A living fossil is an animal that has existed in its present form over millions or even hundreds of millions of years. In order to qualify as a living fossil, a species must exist in the fossil record in its modern form; it must have survived all of the major extinction events, like the K-T extinction that killed off most of the dinosaurs; and it cannot have enjoyed successful diversification by developing into numerous other related species. A famous example is the coelacanth, a fish presumed extinct since the Cretaceous period ended 65 million years ago. The first known living specimen was caught off the coast of South Africa in 1938.
|They are ugly.|
Though inedible, the fish are often caught by accident, putting the species at risk. As a living species that was once thought to be extinct, the coelacanth could also be referred to as a “Lazarus taxon,” an organism that has vanished from the fossil record only to reappear again later.
A more familiar living fossil is the ginkgo biloba tree. Fossil specimens of this tree have been found dating back 270 million years. Individual ginkgo trees are remarkably long-lived; some individual specimens have been aged at more than 2,500 years. These trees are exceptionally hardy as well; in 1945, six trees survived the atomic bomb blast at Hiroshima from a distance of 1.6 to 3.2 miles (1-2 kilometers) from ground zero. The trees still grow there today.
|A fossilized ginkgo leaf from the Eocene epoch.|
The trapdoor spider is the oldest living spider species and the one most closely related to scorpions. Spiders and scorpions are also related to horseshoe crabs, another living fossil that has remained unchanged for at least 450 million years. When you find something that works, you go with it.
|Here they are mating FTW.|
Image credit: Asturnut
Nautili, the marine mollusks with the tubular, spirally shells, are another example of a living fossil. There are six living species of nautilus, which are a type of cephalopod, which makes them a relative of octopi, cuttlefishes, and squid. These other species lost their shells, or internalized them, but the nautilus has kept his. It gets around by sucking in water and then squirting it out.
Image credit: Manuae
The chevrotain, which I like because it has a French name1, is somewhat informally considered a living fossil. There are ten species living in South and Southeast Asia, as well as Central and West Africa, and they are cute as.
|Actually, this one looks kind of angry.|
Image credit: Bjørn Christian Tørrissen
Though not technically a living fossil, the chevrotain is an example of a primitive ruminant. They share characteristics with other ruminants, such as a four-chambered stomach and a dearth of upper incisors. They share several features with pigs, including prominent canine teeth, a lack of facial scent glands, and four toes per foot. Their mating behavior is also similar to that of pigs.
The species was abundant from 34 to 5 million years ago. Modern species live alone or in pairs and give birth to just one offspring per pregnancy. They range in size from 1.5 to 35 pounds (0.7 to 16 kg) and OMG, I want a horsepig that weighs 1.5 pounds.
1 Little goat.↩