Living Fossils

"These anomalous forms may almost be called living fossils; they have endured to the present day, from having inhabited a confined area, and from having thus been exposed to less severe competition."

- Charles Darwin, On the Origin of Species

"Sharks are old: there were sharks in the ocean before the dinosaurs.  And the reason there are still sharks around is that sharks are better at being sharks than anything else is."

- Neil Gaiman

When you observe a chambered nautilus or an alligator gar - or a Cuban crocodile, or a sand tiger shark - it's sometimes hard not to feel like you're glimpsing a remnant of an older, forgotten world.  In truth, these are all species which, superficially at least, appear unchanged from the prehistoric record.  Such creatures - and assorted plants, such as ginkgoes and horsetails - are sometimes described as "Living Fossils."

The term "living fossil," as explained to me by a very exasperated alligator biologist, is often misused by the general public.  It does not mean that the organism remains identical to forms millions of years old, or that evolution has stopped for that species.  Instead, it simply means that it represents a lineage which has undergone relatively little morphological change from its past forms.  None of this means that there is no change.  A great white shark bears great resemblance to a Megalodon (a real one, mind you, not the cheesy super-version which will be swimming across the big screen soon).  It is, however, much smaller, which results in other behavioral and physical changes you would expect in an animal that has seen millions of years of environmental changes.

Perhaps that most dramatic example of a living fossil is the coelacanth, a freaky-looking (that's a scientific term) lobe-finned fish that was unexpectedly hauled out of the Indian Ocean in 1938.  "Unexpectedly", that is, because it was believed to have gone extinct about 66 million years ago, or about the same time that the Tyrannosaurus Rex made its final bow.  Such rediscovered "blasts from the past" are often called Lazarus species, where the animal or plant was thought to be extinct until, surprise, it's not.

The thing with living fossils is it's really hard to tell if they actually are living fossils.  The designation is largely based on morphology and appearance, and it can be difficult to tell if the traits that look primitive actually are primitive, or whether they were seen in the fossil record, disappeared, and then perhaps reemerged in response to new evolutionary pressures.

Living fossils have a special place in our culture and fiction.  You've got King Kong, Godzilla (a mix of living fossils and nuclear radiation), the Creature from the Black Lagoon (reimagined in Guillermo del Toro's The Shape of Water), and The Lost World (the Arthur Conan Doyle version, not the Jurassic Park series).  It seems our science fiction is always pulling us in two directions - looking forward to the future, while at the same time imagining our past catching up with us.

To the best of my knowledge, however, no one has ever written a sci-fi novel about a giant chambered nautilus.