Inferred palaeontology and the lying rocks

At a meeting I attended in Glasgow a while back, a friend of mine - Tom - gave a presentation on his PhD research into the Boda Event, a period of climatic warming during the Ordovician.

How things might have looked in the late Ordovician.

Afterwards he was asked a question by a colleague - David - about the fossils he'd found (or rather, those he hadn't found). Tom assured David that he'd looked carefully for the graptolites in question but simply hadn't found any. As such he could only presume that they hadn't lived in that place at that time.

David assured Tom that they had lived there, though, and that Tom simply hadn't found them. Quite how David knew they were there was unclear, but it raised the prospect of an interesting new branch of geological science - inferred palaeontology.

Just because you've never found one of these as a fossil, doesn't mean it never existed.

Inferred palaeontology is the study of organisms for which there is no physical evidence of their having existed, but which expert palaeontologists are certain did. Freed from the confines of evidence-based fossil studies, such 'experts' (i.e. me) can then give full rein to their imagination, creating fabulous animals that roamed the land or cruised the seas some time in the distant past.

Jellyfish with pointy teeth perhaps? Giant, lightweight whales filter-feeding nutritious dust out of the sky? Pole-legged waderbirds? Their lack of fossil record is an inconvenience, but should not preclude them from appearing in palaeontological textbooks.

Hidden in the nonsense is a real point (somewhere). The fossil record is extremely patchy, yet we trust it to reveal the life of the past since it's all we've got. There is no alternative fossil record with which to compare it.

This might be true, then again, it might not.

Just because it is the only palaeontological dataset available, however, does it mean we have to accept it? Look at all the different animals and plants found on a beach at the modern day. How many of them will ever become fossils? None, probably, and those that do will most likely be shells.

Anything delicate, soft-bodied, or particularly attractive to predators or scavengers, has almost no chance of being fossilized. Yet we use the fossil record to construct extinction models stating that 85% of life died out at the end of the Ordovician (or whatever). Is it likely we are even close to the truth? Is it likely we can get a real handle on the nature of ancient nature?

Maybe not, but perhaps the first thing we can do as palaeontologists is to pay for more attention to modern ecosystems and use them as analogues. We can assess the preservation potential of living animal groups and then test whether this correlates at all to their scarcity in the fossil record. It won't be perfect, but it'll be a start.

It's the same for sedimentary geology.  In 2003, I spent a couple of months in Nevada and California assisting my friend Alex in investigating modern desert river systems. We carried out transects across the Ralston Valley near Tonopah, NV, then across Death Valley and Panamint Valley in California, and pretty much no matter where we dug, all we came across was fine-grained, buff-coloured sediment.
In the buff, in Ralston Valley, Nevada.

Sometimes it had been deformed by the growth of salt crystals, sometimes there was a dash of gravel, sometimes there were calcretes beneath the surface, but almost everywhere we looked it was buff. It was dispiriting and repetitive. Yet as soon as we went to look at Miocene fluvial sediments in the Virgin River valley we found channels, cross-bedding, gravel layers, sands, muds, ripples and all sorts. They bore no resemblance whatsoever to their modern equivalents. What was going on?

Then, nearly a year after we'd been there, there was a major flood in Death Valley. Heavy rain fell on the mountains, came charging down the slopes, channels and fans into the valley and caused widespread damage to the Furnace Creek area. Roads were destroyed, cars upturned, buildings damaged and two people were killed.

Some buildings were almost buried in gravel, indicating deposition of perhaps four feet of sediment. Suddenly it became clear: although the buff sediment represented normality it rarely (perhaps never) got preserved in the rock record because as soon as a powerfully erosive event came along it scoured the buff away. In the future all that would be preserved in the rocks would be a series of channelized gravels and sands and perhaps a pocket of buff here or there.

 
The same must happen in other environments - everyday sediment might last for years but as soon as a powerful event comes along it gets obliterated. And then sediments from a 1 in 20 year storm would get removed by a 1 in 100 year storm, and those by a 1 in 1000 year storm, and so on. Eventually all that is left is a snapshot of a momentous occasion, as opposed to the long term record of day-to-day deposition.

Thus, extracting Earth history from the geological succession becomes akin to extracting the true story of a mass killing from the only survivor, a mentally ill man with a penchant for lying.  If you like a challenge, however, then it's just about the most interesting subject imaginable.

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