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Were any 6 armed "tetrapod" fossils ever found? I've seen some lobe finned fish with two sets of shoulders in an evolutionary bio book... I'm curious because I'd like 4 limbed and 2 winged dragons to have existed :)

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I don't know about dragons, but the fossil record does show that some fascinating, tiny vertebrates (including members of the genus homo) existed some 425 million years ago :). –  terdon Sep 9 '13 at 16:29
    
as i understand it cambrian-->orovician-->silurian-->devonian... vertebrate popped up in cambrian... the attached link is talking about silurian... my question (six armed tetrapod) probably localizes to the Devonian... –  Jasand Pruski Sep 9 '13 at 16:38
    
Sorry, that link is a joke. It is a guy who won an IgNobel for finding what he considers to be fossils of tiny equivalent of various modern life forms, –  terdon Sep 9 '13 at 16:43
    
this research was actually done?!? –  Jasand Pruski Sep 9 '13 at 18:43
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Yup :). You should check out the Annals of Improbable Research and the IgNoble prizes, they're great. –  terdon Sep 9 '13 at 18:48
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1 Answer

up vote 3 down vote accepted

I think, you misidentified the unpaired anal fin of coelacanth as an extra pair of limbs.

I personally haven't ever heard of six-legged vertebrates, although the phenomenon of supernumerary legs is well known as an anomaly. Such anomalies can be easily induced in different vertebrates (including mice: Rutledge et al), if you treat their embrya with retinoid acid (which normally defines embryonic polarity) or fibroblast growth factor. In nature, different factors can lead to development of extra legs, and the most well-known and wide-spread cases are limb abnormalities in amphibians, induced by trematodes and pollution (including retinoid acid mimics?) (Blaustein & Johnson).

That said, I would not be surprised by a discovery of a fossil amphibian with extra limbs. But such a find then should be interpreted as an abnormality, if not proved otherwise. It's true that the fore and the hind limbs are serial homologues, but their number seems to have been fixed very early (in contrast to the number of the fingers).

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this is the original poster of the question (Jasand)... you're probably right about "unpaired anal fin of coelacanth"... I'm not too knowledgeable about evolutionary biology or zoology... kind of a shame though... I was hoping for another lineage of amphibian/reptile like creatures with six limbs instead of 4... oh well, I guess I'll have to be satisfied with 6 limbed arthropods... I recall something about retinoic acid affecting the hox genes... the hox genes being responsible for segmentation in insects, but general space planning in vertebrate... –  Jasand Pruski Jan 11 at 19:59
    
I was looking at a picture of Eusthenopteron, but the picture specifically says "it has paired pectoral and pelic fins with internal bony structure"... I see more fins than that... probably the extras are cloecanth and whatever... I suppose the number of fingers is variable because it began after the sarcopterygians... but I was looking at these lobe finned fish for the hopes of finding more than 2 sets of paired limbs... –  Jasand Pruski Jan 11 at 20:13
    
Yes, the unpaired anal fin creates a very strong feeling of another pair of fins. There is great variability in morphology of the fins in "Agnatha" (jawless fishes), such that even a case of paired anal fins was discovered in one fossil. Both paired and unpaired fins seem to have similar origin in terms of being derivatives of body folds, but I don't know, whether they can be considered true serial homologues. (See also this article). –  har-wradim Jan 11 at 21:05
    
And, please, don't forget to mark the answer as accepted if you find it proper :) –  har-wradim Jan 11 at 21:14
    
Thanks, sorry I'm new to this site... The picture of the fish I was looking at was in lateral view so paired/unpaired was hard to discern... Also thanks for the follow up info... –  Jasand Pruski Jan 13 at 16:52
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