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Re: MORE ON BCF



Message text written by INTERNET:tlford@ix.netcom.com

>Poor, POOR! It's down right pathic if you really look at it. We're (you,
>me, Scientist) are trying to find out what these incridble animals
>looked like, lived, and evolved on very little. Just look at a map of th
>USA, plot out all the states that have the Morrison Formation and then
>look at the rest of the USA, there's a LOT of missing data there. I
>think what each of us should say is, for example, IMHO there were lots
>of small theropods running around the early-late Jurassic, even though
>there isn't any fossils to prove this, and YOU should say, IMHO this
>isn't true, and be able to accept that and other ideas.

        Tracy, calm down a bit!  8-D  No one is saying you're wrong...but
no one is saying anyone else is 100% right, either (or, at least, they
shouldn't be)!  The fact is, for this moment, that _Archaeopteryx_ is the
only Jurassic bird for which there is _unequivocal_ evidence.  Few, if any,
people would believe (methinks) that this means that it is the _only_
Jurassic bird.  Very likely there were others, but again I emphasize that
there is no _unequivocal_ evidence for them.  Based on isolated bones and
teeth, such as those from Dry Mesa and from portugal, respectively...these
certainly _could_ be birds (or even _Archaeopteryx_ itself), but not
unequivocally so.  Clearly most paleontologists wish to come down on the
conservative side of things and assign the bones to something like
"Maniraptoriformes _incertae sedis_," which doesn't say they're _not_
birds, just that they could equally well be a non-avian maniraptoriform
theropod.  I believe the problem here to which you and Matthew (and
probably others) are reacting is simply one of how liberal or conservative
each individual is willing to be with the same body of evidence:  whereas
you are willing to state that the isolated elements in question are avian,
others are not.  Given _only_ these isolated elements, that's the best we
can do 'til newer discoveries tilt the balance towards one side or the
other.

>>>And why is it, I've asked this on the list before, that if a skeletal
>>> element that might belong to an non-avian theropod OR an avian-theropod
>>> that it's always placed into the non-avian theropod?

        Because that's the conservative position, which is, apparently, the
stance from which most paleontologists wish to approach the situation.  I
shan't judge whether this is "good" or "bad"...it just _is_.  Taking the
position that the bones _are_ avian, when there's no way to definitively,
unequivocally prove that as yet, is just as tenuous a position, although
certainly a more liberal one.  The logical question is:  why _should_ we
assume they're avian (that is, make the Null Hypothesis here "The bones are
avian")?

>> Still, it is close enough to the Jurassic/Cretaceous boundry that
>> it makes no real difference.

        Matt, this isn't true, either:  it speaks to the diversity of
avians prior to the Jurassic-Cretaceous boundary, which is strongly desired
information for comparison against the diversity we see _after_ the J-K
boundary.

>>>And what about ichnology? The forgotten science. There are thousands
>>> and thousands of small theoropod prints from the early Jurassic to the
>>> late Jurassic. With some early Jurassic prints that are so small
they'll
>>> fit under a quater. What about the bird (or bird like prints?just
forget
>>> them? Not good enough?)
 
>> Let me quote parts of Padian and Chiappe 1997 pertaining to this issue:
 
>> "Lockley et al. (1992) argue that there are some possible bird tracks in
>> the fossil record as early as the late Early Jurassic (e.g.
>> _Trisauropodiscus_ from Arizona and South Africa), but their criteria
>> are somewhat vague, and have not been demonstrated as unique characters
>> of bird tracks, or of certain taxa within birds (Chiappe, 1995a; Padian,
>> 1997). 

>But this doesn't mean they WEREN'T made by birds. We have ichnologist
>and non ichnologist talking here.
 
        The latter point is true, but then again, it is notoriously
difficult to associate ichnites to even a broader clade of taxa, let alone
more specific taxa, without finding a body at the end of the trackway
(something which, to my knowledge, has never been found for a tetrapod). 
Just because Lockley _says_ the prints are birds doesn't mean they _are_
_unequivocally_ birds.  As you well know, I've worked personally on both
footprints and on body fossils; Lockley and I have had lively
conversations, and maintain different positions, about even attributing
huge Jurassic footprints to either the Theropoda or the Ornithopoda!  Given
that early birds were still extremely similar to their non-avian theropod
ancestors, footprints made by early birds would be _expected_ to be very
hard to distinguish from very advanced, near-but-non-avian theropods, or
even more distant theropods which happened to converge on birds in foot
structure.  Lastly, we must recall that the footprint type is heavily
(although not entirely) dependent on both substrate conditions and
paleoecological conditions -- that is, a theropod walking on muddier
substrate might wish to increase the surface area of its feet to prevent
sinking, so it would spread its toes, and could conceivably make a more
bird-like print (purely hypothetical talk, here).  So while Lockley et al
have attributed prints to birds in the Early Jurassic, they are not
_unequivocally_ birds.  Again, the question is "Why should we assume they
are birds?" instead of "Why should we assume they are not birds?"

>> Molnar (1985) has questioned the birdiness of Ellenberger's South
>> African tracks, saying that the "feather imprints" are actually
>> invertebrate trails that trod over regular tracks.

>And when was Molnar's paper written? Lockley et al, 1992!.<

        Ellenberger's papers on the Late Triassic prints, including the
supposedly feathered _Maisitisisauropus_ prints, are greatly overly split
on taxa; Ellenberger also, apparently, sees things in those prints no one
else I've spoken to about the material has been able to see (same with the
supposed feather impressions he described in _Cosesaurus_).  The possible
integumentary impressions from the Early Jurassic USA (the "sitting
theropod") are easier to see, and somewhat more convincing, but until we
find an Early Jurassic fossil in some lagerstatte with feathers or
feather-like integumentary structures, the Null Hypothesis remains "These
are not the traces of birds."  


           ____/_\,)                    ..  _   
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Jerry D. Harris                         (505) 841-2809
Fossil Preparation Lab                
New Mexico Museum of Natural History        
1801 Mountain Rd NW                           
Albuquerque  NM  87104-1375             102354.2222@compuserve.com