Theropod motion abstracts

[bh480@scn.org]

From: Ben Creisler bh480@scn.org
Theropod motion abstracts

I came across the following abstracts from the American 
Zoologist. Can't recall if they've been posted before:
Carrier, D.R., Lee, D.V. & Walter, R.M. 2000.  Influence 
of rotational inertia on the turning performance of 
theropod dinosaurs.
Annual Meeting and Exhibition of the Society for 
Integrative and Comparative Biology, Chicago, Illinois, 
USA, January 03-07, 2001
Turning agility of theropod dinosaurs may have been 
severely limited by the large rotational inertia of their 
horizontal trunks and tails. Bodies with mass distributed 
far from the axis of rotation have much greater rotational 
inertia than bodies with the same mass distributed close 
to the axis of rotation. In this study, we increased the 
rotational inertia of human subjects 4.6 times, to match 
our estimate for theropods the size of humans, and 
measured the subjects' ability to turn. To determine the 
torque required to execute turns, three subjects performed 
45 degree jump turns on a force platform. When the 
rotational inertia was increased 4.6-fold, the time to 
push-off increased 1.8-fold and the torque impulse applied 
to the ground increased 3.76-fold. To determine the effect 
of the increased rotational inertia on maximum turning 
capability, five subjects performed jump turns in which 
they jumped vertically from a standing position and 
attempted to spin as far as possible before landing. This 
test resulted in a 4.9-fold decrease in the angle turned. 
We also tested the ability of three subjects to perform 
sharp running turns in a tight slalom course of six 90 
degree turns. When the subjects ran with the 4.6-fold 
greater rotational inertia, the time to complete the 
course increased by 34%. Hence, the results from these 
tests suggest that rotational inertia may have limited the 
turning performance of theropods. Characters such as 
retroverted pubes, reduced tail length, decreased body 
size, pneumatic vertebrae, and absence of teeth reduced 
rotational inertia in derived theropods and may have 
improved their turning agility. To reduce rotational 
inertia, theropods may have run with an arched back and 
tail, an S-curved neck, and forelimbs held backwards 
against the body.

Dial, K.P. 2000. On the origin and ontogeny of bird 
flight: Developing wings assist vertical running.
Annual Meeting and Exhibition of the Society for 
Integrative and Comparative Biology, Chicago, Illinois, 
USA, January 03-07, 2001
Discussions on the origin of avian flight fall into two 
philosophical camps: arboreal (tree-down) or cursorial 
(ground-up) hypotheses, both of which are dominated by 
paleontological evidence that fails to adequately address 
logical incremental adaptive stages necessary to achieve 
fully developed flight mechanics. Here, I present a new 
model based on novel behavioral and morphological data 
obtained during post-hatching development of precocial 
gallinaceous birds. This model offers a solution to the 
impasse of previous scenarios on the origin of avian 
flight and differs from the traditional cursorial thesis. 
Daily progress of locomotor performance (e.g., vertical 
and horizontal accelerations of flight and terrestrial 
locomotion) and morphometrics of wing development (e.g., 
wing loading, feather growth) of three species (Chukar 
Partridge, n=10; Japanese Quail, n=10; and Ring-necked 
Pheasant, n=2) from hatching to adult stage were obtained 
using high-speed video (60-250 Hz) and Doppler radar. To 
escape being handled, even one-day-old chicks exhibited 
the following locomotor behavior: they jumped vertically, 
vigorously beat their featherless forelimbs, and 
surprisingly swung their hind limbs through an arc similar 
to that used during over-ground running. Throughout 
development partially formed wings develop significant 
aerodynamic forces that assist the legs. This enables 
birds to "run vertically" achieving substantial heights 
against rough surfaces such as rocks, cliffs, and tree 
trunks. This "Assisted Vertical Running Hypothesis" 
appears consistent with evidence from fossil data and 
provides incremental adaptive plateaus, as revealed by 
ontogenetic trajectories, necessary to achieve fully 
developed avian flight mechanics as observed in living 
species.