Nature

Living Fossils: Creatures from another Era

September 29, 2015 | Sarah Tse

Artist's impression of an adult vampire squid (Vampyroteuthis infernalis)
Photo credit: Cirton/Wikipedia/CC BY-SA 3.0

Relics from the planet’s evolutionary past crawl and swim among us.

When we imagine Earth one billion years ago, or even one million years ago, we expect to see a completely different world full of unfamiliar plants and animals. After all, the planet has undergone dramatic changes since then, so it makes sense that the creatures living on it would also be subject to changing evolutionary pressures.

But a few archaic creatures have weathered out those changes, and their present day forms are barely different from those that existed when our ancestors first roamed the Earth. While all life forms continue to evolve every day, these animals retain many primitive features that still function in modern environments while hearkening back to their ancient origins.

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Vampire squid

Vampyroteuthis infernalis translates to “vampire squid from Hell” — an appropriate moniker, given its cloak-like webbing and red eyes. The vampire squid is the sole survivor of its order Vampyromorphida, which were once far more numerous, about 300 million years ago when they first appeared.

 

Lampreys

Living specimens of these bloodsucking, jawless fish are remarkably similar to a 360 million year old fossil lamprey found in South Africa. Lampreys are the most primitive vertebrates (animals with spines), but have extremely specialized feeding structures that helped them latch onto their prey.

Toothed mouth of a sea lamprey, Petromyzon marinus (I, Drow male/Wikimedia Commons/CC BY-SA 3.0)

 

Elephant sharks

Elephant shark is another misnomer; these ghoulish fish diverged from sharks about 400 million years ago. A study of the elephant shark’s genome revealed that it is the slowest-evolving vertebrate, with DNA sequences that could unravel the history of the evolution of bones .

Elephant fish, aka Australian Ghost Shark (Credit: Melbourne Aquarium)
Australian ghost shark or elephant shark

 

Horseshoe crabs

These strange hybrids between crabs and spiders look like they belong in an Alien movie — they even have blue blood. They’re a common sight on Atlantic beaches, where they get a bit frisky in spring and fall and form nesting groups. Unlike their beach-going neighbors, horseshoe crabs first appeared in the fossil record almost 450 million years ago.

Horseshoe crabs mating (Credit: Asturnut/CC BY-SA 3.0)
Living fossil, horseshoe crab mating on a beach

 

Coelacanths

One of the most famous examples of living fossils, coelacanths have the special distinction of being a “Lazarus taxon.” This term, named after the biblical Lazarus that arose from the dead, refers to groups that disappear from the fossil record only to pop up again after a few periods. Coelacanths were thought to have gone extinct 66 million years ago, until a museum curator found one buried beneath the rest of a South African fisherman’s catch in 1938.

Preserved specimen of chalumnae, aka coelacanth (Credit: Alberto Fernandez Fernandez/CC BY-SA 3.0)

 

Nautilus

These marine mollusks are the only extant family of shelled cephalopods; their closest living relatives are the squishier variety, like octopuses and squids. Nautiluses have existed in this form for the last 500 million years. They are also famous for forming shells that perfectly follow a logarithmic spiral.

Nautilus (Credit: Manuae/CC BY-SA 3.0)
Nautilus

 

Velvet worms

Named after the texture of their coat of sensory bristles, velvet worms have been around in much the same form for over 500 million years. They’re also incredibly weird: they attack via slime, which quickly hardens and immobilizes their prey, giving the worm a chance to inject its prey with digestive enzymes that soften up the insides.

Euperipatoides rowelli, a velvet worm (Andras Keszei/Flickr/CC BY-SA-NC 2.0)
Euperipatoides rowelli, a velvet worm

 

Sea sponges

You might not guess it from their tame reputation, but sea sponges are the world’s most primitive living animals. The oldest sponge fossil, which represents the very first animals to evolve, is dated to 600 million years ago. Even the living ones are incredibly enduring; oceanographers have discovered 9,000-year-old glass sponge reefs in British Columbia’s Queen Charlotte Sound.

Giant sea sponges (Credit: Albert Kok/Wikipedia)
giant sea sponges

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