Re: "Dinosaurs Died Within Hours After Asteroid Hit Earth..."

[Mickey Mortimer <Mickey_Mortimer111@msn.com>]

Dora Smith wrote-

> I understand that a viable theory exists that all modern mammals are
> descended from a cow-sized herbivore that survived the extinction.    I
> don't know how justified that idea is, but it must rest to begin with on a
> cow sized herbivore that survived the mass extinction.    I wonder where
it
> was living at the time?    I doubt it was in a burrow.

Utterly untrue.  At the very least, three mammals had to survive (a
monotreme, metatherian and eutherian).  Indeed, there are arguments
Cretaceous zalambdalestids and 'zhelestids' are part of the placental crown
group, closely related to Glires and one of the 'ungulate' groups
(Afrotheria? Artiodactyla?) respectively.

> Now, I know that a volcano in Indonesia 65 million years ago came within
100
> individuals of driving the human race to extinction.   It appears as if
> those individuals must have lived in Africa at the time, as genetic
evidence
> from modern humans points to an origin in Africa.   That is what one would
> expect given that humans did not yet live in the Western hemisphere,
> Southern Asia was apparently inhospitable and climactic changes would have
> affected Europe and the rest of Asia.

Surely you meant much more recently, and the story itself looks suspect to
me.

> But still it seems a stretch that just one line of coelorusaurian
dinosaurs
> survived when so many lines had evolved in very similar ways.   Apparently
> more than one sort of mammal survived!

More than one type of coelurosaur survived too.  Accepting recent
phylogenies, at least one palaeognath, gallinuloidid, paraortygid,
quercymegapodiid, crown galliform, anhimid, anseranatid, Anatalavis,
presbyornithid, anatid, gaviid, procellariiform, charadriiform, coconiid,
scopid, balaenicipitid, fregatid, pelecanid, sulid, phalacrocoraciid and
anhingid had to survive, and that's ignoring the Lance parrot.

> These definitions of Aves that have been provided all define the class in
> terms of common descent from the unknown nearest common ancestor.   My
> question is, how do we know that this nearest common ancestor was far out
> some narrow limb of the coelorusaurian family tree?

We know this because that's what all the anatomical evidence tells us.
There's some possibility some long-tailed birds were more closely related to
traditionally non-bird dinosaurs (like deinonychosaurs), there's basically
no possibility the short-tailed birds had more than one long-tailed
ancestor, and even less possibility living birds aren't more closely related
to each other than any is to Ichthyornis, hesperornithines,
enantiornithines, confuciusornithids, or any long-tailed theropod.

> You know, I should know the answer to this, and I don't.   I mostly
learned
> that hesperiformes and ichthyoformes (sp?) aren't still around.
>
> Did all toothed birds die out before the end of the Cretaceous?
>
> I had the idea some of them were still around in the Tertiary - but I
could
> very easily be wrong.

Hesperornithines (also called hesperornithiformes) and ichthyornithids
(which currently only includes Ichthyornis) did not survive the K-T event.
Nor did any other toothed birds.  Some Tertiary birds, called pelagornithids
('pseudodontorns'), had toothlike points on their beaks, but these were not
true teeth.

> The way I understand it, although many scientists think that archaeopterix
> is ancestral to birds, others think that they were an evolutionary dead
end
> and not necessarily more closely related to birds than caudipteryx.

Mike explained the ancestor thing.  Almost everyone thinks Archaeopteryx is
more closely related to living birds than Caudipteryx (an oviraptorosaur)
is.

> I know that all other theropods including caudipteryx and the two other
> bird-like ones differed more from modern birds than archeopterix did, but
> not by much; what is more, they and several other therapod dinosaurs were
> undergoing structural changes like those that modern birds have; in bone
> structure, foot structure, arm and wing structure, tail structure, and
> feathers.

Mike was right for the most part- most of the birdlike characters in
Caudipteryx are due to its common ancestry with birds.  But yes, it was also
developing some birdlike characters in parallel to birds.  These include the
toothless maxilla and dentary, low number of dorsal and caudal vertebrae,
and reduced third finger.

> I notice that, for instance, there is uncertainty that Confuciornis is a
> bird and not a non-avian therapod.    In addition to uncertainty that
> caudipteryx and several others were not birds.   Partly because their
> feathers and other features might make them necessarily descended from
> whoever the nearest common ancestor whose existence defines class Aves
was.

Confuciusornis is almost definitely more closely related to living birds
than any long-tailed theropod is.

> We don't have anything from that bird but part of the jaw bone, do we?
>
> As much as I would like my little budgisaurs to have an ancient and
> illustrious history, how can we know on the basis of so little that it is
> not convergent evolution?

We can't know, but we can hypothesize, based on the evidence we have
available.  Convergence is never the null hypothesis, it must be shown to be
so by characters that contradict assignment to whichever group the taxon is
converging with.

Mickey Mortimer