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S.B.Misra, Department of Geology, Memorial University of Newfoundland, St. Johnís, Newfoundland, Canada

Home > Earliest Papers > Anderson  & Misra 1969

Nature, Vol. 223, No. 5210, p. 1076, 1969.

Criteria for Recognizing Pre-Cambrian Fossils

Anderson M.M. and MISRA S.B., (1969)

<<  Thesis Misra 1969a Misra 1969b >>

Comment by R. Goldring:

Comment by R. Goldring:
Reply by Anderson &  Misra
Anderson and Misra1 have described new fossils from the Pre-Cambrian of Newfoundland and ascribe them to impressions of soft-bodied Metazoa, but they do not discuss why they consider the structures to be undoubtedly organic in origin, though the Pre-Cambrian age is beyond dispute. New Pre-Cambrian fossils are reported quite frequently, but only a few of them are accepted as organic. It may therefore be helpful to distinguish the criteria available for distinguishing between organic and inorganic Pre-Cambrian macrostructures (as distinct from microorganisms).
  1. Simple symmetry or abundance is not acceptable criteria.
  2. Chemical analysis of the rock is unlikely to help, particularly in more strongly tectonized sediments,
  3. Ontogeny may be a useful guide.
  4. The structures concerned may suggest a high degree of organic evolution, as with many of the South Australian Pre-Cambrian fossils.
  5. Evidence of movement may be indicative of fossils, especially when considered with evidence of
  6. mode of preservation and burial.

The use of these criteria is well illustrated by the work of Glaessner and Wad, who have carefully described the relationship of the South Australian Ediacara fossils to the overlying and underlying sediment. Wade3 has given an account of their preservation and by sectioning some of the material, she has been able to show just how individuals came to rest on the substrate, how they were entombed, and what happened to them as they decomposed and were fossilized. Obviously it is necessary to collect the sediment overlying the fossil as well that underlying it.

Anderson and Misra1 mention the doubtful Aspidella trerranovica Billings. This though common, is definitely inorganic. Sectioning shows that many specimens are water or gas-escape structures. Others are partly attributable to the manner in which the highly lithified clay and silt grade rock has parted along a changing stratigraphic level, particularly around load and scour structures.

Unfortunately, Anderson and Misra1 give no evidence for the organic origin of their structures and do not relate them to the underlying and overlying sediment. Although an organic origin cannot be disproved, their illustration does show striking resemblances to impressions of cone-in-cone structure.


R. GOLDRING
Department of Geology
University of Reading

Received December 9, 1968, revised May 12, 1969

Anderson, M.M. and Misra, S.B., Nature, 220, 680 (1968)
Barghoorn, E.S., and Tyler, S.A., Science, 147, 563 (1965)
Wade, M., Lithaia, 1, 238(1968)
Schindewolf, O.H., in Geotecktonisches Symposium zu Ebren con Hans Stille (Ferdinand Enke
Verlag, Stuttgart, 1956)


Reply by Anderson and Misra


Our communication1 did not describe new fossils from the Pre-Cambrian of  Newfoundland but rather gave brief details of the presence of a metazoan fauna of this age, because our aim was to announce what we regard as an important discovery, and we indicated quite clearly that details of the fauna would be published elsewhere. We concentrated on the stratigraphical aspects of the fossil locality because it is essential to establish from the outset that the rocks containing them are in fact Pre-Cambrian and not Lower Palaeozoic or younger. It is true that we did not provide evidence of the organic origin of the structures interpreted as fossils, but we assumed, perhaps wrongly, that readers would await this information in the actual account of the fauna.

In view of the fact that the organic nature of these structures is discussed in a paper now in the press2, only a brief summary of the reasons for regarding them as organic will be given here:
  1. their restriction to certain bedding planes;
  2. they lie on these ripple-marked surfaces;
  3. their orientation is unrelated to ripple-marks or to cleavage or other fracture patterns and some commonly straight forms are also found in a curved state;
  4. they are not related to sedimentary structures;
  5. the variety of forms round lobate, spindle-shaped, leaf-shaped, dendrite like;
  6. their variation in size (possibly ontogenetic),
  7. the complexity of some forms;
  8. similarity to known Pre-Cambrian fossils. A general geological account of the fossil-bearing rocks
    is given in ref3.
Any resemblance of the commonest form in the fauna to cone-in-cone structure is illusory, for the cones of these calcareous structures (some times replaced by silica)4 form at right angles to bedding surfaces and not parallel to them, and furthermore, unlike the fossil impressions illustrated, lenses of  cone-in-cone structure developed in the same bed have the same orientation; they possess thickness and the cones interfere with one another so that they do not show a regular alternating left-right arrangement.

M. M. Anderson
S. B. Misra

Department of Geology
Memorial University of Newfoundland,
St. John's, Newfoundland, Canada.
 
Received July 9, 1969

References

  1. Anderson, M.M., and Misra, S.B., Nature, 220, 680 (1968)
  2. Misra, S.B., Bull. Geol. Soc. Amer. (in the press)
  3. Misra, S.B., MS Thesis, Memorial Univ. Newfoundland (1969)
  4. Woodland,B.G., Fieldiana, 18, 187 (1964)