Daniel Smith
Posts: 970
Joined: Sep. 2007
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| Quote (mitschlag @ Feb. 12 2008,05:00) | | Quote (Daniel Smith @ Feb. 11 2008,18:44) | | As to your question of what a transitional ammonite might look like: To me (and you too apparently), they all look alike, but Schindewolf saw so many differences that he said he often could not envision what a transitional would look like between specific lineages. |
Thanks for your reply, Daniel, but it was not responsive to my request for examples of the ammonites that Schindewolf was discussing in his chapter.
Regarding the quote above, where did Schindewolf say that? How could that be true in every case where a transitional might be posited? How could he find (or fail to find) a transitional if he didn't know what it might look like?
I hope you will understand my confusion. |
Sorry for the delay mitschlag, but my time is limited.
I apologize also for not being able (yet) to find you a good example from Schindewolf's chapter on ammonites, (he doesn't give, very often, the specific names of the ammonites he speaks of, so it's hard to find the type of specific example you want), but I did find a pretty detailed example in one of Schindewolf's stony corals examples:
It is found on pages 205 - 208 in the section entitled "The Origin Of Major Types". Look at the figure on page 207, and read the corresponding description of it on the pages already outlined.
What you are looking at here is Schindewolf's breakdown of the splitting off of the heterocorals from the pterocorals. Like the suture line in ammonites, he uses the septal structure in the corals to retrace their evolution.
In this figure, 'e' is the mature Pterocorallia [Rugosa] with 'a-e' its ontogenetical developmental cycle. 'h' is the mature Heterophyllia with 'f-h' its ontogenetical developmental cycle. 'f' is also the most primitive heterocoral - Hexapyllia
Notice the transition from 'b to c' and 'b to f', about which Schindewolf says: | Quote | Hexaphyllia (fig. 3.74f), the most primitive representative of the Heterocorallia, at first shows only a splitting of one lateral pair of protosepta (II) and holds to this very simple developmental stage throughout its life span. The genus Heterophyllia, which follows it (fig. 3.74h), takes another large evolutionary step in the direction already established...
...As we determined earlier, these fundamental, qualitative character differences between the two structural designs make it appear to be completely impossible for the septal apparatus of the heterocorals to have arisen by gradual transformation from the differentiated septal apparatus of the pterocorals. From the very beginning, their structural paths went in different directions. Therefore, the breaking away of the heterocorals can only have come about during a developmental stage very early in ontogeny of the pterocorals, and we were able to pinpoint this stage precisely. It occured in the early juvenile stage after the emplacement of protosepta pair II and before the appearance of protosepta pair III (fig. 3.74b). At that point, immediately after the larva attached itself to the substrate and began to secrete its skeleton, the decisive switch to the new evolutionary direction occured, causing both the suppression of the heterocoral protoseptal pair III and the bifurcation of protoseptal pair II.
Gradual, smooth transitions between these two different developmental types are unknown and scarcely even imaginable. It could be conceivable, of course, that the reduction of protoseptal pair III took place gradually; but with respect to either simple or bifurcate protoseptal pair II, there is a fundamental, dichotomous difference, which cannot be bridged by a gradual transformation. The two characters are clearly correlated--perhaps owing to compensation of skeletal material; they are part of a coherent type-complex, which first appeared in or was produced by an early juvenile developmental stage of the ancestral type, suddenly, without any transition, in a single transformational step.
BQiP, pg. 206, emphasis his |
While this is not exactly what you asked for, it does represent a pretty detailed account of one of the basic tenets of Schindewolf's theory - that the evolution of new types happens during an early ontogenetic stage and proceeds via a quite different developmental path to maturity.
Remember that only 'e', 'h', and 'f' are mature corals, so when he says "Gradual, smooth transitions between these two different developmental types are unknown and scarcely even imaginable", he's talking about a gradual transition from 'e' (the mature Pterocorallia [Rugosa]) to 'f' (the mature Hexaphyllia).
He can't imagine that, but he can imagine a transition from 'b' (an early stage of ontogenetical development of Pterocorallia [Rugosa]) to 'f' (the mature Hexaphyllia).
So this is what a saltational evolutionary event would look like to Schindewolf.
I'll continue to look for other specific examples for you, but I really think Schindewolf's book should be taken as a whole. You should be able to read it for yourself and get a much better idea of his positions (given your background) than I can give you (given mine).
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"If we all worked on the assumption that what is accepted as true is really true, there would be little hope of advance." Orville Wright
"The presence or absence of a creative super-intelligence is unequivocally a scientific question." Richard Dawkins
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