Patterns in the Fossil Record, Part 2

Balancing extremes

A general note of caution is necessary in the discussion of patterns in the fossil record. As with many other aspects of the natural world, the complexity that we find in this field of study tends to transcend our idealized categorizations. This needs to be kept in mind to avoid misrepresentations or the promotion of unbalanced perspectives. Here is a list of apparently contradictory aspects that coexist and emerge when looking at the study of fossils from different angles:

Time: instantaneous and prolonged. Fossils are often produced as evidence for rapid and cataclysmic sedimentation and in most cases this is correct. The process of fossilization generally requires rapid burial for preservation of body parts. At the same time, there are fossils that carry with them the implication of passage of a certain amount of time, such as encrusted and bored shells, organisms growing attached to a hard substrate, or tracks and traces of bioturbation.

Anatomy and Structure: different and similar. The fossil record is a rich archive of organisms that have gone extinct and exhibit morphological characteristics often extremely different from what we are used to in the modern world. It is also evident, however, that many fossil creatures have body plans that can readily be associated with basic structural plans still observed today. For example, in spite of all the alleged eons of evolutionary time, modern bacteria do not appear much different from microfossils interpreted as Precambrian bacteria (Schopf et al., 2015).

Geographic distribution: global and local. The sequential order of distribution of fossils in the geologic record appears consistent on a global scale. Dinosaur remains are found in all different continents and they always occur in Mesozoic layers. However, at higher resolution (e.g., going from the family to species level) very few fossil organisms appear to have a truly cosmopolitan distribution. This implies complications in the correlation of regional schemes of fossil distributions developed for non-overlapping areas of the world.

Stratigraphic distribution: ordered and disordered. We have already described the pattern of ordered distribution of fossil forms through the geologic column. Even in this case, however, it is important to acknowledge that at finer resolution the lowest and highest appearance of taxa are not always easily and univocally determined. Complications include reworking of older fossils in younger sediments, masking of the highest and lowest appearances due to erosion, lack of appropriate sediments for fossil preservation, offset in lowest or highest appearance at two locations due to lateral migration of a community. These factors can cause differences in the relative order of appearance of the same fossil species in different localities.

Quality of the record: complete and incomplete. The fossil record is often presented as a highly incomplete documentation of the variety of life forms that have inhabited the Earth. At the level of individual specimens, the incompleteness is evident in the preservation of only certain parts of the original organism, with others, usually the soft parts, not fossilized. At the level of the whole record, incompleteness is thought to result from discontinuous sedimentation, gaps created by erosion, and the random and infrequent nature of fossilization. Notwithstanding the validity of these points, it is also important to remark the incredible richness of the fossil record. Many fossil forms are preserved in great quantities (e.g., microfossils) and there are numerous instances of specimens with exceptional preservation, including fossilization of soft parts. As for the overall completeness of the fossil record, in many cases the available data appear more than adequate to extract trends and address the shortcomings of a discontinuous record (Foote, 2001).

Fossil record patterns and origins models

There is a fundamental difference between the biblical and Darwinian models on the origin of biodiversity. The biblical model clearly states that numerous distinct groups were created from the beginning, whereas Darwinian evolution sees all organisms as interlinked in a chain of descent with modification from a single common ancestor. In this respect, creationists find good support of their position in the scarcity of transitional fossils and the sudden appearance with high disparity of forms documented in multiple levels of the geologic column. There is, however, much work still to be done to develop an overarching comprehensive model accounting for other patterns in the fossil record. For example, explanations for the ordered distribution and increasing modernity of fossil forms have been addressed by creationists at a general conceptual level, but not always systematically investigated through detailed hypothesis testing. This is in part due to differing views on how much of the geologic record should be considered as formed by the biblical flood.

Those who view most of the Phanerozoic geologic record as the result of diluvial activity rely on a mixture of physical, ecological and behavioral processes to account for the patterns observed in the fossil record (e.g., Clark, 1946; Roth, 1998; Brand, 2009). Mechanisms invoked include sequential inundation of spatially segregated ecological systems of the pre-diluvial world (this hypothesis is known as ecological zonation or biome[1] succession theory), differences in animal mobility and behavior in the face of rising waters, and hydraulic sorting of floating organic remains.

Those who consider large parts of the Phanerozoic rock record as representing pre-flood or post-flood sedimentation, explain the succession of different fossil assemblages as an effect of biological change and migration with time of communities populating the Earth. This scenario appears similar to that proposed in the classic evolutionary interpretation of the fossil record, but there are two crucial differences. First, in the evolutionary model life diversifies from a single monocellular ancestor and evolution implies an overall increase in biological information. However, in the creationist model, modification affects pre-existing created lineages and does not require the generation of new complex biological information (Brand & Gibson, 1993; Wood & Murray, 2003). The second difference relates to the rate of change, which, in the creationist model, is assumed to be much faster than the traditional view of slow gradual accumulation of advantageous traits over millions of years (Brand & Gibson, 1993).

From the perspective of evolutionary models, certain patterns of the fossil record (such as increasing modernity and ordered distribution) are compatible or fit well with the standard paradigm. However, others present challenges to the conventional interpretative framework. The lack of numerous intermediate forms is the foremost challenge, which has been noted since Darwin’s times. A common response is to attribute this problem to the low sampling effectiveness of the fossilization process. However, this assumption has been dismissed by quantifications of the completeness of the fossil record. In the words of Wagner (2010, p.462), “we now have the sediments: but they do not yield what Darwin predicts they should yield.” It should also be noted that when several transitional forms are known along an alleged evolutionary lineage, their morphological traits may show incongruent and conflicting distributions. This implies that the alleged transitional fossils very often cannot be arranged in a sequence that consistently accommodates all the characters undergoing evolutionary modification (Luo, 2007).

The phenomenon of stasis is also a pattern partially counter-intuitive to the evolutionary scenario. The observation of limited or no net change through the entire stratigraphic distribution of a fossil species fits poorly with a model explaining the variety of life forms as the result of continuous modification.

Another pattern which is not straightforwardly accounted for in the evolutionary interpretation of the fossil record is the high disparity shown by new groups at their first appearance. As remarked by Valentine (2004, p. 444), “this record runs counter to what might be expected during the origin of phyla, which would be the divergences of two lineages form common ancestors, at first at the species level only. Then as time passed their differences would become more pronounced, the two lineages becoming as distinctive as average genera, and then as average families, then as orders, and so forth.” Therefore, one would expect disparity to progressively increase as new modifications are acquired, but this appears not to be the case.

Moving forward: areas for future research

The creationist viewpoint would benefit from research exploring more in detail possible mechanisms responsible for some of the patterns observed in the fossil record, especially if these are seen as the result of natural processes being at work before, during and after the flood.

One area deserving more focused attention is the testing of ecological zonation theory. This idea suggests that vertical trends in fossil distributions reflect more an original difference in spatial arrangements of biomes rather than an evolutionary sequence. Interestingly, a similar approach has been presented in the standard scientific literature to explain turnovers in Paleozoic fossil plant assemblages (DiMichele et al., 2008; Looy et al., 2014). Even major dominance shifts in Paleozoic tetrapods appear to be strongly correlated with the disappearance of the coal forest biome (Sahney et al., 2010) or with a switch in the geographic location of the preserved fossil record (Benton, 2012).

Another area deserving attention is the study of sea level fluctuations and their effect on fossil distribution and preservation. It is possible that some patterns in the fossil record are the result of physical processes of deposition rather than evolution through time. Sea level variations could trigger sedimentary processes controlling the appearances and disappearances of taxa (including extinctions and radiations), and replacement and repetition of fossil assemblages (Brett, 1995;1998). An important part of this process would be to consider the difference between transported fossil assemblages and assemblages indicative of minimal transport or fossilized in place.

Finally, studies exploring time implications from the fossil record would also be highly significant. Of particular interest would be an analysis of the relative proportion of fossil concentrations (e.g., shellbeds) formed through slow time-averaging or sudden event deposition.

Conclusions

Fossils represent a unique archive of past life forms. Opening windows in the history of life on Earth, they should be highly valued as sources of information by anyone interested in origin issues.

The significance of fossils is greatly enhanced when they are examined in their stratigraphic context. Acceptance of the geologic column as an empirical construct based on correlation of local observations is therefore essential for the study of general patterns in the fossil record.

Any of the emerging patterns is always undergoing discussion and refinement, but there is a solid base of empirical data that represents the common ground on which both creationists and evolutionists may test their models.

The discontinuities between major fossil groups fit well with the creationist paradigm of an original diversity of created species, and represent, together with high initial disparity and the predominance of stasis over gradual change, a problematic aspect for the evolutionary interpretation of the fossil record. On the other hand, patterns related to orderly stratigraphic distribution of taxa and increasing modernity are currently the less satisfactorily integrated in creationist models.

Treasuring our trust in Scripture and exploring the richness of nature, we should maintain an awareness of the complexity of the fossil record, highlight with balance its many facets, and contribute through rigorous research to a better understanding of some of its aspects.


Ronny Nalin

Geoscience Research Institute


 

Footnotes

[1] A biome is an ecosystem characterized by specific climatic and geographic conditions (e.g., tropical grassland biome, temperate wetlands biome, etc.)

References 

Benton, M.J., 2012. No gap in the Middle Permian record of terrestrial vertebrates. Geology, 40, 339-342.

Brand, L., 2009. Faith, reason and Earth history. Andrews University Press, Berrien Springs, 508 pp.

Brand, L. & Gibson, L.J., 1993. An interventionist theory of natural selection and biological change within limits. Origins, 20, p. 60-82.

Brett, C.E., 1995. Sequence stratigraphy, biostratigraphy, and taphonomy in shallow marine environments. Palaios, 10, p. 597-616.

Brett, C.E., 1998. Sequence stratigraphy, paleoecology, and evolution; biotic clues and responses to sea-level fluctuations. Palaios, 13, p. 241-262.

Clark, H.W., 1946. The new diluvialism. Science Publications, Angwin, 222 pp.

DiMichele, W.A., Kerp, H., Tabor, N.J. & Looy, C.V., 2008. The so-called “Paleophytic–Mesophytic” transition in equatorial Pangea—Multiple biomes and vegetational tracking of climate change through geological time. Palaeogeography, Palaeoclimatology, Palaeoecology, 268, p. 152-163.

Foote, M., 2001. Estimating completeness of the fossil record. In: Briggs, D.E.G. & Crowther, P.R. (eds), Palaeobiology II. Blackwell Publishing, Oxford, p. 500-504.

Looy, C.V., Kerp, H., Duijnstee, I. & DiMichele, W.A., 2014. The late Paleozoic ecological-evolutionary laboratory, a land-plant fossil record perspective. The Sedimentary Record, 12/4, p. 4-18.

Roth, A.A., 1998. Origins – Linking science and scripture. Review and Herald Publishing Association, U.S.A., 384 pp.

Sahney, S., Benton, M. J. & Falcon-Lang, H. J., 2010. Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica. Geology, 38(12), 1079-1082.

Schopf, J.W., Kudryavtsev, A.B., Walter, M.R., Van Kranendonk, M.J., Williford, K.H., Kozdon, R., Valley, J.W., Gallardo, V.A., Espinoza, C. & Flannery, D.T., 2015. Sulfur-cycling fossil bacteria from the 1.8-Ga Duck Creek Formation provide promising evidence of evolution’s null hypothesis. Proceedings of the National Academy of Sciences, 112/7, p. 2087-2092.

Stanley, S.M., 2001. Controls on rates of evolution. In: Briggs, D.E.G. & Crowther, P.R. (eds), Palaeobiology II. Blackwell Publishing, Oxford, p. 166-171.

Valentine, J.W., 2004. On the origin of phyla. University of Chicago Press, Chicago IL, U.S., 608 pp.

Wagner, P.J., 2010. Paleontological perspectives on morphological evolution. In: Bell. M.A., Futuyma, D.J., Eanes, W.F., & Levinton, J.S. (eds.), Evolution since Darwin: the first 150 years. Sinauer Associates, Inc., Sunderland MA, U.S., p. 451-478.

Wood, T.C. & Murray, M.J., 2003. Understanding the pattern of life. Broadman & Holman Publishers, Nashville, TN, 231 pp.

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