Daniel Smith
Posts: 970
Joined: Sep. 2007
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| Quote (mitschlag @ Feb. 15 2008,07:54) | | Quote (Daniel Smith @ Feb. 14 2008,20:01) | I think what you're looking for is on page 140, in his section entitled "Mesozoic Ammonoids": | Quote | This progressive evolution [Note: among Triassic ceratites - D.S.] from smooth shells to those with multibifurcate ribs takes place within a whole cluster of parallel lineages, not always absolutely simultaneously and in many conservative or prematurely extinct lines also not attaining the highest stage of sculpturing, but we can still speak, in general, of a directional, steady progression of sculpture. All these lines then died off conspicuously, after having reached their highest degree of sculptural specialization, at the boundary between the Triassic and the Jurassic--all except one, which remained smooth and undifferentiated and survived this critical juncture to become the starting point of a new cycle of ammonoid evolution, of a renewed and profuse proliferation.
Exactly the same course of sculptural evolution that we see in the Triassic is repeated in the Jurassic-Cretaceous era in the Ammonitacea: at the beginning, there are once more smooth, unsculptured forms; these go on to develop simple ribs, then bifurcate ribs, then multibifurcate ribs (figs. 3.32 and 3.152).
BQiP, pg. 140, (my emphasis) |
Does that help? |
Not really, though I appreciate the effort. I hadn't picked up the reference to Fig 3.152 before, but neither the text nor that figure nor the other Ammonoid figures convey to me a level of discontinuity comparable to that shown in the corresponding text and figures on corals. |
mitschlag,
I'm sure this is not exactly what you're looking for either, but figure 3.37 (on page 134), gives an example of how Schindewolf used suture lines to draw similar conclusions about ammonoids to those he drew from the corals.
Each suture line depicted there represents 1) an ontogenetic developmental stage of two specific ammonoids, ('a' = the Permian adrianitid, and 'b' = the Permian stacheoceratid), AND, 2) a mature phylogenetic stage for various other forms of ammonoids, (with 'a6' and 'b3' being the mature suture lines for the adrianitid and the stacheoceratid respectively). He goes into some detail about this on the surrounding pages, (I also found the same figure repeated later in the book [pg. 209, fig. 3.75] with more explanation there.)
The arrow from 'a3' to 'b1' illustrates the ontogentic stage at which the stacheoceratid splits off from the adrianitid (they share the same first 3 stages -- 'a1-3'). It's not as obvious to the untrained eye as it is from his coral diagrams, but if you study it closely, you can see that the same principle applies.
| Quote | | Quote | | ...we can still speak, in general, of a directional, steady progression of sculpture. |
Inasmuch as Schindewolf explicitly excluded teleological notions, he should have been more circumspect in making easily misconstrued pronouncements like this. But he had another category of mysticism on his mind, unfortunately. |
I don't know what "mysticism" you're talking about. Schindewolf felt that the "direction" was entirely constrained by the original saltational event.
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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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