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RE: Pick one - massive or agile



As a coauthor on the study (and please RTFP) I suppose I should comment on what 
I see as a straw man argument here (useful as I recognize such arguments can be 
in a rhetorical sense...). We are fully aware of the constraints on maximal 
speed and indeed have been quite involved in that research, both experimentally 
and theoretically, which generally shows that limb force (or in some cases 
power; not so much inertia but it is of course part of the picture) is ONE key 
limit on speed. 

Considering that maximal speed running is likely a rather unstable situation, 
slight perturbations to that state might require rapid responses. Hence our 
logic was that responsiveness could under certain situations (i.e. 
perturbations that animals in nature will frequently see) would be more 
limiting, to some as yet unknown degree, in large animals. It is simply 
pointing out that nervous control has often been left out of the game in this 
field of research, and partly due to ignorance of how it actually works across 
a diversity of species. This was one step toward rectifying the situation and 
filled an important gap in the literature, as you'll realize if you poke around 
it.

I wish I were so confident as to be able to say that force would limit 99% of 
the time vs. control 1%. Which would be more limiting would be extremely 
context-dependent in real animals and real environments, which this field is 
beginning to focus on increasingly more (e.g. see recent studies by Daley, Kuo, 
Ferris, Seyfarth, Full and Holmes). There are no studies yet that would 
conclusively answer that question, so I do not think this can yet be rudely 
dismissed as idle "paleofantasy."



-John



-----Original Message-----
From: Heinrich Mallison [mailto:heinrich.mallison@googlemail.com]
Sent: Tue 7/6/2010 3:50 PM
To: dinosaur@usc.edu
Subject: Re: Pick one - massive or agile
 
Maximum speed is obtained by accelerating body parts, be that the
entire trunk and head when jumping, or the limbs when running.

Imagine a hopping frog: it un-fols its limbs very rapidly, and pushes
the entire body forward, accelerating from a stand-stil. In contrast,
a cheetah has a relatively steady trunk speed, but needs to protract
and retract the limbs as rapidly as possible. Which is why fast
running involves reduction of toes (among many other things): the less
distal weight you have to accelerate, the higher up the center of mass
(COM) of your limb, and the shorter the moment arm from the COM  to
the hip.

In both cases, frog and cheetah, a lot of inertia has to be overcome.

regrads
Heinrich

On Tue, Jul 6, 2010 at 4:41 PM, Jura <pristichampsus@yahoo.com> wrote:
> Wouldn't greater inertia have more of an affect on acceleration than maximum 
> speed?
>
> Jason
>
>
> --- On Tue, 7/6/10, Heinrich Mallison <heinrich.mallison@googlemail.com> 
> wrote:
>
>> From: Heinrich Mallison <heinrich.mallison@googlemail.com>
>> Subject: Re: Pick one - massive or agile
>> To: "Erik Boehm" <erikboehm07@yahoo.com>
>> Cc: dinosaur@usc.edu
>> Date: Tuesday, July 6, 2010, 10:11 AM
>> That is true - but not what I was
>> talking about. I was referring to
>> this paragraph
>>
>> >>Large animals may cope with these relatively long
>> delays by simply moving slowly,
>> >>explaining at least in part the low maximum speeds
>> of large mammals (Garland 1983;
>> >>Hutchinson et al. 2006) and providing further
>> evidence for the idea that dinosaurs could
>> >>not be both massive and agile (Hutchinson &
>> Garcia 2002).
>>
>> this is, as I said, utter BS! Reaction times are not that
>> much larger
>> that large dinosaurs could not run at 60 mph! Clearly,
>> locomotion is
>> much more influenced by inertia. Slow maximum speeds are,
>> I'd guess,
>> 99% force/inertia and 1% reaction time limited.
>>
>> So whatever the finding on reaction times is, actually
>> suggesting they
>> have a profound influence on locomotion is nothing but
>> palaeofantasy.
>>
>> Regards,
>> Heinrich
>>
>>
>> On Tue, Jul 6, 2010 at 3:45 PM, Erik Boehm <erikboehm07@yahoo.com>
>> wrote:
>> > Inertia has nothing to do with reaction times.
>> > It can explain slow movement speeds, but not response
>> delays
>> >
>> >> It takes an elephant much longer to notice a fly
>> >
>> >
>> >
>> > --- On Mon, 7/5/10, Heinrich Mallison <heinrich.mallison@googlemail.com>
>> wrote:
>> >
>> >> From: Heinrich Mallison <heinrich.mallison@googlemail.com>
>> >> Subject: Re: Pick one - massive or agile
>> >> To: dinosaur@usc.edu
>> >> Date: Monday, July 5, 2010, 11:22 PM
>> >> Bah, nonsense! The travel time
>> >> increase for nervous signals is utterly
>> >> irrelevant compared to the increase in inertia.
>> That's
>> >> what's slowing
>> >> huge animals down!
>> >>
>> >> Heinrich
>> >>
>> >> On Tue, Jul 6, 2010 at 4:54 AM, Richard W. Travsky
>> <rtravsky@uwyo.edu>
>> >> wrote:
>> >> >
>> >> > http://www.nytimes.com/2010/07/06/science/06obelephan.html
>> >> >
>> >> > It takes an elephant much longer to notice a
>> fly and
>> >> flick it away than it
>> >> > takes a shrew, and the reason is not that
>> the
>> >> elephants great brain is too
>> >> > busy with philosophy, or that it simply does
>> not
>> >> concern itself with flies.
>> >> >
>> >> > Its a matter of round-trip travel time - in
>> the
>> >> nervous system. The trip
>> >> > from the elephants skin to the brain and back
>> again to
>> >> the muscles to flick
>> >> > the tail is 100 times as long as the same
>> trip in a
>> >> shrew, according to a
>> >> > new study published in the Proceedings of the
>> Royal
>> >> Society B.
>> >> >
>> >> > The nervous system acts like an information
>> >> superhighway, sending messages
>> >> > back and forth from the brain throughout the
>> body. The
>> >> bigger the animal,
>> >> > the greater the distance traveled.
>> >> >
>> >> > Nerves have a maximum speed limit of about
>> 180 feet
>> >> per second, said Maxwell
>> >> > Donelan, the studys lead author.
>> >> >
>> >> > It makes sense that in a large animal, like
>> an
>> >> elephant, messages have a
>> >> > longer way to travel, he said.
>> >> > ...
>> >> >
>> >> >
>> >> > http://rspb.royalsocietypublishing.org/content/early/2010/06/24/rspb.2010.0898.full
>> >> > ...
>> >> > As a consequence, larger animals are burdened
>> with
>> >> relatively long
>> >> > physiological delays, which may have broad
>> >> implications for their behaviour,
>> >> > ecology and evolution, including constraining
>> agility
>> >> and requiring
>> >> > prediction to help control movements. ...
>> >> > Large animals may cope with these relatively
>> long
>> >> delays by simply moving
>> >> > slowly, explaining at least in part the low
>> maximum
>> >> speeds of large mammals
>> >> > (Garland 1983; Hutchinson et al. 2006) and
>> providing
>> >> further evidence for
>> >> > the idea that dinosaurs could not be both
>> massive and
>> >> agile (Hutchinson &
>> >> > Garcia 2002).
>> >> > ...
>> >> >
>> >>
>> >
>> >
>> >
>> >
>>
>
>
>
>