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

Re: Swimmin' dinos, fish milk, avian polyphyly (was RE: Sheesh)

--- Tim Williams <twilliams_alpha@hotmail.com>

> David Marjanovic wrote:
> >In her talks at the 2nd Intl. Paleont. Congress
> (Beijing, last June) and at 
> >the SVP meeting, Sanja HiniÄ&#8225; showed that
> *Baptornis* surprisingly patterns 
> >with wing-propelled divers, unlike *Hesperornis*.
> Hmmm... Martin and Tate (1976) feature a skeletal
> reconstruction of 
> _Baptornis_ that shows it with vestigial wings, like
> _Hesperornis_.  The 
> wing skeleton has shrunk to a hatpin.

HINIC-FRLOG, Sanja, MOTANI, Ryosuke, Univ. of
California, Davis, CA
The anatomical features of extant Neornithes are
expected to reflect physical constraints
during locomotion. If identified, these properties may
also be applicable to extinct birds for
which direct ecological and behavioral observation is
lacking. In order to infer locomotory
attributes of fossil birds, it is necessary to show
that osteology alone can be used to distinguish
between different locomotor modes in extant birds.
We compiled data on locomotor preferences and
anatomical features of 206 species of
extant birds. Using a statistical approach we
demonstrate that physical constraints of avian
environments are reflected in osteological features.
Principal component analysis (PCA) of
living avians identified subsets of osteological
features that are useful in separating diving,
swimming, and flying species. When superimposing
fossil species, Hesperornis regalis is
placed within the distribution of foot-propelling
underwater swimmers, whereas Baptornis
advenus appeared among wing-propelled divers. This is
the first quantitative test of underwater
swimming ability of hesperornithiform birds.
We investigated the biomechanical significance of the
width of the hip and the length
of the cnemial process of the tibiotarsus. Previous
workers already associated these features
with swimming modes, but the reasons for the
association have not been rigorously tested.
The narrow hip was believed to contribute to a
teardrop body shape that reduced drag forces
while moving through the water. However, these divers
spread the feet widely even when
gliding through the water, eliminating the
contribution of the narrow hip to reduce drag.
Similarly, the long cnemial process has been
associated with increased cross sectional area
of the femoral muscles producing power for underwater
propulsion; however, the femur is
stationary throughout the swimming cycle. We argue
alternatively that: relatively narrow
hip increases force transmission efficiency by
bringing the hip joint closer to the center of
mass; enlarged cnemial process reduces the range of
motion around the knee and increases
propulsive power of the tarsometatarsus.



Telefonate ohne weitere Kosten vom PC zum PC: http://messenger.yahoo.de