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RE: New Mesozoic bird papers (advance publication)
Brad McFeeters wrote-
> If the claws were used for something other than climbing, why were they lost
> at the same time birds developed the ability to ascend without climbing?
> It's obviously not an airtight deduction, but still an interesting
> observation to think about, especially if the correlated claw reduction +
> improved backstroke evolved more than once in different bird clades (did it?
> I haven't read the paper yet either).
Simply put, claws weren't lost at that point. Compare Sapeornis' claws to
Eoenantiornis' and you'll see no great difference. Both are strongly curved
with large flexor tubercles, yet I think the consensus is that enantiornithines
could take off from the ground while omnivoropterygids were worse off than
confuciusornithids (unossified sternum, often short coracoid, etc.). Even
basal euornithines like Jianchangornis and Yixianornis had well developed
(albeit less curved and smaller) claws, despite having a pectoral apparatus
extremely similar to Aves. In general, the claws do reduce going from
Archaeopteryx to Aves but there was a lot happening on that lineage besides
improving the takeoff. For instance, the second digit was becoming more robust
and stiffer to support the primaries and the first digit was becoming reduced
in size and developing an alula.