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Re: Underwater Flight



HP Rob Gay wrote:

> Now, does this suppose that these theropods are already feathered when
they
> enter the water?

Yes.
I (unlike Ebel) also suppose that wing feathers were already present.

> Because if they aren't, I see no pressure for them to
> evolve feathers, once aquatic. What made theropods special from, say,
> icthyosaurs and mosasaurs? They didn't evolve feathers.

Exactly.

> And animals with
> covering that spend most of their time in the water tend to reduce the
size
> of their covering, both in length (penguin) and total area (cetaceans). It
> seems like the pressure in an aquatic environment is biased against the
> begining of flight.

Animals of Archie-size, however, which never became fully aquatic and still
used their wings in brooding as well as for locomotion...

> Also, on the comment earlier about segnosaurs; if they were
saurapodamorphs,
> even with their dino-fuzz, then what implications does this have for the
> origin of fuzz (is it a basal character, like mammal fur?), and what would
> this mean for BCF?

It fits the hypothesis that dinofuzz/protofeathers is a synapomorphy of
Ornithodira or so, which bases on the assumptions that pterosaur fur looks
like feather shafts and that endothermy is a synapomorphy of Ornithodira
too. All unproven, all more or less testable.
        If they were not sauropodomorphs, which is current consensus and
quite likely, well, then, you'd expect feathers on the sister group of
oviraptorosaurs.

and HP Jaime A. Headden answered:

>   Chatterjee has suggested that it was possible for dinosaurs to
> develop feathers through a gliding phase previous to the "run to
> the sea," so that feathers were already developed.

I think that Chatterjee, when writing his 1997 book, first developed his
version of trees-down, then read the Ebel article, found it convincing and
tried to combine both hypotheses. The outcome is rather odd IMHO. Anyway,
Chatterjee doesn't cite Ebel, so he may have come to Ebel's conclusions
independently ("convergently").

> As has been
> demonstrated (I forget by whom, possibly Olson or Cracraft) that
> penguins [like auks] stem from a lineage of fully-flighted
> birds. That hesperornithiforms are basally flighted by the most
> primitive forms, shows that no form is plesiomorphically
> aquatic, and so feathers must have originated outside of the
> pressure of a liquid environment, and in fact that a water
> environment acts to decrease feathers as a motivational
> structure. Foot-propelled animals (such as grebes and
> hesperornithiforms) reduce pectoral anatomy, whereas penguins as
> wing-propelled divers, reduce only their aspect ratio and
> increase four-limb anatomy and bulk.

Completely correct. However, that all pygostylians at least
plesiomorphically fly is not an argument that flight may not have evolved in
an originally flightless SEMIaquatic form. Dipper analogy once more.