Re: Vendian Lichens

[Benjamin Martin Waggoner <bmw@xxxxxxxxxxxxxxxxxxxx>]

Sure, the Retallack papeer is outstanding and provocative and a good shaker
upper. But hypotheses should not be accepted because they're good shaker
uppers, but because they're tested and testable. As I pointed out in my
first post, we have plenty of outstanding, provocative, shaking-upping
hypotheses for the affinities of the Vendian fauna: protists (Zhuravlev
1993, N. Jb. Geol. Palaont. Abh.), macroalgae (Ford 1958, Proc. Yorkshire
geol. Soc.; Boynton 1977, The Mercian Geologist), metazoans in extant
phyla (e.g. Jenkins 1992, in Lipps and Signor (eds.) The Origin and Early
Evolution of Animals), metazoans but not in extant phyla (Buss and Seilacher
1994, Paleobiology), an extinct kingdom (Seilacher's other papers), and now
lichens. They all refer to the same fossils; they can't all be right. What
we need is testability.
Retallack does go farther that some people I could mention in trying to
test his hypothesis. However, his tests are inadequate. Here's why:

1) He uses a fossil jellyfish from Mazon Creek for comparison with the
Vendian macrofossils. Traditionally, the Vendian "medusoids" were considered
to be jellyfish, but it's now thought that they were benthic polypoid
organisms (see Jenkins's paper I cited above). Benthic cnidarians have
firmer, less fluid tissue with more complex arrangements of collagen fibrils
than medusoids, in the instances I know of where comparisons have been made
(see Wainwright et al.'s 1977 book _Mechanical Design in Organisms_). Also,
the Mazon Creek jellyfish represent an allochthonous fauna, and many
specimens show signs of having begun to decay before fossilization (Foster
1977, in M.H. Nitecki (ed.) Mazon Creek Fossils); this is not comparable
to recent interpretations of many Vendian biotas as autochthonous and
rapidly buried. Foster concludes in his study that the features of
fossil scyphozoans reflect preservation history more than original 
morphology. 
In short, one species of fossil jellyfish from an allochthonous fauna
preserved in a siderite nodule is not a good standard of comparison
with which to compare an entire biota of benthic organisms preserved
in situ in a number of facies.

2) I haven't measured this carefully (give me time) but in the material
I've seen from the White Sea, trace fossils are preserved in the same beds
as the body fossils - sometimes on the same slab - and these traces also
show relief. I have no reason to think that traces are always flatter than
body fossil impressions, although I haven't measured this systematically,
nor has anyone else as far as I know. These traces are horizontal
surface trails or shallow burrows. Some of them may have been firmer
structures than the surrounding sediment - stuffed burrows, compacted
fecal pellets, mucus--stabilized traces, and so on - but they probably
were not firm, hard structures. They show comparable relief to the body
fossils, but that doeesn't make them strands of wood-like material.
In other words: the relief of an impression is not the same as the
hardness of the thing that made it. I've seen counterpart casting on
some Vendian fossils - features originally on one side of the organism
"strike through" onto the other side of the fossil - implying that
the organism compacted to an extremely thin layer, even though its
impression may show considerable relief. There are also plenty of Vendian
fossils showing organisms that were bent, wrinkled, or folded - which
strikes me as not very characteristic of wood.

3) I have spent hours examining White Sea Vendian fossils - including
the holotypes from which Retallack made his drawings - and I can safely
say that Retallack's drawings do not depict the fossils accurately. He
made them from photos (many of which were originally published in 
Russian publications and are not of the best quality), which is a
dangerous thing to do; also, he draws every little crack and irregularity
in the fossil but does not draw the background rock matrix at all.
This makes his drawings of "medusoids" look much more crinkly and
"lichenous" than the actual material is. I'm not accusing him of
conscious falsification, but so many drawings of these fossils incorporate
the artist's biases - two reconstructions of the same organism, ostensibly
from the same fossils, often look completely different. Compare published
drawings of these fossils from several sources and you'll see what I mean.
If the UC-Davis paleontologists, or anyone else for that matter, are
interested in looking at actual fossils, Berkeley has a collection of
White Sea fossils, as well as casts of the holotypes in the collections
of the Paleontological Institute in Moscow.

This post has been a bit lengthy; I assure you, Hal, that I haven't said
all there is to say. One parting shot: You mentioned that if all Vendian
organisms had equal resistance to compaction, it wold imply that they form
a natural group. I seriously doubt that they all had equal resistance to
compaction (see also Wade 1968, Lethaia v. 1). There are perhaps one
hundred genera of Vendian body and trace fossils - OK, maybe 50-70 if you're
a hardcore "lumper"- known from tuffs, sandstones, siltstones, and 
limestones. Retallack measured the relief of three genera from one locality.
I remain unconvinced that this is an adequate test of a hypothesis that
is supposed to apply to a globally distributed biota of organisms with
fairly diverse moorphologies.

Comments unabashedly solicited.

As ever,
Ben Waggoner
Rogue Grad Student
UC-Berkeley

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"Ecrasez l'infame!" -- Voltaire
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