baby bichirs and their external gills

[windeindoiel]

So I read this book (At the water's edge, I can't remember the author, and am too lazy to look it up) and it talked about how once something is lost, it can't evolve back exactly how it was in the first place. So when fish came out of the water, they lost their gills. Then amphibians, in particular axolotyls and some other salamanders, had to evolve some form of gills again, so they evolved "feathery" external gills. I know that though unlikely, it's possible for different animals to evolve similar structures independantly. I'm curious about how young bichirs have external gills, why, how... all that good stuff. :P Thanks.

[Toirtis]

Excellent question, and although I know a few evolutionary biologists that probably have some interesting hypothoses on the subject, the short answer is that we really don't know. What really piques my curiousity is why bichirs have them in the first place, especially only as juveniles (again, not dissimilar to most salamanders, who also lose them as they mature).

That book was by Carl Zimmer, by the by.

[windeindoiel]

I couldn't remember the first name, and I knew it was either Zimmer or Zimmerman, I liked the book, makes me think I want to study how and why structures evolve.

I posted the same question on another message board, I got the response that bichirs go through a larval phase, which doesn't really answer my question, but makes me think of a few more.

I talked to one of my professors about it too, and mostly he just stressed that structures can evolve independantly. Which also doesn't really answer my question.

What I'm really interested in is the same thing you're curious about, if ever you talk about it to one of those friends or one of those friends doesn't mind answering some questions of an inquiring mind, I'd love to dig into this a little more.

[Toirtis]

I posted the same question on another message board, I got the response that bichirs go through a larval phase,

Which is true, many fish do, although most do not go through a srage that includes such advanced and prominant external gill dtructures.

I talked to one of my professors about it too, and mostly he just stressed that structures can evolve independantly.

Quite true, and far from the only example....it is also possible that there is some common ancestor, however, we simply do not have enough of a fossil record to determine that.

What I'm really interested in is the same thing you're curious about, if ever you talk about it to one of those friends or one of those friends doesn't mind answering some questions of an inquiring mind, I'd love to dig into this a little more.

I will see what I can do...I have an acquaintance that is more versed on the evolutionary links and history of the Chondrostei than I....but the interesting part is how the bichirs have these (as well as the caudates), when they (as part of the Actinopterygii) branch off from the Osteichthyes in a very different evolutionary route than do the Sarcopterygii (from which the Amphibia come.)....it really could just be a case of a successful structure evolving independantly, yet nearly identically.