[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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



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
> 20-foot long 
> coelophysians/herrerasaurs/avepods that I've
> forgotten about.
> 
> Ivan
> 
>
_________________________________________________________________
> Take a break! Find destinations on MSN Travel.
> http://www.msn.com.sg/travel/
> 
> 



        
        
                
___________________________________________________________ 
Does your mail provider give you access to messages sent to other POP email 
accounts, like your work account? 
Get Yahoo! Mail http://uk.mail.yahoo.com