>One of the trends in fish evolution is the reduction of the scales. in
>the fish I work with for my senior thesis they are about 300my old. >they
>have incredibly thick scales. as the fish become more refined the
By refined do you mean that you find early fossils next to PBR cans, and
later fossils near martini glasses?
It’s important to remember that reduction in scales only occurs in one
lineage- the teleosts! – and it is not entirely unidirectional! One of the
most derived groups of fishes, the Tetraodontiformes (cowfishes,
trunkfishes, porcupinefishes, molas, etc), are characterized by modification
of scales into plates, shields, or spines! Contemporary sturgeons,
paddlefishes, gars, bichirs, bowfins, etc. are remarkably similar to members
of those groups from eons ago, and have not exhibited scale reduction!
Modern-day sturgeons are just as “evolved” as are darters or sculpins or
flounders or trout! One shouldn’t look at derived groups of fishes as “more
advanced” or “more highly evolved…” that’s inaccurate and implies that such
groups are somehow “better” than basal taxa.
Why would you want a classification based on characters that a group lacks?
Such an artificial group is the taxon “Invertebrata” – they don’t have a
backbone, so they’ve GOT to all be closely related, right? Wrong!
The only appropriate methodology for classification is on the basis of
shared, derived traits… whether those traits be skeletal, behavioral,
genetic, physiological, or any other observable character.
A few words on books-
Nelson is good, but earlier versions of “Fishes of the World” are cheap via
used book sellers (I found a 3rd edition for $15 not long ago!). Highly
recommended. Pough’s “Vertebrate Life” isn’t bad for an overview of
vertebrate zoology, and can often be found used very cheap. Gergus and
Schuett’s “Labs for Vertebrate Zoology: an evolutionary approach” is one of
the best books if you want to get your hands dirty and understand how
various characters change across various vertebrate groups.
cheers,
Dave
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