What's a "Living Fossil"?
What is a “Living Fossil”? The term usually describes an organism that closely resembles its ancestors in the fossil record more than any contemporary organisms, and is not closely related to any still-living species. Living fossils usually have a slow rate of evolution, and thus can appear to have been largely unchanged over millions of years. These creatures often have unique traits that make them unusual among other members of the animal kingdom.
Arguably the most famous living fossil is the coelacanth (pronounced SEE-LA-CANTH). For a long time, this group of fishes was only known from fossilized remains and was thought to have gone extinct around the same time as most of the dinosaurs, around 65 million years ago. Then, in 1938, a living coelacanth was caught off the coast of South Africa. Since then, many more have been found, and a second species was even described in 1999. Coelacanths possess many interesting features not seen in most other fish, including a second, smaller tail fin that emerges between the top and bottom half of the first tail, and arm-like fins that identify it as a member of the so-called “lobe-finned fishes”. Today, almost all bony fish are members of a group known as “ray-finned fishes”, but coelacanths and a few other living fish are the last remnants of the more primitive lobe-finned fish. Where did the rest of the lobe-finned fish go? Well, many became extinct, but others simply evolved. In fact, they’re believed to be the direct ancestors of all tetrapods – a group that includes all reptiles, birds, and mammals…and yes, that includes humans!
While the coelacanth might be the most famous living fossil, it’s far from the only one. On the invertebrate side of things, there’s the horseshoe crab. Despite their name, these strange sea-dwelling arthropods are more closely related to spiders and scorpions than to true crabs and other crustaceans. Horseshoe crabs have existed, largely unchanged, for over 400 million years. While they look rather fearsome, horseshoe crabs are completely harmless, and in fact can be quite beneficial to humans. Their blood has a unique feature that can detect and isolate viruses, bacteria and other toxins, and is used in the medical industry to test the purity of medicines. A compound in their blood may also have antibiotic properties. While horseshoe crabs usually travel along the sandy sea floor with their many legs, they are also known to swim – upside down!
Now let’s move from the ocean to the sky, where we find living fossils among the birds. The pelican has existed in a very similar form to the pelicans we know today for over 30 million years. Their advanced bills are long and thin, with large pouches that they use to catch prey by dive-bombing into the water and scooping it up. This interesting adaptation is fully present in ancient pelican fossils, remaining virtually identical to the bills of modern pelicans. In fact, almost all pelicans extinct and living are sorted into the genus Pelecanus, meaning they are all quite closely related. Pelicans are among the heaviest living bird species, and also have some of the largest wingspans. The Dalmatian pelican is the largest - it’s wingspan can be more than 10 feet!
While we often think of mammals as one of the more recent groups of animals to develop, they have quite a few living fossils of their own. The platypus of Australia is one well-known example. This odd-looking creature is one of the only mammals still living today that lays eggs instead of giving birth to live young. This animal, with its webbed feet and leathery duck-like bill, was initially thought to be a hoax when the very first specimens were examined. The modern platypus has been around for about 100,000 years, but its relatives date back to somewhere between 20-50 million years. The earliest egg-laying mammals, ancestors of the platypus, may have been around for more than 150 million years, as fossils have been found in South America, meaning they were around when the two continents were connected.
Aardvarks are yet another example of a living fossil mammal. They have characteristics that are similar to pigs and anteaters, although they are not believed to be closely related to either group. Their relationships to other animals are poorly understood, and they are the only living member of the Orycteropodidae family, which itself is the only family in the order Tubulidentata. This group of mammals has existed for about 20 million years, although most of the species within went extinct by around two and a half million years ago, leaving the aardvark as the sole representative. A native of Africa, the aardvark uses its long pig-like snout to sniff out its food source – ants and termites.
Other living fossils include the okapi, the red panda, and the koala. The okapi, a relative of the giraffe, is the sole remaining species of the genus Okapia, which likely split from other giraffes around 20 million years ago. The red panda, while not as ancient as some other living fossils, is notable for its confusing classification history. It was once thought to be related to bears and raccoons before finally being classified as a relative of the mustelids – a group that includes ferrets, badgers, otters and wolverines. The koala, also sometimes incorrectly associated with bears, is a marsupial – like kangaroos, wallabies and wombats – meaning its young live in a pouch attached to the mother for the first part of their lives. However, it is the only remaining species within its family. These tree-dwelling Australian mammals eat a diet of almost entirely eucalyptus leaves, which are not very nutritious and thus don’t provide the koala with a lot of energy. They can sleep up to 20 hours a day!
Living fossils can be an important tool that allows scientists to better understand prehistoric animals that have been extinct for many millions of years. Most fossil animals are known primarily from skeletal material, so having a close living relative can provide a good reference for what the extinct animal looked like in life, including features that may not be preserved in the fossil record. It should go without saying that, as some of the last surviving members of their families, the conservation of these species is important. Unfortunately, many of these creatures – such as the okapi, red panda, koalas, and some pelicans – are listed as endangered or vulnerable. Others like the platypus are near threatened, and some species like the coelacanth are so poorly understood that accurate numbers are difficult to determine, though one species is thought to be critically endangered. Protecting these species is vitally important, as they provide us with a view into our planet’s history.