[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: bird origins



>The modern felids (from wild cats and ocelats upt to jaguars and leopards)
>work very well both on the ground and up in trees.

I wonder how well they'd do if animals of this size had a stiff tail.
---

>>None of the arboreal characters Sereno cites for Sinornis
>>have been described for any theropod.
>
>Nor are they found in Archaeopteryx.

As Feduccia's paper suggests, Archie may well have been a percher. It looks
to me like Archie is transitional between theropods and Sinornis with respect
to arboreal foot adaptations.
---

>For most aspects of biology, mass is the most important measure of size.
>However, I agree that length is probably a better measure

>>       - Sinornis      < 1'

>Sinornis is quite a bit smaller - between finch and cardinal, approximately.

>>       - Archie        < 3'
>>       - Dromaeosaur     6'
>>       - Troodon         6'
>>       - Velociraptor   10'
>>       - Deinonychus    10'

>Hold on there.  Velociraptor is not, has never been, nor ever will be
>(probably) 10' long.  It was a small animval, 6' for a large individual.  As
>most of you know, the animal called "Velociraptor" in Jurassic Park is
>actually Deinonychus (they actually use the trivial name "antirrhopus" in
>the text).  Although Greg Paul did synonymize the two genera, most people
>who work on theropods would agree that that's going a bit too far (although
>we also agree that Velociraptor and Deinonychus are members of the subfamily
>Velociraptorinae).
                                                 
Hold on there, don't we mean Utahraptor? Besides the point is that
Archie again appears transitional in size between (pick your theropod) 
and Sinornis. 

>>I'll restate it by saying that it's easier to navigate through trees with
>>a one foot broomstick out your butt than it is with a 3 foot broomstick.
>
>It depends how deep the forest is - in a less dense region, the "broomstick"
>would be a useful counter-balance (antirrhopus).

A broomstick that is continously whacking and scraping branches presents
more of a liability than an advantage for an arboreal lifestyle. I would
speculate that Archie precursors had evolutionary pressure for smaller
length(which are noticeable by the time Archie appears) and shorter tails
(which is apparent by the time Sinornis appears).
---

>>I would suspect that beach runners exhibit a similar wear since quartz 
>>registers 7 on the Mohs scale no matter if it's in the desert or on a beach.
>
>But there was next to nil quartz sand in the Solnhofen carbonate banks.  It
>was mostly a limey mud.  Carbonates, especially as mud, would have very low
>Mohs hardness.

Ah, but lets consider the environmental reality for a moment. The Solnhofen-
Eichstatt deposits are carbonate since they were laid down in a lagoon 
environment, but the near-shore environment where trees could grow would
probably be dominated by silica sand. 

The Archie fossils most likely record events where an Archie was either 
washed from the near-shore out into the lagoon or fell in for some reason 
while flying/gliding over the lagoon's waters. It couldn't have lived in 
the lagoon proper where the limy muds are.
---

>>We have a consensus! Seems like everyone agrees that birds were arboreal
>>by no later than 135 million years ago. I predict that this date will be
>>pushed back even farther in future studies.
>> 
>
>This is probably true for Sinornis' lineage.  However, almost all other
>Mesozoic birds (Icthyornis, Hesperornis, Patagopteryx, the
>Enatornithoformes, etc.) are demonstrably nonarboreal.  Thus, Sinornis shows
>that birds were capable of evolving arboreal forms, but is phylogenetically
>distant from the common ancestor of modern perchers/tree dwellers.

I'm not sure I understand what you mean here. All of the other Mesozoic
birds you mention show up later than Sinornis in the fossil record. This
would indicate that with Sinornis you possibly have the basal position 
within Aves for a fully-flighted bird. Thus, Sinornis could be viewed as
a possible common ancestor of all later birds.

My scenario involves flight evolving first (arboreality required until a 
plausible cursorial scenario is devised and I'm not holding my breath) 
with some birds later adapting to fish-eating, some remaining perchers, 
and some becoming terrestrial flightless birds. Could you elaborate on
how you place Sinornis phylogenetically WRT Archie, Sinornis, and the
other Mesozoic birds?