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

["David Marjanovic" <david.marjanovic@gmx.at>]

> However, it's Saturday morning, and I can't resist just one, tiny post...

I know that feeling...

> Incidentally, Deinosuchus must have grown much faster than any modern croc
> (even in captivity with optimal conditions) to reach 10 m in 50 years.
Even
> known-age crocs of 70 to 80 years old top out at 5 to 6 metres, although
the
> formative years of their life were spent in the wild which dictates future
> growth rates and maximum size. The biggest captive-born croc I know of is
> just shy of 6 metres after 30 years.

Gregory M. Erickson*, Christopher A. Brochu [who else?]: How the 'terror
crocodile' grew so big. Nature 398, 205f. (18. 3. 1999)

* erickson@bones.stanford.edu (no idea if this address still works).

"*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."

> Jura wrote, and David replied:
>
> > > As for reptiles, how big do you want.
> >
> > Over about 1 tonne and terrestrial.
> >
> > > We have huge snakes, turtles, crocs and
> > > lizards.
> >
> > All stopping at or near 1 tonne, AFAIK.
>
> The largest captive crocs that have been weighed have approached 1200 kg.
> Extrapolations from known-sized crocs would put the largest measured crocs
> (6.3 metres) closer to 1500 kg. [...]

OK, but these are still semiaquatic...

> Regarding Deinosuchus, David wrote:
>
> > Semiaquatic, and only 10 m long (for decades it had been estimated at 15
> m).
>
> I've always wondered: what reason is there to believe that fossil
> Deinosuchus found to date represented animals of maximum size for that
> species, or that they were male (which exceed females in size by up to 40%
> in extant crocs)? On a normal distribution curve, mean size for adult male
> C. porosus for example is around 4 to 5 metres, yet rare individuals
> exceeding 6 metres have been found. Mean female size is around 3 metres,
> with rare individuals reaching 3.5 metres.

I don't know. All I have is from the above article, under Fig. 2: "The data
for individuals from extinct clades ([...] specimen numbers are available
from the authors on request) are based on growth line counts in dorsal
osteoderms extrapolated to total body length."

> Jura wrote:
>
> > > Crocs are no to migrate long distances over land to find new
waterholes,
> > > though it isn't as regular as the other examples.
>
> David replied:
>
> > How far?
>
> [...] As for terrestrial migration, this normally occurs during the dry
> season or drought where water holes start to dry up. Distances between
> adjacent water holes along a river course are rarely more than a few km
(and
> typically less than 1 km), but the longest distance I know of was around
50
> km over several weeks (I don't remember the exact time): an animal which
was
> relocated and which homed back to its point of capture overland,
eventually
> getting caught in a bushfire. It died about 5 km from its destination.
> There's not enough known to say whether such a distance is usual.
>
> Observations of croc movement overland suggest that they use the high walk
> form of locomotion (the animals lifts its entire body trunk off the
ground),
> and that speeds are relatively slow (less than 5 km / hr) but sustained.

This is more interesting...

> 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?

> I'd go with Bennett's findings here. Exercise time to exhaustion has been
> confirmed by several studies to scale with body mass - so very large crocs
> have much greater anaerobic capacity. However, it's not so simple.
> Crocodilians exert massive amounts of power over short periods of time (a
> large croc [>5 m] can separate the front half of an average sized ungulate
> >from its posterior portion with a flick of its head), then they have a
> period of rest with little activity, and then they exert massive power
> again, and so on until exhaustion. Capturing crocodilians reveals this
> activity pattern. In other words, they can exert hyperanaerobic power for
> long periods, but not continuously (and decreasingly over time).

"Megadinosaurs" would need continuous power...

Thanks for the refs!