Re: [Re: [Part 2: Terramegathermy (very long, too)]]

[archosaur@usa.net]

"David Marjanovic" <david.marjanovic@gmx.at> wrote:

> Gregory M. Erickson*, Christopher A. Brochu [who else?]: How the 'terror
> crocodile' grew so big. Nature 398, 205f. (18. 3. 1999)
> 
> "*Deinosuchus* is a giant crocodylian from the Late Cretaceous period of
> North America. It was 8 to 10 metres long and weighed between 2,500 and
> 5,000 kg, three to five times more than the largest crocodiles alive today.
> [...] Did it exhibit accelerated growth rates, like its dinosaurian
cousins,
> or did it simply maintain primitive reptilian rates for decades (as was
once
> [citing a paper from 1978] proposed to explain gigantism in dinosaurs)?"
The
> latter, say the authors. They counted growth rings in dorsal osteoderms,
> giving longevity of several specimens (estimated to have been 8.43 to 9.10
> m) of 50 and 51 years (+-2). "*Deinosuchus* showed similar rates (about 0.3
> metres per year) to other crocodylians from the phylogenetic bracket during
> the first five to ten years of life, but maintained these juvenile growth
> rates for several decades (Fig. 2)." Bone is lamellar-zonal, in contrast to
> the fibro-lamellar bone of the fast-growing dinosaurs. "The evolution of
> increased metabolic rates in dinosaurs is believed to have facilitated the
> evolution of gigantism by enabling them to build their skeletons swiftly
> using fibro-lamellar bone. *Deinosuchus* achieved the same outcome, but it
> took much longer. Dinosaurs of similar size to *Deinosuchus*, such as
> hadrosaurs [...], reached adult size in only seven to eight years, whereas
> the giant crocodylian required more than 35 years [for 7 m]. We believe
that
> the retention of an ectothermal [read bradymetabolic] physiology
constrained
> *Deinosuchus* to the deposition of slow-forming somatic tissues (such as
> lamellar bone) throughout development, necessitating a greater
developmental
> time to reach dinosaurian proportions."

+++++++++++++++++++++++++++++

I have my qualms with this study because they used the dorsal osteoderms.
Osteoderms don't go through wear and tear like the rest of the bones in (or
on) the body. 

Again I must ask (perhaps if HP Chris Brochu is onlist right now) why use the
osteoderms and not the vertebrae or long bones. I'm guessing this must have
something to do with what material there was to work with, but I could be
wrong.

__________________________

> > However, this is strongly dependent upon croc size - bigger animals   > >
have greater anaerobic capacity, but they have much greater bulk to  > > move
around. I would doubt that most adult crocs could keep this up  > > for more
than a few minutes at a time, and galloping (in some        > > species)
typically lasts for no more than 5 to 10 seconds before     > > exhaustion.
[...]
> 
> Now extrapolating this to "megadinosaurs" indicates that the latter must
> have been tachyaerobic, doesn't it?


+++++++++++++++++++++++++

Ah ah ah now, while crocs might be closer phylogenetically, when it comes to
lifestyle, land tortoises and varanids might be better examples. Crocs have
proportionately short legs and a body generally adapted to a semi-aquatic
highly anaerobic existence. They don't make for the best examples when it
comes to sustained aerobic activity. But, they don't make good examples
because of their recent adaptations, not because they are bradymetabolic.
Their gizzards, diaphragm, four chambered heart, and secondarily sprawling
stance all attest to that.

Megadinosaurs would be better compared to large varanids and even large
tortoises, rather than large crocodiles. At least in this area.

Jura


Jurassosaurus's Reptipage: A page devoted to the study of and education on,
the reptilia:

http://reptilis.net

____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=1