Climatic controls on the ecological ascendancy of dinosaurs

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Nesting at extreme polar latitudes by non-avian dinosaurs

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The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: cranial anatomy,functional morphology,taxonomy, and relationships

The cranial anatomy of the Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962 is described in detail for the first time on the basis of two principal specimens: the holotype (SAM‐PK‐K337) and referred skull (SAM‐PK‐K1332). In addition several other specimens that have a bearing on the interpretation of the anatomy and biology of Heterodontosaurus are described. The skull and lower jaw of Heterodontosaurus are compact and robust but perhaps most notable for the heterodont dentition that merited the generic name. Details of the cranial anatomy are revealed and show that the skull is unexpectedly specialized in such an early representative of the Ornithischia, including: the closely packed, hypsodont crowns and ‘warping’ of the occlusal surfaces (created by progressive variation in the angulation of wear on successive crowns) seen in the cheek dentition; the unusual sutural relationships between the bones along the dorsal edge of the lower jaw; the very narrow, deeply vaulted palate and associated structures on the side wall of the braincase; and the indications of cranial pneumatism (more commonly seen in basal archosaurs and saurischian dinosaurs). Evidence for tooth replacement (which has long been recognized, despite frequent statements to the contrary) is suggestive of an episodic, rather than continuous, style of tooth replacement that is, yet again, unusual in diapsids generally and particularly so amongst ornithischian dinosaurs. Cranial musculature has been reconstructed and seems to conform to that typically seen in diapsids, with the exception of the encroachment of M. adductor mandibulae externus superficialis across the lateral surface of the temporal region and external surface of the lower jaw. Indications, taken from the unusual shape of the occlusal surfaces of the cheek dentition and jaw musculature, are suggestive of a novel form of jaw action in this dinosaur. The taxonomy of currently known late Karoo‐aged heterodontosaurids from southern Africa is reviewed. Although complicated by the inadequate nature of much of the known material, it is concluded that two taxa may be readily recognized: H. tucki and Abrictosaurus consors. At least one additional taxon is recognized within the taxa presently named Lanasaurus and Lycorhinus; however, both remain taxonomically problematic and their status needs to be further tested and may only be resolved by future discoveries. The only other named taxon, Geranosaurus atavus, represents an invalid name. The recognition of at least four distinct taxa indicates that the heterodontosaurids were speciose within the late Karoo ecosystem. The systematics of Heterodontosaurus and its congeners has been analysed, using a restricted sample of taxa. A basal (nongenasaurian) position within Ornithischia is re‐affirmed. There are at least four competing hypotheses concerning the phylogenetic placement of the Heterodontosauridae, so the evidence in support of the various hypotheses is reviewed in some detail. At present the best‐supported hypothesis is the one which places Heterodontosauridae in a basal (non‐genasaurian) position; however, the evidence is not fully conclusive and further information is still needed in respect of the anatomy of proximate outgroups, as well as more complete anatomical details for other heterodontosaurids. Heterodontosaurids were not such rare components of the late Karoo ecosystem as previously thought; evidence also suggests that from a phylogenetic perspective they occupied a potentially crucial position during the earliest phases of ornithischian dinosaur evolution. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011.     

Biostratigraphic significance of a new early sauropodomorph specimen from the Upper Triassic of southern Brazil

The Wachholz site (Caturrita Formation, Late Triassic), in Agudo, Rio Grande do Sul (RS), southern Brazil, has yielded several sauropodomorphs. This includes CAPPA/UFSM 0002, described here based on associated elements from the basalmost portion of the site. The specimen possesses a set of traits shared with typical ‘prosauropods’: a concave caudal margin of the trunk neural spines and a broadly convex proximal end of metacarpal V. However, it also retains some plesiomorphic features, for instance, the slender pedal digit I. Some bones closely resemble those of Unaysaurus tolentinoi, the other definitive sauropodomorph from the Caturrita Formation, an affinity corroborated by a new phylogenetic analysis. An updated biostratigraphic framework correlates the Wachholz, Água Negra (São Martinho da Serra/RS) and Botucaraí Hill (Candelária/RS) sites based on their sample of sauropodomorphs. In addition, the record of Jachaleria in the Botucaraí Hill site, a dicynodont also known from early Norian deposits of Argentina, indicates an equivalent age to deposits bearing U. tolentioni. Accordingly, a more constrained age is proposed for the Água Negra site. This is important as the early Norian marks the transition from an epoch of low sauropodomorphs representativeness to a period of extreme abundance of the group in Early-to-Middle Mesozoic ecosystems.     

The northernmost sauropod record in the Northern Hemisphere

Isolated sauropod teeth from the Early Cretaceous Teete locality in Yakutia (Eastern Siberia, Russia) are the only evidence that sauropods lived in high latitudes (palaeolatitude estimate of N 62°) in the Northern Hemisphere. The spatulate broad tooth crowns of adult individuals lack marginal denticles while these are present in a juvenile tooth. The teeth have overlapping facets and likely belong to a basal macronarian. The juvenile tooth indicates that sauropods reproduced in high latitudes and possibly stayed there around the year. The Teete vertebrate assemblage comprises both endothermic, or presumably endothermic tetrapods (theropod dinosaurs, tritylodontids and mammals), and ectothermic tetrapods (salamanders, turtles, choristoderes and lizards), but no crocodyliforms. This suggests a temperate climate, with an annual mean temperature well above freezing level but below 14°C.     

The role of ontogeny on character polarization in early dinosaurs: a new specimen from the Late Triassic of southern Brazil and its implications

Only recently, new ontogenetic series of early dinosaurs and related groups have been described. Here, we present an isolated immature dinosauriform femur from the Late Triassic of southern Brazil and investigate its influence on character polarization. Because the specimen shares a number of synapomorphies with Pampadromaeus barberenai, herein we postulate that it corresponds to a juvenile individual of that taxon. Accordingly, we investigate the morphological variation between juvenile and mature individuals of P. barberenai. Scoring these character states into a published phylogenetic data-set of Dinosauromorpha reveals that morphological variation is higher than that observed among closely-related taxa. Ontogenetic variation thus exerts influence on character polarization. In addition, modification of the scores affected by ontogeny produces different topologies, as noted by the reduction in both the number of most parsimonious trees and number of steps, and increased inclusivity of some clades and reduction of polytomies as well. Our study, together with other recent contributions, sheds light on the morphologic pathways seen during dinosauromorph ontogenetic development, which is crucial to more reliably assess phylogenetic reconstructions and macroevolutionary patterns of this widespread and successful group.     

First evidence of an ankylosaur (Dinosauria,Ornithischia) from the Jurassic Qigu Formation (Junggar Basin,NW China) and the early fossil record of Ankylosauria

The first evidence of an ankylosaur from the Late Jurassic Qigu Formation of the southern Junggar Basin (Xinjiang, northwestern China) is described, based on an isolated caudal vertebra that was discovered together with fragmentary remains of other dinosaurs, including stegosaurs, sauropods, and theropods. The caudal vertebra is characterized by the following features: (i) elliptical morphology of the centrum, being wider than high; (ii) short antero-posterior length of the centrum; (iii) pronounced transversely extending ventral groove; (iv) massive transverse process, that is longer than the centrum diameter; (v) transverse process meeting the centrum high at the dorsal half and at a relatively flat angle; (vi) transverse process making a broad contact with the neural arch without forming a proximo-dorsal projection; and (vii) notochordal prominence present in the centre of the anterior articular surface. The study specimen represents only the second record of an ankylosaur from the Jurassic of Asia — aside from the slightly older Tianchisaurus from the early Upper Jurassic Toutunhe Formation, equally from the Junggar Basin. It helps to fill a gap in our knowledge of the early evolution of these armoured dinosaurs. Additionally, this discovery highlights the potential of the southern Junggar Basin to yield a rich vertebrate fauna and thus to provide an important insight into Late Jurassic ecosystems of Central Asia.     

Limusaurus inextricabilis (Theropoda: Ceratosauria) gives a hand to evolutionary teratology: a complementary view on avian manual digits identities

It is widely accepted that birds are rooted within theropod dinosaurs. However, there is controversy between palaeontological and developmental data regarding manual digit identities of birds and their tetanuran ancestors (I, II and III vs. II, III and IV). To resolve this conflict, the principle of a frame‐shift has been considered. Identities of digits I–III would develop on condensations 2–4. Nevertheless, the discovery of the basal Ceratosauria Limusaurus inextricabilis has been used as a reference to define the digital identity of Tetanurae as II–IV. The new concept of evolutionary teratology states that certain anatomical structures identified in evolutionary lineages are viable developmental anomalies (‘adaptive’ or not), becoming part of the considered groups. The features of Limusaurus' forelimb match teratological characterization. This diagnosis, associated with the variations previously identified in derived Ceratosauria taxa (Carnotaurinae), underline an anatomical and developmental independence (regarding evolutionary conserved mechanisms) compared with Tetanurae and therefore birds. Consequently, Limusaurus should not be used as a reference concerning the identity of avian manuals digits. Evolutionary teratology supports identities I, II and III of the tetanuran manus via a frame‐shift that did not occur in the Ceratosauria lineage. © 2016 The Linnean Society of London