NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/talk/origins/16615

Internet Message Format | 1993-01-24 | 5.6 KB

Path: sparky!uunet!news.tek.com!tekig7!tekig6!alanf
From: [e-mail] (Alan M Feuerbacher)
Newsgroups: talk.origins
Subject: Re: Muscle tissue from mouse to sauropod
Message-ID: <[e-mail]>
Date: 23 Jan 93 18:44:46 GMT
References: <[e-mail]>
Sender: [e-mail]
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 106

In article <[e-mail]> [e-mail] (news) writes:
>
>We've seen one poster claim that reptile muscle is twice as good as ours,
>and that this has been proven more dynamically than possible via microscope
>test.  I've got three problems with this.
>.....
>3.  It isn't even relevant.  Sauropods resembled reptiles in no way, shape,
>or manner, and may actually have been mammals or near-mammals.  They walked
>with their legs under them like large mammals, as opposed to reptiles other
>than snakes, which walkin the familiar splayed manner, and their metabolism
>was, in all likelihood, warm-blooded.

The point was not to prove that sauropods were or were not mammals,
but that no one knows what their physiology was.  Given that, there
is no basis for you to assume that they were so much like Kaz that
you can blindly apply a single scaling equation to all life forms.
This has been experimentally proven; see below.

The article I pointed out was from the journal _Evolution_, Vol. 45,
No.1, February, 1991, pages 1-17, John Ruben, Department of Zoology,
Oregon State University.

Ruben stated that _Archaeopteryx'_ skeletal structure indicated that
it supported a relatively small mass of wing muscles, compared to
modern birds, and that because various other features indicate it
was certainly capable of flight, something was missing.  The missing
piece he filled in by hypothesising that it was "a flying ectotherm,"
i.e., it had reptilian musculature.  He supported this by noting the
close similarity of _Archaeopteryx'_ skeleton to certain small
dinosaurs, which he views as most likely cold-blooded.  The question
of endothermy versus ectothermy in dinosaurs is still very much
debated, and some workers wonder if the question can ever be answered.
Interestingly, some reptiles (a sea turtle) and even fish (bluefin
tuna) have a certain amount of thermoregulatory ability.  But the
problem is irrelevant to the point we are discussing.

Given this background, note what Ruben states:

   If _Archaeopteryx_ were ectothermic, it may well have achieved
   powered, flapping flight, as well as ground-upward, standstill
   takeoff, with less than one-half the flight-muscle volume of
   modern birds.

   This is related to a previously unrecognized attribute of
   reptilian muscle physiology:  During "burst-level" activity,
   major locomotory muscles of a number of active terrestrial
   squamate reptiles generate at least twice the power (watts
   kg^-1 muscle tissue) as that of birds and mammals.  Furthermore,
   patterns of metabolic power output during intense exercise in
   crocodiles... suggest high-power locomotory muscle tissue occurs
   in a broad range of diapsid reptiles.

   Enhanced reptilian muscle power is probably due to a variety of
   factors, including elevated intramuscular contractile fiber
   concentration of mitochondria-poor reptile muscle, and
   particularly, high contractile velocity facilitated by
   accelerated ATP turnover and high specific activities of
   myosin-ATPase and rate-limiting ATP-forming glycolytic
   enzymes....  Accordingly, even though lizards and mammals attain
   similar sprint speeds..., skeletal muscle mass in reptiles is
   less than in equivalent-size mammals (reptilian skeletal muscle
   mass, in grams, scales according to the equation
   0.19 [grams total body mass^1.09]; for mammals, the equation is
   0.42 [grams total body mass^1.01].

   Utilization of high-power, reptile-type flight-muscle to support
   powered flight seems consistent with _Archaeopteryx'_ relatively
   reduced pectoral surface area....  [Various] observations are
   strongly indicative that _Archaeopteryx'_ capacity for
   generation of flight-muscle power was at least equal to that of
   many living birds.  If _Archaeopteryx_ possessed physiologically
   reptilian skeletal muscle (at 450 W kg^-1), and if the ratio of
   its pectoral muscle to total muscle mass were only 7%, rather
   than the 15-20% of many extant birds (at 150-225 W kg^-1), its
   flight muscles would have generated comparable power, but these
   muscles would have required far less skeletal area for their
   origin.  This argument would resolve much of the apparent
   discrepancy between external and internal flight apparatus in
   _Archaeopteryx_.

Ruben then proposes that many birds evolved towards optimization
for stamina, which resulted in full endothermy and lower-power
muscles.  He concludes with:

   There is ample justification for further investigation of the
   taxonomic distribution and physiology of high-power muscle
   tissue.  Confirmation of the presence of high-power locomotor
   muscle tissue in all modern diapsid reptiles, and, by extension,
   all diapsid reptiles, would have profound implications for the
   reconstruction and functional interpretation of a variety of
   extinct forms not dealt with here, including dinosaurs and
   pterosaurs.

With the foregoing in mind, your conclusion here is unwarranted:

>There is no conceivable way that any creature which eats grass and low-value
>food, and whose weight is therefore mostly digestive mechanism, is going
>to be remotely close to being as strong or capable of lifting as much weight
>as a top human power-lifter such as Kazmaier.
>
>If Kaz couldn't stand in our gravity at 70,000 lbs, then neither could a
>sauropod dinosaur.

Alan Feuerbacher
[e-mail]