Living fossils is a common misnomer and promotes a false idea.

Perhaps you have heard of the term ‘living fossils’ in reference to animals that are alive today yet pose a remarkable similarity to long extinct prehistoric animals. Some of the most notable of which being the horseshoe crab or the coelacanth though there are many more popular examples such as: Ginkgo, crocodilians, sharks, mantis shrimps, triops, and also nautilus.

At times they are also used to question the existence of evolution due to their supposed inability to evolve over millions of years and also promote other pseudo-scientific ideas. 

However the belief that these organisms disprove evolution in any way is sorely misplaced, it was in fact Charles Darwin who coined the term ‘living fossil’ in the book in which he introduced the concept of evolution: ‘The Origin of Species’ . In it he states, “ 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.” The basic idea behind evolution is that changes in environmental conditions means that organisms best adapted to them will survive and reproduce. In the quote Darwin states that due to a lack of, or slower rate of changes in the environment causes a much slower rate of evolution. Evolution operates by the principle of if it ain’t broke don’t fix it.

When studying extinct variants of these ‘living fossils’  there are rather clear differences between them and their modern ‘unchanged’ counterparts demonstrating evolution has occurred regardless of how big or small. Due to this fact some scientists question the validity of the term living fossil and instead prefer the term stabilomorph - animals that show a slower rate of evolution.

The coelacanth is a particular favourite of those who use the existence of stabilomorphs to promote pseudoscientific ideas. Until 1938 it was believed to have been extinct for 66 million years after the K-Pg mass extinction event (the same one that killed the dinosaurs) and the fossil record at the time reflected this. As such, it is often used to suggest that as they lived alongside dinosaurs and they now live alongside us, there's a possibility that humans also lived alongside dinosaurs and perhaps they still live among us as the Loch Ness monster, the Mokele-mbembe, or the Ropen. The basis of this argument being that despite there being a huge gap in the fossil record for these organisms and also no contemporary examples, the same was true of the coelacanth until 1938 when we found it was in fact still alive, however there is a serious issue with this argument due to how fossilisation takes place. Dinosaur bones are thick and hard to break. Fish bones are thin and spindly and I often swallow them. Which is more likely to survive 10s of millions of years under huge amounts of pressure in shifting rocks? Dinosaur bones. This rarity of the fossilisation of fish leads to the gap in the fossil record of coelacanth and so the same logic cannot be applied to dinosaurs due to how relatively easy they are to fossilise.

Even with a gap in the fossil record it seems obvious that the use of coelacanth to justify pseudo-scientific ideas is clearly wrong. Additionally, this gap has been closed due to the discovery of fossils between the K-Pg mass extinction and now.