[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

New in Paleobiology - myrmercophagous Mononykus & origin of flight stroke

Two topics that have been frequently addressed on the DML... (I'm looking forward to reading the papers, though I've only seen the abstracts so far.)

Senter, P. (2005). Function in the stunted forelimbs of _Mononykus olecranus_ (Theropoda), a dinosaurian anteater. Paleobiology 31(3): 373-381.

Abstract: "_Mononykus olecranus_, a theropod dinosaur from the Upper Cretaceous of Mongolia, exhibits reduced forelimbs with a single functional digit. These bizarre forelimbs have aroused great curiosity as to the behavior of the animal, but until now no functional study on the forelimbs of _Mononykus_ has been undertaken. Here I show that the orientation and range of motion in the forelimb elements of _Mononykus_ are such that the humeri sprawl laterally, the antebrachia are held subvertically, the palms face ventrally, and intramanual movement is restricted to subparasagittal motion. This is a radical departure from the typical theropod condition, in which the palms face medially and intramanual movement is transverse. The results of this study confirm that the forelimbs of _Mononykus_ could not have been used to grasp prey or dig burrows, but were well suited for scratch-digging or hook-and-pull movements such as are used by extant anteaters and pangolins to open tough insect nests. _Mononykus_ likely occupied a niche equivalent to that of an anteater or pangolin, an unusual niche for a dinosaur."

Gatesy, S.M. and Baier, D.B. (2005). The origin of the avian flight stroke: a kinematic and kinetic perspective. Paleobiology 31(3): 382-399.

Abstract. "Flying birds flap their wings to generate aerodynamic forces large enough to overcome weight and drag. During this behavior, the forelimbs are displaced and deformed in a complex, coordinated sequence of movements collectively known as the "flight stroke." Despite an influx of relevant fossil material and new functional insights from extant birds, the historical origin of the avian flight stroke remains poorly resolved. Potential behavioral precursors have been identified primarily on the basis of kinematic resemblance-similarity of movement irrespective of underlying mechanisms. We discuss fundamental issues of motion analysis that are frequently overlooked by paleontologists, and conclude that a purely kinematic approach is insufficient. Consideration of kinetics, the forces responsible for motion, offers a more complete picture of flight stroke evolution. We introduce six kinetic components that interact to determine a limb's trajectory. Phylogenetic mapping reveals that forelimb loading patterns have undergone at least two major transitions on the line from basal archosaur to modern bird. Using this kinematic and kinetic perspective, we offer four specific criteria to help constrain and evaluate competing scenarios for the origin of the avian flight stroke."