A recent article in Science begins by observing that the lack of evolutionary ancestors for the animal phyla that appear abruptly in the Cambrian explosion has been troubling to many evolutionary scientists:
Ever since Darwin there has been a disturbing void, both paleontological and psychological, at the base of the Phanerozoic eon. If his theory of gradualistic evolution be true, then surely the pre-Phanerozoic oceans must have swarmed with living animals — despite their conspicuous absence from the early fossil record.
(N. J. Butterfield, “Terminal Developments in Ediacaran Embryology,” Science, Vol. 334:1655-1656 (December 23, 2011).)
The articles goes on to explain that in 1998, tiny fossil animal embryos were reported that offered “palpable relief” to those evolutionary scientists worried about the lack of Precambrian ancestors.
However, new analyses of these microfossils now strongly suggest that they were not multicellular animals, and thus could not be Precambrian multicellular metazoa that have long been the holy grail for evolutionary paleontologists. Rather, they likely represent single-celled amoeba-like organisms. As the article continues:
All was not as it seemed, however, and new data from Huldtgren et al. on page 1696 of this issue look set to revoke the status of these most celebrated Ediacaran fossils.
A Science Daily article on the study explains that many Darwinian scientists will be dismayed by the results of this study:
Professor Philip Donoghue said: “We were very surprised by our results — we’ve been convinced for so long that these fossils represented the embryos of the earliest animals — much of what has been written about the fossils for the last ten years is flat wrong. Our colleagues are not going to like the result.”
How did the investigators determine the nature of these ancient organisms? The fossils were exceptionally well preserved, such that, as the lead author on the paper stated, “the fossils are so amazing that even their nuclei have been preserved.” These allowed the authors to determine that these were in fact eukaryotic organisms, but not multicellular animals. The commentary in Science summarizes:
Wherever the Doushantuo fossils eventually end up, it will clearly not be within “crown-group” Metazoa. Does this then mean there were no early Ediacaran animals? Not at all. No fossil assemblage, however well preserved, provides a full account of past diversity, particularly when the local conditions are so extraordinary as to fossilize nuclei and other intracellular constituents. The “exceptional” fossil record is, by any measure, woefully unrepresentative and incomplete.
(N. J. Butterfield, “Terminal Developments in Ediacaran Embryology,” Science, Vol. 334:1655-1656 (December 23, 2011). )
Thus, we are told that the reason why Precambrian multicellular evolutionary ancestors to the Cambrian animals aren’t found is because the fossil record is incomplete. Ironically, these microfossils provide a rebuttal to that argument.
Clearly these Precambrian strata were more than capable of preserving small soft-bodied fossils. Yet all we keep finding are single-celled organisms or the enigmatic Ediacaran fauna — neither of which could serve as evolutionary ancestors for the complex animal phyla that appear in the Cambrian. How come?
In a candid moment, the Science Daily article further notes that “fossil evidence of these major evolutionary transitions is extremely rare.” You don’t say. It seems that these Precambrian microfossils don’t help fix that problem.