Re: KT boundry event


John Harshman wrote:
Bill Hudson wrote:

uraniumcommit...@xxxxxxxxx wrote:

John Harshman wrote:


[snipped]


And are you actually saying that Cretaceous ducks are not birds?

They are, if they are substantially like contemporary ducks.


ok, but see below.


If so,
are any extinct birds actually birds? Is the dividing line actually the
K/T boundary, and if so why?

The dividing line has to be drawn somewher, doesn't it? The KT boundary
is a reasonably good place to draw the line.



I suggest you look up the terms 'Cretaceous' and 'K/T boundary', and
then get back to us.

The point is that you are trying to draw a temporal division for
'birds', and that it makes no sense to do so. 'Bird' is defined not by
"when" but by "what". And the "what" definition of 'bird' makes them
'avian dinosaurs'.

I dare say that for almost all people if you plopped a live specimen of
a cretaceous duck in their pond, they wouldn't be able to tell the
difference from a mallard.

If they looked at all they would. The known Cretaceous duck is a
presbyornithid, which had long legs like a stilt. I know people who
can't tell coots from ducks, but I've never seen anyone yet confuse an
egret with a duck.

But your point is valid. The K/T boundary is the silliest possible way
to distinguish birds from non-birds. Consider a species that survives
past the boundary. Yesterday it wasn't a bird. Today it's a bird. Did
that make any sense?

If the group on one day is drastically cut down in number and variety,
then yes it does. It's not the passgae of time that marks the division
across the KT boundary, it's that big bright light....and loud noise...

If there were numerous proto-avians and avian dinosaurs before the KT
event, some of which resembled modern birds and others that did not,
and then the day after the big bad boom the situation changed
drastically so that only those creatures that shared the general sort
of charactersitics that we classify as 'birdish' remained, then it
makes perfect sense. here today, gone tomorrow. The group was redfined
by the KT boundary event, not by me.

I also think that for most people if you
showed them a living specimin of Archaeopteryx, Confuciusornis,
Hersperonis or Ichthyornis they would also say "bird".

So going based on even the 'colloquial' definition I don't think your
argument holds up.

[snipped]


.

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