Re: BIRDY _ARCHAEOPTERYX_

["John V Jackson" <jjackson@interalpha.co.uk>]

--Original Message-- From: Matthew Troutman <m_troutman@hotmail.com>Date: 07
November 1998 08:09



>Clearly there are two different ways of interpreting evidence at work
>here...
>
>In a previous post, John Jackson discounted the birdlike features of
>_Archaeopteryx_ as "flight-adaptations" that are "easily reversible in
>secondarily flightless forms".  Tell me, is a (not a hooked
>ectopterygoid, my mistake!) triradiate palatine in _Archaeopteryx_ a
>flight adaptation?

As I mentioned some months ago, there are indirect results in the skull
arising from flying/non-flying differences.  Of course, everything in a
flier's body is subject to extreme weight saving pressure, and this is a
main cause of changes (in addition to wing mechanics), but it is also likely
that sheer size would lead to different optimal structures. Also Archae
probably ate invertebrates, or possibly flimsy pterosaurs whereas some later
flightless mani's ate beefier stuff.  Some things are just to complex for us
to make sensible guesses at, and a lot to do with the palaeontology of birds
skulls falls into this category.


>Let me end with a quote from the abstract of Elzanowski and Wellnhofer:
>
>     Being unrelated to locomotion, the avian features of the skull
>demonstrate that _Archaeopteryx_ is a bird rather than a feathered
>nonavian archosaur (p. 81).

So changing physical size by an order of magnitude or two has no effect?
What about the *results* of being able to fly?  How can E & W be sure that
some of these skull changes are not required to protect a flightless animal
from falling on its nose from a height of five feet for example?  It is
generally accepted that weight is an important factor in bird skull design -
it's the reason given for their change from teeth to beaks.  Presumably they
also decreased the force of their bite.  Presumably this would be reflected
in skull structure.  It is difficult to say anything for certain about
palaeontology, but much easier to be certain about palaeontologists; the
above statement by E & W is wrong.  Incidentally, are they saying that the
difference is so great that evolution between birds and "proper dinos" in
either direction is impossibe?  Also, I would be intrested to see what skull
similarities are shared between Archae and
_Protarchaeopteryx_/_Caudipteryx_.

>
>>Might not the first feathered flier fit in well with the ancestor of
>the
>>most successful group of K theropods?
>
>But it is too birdlike to be the ancestors of K theropods!  Tell me, do
>you think that the characters above are related to flight?

(See above.)


>
><<...just like the opposing theory!  No-one has evidence for *any* J
>precursor to Archae apart from a few unusually small teeth which could
>be anything. Apart from cladistics and historical accident, there is no
>evidence that the direction of relationship is _Velociraptor_ -> Archae;
>and time would seem to point the arrow the other way.>>
>
>"Could be anything"!  I think that the teeth are described as
>maniraptoriform in character.  Padian also described some Morrison
>maniraptorans or maniraptoriforms.

Padian also said Archae did not display any particularly arboreal
adaptations.  He also said that the mechanically totally unsuited
maniraptoran hand was designed to give "killer blows" (rather than for
hooking and pulling).  I think I'll take his opinion on an animal for which
he has only the teeth with a pinch of salt.



>How can _Archaeopteryx_ be a K
>theropod progenitor?

I don't think it requires too great a leap of the imagination to see it
leading to _Protoarch/Caudipteryx_, and thence Ovi's, nor to something like
_Rahonavis_ -> _Veloci_, do you?  Oh - perhaps you mean a progenitor of
*all* theropods.  Well, time would rule out Archae, certainly.  The thing
is, there are "theropods" and "theropods", aren't there?!

>The fossil record is meager in many areas and
>cannot be considered as the most reliable chronical of what really
>happened.

I'm not sure this helps your argument more than it does mine!



>_Archaeopteryx_ is theropod-like in most of its features, but
>as outlined above it shows features that are not related to flight and
>are not found in nonavian theropods:
>
>1)  Roughly triangular skull where the premaxillary forms a point.

Loss of bite force particularly at the front of the snout due to weight
loss, eating smaller prey, both, or possibly other things too.

>2)  Possible mesethemoid above the dorsal margin of the antobital
>cavity.

General change in skull structure (see above).

>3)  Unserrated, triangular, crocodilian-like teeth.

How many insectivores are known with serrated teeth?  Only flesh-rippers
need them (and not all of them: mammals slice, crocs swallow whole or use
their short necks to twist or just "flip" the prey in two. [Cor did you see
that program the other day where the croc had a pig in its mouth and just
flicked its head and the back half of the pig just vanished in the space of
a couple of frames?!!  But I digress]).

>4)  ?Loss of contact between jugal and postorbital and squamosal and
>quadratojugal (Elazanowski and Wellnhofer state the elements may be too
>short to reach each other).
>5)  Postorbital process.
>6)  Small squamosal.
>7)  Non-verticalized braincase.
>8)  Derived paraoccipital process.

General lightening of skull/other changes (see above).

>9)  No sagittal crest.

If it was for display purposes it would have been quite labile; loss of
weight benefit would have impelled the change.  If it was for muscle
anchoring, decreasing jaw muscles would have been adequate reason for losing
the crest, and for regaining it.

>10)  Possible incipently double-condyled quadrate (not in the classic
>sense; Elzanowski and Wellnhofer state that a double-condyled quadrate
>cannot be ruled out in _A. bavarica_ contrary to what has been said by
>numerous people).

(See above)

>11)  Single sternum.

A strong sternum is pretty useful for flying, don't you think?  Another less
obvious point is that the thorax front in a non-flying theropod must be able
to sustain hard impacts without permanent damage so they have rubbery
cartilagenous components in those bones.  It may well be that their furculae
didn't ossify until they reached an age where they didn't fall over so much.


>12)  Differing caudal vertebral count in _Archaeopteryx_ and K
>theropods.

I need hardly say that Archae/droms/other K theropods had special
differences in what  asked from their tails.


>Time does not determine the phylogeny, morphology does.

We get a better understanding of phylogeny if we think carefully about
morphology, and don't ignore time.


Regards,

JJ