Hi Rob,
Mainly I should explain that convergent evolution is a term used to
describe where things have evolved from something very different,
towards something similar, due to some similar factor of their
lifestyle. Yes, the thylacine shows similarity in its head structure to
a wolf or fox and this is a good example of convergent evolution but
there needs to be a link to make the concept sensible. The link being
the predatory lifestyle in a terrestrial mammal. As such, convergent
evolution is just a phrase used by us to describe a situation. It is not
a thing that someone can with certainty say where the defining line is
as to what does or does not qualify. That a leg of a insect and of a
vertebrate have the same function and the wing of an insect and a wing
of a bird may show similarities of shape due to use in aerodynamics is
also convergent evolution, if you wish to extend the term to a use so
broad it becomes almost silly to call it that. Doing so can make the
term so vague it is not useful.
However there is hardly any similarity between lyrebirds and peacocks,
upon which to hang any kind of link. The peacock (like most chickens,
oops, pheasants) is primarily a seed eater, the lyrebird is a predator
of leaf litter living invertebrates. There are all kinds of other
approaches to polygamous behaviour and yes they usually involve strong
sexual dimorphism. Of these two, one uses its tail in sexual display and
the other does not (but pretends to). That is the biggest similarity.
About their size, the peacock is a big pheasant and the lyrebird is a
big passerine but the two species are nowhere near similar in size.
Philip Veerman
24 Castley Circuit
Kambah ACT 2902
02 - 62314041
-----Original Message-----
From: Rob Geraghty
Sent: Monday, 12 October 2009 8:22 PM
To: Canberrabirds
Subject: Speaking of peacocks
--- On Mon, 10/12/09, Anastasia Dalziell <>
wrote:
> No relationship between the two!
OK, not genetic then.
> The closest relative of the lyrebirds are the scrub birds. And yes,
> lyrebirds are very unusual for a passerine and continue to cause
> taxonomic confusion (the troublesome birds!).
Then it seems to me that it's a bit of convergent evolution. Granted,
the features are superficial, but it seems to me that the size of the
bird and particularly the display with the tail are similar. There
could be other aspects such as feeding habits, what part of a forest it
feeds in, what it feeds on. Of course I've never seen peacocks in the
wild. Where the peacock went for a riot of colour, the lyrebird went
for complex song.
I'm thinking of convergent in a similar way to the thylacine and perhaps
the fox. Very different animals genetically, but superficially similar
because of similarities in their ecological niche. I was going to
compare the thylacine to a wolf, but wolves are pack animals and I've
never heard of thylacines being anything other than loners.
Rob
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