group hunting

[Bill Adlam <wa105@mead.anglia.ac.uk>]

Jon W. wrote:

>There's also the fact that the degree of dimorphism varies among different
>species.  Some bird species have larger females.  A few have noticeably
>larger males.  And many show no significant dimorphism, male and female so
>similar that you have to examine them close up to tell them apart.  IIRC,
>there's a correlation between the degree of dimorphism and the degree to
>which care of the nest and young is shared.

Most birds have about equal-sized sexes (but the male is often a bit more 
brightly coloured or sings more) and share parental care.  Ostrich males are 
bigger and they raise the chicks (from several females) alone.  Birds of 
paradise and peafowl have much more flamboyant males, perhaps a bit larger 
but I'm not sure, and the female rears the young.  Raptors (the aerial ones) 
are perhaps the most relevant - they have larger females and share 
responsibility for parental care.

I can't draw any conclusion from this except that size dimorphism is possible 
and either parent or both may raise the chicks.

[Jaime said my T. rex idea]
>> Sounds like wolves and hyenas, who are matriarchal in hierarchy.
>Hyenas are matriarchal, but wolves are not.  A wolf pack is dominated by the
>alpha male, and male wolves are decidedly larger than females.

I think that wolves have parallel hierarchies (male and female), like many 
primates.  In wolf packs it's usual for only the alpha male to breed, but  
also only the alpha female.  IIRC, only in particularly good years does a 
second or third female breed, but I'm not sure whether she mates with the 
alpha male or another one.  To summarise: lion prides contain many breeding 
females and few breeding males (and juveniles), wolf packs contain one 
breeding pair and many nonbreeding adults of both sexes.  Is that correct, 
Mr. Woolf?  

>Or unless there's more to the matter than we think.  We have what -- a dozen
>halfway decent rex skeletons known?  Maybe fifteen?  Not much of a
>population base to be speculating on.

Additional halfway decent skeletons of T. rex and other theropods are needed 
to verify that the morphs are different sexes, and the robust ones are 
female.  But I don't expect a skeleton would need to be even halfway decent 
to judge whether it's robust or gracile.  Surely some fragmentary remains are 
diagnostic (of morph and to genus or preferably species)?

I was speculating on the fact that the sexes do differ; the sex bias was a 
prediction generated by my theory.  Further evidence will prove me either 
possibly right or definitely wrong.

>                                    ...Especially not when I can't think of
>any mammal species that has an M/F sex ratio that's noticeably off 1:1.  Not
>every male ever gets to mate, but there are more or less as many males as
>females born.

Some pinnipeds, most notably elephant seals, have female-biased sex ratios at 
birth.  Besides, would you prefer a theory which only predicted what was 
already expected?

                                                        All the best,

                                                                        Bill