P. J. Bishop, C. J. Clemente, R. E. Weems, D. F. Graham, L. P. Lamas, J. R. Hutchinson, J. Rubenson, R. S. Wilson, S. A. Hocknull, R. S. Barrett, D. G. Lloyd
Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds.
Journal of the Royals Society Interface 2017 14 20170276
How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width—the mediolateral (transverse) distance between successive footfalls—was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk–run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history.
Novella L. Razzolini & Hendrik Klein (2017)
Crossing Slopes: Unusual Trackways of Recent Birds and Implications for Tetrapod Footprint Preservation
Ichnos (advance online publication)
In a neoichnological study, the trackway of a small recent bird (Limicola- like) crossing the slope of a river bank is documented and analyzed in detail. It was preserved along the Issene River in the western High Atlas of Morocco. Photogrammetry and 3-D techniques revealed three different phases of the trackmaker's movement that were essentially controlled by the biomechanical adaptations of the limbs and by the differences in how the foot was indented from up to down slope on the tilted, mud-cracked surface of the tilted mud-cracked surface. The slope of the surface is reflected in the variation of different track parameters, such as stride length, pace length, pace angulation, and imprint depths of different digits. A “didactyl” or fully collapsed morphology preservation pattern is observed as an intra-trackway morphological variation along the whole trackway. Tracks preserve only the up-slope digits: left tracks typically preserve only digit III and IV impressions, while right tracks preserve only digit III and II impressions. The selective absence of impressions of the other digits is interpreted to be the combined product of a water saturated/damp consistency of the sediment at the time of track formation and of the “down-facing” position of the unimpressed digits the latter reflects the differences in the bearing capacities of the “up-slope” portion of the limb versus the “down-slope” portion. The study may be helpful for understanding fossil counterparts formed on similarly uneven terrain.