. Other theropods from the Santana Formation are briefly reviewed. Mirischia is a compsognathid, more similar to the European Compsognathus than to the Asian Sinosauropteryx.

Sexual selection in prehistoric animals: detection and implications

Many fossil animals bear traits such as crests or horns that probably functioned as sexually selected signals or weapons. Interpretations of these structures as functioning in mate choice or intrasexual contests are often controversial, with interpretations based on biomechanics or physiology being favoured by many. Although testing hypotheses based on sexual selection can be difficult, especially given that there is no single, reliable means of recognising sexual selection, we argue that it is not impossible; indeed, there are now several cases where sexual selection is strongly supported. In other cases, a careful study of features such as sexual dimorphism, ontogeny, and allometry, coupled with testing of alternative hypotheses, will be necessary to distinguish between possible explanations for exaggerated features.

Fossil Seals from Late Neogene Deposits in South America: A New Pinniped (Carnivora, Mammalia) Assemblage from Chile

A new monachine phocid pinniped assemblage from the north–central coast of Chile is described. The material was recovered from a marine bonebed of the Bahia Inglesa Formation which, based on macro– and microfossil evidence, is probably Late Miocene–Early Pliocene in age. At least two genera, Acrophoca and Piscophoca (both originally described from the Pisco Formation of Peru), are present. The Chilean material is significantly different from that of the two described species from the Pisco Formation and probably represents new species, though these are not named pending description of new material reported from Peru. The postcrania are morphologically intermediate between the northern Phocini and southern Lobodontini. The Bahia Inglesa Formation pinniped assemblage represents the first occurrence of fossil seals in Chile, and provides valuable information regarding the late Neogene radiation of monachines in the Southern Hemisphere. The occurrence of Acrophoca sp. in beds underlying a condensed Mio–Pliocene bonebed suggests that these strata are no older than Late Miocene.

Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia

Beginning with Bucklands 1824 description of Megalosaurus, the Geological Society of London played a leading role during the 19th century discovery of dinosaurs in Britain. Here we review the societys role and assess the current knowledge of saurischian dinosaurs in the country. Of Britains 108 dinosaur species (excluding nomina nuda and objective synonyms), 32% have been named in the pages of Society publications. Britain has a rich and diverse dinosaur record ranging from the Rhaetian to the Cenomanian, and includes a surprising taxonomic diversity. Alleged Lower and Middle Triassic dinosaurs from Britain are suspect or erroneous. Sauropodomorphs represent all of the major clades and several have their earliest global appearances in the British record (Diplodocoidea, Rebbachisauridae and Titanosauria), implying that this region was biogeographically important for this group. The British theropod record is diverse, and includes the earliest spinosaurids, carcharodontosaurids and coelurosaurs. Although some specimens are represented by near-complete skeletons, much material is fragmentary and indeterminate, and c. 54% of British dinosaur taxa are considered nomina dubia. In part this high number results from the genesis of dinosaur science in Britain and the corresponding obsolescence of supposedly diagnostic characters.

A basal thunnosaurian from Iraq reveals disparate phylogenetic origins for Cretaceous ichthyosaurs

Cretaceous ichthyosaurs have typically been considered a small, homogeneous assemblage sharing a common Late Jurassic ancestor. Their low diversity and disparity have been interpreted as indicative of a decline leading to their Cenomanian extinction. We describe the first post-Triassic ichthyosaur from the Middle East, Malawania anachronus gen. et sp. nov. from the Early Cretaceous of Iraq, and re-evaluate the evolutionary history of parvipelvian ichthyosaurs via phylogenetic and cladogenesis rate analyses. Malawania represents a basal grade in thunnosaurian evolution that arose during a major Late Triassic radiation event and was previously thought to have gone extinct during the Early Jurassic. Its pectoral morphology appears surprisingly archaic, retaining a forefin architecture similar to that of its Early Jurassic relatives. After the initial latest Triassic radiation of early thunnosaurians, two subsequent large radiations produced lineages with Cretaceous representatives, but the radiation events themselves are pre-Cretaceous. Cretaceous ichthyosaurs therefore include distantly related lineages, with contrasting evolutionary histories, and appear more diverse and disparate than previously supposed.

New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium

It says something about the invigoration of dinosaur research that an enormous technical tome, 624 pages long and containing 36 chapters, could be produced on horned dinosaurs (or ceratopsians) alone. New Perspectives on Horned Dinosaurs, published in 2010 and edited by Michael Ryan, Brenda Chinnery-Allgeier and David Eberth, stems from the Royal Tyrrell Museum Ceratopsian Symposium, held at Drumheller, Alberta, in September 2007. The organisers of this meeting were inspired by the major upsurge in horned dinosaur research currently underway – it involves the description of new taxa, a renewed interest in anatomy, behaviour and functional morphology, and the application of new techniques to such areas as the mechanical behaviour of bone, niche partitioning, phylogeny, biogeography and ontogeny. Despite the popular name, not all horned dinosaurs are horned. Ceratopsia in fact includes psittacosaurids (a group of Asian bipedal forms, the skulls of which are often superficially likened to those parrots), the deep-headed, hornless leptoceratopsids, an assemblage of smallto medium-sized, mostly quadrupedal forms that were once grouped together as protoceratopsids (they have bony frills, and some, like the eponymous Protoceratops, have short or incipient nasal horns), and the members of the large-bodied, horned Zuniceratops þ ceratopsid clade. Ceratopsidae includes both the mostly long-frilled chasmosaurines with their long supraorbital, postorbital or brow horns, and the mostly short-frilled centrosaurines with their long nasal horns and typically short (or absent) postorbital horns. Zuniceratops and several other fossils seem to show that postorbital horns are primitive for the Zuniceratops þ Ceratopsidae clade. Protoceratops, ceratopsids and their frill-headed kin (i.e. all ceratopsians closer to Triceratops than to Psittacosaurus) are united within Neoceratopsia, while the node-based clade that includes Protoceratops and Triceratops is termed Coronosauria (Sereno 1998). New Perspectives on Horned Dinosaurs consists of five sections: overview; systematics and new taxa; anatomy, functional biology and behaviour; phylogeny, biogeography, taphonomy and paleoenvironment; and the history of collecting. The bulk of the book is made up of the second and third section. The first section includes a single article and the last section includes two articles. Virtually all contributions are very well illustrated and there is even a colour plate section. The book is large format (c. 29 £ 22 cm) and hence very different from most of the other multi-authored dinosaur-themed volumes published by Indiana University Press. The quality throughout is high and most students of the Ceratopsia were evidently compelled to contribute interesting work. Some articles do stand out as especially interesting, strong or both. Peter Dodson’s opening article (the single contribution in Section 1) – ‘Forty years of Ceratophilia’ – provides an excellent, personal overview of ceratopsian studies of the past four decades. Dodson says that his apparent modern role as ‘the dean . . . of ceratopsian studies’ (Dodson 2010, p. 3) is a sort of happy accident; we know, in fact, that he is deserving of this role, having led work on the group through innovation, excellent research and brilliant writing (Dodson 1996). The ‘genealogy of Dodson ceratopsian students’ is a really nice touch, paralleling the efforts of other palaeontologists to produce phylogenies of academic ‘relatedness’. Among other articles that really stand out, Dodson, You and Tanoue’s article on the basicranium and palate anatomy of psittacosaurids and non-ceratopsid neoceratopsians includes some wholly new anatomical information. Scott Sampson and Mark Loewen’s chapter is an excellent review of ceratopsid biogeography and phylogeny. One of their main conclusions – perhaps surprising to those who think that there might now be too many ceratopsids in Late Cretaceous North America! – is that ‘diversity will increase greatly once less explored geographic regions and temporal intervals are subject to greater sampling’ (Sampson and Loewen 2010, p. 423). Indeed, as anyone who’s even vaguely aware of horned dinosaur diversity will know, a surprising number of new (mostly North American) taxa have been named within the last few years. The volume itself includes the names of no fewer than six new taxa (one of which represents a renaming, not a wholly new taxon). Coahuilaceratops magnacuerna Loewen et al., 2010 is a new chasmosaurine from the Cerro del Pueblo Formation of Mexico, notable for its gigantic, massively robust postorbital horncores, among the largest of any ceratopsian. Phylogenetic analysis recovers it as a close relative of Anchiceratops and Arrhinoceratops (Loewen et al., 2010) (though see Sampson et al., 2010). The second new taxon, Diabloceratops eatoni Kirkland and Deblieux, 2010, is a new brow-horned centrosaurine from the Wahweap Formation of Utah, named for a spectacular skull. Its nasal horn is tiny, the epijugal processes on the cheeks are especially long, and slender, outwardly curved