Daniel Smith
Posts: 970
Joined: Sep. 2007
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| Quote (JAM @ Jan. 31 2008,19:48) | | Quote (Daniel Smith @ Jan. 29 2008,18:53) |
And for you JAM:
| Quote | It is true that we know of countless lineages with continuous transformation, in as uninterrupted a sequence as could be desired. However, each time we go back to the beginning of these consistent, abundantly documented series, we stand before an unbridgeable gulf. The series break off and do not lead beyond the boundaries of their own particular structural type. The link connecting them is not discernible; the individual structural designs stand apart, beside one another or in sequence, without true transitional forms"
ibid, pp 102-103 |
The only "gaps" Schindewolf was concerned with were at the beginning of a "structural type". He makes that abundantly clear throughout the book. Furthermore, since Schindewolf had already mapped out a line of descent for the hammatoceratins, this cannot constitute one of his "gaps". |
Sure it does. The additional evidence (which, remember, Schindewolf claimed would never be found because it did not exist) supporting two lineages over one eliminates at least two of his vaunted gaps. |
I'm sorry to have to do this to you JAM, but it appears I was wrong when I said Schindewolf held to the 'one lineage' hypothesis. A more careful reading reveals that Schindewolf believed the hammatoceratins to be a superfamily that could be divided into two separate lineages. It's a little hard to follow the author's descriptions of the two hypotheses unless you break them up. Here's the 'single lineage' hypothesis:
| Quote | | There are essentially two interpretations. The latest and most complete classification of the Jurassic Ammonitina, (Donovan, Callomon & Howarth, 1981), followed in some recent works such as Wiedmann & Kullmann (1996), considers the hammatoceratins as a subfamily within the Phymatoceratidae Hyatt, 1867, which is itself included in the Hildocerataceae. For those authors, the hammatoceratins are a single lineage giving rise to all groups of post-Aalenian Ammonitina: Sonniniidae, Strigoceratidae, Haplocerataceae and Stephanocerataceae (Fig. 1a). Most authors agree with these relationships, albeit with some slight refinements; Sandoval (1986), for example, suggests the Haplocerataceae derived rather from the Graphoceratidae Buckman, 1905. |
And here is the two lineage hypothesis:
| Quote | | The alternative interpretation has been proposed by several authors (e.g. G´eczy, 1966;Westermann, 1993; Rulleau, Elmi & Thevenard, 2001) based on different taxonomic conceptions. The hammatoceratins are thought to be a superfamily, as suggested by Schindewolf (1964, 1965) and Tintant & Mouterde (1981), however, the main difference with the preceding classification is that the hammatoceratins may be divided into two separate lineages, following Westermann (1993). For Rulleau, Elmi & Thevenard (2001), these two lineages are the Hammatoceratidae Buckman, 1887 and the Erycitidae Spath, 1927, each of them with its own descendants: Sonniniidae, Strigoceratidae and Haplocerataceae for the former and Stephanocerataceae for the latter (Fig. 1b). |
They summarize thus:
| Quote | | It would be wrong to see the disagreement over these two phylogenetic hypotheses as evidence of a nomenclatural morass. Both interpretations lead to the conclusion that the hammatoceratins are not a clade (that is, not a monophyletic group), and the second hypothesis holds that the late Aalenian radiation proceeded from two different clades. |
So what did the authors conclude?
| Quote | | The principal result of the cladistic analysis presented here is that the ammonites under study form two groups, each including members of the hammatoceratins root group and their late Aalenian descendants. This confirms that the hammatoceratins group is in fact an association of two lineages (‘Hammatoceras group’ and ‘Erycites group’) that diverged early on, during the Toarcian stage, in the history of the emerging clade as suggested by Rulleau, Elmi & Thevenard (2001). Late Aalenian and Bajocian genera are distributed between these two lineages, confirming that the Stephanocerataceae derived from the ‘Erycites group’ and that the ‘Hammatoceras group’ gave rise to all the other Bajocian groups. The consequence is that the late Aalenian ammonite radiation progressed from two separate clades rather than one. |
Thus, much to your chagrin I'd suppose, the paper you cited to undermine Schindewolf actually ends up supporting him!
Ya gotta love science!
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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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So, "mode of life" was already changing long before the reduction of digits to Schindewolf's one-toed horse: 
