Dissent on Bangiomorpha

Bangiomorpha pubescens

Figure 5 from Butterfield 1990. Bangiomorpha pubescens.

In my post on Bangiomorpha, I said

…Bangiomorpha was probably a red alga. This conclusion seems to be accepted by most everyone in the field. In fact, I don’t know of any dissenters, and that kind of consensus is rare for fossils this old.

I guess I didn’t look hard enough, because reader not the FTB Stewart commented

Cavalier-Smith dissents (dissented?) from the consensus

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New fossil proves plants are younger than previously thought

That’s not a headline you’re likely to see again. Hopefully it made you think something along the lines of “how does that work, exactly?” Because it doesn’t. If your estimate of the age of a taxon is based on its oldest known fossil, finding a newer fossil isn’t likely to change that estimate. If it’s an extinct group, a newer fossil might show that it stuck around later than you thought, but not that it originated later. Paleontologists recognize that fossil-based estimates of ages are almost always underestimates, since the fossil record is spotty (and generally spottier the further back you go).

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One of the problems with a big tent

…is that the people in your tent only share some of your views. And one of the problems with having a blog is that it’s searchable, so that when you say ‘no one in my tent ever said x,’ it’s easy to show that it’s a lie.

Within the intelligent design tent, there are people like Michael Behe, who believe that species change over time and that they evolved from a common ancestor, differing from evolutionary biologists only in their insistence that some aspects of biology must have been designed:

I am not a creationist and have no reason to doubt common descent.

There are also people in the tent like Casey Luskin, Stephen C. Meyer, and Jonathon Wells who doubt, and spend a lot of their time attacking, common descent (see “Intelligent design’s relationship with common descent? It’s complicated.“).

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(Probably not) Precambrian Volvox

A new(ish) paper in National Science Review evaluates the evidence for various interpretations of Ediacaran microfossils from the Weng’an biota in South China (Xiao et al. 2014. The Weng’an biota and the Ediacaran radiation of multicellular eukaryotes. Natl. Sci. Rev., 1:498–520.). I recommend checking it out; it’s open access, and there’s a lot of interesting stuff in there that I’m not going to address.

These fossils are undoubtedly multicellular, probably eukaryotic, and extremely enigmatic. Their age (582-600 million years) means they could have important implications for the evolution of multicellularity, and their exceptional preservation in great numbers creates the potential for reconstructing their life cycles in great detail. Some of the Weng’an fossils have been interpreted as volvocine algae, an interpretation that I find highly unlikely.

Some of the Weng’an fossils are thought to represent red algae, and this would not be terribly surprising, since red algae have been around for at least 1.2 billion years. Others, for example the tubular fossils, are more problematic, with interpretations as diverse as cyanobacteria, eukaryotic algae, crinoids, and cnidarians.

Fig. 8 from Xiao et al. 2014

Figure 8 from Xiao et al. 2014: Schematic diagram showing diagnostic features of the five recognized species of tubular microfossils in the Weng’an biota.

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