[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
I've just dug the following abstract out, and I post it here, not because I
agree at all with what it says, but because I doubt if many others that are
interested will have seen it before. It's a bit dated (1989) and is abstract no.
342 in _American Zoologist_ 29: 1A-195A
ON WHY THE DINOSAUR COULD NOT EVOLVE FLIGHT.
S.F. TARSITANO. Southwest Texas State Uni., San Marcos.
Recent hypotheses concerning the origin of birds from theropod dinosaurs have
failed to address anatomical, aerodynamic and energetic obstacles to evolving
flight from a cursorial biped. These obstacles include: 1) the need to overcome
gravity, 2) the need to compensate for drag, 3) the inability to flatten the
abdomen for gliding essential in the early evolutionary stages of flight, 4) the
fact that selection in theropods is on the wrong girdle, i.e. pelvic instead of
pectorial, 5) the weight and body proportions (center of mass) cannot be
compensated for by the theropod's reduced lifting surfaces, 6) the air current
for flight must be created by running or jumping, 7) the coelurosaur coracoids
are reduced, 8) coelurosaurs lack a siphonium and 9) the boundary layer
hypothesis of feather origin precludes feather formation in theropods. Any one
of these obstacles should eliminate theropods from a sister group relationship
with birds. However, none of these obstacles are encountered by small, arboreal
thecodonts such as the recently discovered _Megalancosaurus_.
Another abstract (relevant to discussions past and present on this list) in the
same volume is:
VISPO, C.R. and BAKKEN, G.S. 1989. Thermoregulatory behaviour of the 13-lined
ground squirrel (_Spermophilus tridecemlineatus_).
'The behaviour and body temperature of squirrels in a west-central Indiana
population was recorded simultaneously with microclimate data... Using stepwise
multiple regression models, we... could account for up to 10% of the variance
in 4 above-ground activities (alert, feeding, head down, walking). Time spent
in each activity declined gradually when (operative temperature) was greater
than 40 degrees C or less than 30 degrees C. Data from the literature and our
laboratory work indicates that this 30-40 degree C thermal neutral zone for
activity approximates the thermal neutral zone for activity. By reverse
optimality, this suggests that even during the temperate summer the behaviour
of ground squirrels may be influenced by thermoregulatory requirements.'
So, (elsewhere) the critter has been described thus: 'in practise, it's
"Control, control, you must learn control!"
Another dodgy quote..