Wednesday, August 6, 2014

Hand Transition

There is a group of researchers and academics (eg. Feduccia et al) that makes a very strong case that birds did not evolve from dinosaurs.

One important aspect of their argument is the discrepancy in digits (fingers) between dinosaurs and modern birds. The evidence indicates that birds have digits II-III-IV while dinosaurs have I-II-III.

I agree with the researchers and academics that birds did not evolve from dinosaurs.
I go a step further and suggest that the ancestors were pterosaurs.
Pterosaur hands and basal paraves hands are such that a very straightforward transition is possible.

Here is the proposed transition:

2-3-4-5-x Pterosaur
x-2-3-4-x Basal Paraves 
x-2-3-4-x Basal eumaniraptora
x-1-2-1-x Modern bird

Summary of Changes:
The first step occurs in pterosaur with the loss of the 5th digit (V).
Then in the transition to basal paraves:
The first finger was lost. 
The second finger lost one phalanx. 
The third finger lost one phalanx. 
The fourth finger was shortened and lost one phalanx. 

Note that the pterosaur to bird theory is also consistent with a frameshift, which also produces the same pattern as above. (See here for details). 

Alternative based on Yi qi:
2-3-4-5-x Pterosaur
2-3-4-x-x Yi qi (the rod-like bone is the 4th finger metacarpal)
2-3-4-x-x Scansoriopteryx 
2-3-4-x-x Basal eumaniraptora
1-2-1-x-x Modern bird

Note that David Peters make an interesting case for the idea that the Yi qi "styliform element" is a displaced radius and ulna.

Dinosaur hand transition reference:,d.aWw

Also see the July 30 post.
New studies by Larsson and Wager, and by Feduccia and Nowicki of the embryogenesis of birds undisputedly show Anlagen for five fingers. This has important implications. First, the early presence of digit I, and its later disappearance, indicate that the evolutionary reduction of digits occurred via developmental arrest followed by degeneration. Second, it shows that the digits in the wings of birds develop from Anlagen II–IV. This suggests that the hypothesized descent of birds from theropods might be problematic, because theropods are assumed to have digits I–III.

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