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Re: taxonomy is not stratigraphy (was Re: JVP 25(2): New Dinos, Birds, Discoveri




--- don ohmes <d_ohmes@yahoo.com> wrote:

> >>> Simply put, if you take the adult size of any of
> the
> potential prey species of a large dinosaur predator,
> then think that this animal produced as many as
> 10-30
> young per year,


  Many eggs were probably plundered before they could
hatch.




> taking on average much longer to
> mature than equivalent mammals 


  IIRC there have been studies indicating that
juvenile hadrosaurs grew very quickly, taking only
about 5 years or so to mature. Another study IIRC
indicated that camarasaurs became adults after about
18 years.


>(especially given the
> fact that they were an order of magnitude larger as
> adults, and significantly smaller as juves), then
> there is no shortage of potential non-adult prey for
> given predators. Although it is undoubtedly sexy,
> dangerous, and exciting to think of large theropods
> attacking adult herbivorous dinosaurs, really there
> is
> no requirement for them to do so. 


 They why is there evidence that they did? There are a
number of hadrosaur tails with bite marks. Happ said
that SUP 9713 was a mature Triceratops. Even armored
dinosaurs show evidence of attack.


>The sheer number
> of
> non-adult individuals of these prey species would
> provide an almost limitless bounty.<<<
> 
> Were the large theropods existing in a vacuum? No
> medium or small predators? 

 Exactly. Troodont teeth have been found in
association with hadrosaur nests. The great diversity
of small theropods in tyrannosaur environments has
been attributed to tyrannosaurs feeding their young,
leaving small prey to a variety of small theropods.




>Surely it is a safe
> assumption that the competition for sauropod flesh
> was
> intense at all stages of development. Note that as
> sauropods progressed to adulthood they would outgrow
> their predators in a size sequential progression,
> providing an (at least seasonal) positive size
> selection for the entire predator suite. Perhaps the
> adult sauros were out of reach,


 I don't know the age of the sauropods with healed
bite marks but remember Bakker's theory that allosaurs
compensated for weak jaws by running into prey with
jaws wide open? Such a tactic would be better suited
to adult than juvenile prey.  AFAIK the sauropod
pursued by the Acrocanthosaurus, based on the trackway
evidence, was not a very small one.



> but that doesn't
> negate the advantage of predator size. In fact,
> logically it augments the selective advantage of
> predator size by reducing available resources and
> increasing interspecific competition. "Almost
> limitless bounty"? In theropod dreams, maybe. 
> 
> --- Denver Fowler <df9465@yahoo.co.uk> wrote:
> 
> > When it comes to comparisons, far too many people
> > look
> > to the african serengeti for parallels with
> dinosaur
> > evolution and ecology. These comparisons are
> > understandable: the african savannahs are very
> > easily
> > observable: big open plains with some very large
> > inhabitants, and they do contain an ecosystem
> > largely
> > unaffected by the megafaunal extinctions of 10ka
> > (hence reasonably intact).
> > 
> > However, much of what people believe they
> understand
> > about these places is subject to much bias, and
> alot
> > of that is subject to what a handful of TV
> producers
> > thinks looks good, or is biased by the fact that
> the
> > savannah is an unusual megafaunal ecosystem.. even
> > for
> > africa.
> > 
> > Really, savannah ecology is an inappropriate
> > comparison to that of dinosaurs. First of all,
> > savannah relies upon seasonal grasslands, which is
> > of
> > course an entirely non-mesozoic phenomenon. Lions
> > only
> > exist in prides because of the need to hold down a
> > large territory because of migrational prey. Much
> > <admittedly not entirely solid> evidence points
> > towards north african lions living a mostly
> solitary
> > existence (before they all disappeared, and in
> > concordance with pretty much all other known felid
> > species), and indeed <of course> most male
> savannah
> > lions live such an existence. We don't see these
> > guys
> > on TV so much, because they aren't nearly as
> > exciting
> > as seeing pride hunting females, nor as
> > politico-socially interesting as seeing a bunch of
> > lionesses do all the work for a big old lazy male
> > (or
> > pair of males). But male lions constitute 50% of
> the
> > actual lion population, even if they barely make
> it
> > onto TV at all (males that take over prides might
> > end
> > up lazy, but all the other poor buggers have to go
> > hunt their own lunch, and frequently hunt smaller
> > prey, thereby creating a separate niche from the
> > female pride-lions).
> > 
> > Then there is the point that typical large
> mammalian
> > herbivores produce at most 2 young per year,
> > typically
> > maturing relatively quickly. thus biomass
> (regarding
> > potential prey for mega-predators) in most modern
> > mammalian ecosystems is tied up in at least
> > subadult-size animals. dinosaur demographics were
> > entirely different to this, and likely had no
> modern
> > analogue.
> > 
> > Simply put, if you take the adult size of any of
> the
> > potential prey species of a large dinosaur
> predator,
> > then think that this animal produced as many as
> > 10-30
> > young per year, taking on average much longer to
> > mature than equivalent mammals (especially given
> the
> > fact that they were an order of magnitude larger
> as
> > adults, and significantly smaller as juves), then
> > there is no shortage of potential non-adult prey
> for
> > given predators. Although it is undoubtedly sexy,
> > dangerous, and exciting to think of large
> theropods
> > attacking adult herbivorous dinosaurs, really
> there
> > is
> > no requirement for them to do so. The sheer number
> > of
> > non-adult individuals of these prey species would
> > provide an almost limitless bounty. 
> > 
> > The tendency of televison producers, and
> scientific
> > researchers, to dwell on savannah ecology the last
> > 20
> > years or so (understandable, since it is so easily
> > filmable and exciting, and given socio-economic
> > advances), has led to bias in how people want to
> > interpret dinosaur ecology. The simple fact is
> that
> > most modern predators hunt alone. Most modern
> > predators hunt prey signficantly smaller than
> > themselves. If you want to use modern ecosystems
> as
> > a
> > comparison then you should draw the conclusion
> that
> > tyrannosaurs et al lived lives not nearly as
> > exciting
> > as Hollywood might like us to believe.
> > 
> > Denver.
> > 
> > 
> > biomass in dinosaurs is 
> > 
> > 
> > 
> > --- Ivan Kwan <dino_rampage@hotmail.com> wrote:
> > 
> > > >While the argument of massive herbivores being
> > the
> > > selective pressure for
> > > >massive carnivores is a wonderful story, it
> > doesn't
> > > seem to play out in, at
> > > >least, any modern ecosystem. All super
> carnivores
> > > today are many times 
> > > >smaller
> > > >than half that of the largest herbivore in the
> > same
> > > ecosystem.
> > > plus the fact that hunting buffalo must be
> > > infinitely more rewarding than 
> > > scuffling over warthog piglets during the dry
> > > season. (Think this must be 
> > > some prerequisite for almost any documentary
> > > featuring lions - insert long 
> > > drawn-out battle between buffalo and lions)
> > > 
> > > In any case, the idea that theropods evolved
> > > gigantism in response to the 
> > > ever-increasing size of sauropods is a
> tantalising
> > > idea, but unfortunately 
> > > one that I'm afraid is difficult to test, due to
> > the
> > > imperfection of the 
> > > fossil record. However, at the moment,
at least,
> I
> > > think we do have evidence 
> > > that it was the herbivores that first
> 'developed'
> > > the tendency to grow to 
> > > much larger sizes, case in point being the
> > > prosauropods/basal 
> > > sauropodomorphs. Unless there are actually some
> 
=== message truncated ===


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