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

Re: CONVERGENCE HAPPENS



>You're skirting the issue. Are you proposing a complete overhaul of
>what we know about squamate phylogeny and evolutionary trends? Putting
>amphisbaenians inside Platynoa would require many reversals and
>convergences. Listen and listen well, convergence happens and sometimes
>it is very strong. Gaviiforms, podicepiforms and hesperornithids share
>many features realted to swimming, and some have argued for monophyly of
>these three groups, but in retrospect these features are probably not
>homologous because of the subtle differences in knee structure, swimming
>style, and shared derived features with other birds. If we try to
>account for all convergence that happens in all our accepted
>phylogenies, we end up with birds and mammals as sister-groups, dipnoans
>and tetrapods as sister-groups, lycopsids as the closest group to seed
>plants, crocodylomorphs and birds as sister-groups, cetaceans as
>ichthyosaurs, sauropterygians and ichthyosaurs as sister-groups, bats as
>pterosaurs, pterosaurs as mammals, etc. etc. etc.

I wasn`t actually refferring to your squamate arguement. On that, I don`t
know either way.I just suspect Convergence as an explanaition of the
numerous similar characteristics between Pterosaurs and Birds. Your right,
...sometimes convergence happens!....(SOMETIMES  it is used when there is no
other way to explain such similarities to ones liking). I use Feduccia as a
clear cut example. Due to embryological evidence that seemingly directly
contradicts a Dino-Bird connection, he automatically dismisses any (and all)
Dromaeosaur-Bird similarities as Convergence! I just wish there were a way
to prove or disprove convergence. In all cases where it is used, the claim
for its existance should REQUIRE proof! It should not be used as a
convenient label.


>The lack of furcula in some _Archaeopteryx_ specimens is likely a
>preservational or ontogenetic characters. _Archaeopteryx_ is obviously
>a flying creature and I can find few characters that indicate that it is
>on the way to becoming secondarily flightless. For your logic to work,
>ALL basal birds were on the way to becoming secodarily flightless. A
>more parsimonous interpretation is that we are actually witnessing the
>transformation of the coracoid from a slightly specialized state in
dromaeosaurs to the modern avian coracoid.
>

Maybe the species that were becoming secondarily flightless tended to hang
out near the shore, where they were not only likely to catch a meal, but
their remains more likely to be preserved in a depositional enviornment.
I,for one, think that a vast majority of avian forms are yet to be found,
especially the smaller and more fragile upland varieties. I hope someday
some of these species will be found to fill the gap since the mid-Triassic!