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Re: Size of *Neoceratodus africanus* and/or *N. tuberculatus*
"Briefly, there are several large to very large theropods that do not
appear to have been specialized for taking big prey:
_Therizinosaurus_, _Gigantoraptor_, and possibly _Deinocheirus_
(especially if an ornithomimosaur)."
I'm really not trying to be insulting or condescending here, so I
apologize if it seems that way, but:
Those are all members of groups that are noted for their
potential/probable omnivorous or herbivorous tendencies.
Therizinosaurs in particular do not seem to have been built for
hunting, and have marked adaptations for herbivory. Plants are
obviously a much more readily harvested source of biomass for the
purposes of attaining large size, yet spinosaurs bear no obvious
traits for doing so.
And you'll note that I said "**pretty much** every other group of
theropods." Granted, I could have specified "carnivorous" or even
"hypercarnivorous." But what come to mind are things like megalosaurs,
sinraptorids, carcharodontosaurs, derived tyrannosaurs, and, to a
somewhat lesser extent, dilophosaurs and abelisaurs. Big dromaeosaurs,
too, and I guess the larger noasaurs as well.
All are generally medium to large (20-50 ft) predators with no such
profound specializations as spinosaurs, indicating - again, obviously
- that something weird was going on with the latter. The typical range
of generic sauropods and small-to-medium ornithischians were AFAIK
available to (and probably utilized by) spinosaurs, yet no other group
that presumably hunted such prey developed such perplexing traits.
And if you're hunting small terrestrial prey all the time, doesn't it
make sense to be a bit smaller - than the biggest spinosaurs, at
least? They couldn't have been all that fast, which implies that their
prey items were either slow, unobservant, or fooled by some sort of
excellent camouflage/ambush technique. I dunno.
"All this tells me is that spinosaurids had different prey preferences
to carnosaurs, tyrannosaurs etc, with spinosaurs including a higher
proportion of smaller prey items in their diet (small ornithopods,
Right, but again, why the gigantism on a diet of morsels? It would
seem to me that feeding on small prey all the time while supporting a
multi-ton biomass implies a) plesiomorphic large body size and b) a
severe lack of suitable large game in the local environment, forcing
heavy specialization on smaller prey items in order to maintain the
large body size (which itself could be correlated to mating success or
predator avoidance or what have you).
Yet we know that suitably large prey was available, because it was
supporting huge carcharodontosaurs and fairly large noasaurs (and
spinosaurs, as with the ingested *Iguanodon*). I suppose this doesn't
rule out the above; it would just mean that spinosaurs moved into
those areas after picking up their unique traits. Or, perhaps, that
competition/predation by those sources was sufficiently intense to
force the specialization just to survive.
The other plausible option in my mind is simply that a particular food
source, one promoting specialization, was so comparatively abundant
that it was just waiting for a predator to tap into specifically. In
apparently theropod-rich, herbivore-poor environments like those of
*Spinosaurus*, and that would appear to be fish (and other aquatic
targets) - even if they were only seasonally available. A sufficiently
rich harvest of fish each year, providing vital fats and protein to
survive the next hard season, could perhaps prompt a degree of
specialization. Of course I'm not sure that would really be true for
all spinosaurs in various other habitats, but maybe that set of
conditions was the locus of their evolution.
"You could be right. The cranial adaptations of spinosaurs might
indeed have been geared toward improved piscivory. But I doubt this
is why spinosaurids got so big."
I can certainly agree with that. I don't think diet was the cause of
their size. But whatever they were eating had to be capable of
enabling that size, so it must have been pretty readily available in
one sense or another.
"I might suggest that the young did indeed focus on fish for their
main diet but the largest adults turned into greater opportunists over
time. If great predators such as this were seasonal hunters and knew
when certain lakes dried up where and when then suddenly great size is
a huge advantage. The giant can stay and eat the easy to catch fish
leaving the smaller Spinosaurs hungry. Sometimes if a lake isn't
completely dry but merely shallow or if there is a bottle neck in a
river then the largest Spinosaurs, still holding sway the way the
biggest meanest bears take the best fishing spots, then their giant
well formed fishing jaws would still come in handy for opportunistic
That's an interesting thought. Given their bulk, it would make sense
for adult spinosaurs to be less picky and more catholic than the young
ones, although you'd have to be pretty big to take full-sized giant
lungfish or coelacanths. I'm not sure how common juvenile fish would
have been, but they could have been a key food source for the
youngin's. Especially if there was a lot of pressure on small
terrestrial prey from noasaurs and/or dromaeosaurs, in addition to
pressure from the other direction due to carcharodontosaurs.
And the seasonality aspect was probably important for *Spinosaurus*,
at least; not so sure about *Baryonyx*.
Competition/limited access to large prey, predation risk, seasonally
abundant prey availability, mate selection . . . no one cause, I'm