Some recent papers that may be of interest:
The rock dove (or common pigeon), Columba livia, is an important model organism in biological studies, including research focusing on head muscle anatomy, feeding kinematics, and cranial kinesis. However, no integrated computer-based biomechanical model of the pigeon head has yet been attempted. As an initial step towards achieving this goal, we present the first three-dimensional digital dissection of the pigeon head based on a contrast-enhanced computed tomographic dataset achieved using iodine potassium iodide as a staining agent. Our datasets enable us to visualize the skeletal and muscular anatomy, brain and cranial nerves, and major sense organs of the pigeon, including very small and fragile features, as well as maintaining the three-dimensional topology of anatomical structures. This work updates and supplements earlier anatomical work on this widely used laboratory organism. We resolve several key points of disagreement arising from previous descriptions of pigeon anatomy, including the precise arrangement of the external adductor muscles and their relationship to the posterior adductor. Examination of the eye muscles highlights differences between avian taxa and shows that pigeon eye muscles are more similar to those of a tinamou than they are to those of a house sparrow. Furthermore, we present our three-dimensional data as publicly accessible files for further research and education purposes. Digital dissection permits exceptional visualisation and will be a valuable resource for further investigations into the head anatomy of other bird species, as well as efforts to reconstruct soft tissues in fossil archosaurs.
Flight is a key feature in the evolution of birds. Wing anatomy reflects many aspects of avian biology such as flight ability. However our knowledge of the flight musculature has many gaps still, particularly for the distal wing. Therefore, the aim of this work is to investigate the formâfunction relationship of the forelimb myology of birds to understand the role of individual muscles during flight. Dissections of six species of birds of prey were performed to collect numerical data of muscle architecture, which is the primary determinant of muscle function and forceâgeneration capacity. Birds of prey are a highly diverse group that presents different flight styles throughout the taxa, making them a good model for our purposes. Wing muscle mass isometrically scaled with body mass1.035, muscle length to muscle mass0.343 and fascicle length (FL) scaled allometrically to muscle mass0.285. The shoulder musculature scaled differently than the other regions where the fascicle length increases more slowly than would be expected in geometrically similar animals, which affects flight mechanics. A proximalâtoâdistal reduction of muscle mass occurs, which helps to minimize the wing moment of inertia during flight whilst allowing precise control of the distal wing. Interestingly the distribution of muscle mass appeared to be speciesâspecific, suggesting a functional signal. This study provides numerical information of muscle architecture of the avian wing that helps us to understand muscle function and its implication in flight, and can be used in future studies of flight mechanics.
Traits that interact to perform an ecologically relevant function are expected to be under multivariate non-linear selection. Using the lower jaw morphology as a biomechanical model, we test the hypothesis that lower jaw bones of lizards are subjected to stabilizing and correlational selection, associated with mechanical advantage and maximum bite force. We used three closely related tropidurine species that differ in size, head shape and microhabitat: Eurolophosaurus nanuzae, Tropidurus hispidus and Tropidurus semitaeniatus. We predicted a common pattern of correlational selection on bones that are part of in-levers or part of the out-lever of the lower jaw. The predicted pattern was found in E. nanuzae and T. hispidus, but this could not be shown to be statistically significant. For T. semitaeniatus, we found significant disruptive selection on a contrast involving the surangular, and also significant directional selection on linear combinations of traits in all species. The results indicate that the non-linear selection on lower jaw bones does not reflect an optimum to enhance mechanical advantage in all species. Divergent functional demands and specific ecological contexts of species seem relevant in shaping patterns of selection on morphology.
Osteoderms constitute a morphological system that plays an important role in squamate systematics. However, their study and visualization have always been difficult due to their isolated occurrence in the skin, among the first organs to be removed during the skeletonization process. Highâresolution Xâray computed tomography (HRXCT) offers a nondestructive means of visualizing osteoderms both in their natural relationship to each other and to the underlying cranial bones. Although it is often stated that Varanus komodoensis has a âchain mailâ of osteoderms, this morphological system was never described in this taxon. Further, given its size, it might be expected that V. komodoensis would present the extreme of osteoderm development in extant varanids, a group that tends to have weaklyâdeveloped osteoderms or none at all. Indeed, our HRXCT scan of a 19âyearâold captive individual reveals an elaborate mesh of cephalic osteoderms that are incredibly numerous and morphologically diverse. We describe this skeletal system and compare it to the cephalic osteoderms in other varanoids.