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[dinosaur] Bird vestibular ecomorphology + secondary temporal fenestrae + bipedal locomotion and center of mass

Ben Creisler

Some recent papers with dino implications:

Roger B. J. Benson, Ethan Starmer-Jones, Roger A. Close and Stig A. Walsh (2017)
Comparative analysis of vestibular ecomorphology in birds.
Journal of Anatomy 231(6): 990â1018Â
DOI: 10.1111/joa.12726

The bony labyrinth of vertebrates houses the semicircular canals. These sense rotational accelerations of the head and play an essential role in gaze stabilisation during locomotion. The sizes and shapes of the semicircular canals have hypothesised relationships to agility and locomotory modes in many groups, including birds, and a burgeoning palaeontological literature seeks to make ecological interpretations from the morphology of the labyrinth in extinct species. Rigorous tests of formâfunction relationships for the vestibular system are required to support these interpretations. We test the hypothesis that the lengths, streamlines and angles between the semicircular canals are related to body size, wing kinematics and flying style in birds. To do this, we applied geometric morphometrics and multivariate phylogenetic comparative methods to a dataset of 64 three-dimensional reconstructions of the endosseous labyrinth obtained using micro-computed tomography scanning of bird crania. A strong relationship between centroid size of the semicircular canals and body size indicates that larger birds have longer semicircular canals compared with their evolutionary relatives. Wing kinematics related to manoeuvrability (and quantified using the brachial index) explain a small additional portion of the variance in labyrinth size. We also find strong evidence for allometric shape change in the semicircular canals of birds, indicating that major aspects of the shape of the avian labyrinth are determined by spatial constraints. The avian braincase accommodates a large brain, a large eye and large semicircular canals compared with other tetrapods. Negative allometry of these structures means that the restriction of space within the braincase is intense in small birds. This may explain our observation that the angles between planes of the semicircular canals of birds deviate more strongly from orthogonality than those of mammals, and especially from agile, gliding and flying mammals. Furthermore, we find little support for relationships between labyrinth shape and flying style or wing kinematics. Overall, our results suggest that the topological problem of fitting long semicircular canals into a spatially constrained braincase is more important in determining the shape of the avian labyrinth than the specifics of locomotory style or agility. Our results tentatively indicate a link between visual acuity and proportional size of the labyrinth among birds. This suggests that the large labyrinths of birds compared with other tetrapods may result from their generally high visual acuities, and not directly from their ability to fly. The endosseous labyrinths of extinct birds and their close dinosaurian relatives may allow broad inferences about flight or vision, but so far provide few specific insights into detailed aspects of locomotion.


Andrzej Elzanowski & Gerald Mayr (2017)
Multiple origins of secondary temporal fenestrae and orbitozygomatic junctions in birds.
Journal of Zoological Systematics and Evolutionary Research (advance online publication)
DOI: 10.1111/jzs.12196

Orbitozygomatic junctions (bony connections between the postorbital and zygomatic processes) and secondary temporal fenestrae have long been known to occur in a few avian species, but no comprehensive study of this phenomenon has ever been published. Having surveyed all non-passerine and most passerine families, we established that the orbitozygomatic junction evolved 18â20 times independently in Cracidae, Phasianoidea (Odontophoridae and Phasianidae), Gastornis, Columbidae (three times), Pteroclidae (Syrrhaptes), Aptornis, Thinocoridae (Thinocorus), Scolopacidae (possibly twice), Ciconiidae (twice), Brachypteraciidae (Uratelornis), Picidae (Picus spp.), Psittacidae (Melopsittacus), Cacatuidae, and Alaudidae (twice). The junction arises in evolution as a result of either elongation of the two processes that meet at angles or the appearance of a bony cross-bridge in place of a ligament or aponeurosis. In the first case, the junction is initially non-adaptive, as indicated by its extreme variation (e.g., in Cracinae and Ciconiidae), and may or may not prove functional as an exaptation. Whenever adaptive, the junction supports an expansion of the adductor mandibulae externus (primarily its pars media). In addition, a rostral extension of the tympanic wing has come to cross the temporal fossa in Strigidae (at least twice) and probably Podargus. Altogether, secondary bony connections across the temporal fossa evolved independently at least 21â23 times in neornithine birds.


C. J. Clemente, P. J. Bishop, N. Newman and S. A. Hocknull (2017)
Steady bipedal locomotion with a forward situated whole-body centre of mass: the potential importance of temporally asymmetric ground reaction forces.
Journal of Zoology (advance online publication)
DOI: 10.1111/jzo.12521

Bipedalism has repeatedly evolved in many independent lineages throughout tetrapod history. Despite being widespread, the fundamental biomechanical factors involved in bipedalism remain unclear. This study experimentally investigated bipedalism in facultatively bipedal lizards and obligatorily bipedal birds to explore temporal asymmetry in the vertical component of the ground reaction force (Fz). Both lizards and birds showed significant temporal asymmetry â with higher vertical forces exerted earlier in the stance â as indicated by three different measures computed from force-time profiles. This result parallels those reported previously for other bipedal animal groups that have a forward situated whole-body centre of mass (COM), such as kangaroos and non-human primates. Humans, in contrast, exhibit an orthograde posture with the COM close the hips, and show little temporal asymmetry in Fz, particularly during walking. Across a wide range of quadrupedal animals, temporal asymmetry is quite variable. Collectively, these results suggest that an âearly-skewedâ Fz may be an important feature of steady bipedal locomotion when the COM is forward of the hips, although an exact mechanism of cause-and-effect, if one exists, remains to be established. This finding has relevance for attempts at better understanding bipedal locomotion in extinct animals that likely had a COM located forward of the hips, such as carnivorous dinosaurs.

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