The only reason we are able to so vividly imagine life on the earth before our own time is thanks to the fossil record. It’s something we are so used to as a reality that it’s easy to forget how miraculous and, frankly, bizarre the process is.
Think about it for a second. Imagine someone had made it to adulthood without ever hearing about fossils or prehistoric life at all, how would you explain it to them?
There used to be millions of reptiles the size of buildings roaming the planet. Wow! When? Literally one hundred million years ago. That’s a ludicrous amount of time. How can you possibly know? We find their bones. Cool, like in the dirt? No actually inside rocks. How did they get there? That rock used to be more like mud. Oh, and the bones are made of rock now too. Weird, so you dig underground to find them? Sometimes. Sometimes they’re five hundred foot in the air on a cliff. How did they get there? The ground moves. That was also under the sea then. This is ridiculous, anything else I should know? The reptiles are birds.
Such a miraculous process is, however, complicated, with no shortage of chances that the whole venture will fail. Only the tiniest fraction of animals once alive actually end up preserved as fossils. The rest are lost forever.
All this to say that the fossil record is amazing, but also unreliable. It’s riddled with bias and gaps in the data. There are some entire genera of animal we know only from a single isolated fossil.
One of the most remarkable artefacts of this unreliability is that it means some animals can effectively hide millions of years of their existence.
Say for example we find fossils of a creature regularly in the Ordovician period, 450 million years ago. The fossils of this particular creature then suddenly stop appearing in the rock, and you assume this means it has gone extinct at this time. However, out of nowhere the fossils suddenly reappear during the Devonian, 370 million years ago, having been absent for 80 million years worth of history and seemingly skipping an entire geological period (the Silurian).
To all the world, it looks as though this creature has come back from the dead. And so, scientists gave them the name ‘Lazarus Taxa’, after the biblical character. I can only assume they didn’t go with any zombie-related names so as to not give nightmares to small children reading books on palaeontology.
Now, of course, the animal didn’t actually come back from extinction, that’s impossible*. It must have existed that entire time, it is purely that no fossils have been found from the time in between.
That span of time where we know the animal existed but can find no trace of them is fittingly known as a Ghost Lineage. So at least one term successfully stuck to the spooky theme for this October, after the zombie disappointment we just went through.
The reason for this absence could have been that there genuinely was a reduction and then regrowth in their population size, simply making it less likely they would have been fossilised. It could be that good fossil-bearing rocks of the missing time are harder to come by. Or it could even have just been bad luck.
Now I admit, the time periods I used in my above example aren’t the easiest to picture, so I’ll put it in an easier to describe context. That is the equivalent of something last known of during the midst of the dinosaur era, suddenly reappearing alive today. Which is precisely what the most famous Lazarus Taxon of all did.
The coelacanth was a lobe-finned fish, somewhat related to lungfish, known exclusively from ancient remains. The oldest members of the coelacanth family dated back over 400 million years and, judging from its last appearance in the fossil record, it must have gone extinct during the late Cretaceous, about 80 million years ago. It looked as though they persevered for three hundred million years and the poor thing couldn’t survive long enough to get to see a T. rex.
Or at least, that was the scientific consensus in 1938, before Marjorie Courtenay-Latimer reported one as freshly caught on a South African dockyard.
The coelacanth, known exclusively from fossils for 99 years, was alive and still swimming around the coast and islands of the Indian Ocean.
And thus, we owe one of the greatest scientific discoveries of the century to Hendrick Goosen, captain of the good ship Nerine, calling his local museum to report finding a particularly funky looking fish he thought they might like to see. It’s a good lesson in the importance of keeping up healthy relationships with your local museums, and respecting the keen eye of an experienced fisherman.
Whilst the coelacanth is undoubtedly the most famous, incredibly, it is not the only Lazarus taxon example to have pulled this trick. There are multiple examples of occasions where fossils have been excavated, expertly described, and named as a new extinct species, only for the real thing to subsequently turn up very much alive just down the road.
The South American Bush Dog is a particularly confusing example, as it was known to be extinct and alive simultaneously. Famed Brazillian palaeontologist Peter Wilhelm Lund discovered fossils of an extinct carnivore in a forest cave which he dubbed Speothos venaticus in 1842. And then, less than twelve months later, he discovered some undeniably alive mammalian carnivores and named them Icticyon venaticus. He didn’t realise he’d just found his fossil Speothos risen from the grave, and neither did anyone else for around 100 years.
The Lazarus Taxa with the largest known Ghost Lineage are the Monoplacophora, which are deep sea molluscs. Unless you’re particularly fond of molluscs, I don’t think you could call them the most amazing things to look at, but the gap in their fossil record is nothing short of spectacular.
These small shelled creatures were rediscovered for what they truly were in 1952, having not been seen in the fossil record for 375 million years. The gap between their last appearance and now is greater than the span between their once-supposed extinction and the origin of truly complex multicellular life.
Being a Lazarus Taxon isn’t exclusive to animals either. It can happen with plants too, such as the Dawn Redwood tree. It too was known exclusively from fossils until living examples were found in China in 1944.
At this point you may be asking how that can happen. An animal can be sneaky, hide, run, evade capture. But how could people possibly miss a 50 metre-high immovable tree? Well, to that I say this; go for a walk in the woods hundreds of miles away from civilisation and tell me every single species of tree you see and whether any of them shouldn’t be there. Can you? CAN YOU?
I suppose you could also say, in a very wrong and unscientific way, that the term Lazarus Taxon could also be applied to an abstract concept. Say for example, an outreach and engagement project focused on palaeontology which seemingly died due to being starved of funds many months ago, only to have it re-emerge in October, shiny and new, pretending that absolutely no time has passed. Welcome back to the Bristol Dinosaur Project everyone.
About The Author
Rhys Charles has been the head of the Bristol Dinosaur Project since November 2016. His next book, “The Little Book of Dinosaurs” is available to buy from the 22nd October 2024. (@tweetodontosaur)