Earlier this week, I wrote that fungi are weird. Fungi are also old. Probably.

Recently discovered fossils from Arctic Canada have been interpreted as fungi, an important finding since the sediments in which they were found date to 0.89-1.01 billion years ago, around half a billion years older than the next oldest unambiguously fungal fossils. Corentin Loron and colleagues have described microfossils from the Grassy Bay Formation and presented several lines of evidence that they represent ancient fungi.

Loron and colleagues first argue that the fossils are eukaryotic:

This combination of complex morphology, right-angle branching, multicellularity, bilayered wall ultrastructure, compositional recalcitrance and relatively large size (not by itself a criterion) permits the unambiguous placement of the microfossil O. giraldae among eukaryotes; together they indicate the presence of a complex cytoskeleton, which is absent in prokaryotes.

Aside from the morphology and cell wall structure, a critical piece of evidence for a fungal origin is chemical. Using using Fourier-transform infrared (FTIR) spectroscopy, Loron and colleagues showed that the fossils contain a signature of chitin, a major component of fungal cell walls. Fungi aren’t the only eukaryotes that use chitin (as the authors acknowledge), but they are the only ones that use chitin and look like these fossils:

Several multicellular micro- and macro-organisms (including pseudofungi, some life stages of xanthophyte algae, and slime moulds) are known to exhibit morphologies of ramified branching and terminal spheres that are broadly similar to the microfossils discussed here; however, the combination of morphology, wall ultrastructure, chitin and/or chitosan chemistry, and the absence of cellulose shown by the microfossils are most consistent with a fungal affinity. Other organisms that produce chitin (arthropods, chrysoflagellates, diatoms and ciliates) are morphologically very distinct from our specimens.

I’m neither a paleontologist nor a mycologist, so I don’t have the expertise to evaluate these claims. I do, however, have some thoughts on how they support intelligent design. They don’t, but Denyse O’Leary appears to think they do.

Over at Uncommon Descent, she quotes a secondary article about the fossil fungi (from Phys.org) and comments,

If so, not nearly as much time from the Big Bang onward for all that complexity to just sort of slosh into existence…

Leaving aside that no one thinks complex multicellularity “just sort of slosh[es] into existence,” let’s think about just how much time that leaves. If these fossils push back the origin of fungi from 400 to 1100 million years, that would reduce the time from the Big Bang from about 13.4 to about 12.8 billion years. Is O’Leary seriously suggesting that 13.4 billion years would be long enough to evolve fungi, but 12.8 would not?

How the Big Bang is even relevant is a mystery to me; the more useful date is the origin of eukaryotes. Estimates vary widely, but eukaryotes are generally thought to have originated around 1-6-2.1 billion years ago. If so, these fossils are around 0.6-1.6 billion years younger. 600 million years (at the low end) to evolve these not very complex structures. Will Ratcliff’s multicellular “snowflake” yeast consistently evolve from unicellular yeast within 60 days, or about one 3.6 billionth of that time.

O’Leary also seems to think these fossils are a big surprise to evolutionary biologists:

Fungi were thought to have appeared about half a billion years ago but…

That’s not true, though, and she would know this if she’d read the original article instead of relying on secondary sources. The Phys.org article does say, incorrectly, that

For decades, the earliest known fungi—organisms such as mushrooms, mould and yeast—was thought to have appeared on earth around half a billion years ago.

It’s true that the earliest known, unambiguously fungal fossils were around half a billion years younger than these (there are also some older fossils that are suspected of being fungi):

To date, the earliest uncontested fossil fungi are specimens from the 410-million-year-old Rhynie chert of Scotland and arbuscular spores of glomeromycotan fungi from Wisconsin that date to 450 Ma, in the Ordovician period.

But nobody thought that those were the oldest fungi:

These fossils have been used as the main calibration points for molecular-clock estimates that place the origin of fungi between 1,060 and 740 Ma—although this date may be older…

A quick visit to timetree.org shows that published estimates for the divergence between fungi and animals range from 900-1600 million years (the 64 million year estimate is obviously included in error; the paper it comes from has nothing to do with fungi, and I have emailed the editors to let them know about this*):

That’s a wide range, but molecular clock estimates are just that: estimates. They are sensitive to the assumptions of the model, the parameters chosen, and, critically, on the interpretation and dating of the fossil calibrations used. Evolutionary biologists know, or should know, to always take molecular clock estimates of the age of a lineage with a grain of salt.

That said, let’s take a look at these estimates in light of the new fossils. Remember, they were dated between 890 and 1010 million years ago. A fossil can only provide a minimum age for a group, never a maximum (see “New fossil proves plants are younger than previously thought“), so we should expect fungi to have appeared before 890-1010 million years ago. If the fossils are at the young end of the range, all of these estimates are possible (disregarding the absurd 64 million year one); if they are at the older end, nearly all of them are.

Regarding O’Leary’s assertion that fungi were “thought to have appeared about half a billion years ago,” nothing could be further from the truth. The oldest previously-known fungal fossils were 450 million years old, but no one (no one with a clue) thought fungi were that young. The median estimate above (again excluding the snail one) is 1296 million years, the mean 1253 million.

As I said before, I lack the expertise to judge whether or not these fossils really represent fungi. But if they do, billion year old fungi would not be a surprise to evolutionary biologists. They are exactly what was predicted. It’s possible I missed it, but I don’t remember seeing any predictions of billion year old fungi on Uncommon Descent.

 

*Since I wrote this, I have heard back from the timetree administrators. They are aware of the problem and plan to fix it.

 

Stable links:

Loron CC, François C, Rainbird RH, Turner EC, Borensztajn S, Javaux EJ. 2019 Early fungi from the Proterozoic era in Arctic Canada. Nature (doi:10.1038/s41586-019-1217-0)

Ratcliff WC, Denison RF, Borrello M, Travisano M. 2012 Experimental evolution of multicellularity. Proc. Natl. Acad. Sci. USA 109, 1595–1600. (doi:10.1073/pnas.1115323109)

Yuan X, Xiao S, Taylor TN. 2005 Lichen-like symbiosis 600 million years ago. Science 308, 1017–1020. (doi:10.1126/science.1111347)