Shake a tail feather: the evolution of the theropod tail into a stiff aerodynamic surface

Theropod dinosaurs show striking morphological and functional tail variation; e.g., a long, robust, basal theropod tail used for counterbalance, or a short, modern avian tail used as an aerodynamic surface. We used a quantitative morphological and functional analysis to reconstruct intervertebral joint stiffness in the tail along the theropod lineage to extant birds. This provides new details of the tail's morphological transformation, and for the first time quantitatively evaluates its biomechanical consequences. We observe that both dorsoventral and lateral joint stiffness decreased along the non-avian theropod lineage (between nodes Theropoda and Paraves). Our results show how the tail structure of non-avian theropods was mechanically appropriate for holding itself up against gravity and maintaining passive balance. However, as dorsoventral and lateral joint stiffness decreased, the tail may have become more effective for dynamically maintaining balance. This supports our hypothesis of a reduction of dorsoventral and lateral joint stiffness in shorter tails. Along the avian theropod lineage (Avialae to crown group birds), dorsoventral and lateral joint stiffness increased overall, which appears to contradict our null expectation. We infer that this departure in joint stiffness is specific to the tail's aerodynamic role and the functional constraints imposed by it. Increased dorsoventral and lateral joint stiffness may have facilitated a gradually improved capacity to lift, depress, and swing the tail. The associated morphological changes should have resulted in a tail capable of producing larger muscular forces to utilise larger lift forces in flight. Improved joint mobility in neornithine birds potentially permitted an increase in the range of lift force vector orientations, which might have improved flight proficiency and manoeuvrability. The tail morphology of modern birds with tail fanning capabilities originated in early ornithuromorph birds. Hence, these capabilities should have been present in the early Cretaceous, with incipient tail-fanning capacity in the earliest pygostylian birds

New information on the braincase and inner ear of Euparkeria capensis Broom: implications for diapsid and archosaur evolution

Since its discovery, Euparkeria capensis has been a key taxon for understanding the early evolution of archosaurs. The braincase of Euparkeria was described based on a single specimen, but much uncertainty remained. For the first time, all available braincase material of Euparkeria is re-examined using micro-computed tomography scanning. Contrary to previous work, the parabasisphenoid does not form the posterior border of the fenestra ovalis in lateral view, but it does bear a dorsal projection that forms the anteroventral half of the fenestra. No bone pneumatization was found, but the lateral depression of the parabasisphenoid may have been pneumatic. We propose that the lateral depression likely corresponds to the anterior tympanic recess present in crown archosaurs. The presence of a laterosphenoid is confirmed for Euparkeria. It largely conforms to the crocodilian condition, but shows some features which make it more similar to the avemetatarsalian laterosphenoid. The cochlea of Euparkeria is elongated, forming a deep cochlear recess. In comparison with other basal archosauromorphs, the (C) 2016 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution Licens

Clarifying marine invasions with molecular markers: an illustration based on mtDNA from mistaken calyptraeid gastropod identifications

Species invasions are occurring at an increasing rate in coastal environments. Accurately identifying introductions is a critical issue to take full advantage of the new invasion databases. Further, life history differences between morphologically comparable species may require that different management strategies be instigated to effectively control different species. Facing this problem, we used molecular approaches and documented a case of mistaken identification in a group of marine invertebrates, the calyptraeid gastropods. Members of this group have repeatedly and successfully invaded new habitats after anthropogenic introduction, especially in estuaries and bays on the west coast of the United States of America. For example, Crepidula fornicata, native to the east coast of the USA, has been reported from at least five USA west coast estuaries. We sequenced a fragment of the COI gene of a sample of putative C. fornicata from Humboldt Bay, California. By constructing a phylogeny of these and other calpytraeid gastropod sequences, we discovered that the individuals were C. convexa, the convex slippershell. In contrast to C. fornicata, C. convexa has large, demersal eggs and larvae are well developed at hatching. Its potential for dispersal is therefore lower as compared to C. fornicata and therefore any strategy to manage the invasion should take this into account. In the present study, we demonstrated the utility of molecular tools that can be used by non-taxonomic experts, to quickly and accurately identify alien species – an important first step in any study of invasion biology.Dugald J. McGlashan, Mark Ponniah, Phillip Cassey, Frédérique Viar