tgamble

A OEC posted this on another board.

Seems to be a lot of BS here. All 70 phyla appear suddenly. I'm possitive that's just wrong but a reference is given. Anyone have that book?

Aren't vertebrates chordates? So how can they appear seqencially. I'm lost there.

What is this about the "simultaneous appearance of echinoderms, hemichordates, chordates--even craniate chordates--and vertebrates" Sounds absurd to me.

Thanks for the help. The forum (and post) is located here <a href="http://206.47.72.231/WebX?14@206.kJKZaZfyakH^4065@.eeb50e7/34899" target="_blank">http://206.47.72.231/WebX?14@206.kJKZaZfyakH^4065@.eeb50e7/34899</a>

bluefugue

I think chordates predate vertebrates, and vertebrates are a subset of chordates. Not sure, though.

ps418

I'm feeling lazy right now, so I'm not going to spend much time on this. But here are a few links to relevant information that you should study and become familiar with:

<a href="http://www.asa3.org/ASA/topics/Evolution/PSCF12-97Miller.html" target="_blank">Precambrian to Cambrian Fossil Record and Transitional Forms</a>

<a href="http://www.uni-wuerzburg.de/palaeontologie/Stuff/casu5.htm" target="_blank">International Subcommission on Cambrian Stratigraphy</a>

<a href="http://www.pnas.org/cgi/content/full/97/9/4426" target="_blank">PNAS: Cambrian explosion: slow fuse of megatonnage?</a>

<a href="http://www.glenn.morton.btinternet.co.uk/cambevol.htm" target="_blank">Phylum level evolution</a>

<a href="http://cas.bellarmine.edu/tietjen/Ecology/early_animal_evolution.htm" target="_blank">Early Animal Evolution: Emerging Views from Comparative Biology and Geology </a>

A few points to focus on.

1. For the 50th time, all animal phyla do not appear "all at once" during the CE! Many do, not all. If your friend insists on repeating this claim like a mantra, I would demand he back up his claim with specific data as to where each of these phyla make their first appearance. He'll fail miserable to provide such data, I assure you. Several phyla are now known to have originated well before the CE, including sponges, mollusca, annelids, cnidaria, and arthropoda. If once takes the molecular clock seriously, then most phyla existed well before the CE.

The image below plots the first undoubted occurence of various phyla against time, As you can see, the first unequivocal occurence of many animal phyla is long after the CE:



Porifera, arthoropoda, and mollusca should be moved backwards to the Vendian to reflect recent discoveries. If I were you, I would ask your friend which deposits each of his "70" phyla make their first appearance. He can not cite representatives of each phyla from Cambrian deposits.

There certainly aren't 70, or even 30 phyla represented in any of the early Cambrian deposits Im aware of, including the Burgess Shale, Chengjiang, and Sirius Passat put together. The claim that all phyla appear in a 3Ma interval is totally unsupported by any geologic evidence. I would press this point until he backs up his claim with some evidence.

WHERE ARE THESE 70 PHYLA? LOCATIONS AND SPECIFIC LITERATURE CITATIONS PLEASE!

Another point here is that the "explosion" is not really an explosion in complexity. Keith Miller writes:

Many metazoan groups appeared before the Cambrian, including representatives of several living phyla. Furthermore, the many small scale, plate, and spine-bearing organisms of the earliest Cambrian, while sharing characteristics with several living phyla, are also similar enough to each other to be classified by some workers into a single phylum.33 Even when the metazoan fossil record for the entire Cambrian is considered, the morphological disparity cannot be equated with that of living organisms, unless the subsequent appearance of all vertebrate and insect life be ignored. In addition, many living phyla, including most worm phyla, are unknown from the fossil record until well into the Phanerozoic.34 Thus, to claim the near simultaneous appearance of virtually all living phlya in the Cambrian is not an objective statement of the fossil evidence but a highly speculative, and I believe unsupported, interpretation of it35

Finally, there is a question of whether the rapid diversification of metazoans in the Late Precambrian and Early Cambrian reflects an equally rapid increase in complexity. An interesting study by Valentine and others uses the number of cell types as a useful measure of morphological complexity. They plot the estimated times of origin of major body plans against their cell type numbers. The resulting plot shows that the upper bound of complexity has increased steadily and nearly linearly from the origin of the metazoa to the present. Furthermore, they conclude that "...the metazoan `explosion' near the Precambrian/Cambrian transition was not associated with any important increase in complexity of body plans...36 This suggests that the appearance of new higher taxa in the Cambrian did not involve the sudden appearance of major new levels of complexity.

The Valentine ref is:

J. W. Valentine, A. G. Collins, and C. P. Meyer, "Morphological Complexity Increase in Metazoans," Paleobiology 20 (1994): 131.

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theyeti

If that's lazy, I'd hate to see highly motivated.


theyeti

edge

Great stuff. I might add that the true nature of the so-called Cambrian explosion seems to be the rather sudden adaptation of hard body parts rather than an explosion of diversity. It is curious that this event coincides with inferred changes in ocean chemistry where (if I remember correctly) the seas reached carbonate saturation.

What Roger doesn't seem to understand is that just because these various creatures are found together doesn't mean that they originated at the same time. As usual, a creationist gets part of the story right and then alters other facts to make them fit a model.

tgamble

Thanks patrick. I knew you'd show up.


The only citation he gave was Richard A. Kerr, "Evolution's Big Bang Ges Even more Explosive," and what is quoted doesn't seem to be very accurate. I don't know if the quote is out of context, outdated or just plain wrong.

tgamble

Maybe I'm reading this wrong but this seems to conflict with what you're saying. "all major groups...origonated in the cambrian" "This sudden appearance of many groups..." Maybe it's just poor word choice but I'm a little mixed up. <img src="confused.gif" border="0">

ps418

Regarding the emergence of biomineralization - since Tgamble's friend is an OEC, he probably accepts that eukaryotic prostistans existed for hundreds of millions of years before the CE. Why is it that these organisms only started secreting shells in the Vendian Cambrian? From Culver 1991, cited on the Phylum Level Evolution page above:

“Discussions concerning the appearance of skeletonization near the base of the Cambrian [about 550 Ma (million years ago)] are often restricted to metazoans and take little account of the acquisition of hard parts by protists at the same time. For example, hypotheses relating the evolution of skeletonization to increases in body size and to detoxification of excess calcium in metazoans do not apply to protists and hence are weakened by the appearance of testate protists in the Early Cambrian. However, this appearance is not inconsistent with the hypothesis, applicable to both metazoans and protists, that the initial function of skeletons was to protect the organism, primarily against predation. The presence of agglutinated foraminifera in the Lower Cambrian, probably Atdabanian Stage-equivalent strata, of the Taoudeni Basin, West Africa is reported here. These specimens extend considerably the known geologic range of several genera, they represent the earliest known unequivocal foraminifera, and they further remind us that protists as well as metazoans should be considered in accounting for the origin of skeletalization.”

Culver,Stephen J. 1991. “Early Cambrian Foraminifera from West Africa,” Science 254(1991):689.


It is possible at least that the ocean's chemistry passed some chemical threshold during this period, which allowed for mineralized skeletons. We know that there were major changes occuring in the oceans at this time. The early Cambrian was characterized by deposition of phosphorites. The largest ever carbon istope excursions also occured at the end of the Proterozoic.

See for instance Kaufman et al., 1997. Isotopes, ice ages, and terminal Proterozoic earth history, PNAS Vol. 94, pp. 6600-6605).

On the other hand, there are some cases of exceptional preservation in the neoproterozoic, and it could be argued that we should find more early metazoans there. Of course it is possible yet that we could find some more interesting things.

The neo-Proterozoic Doushantuo phosphorites (~570Ma, well over 20Ma before the base of the Cambrian) from south China have yielded evidence for tiny Precambrian eumetazoans, cnidarians (see below), tiny embryos in various cleavage states also (Nature 391, 553 - 558) [although this identification has been questioned], and sponge spicules assigned to the class Demospongiae (Science 279, pp. 879-882). The image below shows a putative sponge from this formation, from Zhang et al. Science, 282, p, 1783.



Microscopic images of fossils from Wengan phosphorites. (A) Longitudinal section of a mushroom-shaped sponge with a holdfast (h), a stalk (st), and a crown (c). Specimen has been cracked during the Late Diagenesis; si, diagenetic silica. Surface ornamentation in the square is magnified (insert). Scale bar, 100 µm. (B) High magnification of the sponge in (A), showing the randomly dispersed monaxial spicules (s) in the mesohyl. Scale bar, 25 µm. (C and D) Two partially fractured spicules, showing their internal axial canal (ac). Scale bar, 2.5 µm

Xiao et al. (2000) report structures that they interpret as cnidarian, which is another one of the phyla which definitely appear before the CE.

Eumetazoan fossils in terminal Proterozoic phosphorites? Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 25, 13684-13689, December 5, 2000

Here's one of the images from their paper:


Fig. 2. Sinocyclocyclicus guizhouensis, tabulate fossils interpreted as possible stem cnidarians. (A) Twenty clustered tubes, seen in oblique section. (B) Detail of slightly curved cross-walls. (C) Tube showing expansion at top. (E) The same specimen at higher magnification, illustrating the thickening and curvature of cross-walls where they meet tube walls (arrow). (D and J) Tube with large chamber at upper end; cross-walls are incomplete and curve downward to make side walls of the chambercross-walls beneath the chamber are complete. (F) Tube with phosphatic rim along inner surface of tube walls and both complete and incomplete cross walls, preserved as boundaries between the phosphatic infillings of adjacent chambers. (G) Detail of complete and incomplete cross-walls (arrow in F). (H) SEM of tube with a bulbous structure at the end (arrow), as well as a laminated phosphatic rim on the tube wall. (I) Folded tube, demonstrating original flexibility of wall. (The scale bar in A represents 100 µm for A and F; 25 µm for B, D, and E; 60 µm for C; 20 µm for G and J; 200 µm for H; and 150 µm for I.)

Oh, another point for Tgamble. Why leave plant phyla out of the discussion? They appear throughout the Phanerozoic. From the Phylum Level Evolution page again:

Period # total phyla which appear in period
Recent 13
Eocene 2
Cretaceous 2
Jurassic 1
Triassic 3
Carboniferous 5
Devonian 4
Silurian 1
Ordovician 1
Cambrian 9
Vendian 4

ps418

Those groups which do not date back to the Cambrian, with the single exception of the Bryozoa, do not possess mineralized skeletons. It is likely that all major animal groups, even those which have not left us fossils, originated in the Cambrian.

Sure, that's quite possible, but its not demanded by any paleontological evidence, as your friend seemed to believe when he said.

Fossils previously found in Yunnan province (at sites discovered nearly 100 years ago) and in the Burgess Shale deposits of the Canadian Rockies tell us that all animal phyla (more than 70) ever to exist in Earth's history appeared "at once" about 540 million years ago.

My point is only that there is certainly no basis for asserting that all extant phyla appeared within a 3 million year window at the beginning of the Cambrian, or even by the end of the Cambrian, ~35-40 million years later.

Unless, as I said, you take the molecular clocks at face value, in which case most phyla would have originated well before the CE.

And one more point, if all the phyla did originate in the Cambrian, the late appearance of many of them in the fossil record would force your friend to admit that soft-bodied organisms can exist for up to hundreds of millions of years without leaving a significant fossil record, in which case he could hardly argue with the idea that soft-bodied ancestors for the Cambrian-originating phyla existed but were not preserved.

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Valentine Pontifex

The quoted OEC said:

Patrick has already brought up many good points of against what this creationist has said. I add a point that the above statement does not make much sense. Phyla are by definition a very major rank of taxa. If evolution is true, one would expect that the higher the "rank" of the taxa, the older the group. Homo sapiens appeared after the first Homo which appeared after the first primates which appeared after the first mammal which appeared after the first vertebrate which appeared after the first chordates. Thus that one does not see new
phyla appearing all the time is very unsurprising. Any newly evolved taxa will not be a phylum via the definition of phylum.

Another thing to consider is that a new way to "design" an animal can hardly be expected to happen regularly as the OEC seems to imply it should. Indeed, for one to evolve today would have a very serious obsticle: namely all the other phylums that exist today. Thus it should not be shocking that the period of rapid formation of the taxa we now call "phyla" did not last forever.

Furthermore the Cambrian Explosion is hardly unique. It reflects a pattern seen many other places in the geological column. When the dinosaurs and many other groups dies out 65 mya, there was a very "rapid" adaptive radiation that mammals diversified to fill many of the niches vacated by the dinosaurs.