Which extinct creatures live on the seabed

Even then, multiple such crinoids and corals were found by scientists across the marine world, but none as intertwined as the ones found recently. Also read: Three-year old Mtoto, Africa's earliest known human burial from 78, years ago. The two species of coral are "Abyssoanthus" and "Metridioidea", with the former being extremely rare. Once the interior structures were identified, DNA barcoding was used to understand the species. This blue-green microbe called a cyanobacterium was likely the first photosynthetic organism—and it was a game changer in the story of life on Earth.

Over millions of years, oxygen continued to accumulate in the atmosphere, thanks to cyanobacteria and other photosynthetic organisms. It was this oxygen that would allow complex life to thrive in the millennia to come. By million years ago the first supercontinent, Rodinia, formed. It is unclear exactly how big Rodinia was, although it is likely that its core landmass was the land that is now North America.

On either side of the continent were the Panthalassic and the Pan-African Oceans. The first recorded complex life forms appear around million years ago, though they were very different than the creatures we are familiar with today. Many were soft-bodied, with only a few tube-like creatures having a stiff outer sheath.

In some places, forests of fern-like fronds covered the ocean floor, but since they grew at depths beyond where light could reach they obtained energy by absorbing nutrients, like carbon, directly from the water rather than through photosynthesis. Unlike the filter feeding invertebrates of today, such as sea pens, these Ediacaran fronds likely did not have digestive organs and instead directly absorbed simple molecules, in a similar manner as bacteria.

They also likely left no living descendants. Other creatures relied on a thick microbial matt that covered the ocean floor for a source of energy. The first animals feasted on this dense matt of microbes. Some were unnamed burrowers, known only by the trails they left behind that evolved from aimless wanderers to proficient consumers with organized foraging routes.

Other creatures, believed to be the early ancestors of animals, had bilateral symmetry, meaning that the left and right sides of the body were mirror images of each other. Spriggina is often compared to later arthropods, like the trilobites. The earliest confirmed animal, Dickinsonia moved along the seafloor, periodically parking in one place to consume the microbes and once that spot became depleted, moving to a more plentiful site.

Another, Kimberella , had a proboscis that it used to rake the microbes towards itself to feed. These creatures have a hint of familiarity, but one of the most unique creatures of the Ediacaran is Tribrachidium.

It had three spiraling arms that coiled into a disk. Trilateral symmetry, a rarity today, was a common feature in Ediacaran creatures. Viewed from space, the Paleozoic Earth would be a foreign world. During this era, seas flooded the continents and receded several times.

During the early Paleozoic three small continents— Laurentia, Siberia, and Baltica—split apart from the rest of the supercontinent Gondwana and formed the Lapetus Ocean in between.

This new continent called Euramerica, and three newly-formed oceans, the Iapetus, Rheic, and Paleo-Tethys, spanned the smaller continents and Gondwana. By the end of the Paleozoic, the supercontinent Pangaea was beginning to take shape. Euramerica plowed into Gondwana, an event that caused many of the low-lying seas to dry up.

Surrounding the entire continent, the Panthalassic Ocean covered the rest of the globe. Plants began to grow on land during the Ordovician, followed by invertebrates during the Silurian and finally vertebrates during the late Devonian. These early land dwellers were amphibian-like, eventually giving rise to reptiles by the end of the era. Some researchers think this happened due to a combination of a warming climate, more oxygen in the ocean, and the creation of extensive shallow-water marine habitats.

This environment would be ideal for the proliferation of new types of animals, including those that were larger and more complex in their body shapes and ecologies than their ancestors. On the seafloor, sponge-like creatures called Archaeocyatha grew in dense mounds and became prolific reef builders of the ocean. Though the first creatures to have shells arose in the Ediacaran, by the Cambrian this body feature became more common and it would prove as a critical defense mechanism against hungry predators.

Many of these creatures were discovered in the Burgess Shale , an area of the Canadian Rockies with a large deposit of preserved Cambrian-age fossils. The largest and most fearsome looking predators to roam the seas during the Cambrian were the anomalocarids. The largest intact specimens discovered reach up to 3 feet in length.

Some species of anomalocarids used two curled appendages to capture their prey and reel it in to a square ring of jagged teeth. They would also use crushing jaws to tear through the protective armor of hard creatures like trilobites.

But unlike many of its relatives, one species of anomalocarid doesn't seem to be an apex predator. Like the whale shark and basking shark of today, the large shrimp-like creature called Tamisiocaris borealis was a filter feeder, and likely the first ever to live in the ocean. Scientists think the feather-like structures on its head were used to rake plankton from the sea.

The appendages had finely spaced spines, further divided by smaller spines, which would have formed an efficient trap for small plankton. Another formidable predator, Hurdia victoria has been nicknamed the Tyrannosaurus rex of the Cambrian era due to its relatively large size.

While it never reached the size of the largest anomalocarids, some specimens reached 50 cm around 20 inches , which was large for a time when most animals were about as big as a fingernail. Its prey consisted of trilobites and other smaller animals crawling on the seafloor. But not all predators stalked their prey from above. The ancient worm Ottoia prolifica lived in a self-constructed u-shaped home below the ocean floor. From there, Ottoia prolifica ambushed prey, which it would swallow headfirst.

Most of its prey were small shelled animals related to mollusks, as well as worms, though there is evidence that they sometimes resorted to cannibalism. Hallucigenia sparsa , a worm, is notable for the porcupine-like spikes that covered its back—an efficient way to ward off hungry jaws. Opabinia took a different approach and evolved five mushroom-like eyes that allowed it to see predators approaching from many directions.

Additionally, its segmented portions were filled with fluid in order to be more flexible, an important trait for avoiding capture. Perhaps the most famous creatures to emerge during the Cambrian were the trilobites. Relatives of insects, crabs, and spiders, there were over 20, trilobite species that lived between the Cambrian and the end of the Paleozoic Era when they went extinct, some million years ago. Prolific survivors with a segmented body plan that could be easily modified and altered, they soon dominated the seafloor.

It seems no method for catching food was beyond the scope of what a trilobite could do—predation, scavenging, filter feeding, and even forming a symbiotic relationship with bacteria were all methods of feeding employed by at least one species.

There is also evidence that trilobites were social creatures, migrating caravan style across the seafloor and meeting for mass molting events where they collectively shed their hard exoskeletons. As jawed and stealthy predators began to emerge, their simple body plans proved to be easy fodder for predators, but the trilobites adapted in stride.

Some would curl up like pill bugs, their segments fitting together like a lock and key. Others developed thorny spines that would make it difficult for probing jaws to take hold and bite. Burrowing underneath sand and mud was another hiding tactic. Throughout the existence of Earth, the explosions and extinctions of life often take their cue from global changes. The quadrupling of diversity during the Ordovician is no different.

During this period, most of the continental land was a part of the supercontinent Gondwana. Through the movement of plate tectonics, Gondwana gradually shifted south until it reached the South Pole. As this happened, the balmy, moderate temperatures of the planet turned ice cold, massive glaciers formed, and sea level dropped as much of the water used to form the ice came from the sea. During the Ordovician, the majority of ocean life still lacked a backbone.

Instead, life relied on stiff structures, like shells, to protect them from predators. Trilobites, armored by their stiff exoskeleton, remained prominent seafloor dwellers. Clams developed a dual shell system with left and right halves while brachiopods , a lesser-known shelled invertebrate, evolved top and bottom valves and occupied the muddy bottom. Predators, too, required a tough outer skeleton.

The eurypterids, a group of arthropods, were some of the most fearsome predators and could grow up to six feet 2 meters. With long tails that ended in a spike, they are often called "sea scorpions. Their simple shells evolved into complex spirals like the one still used by the nautilus. Scientists have used a variety of methods to estimate the global number of marine species and each has its limitations.

A common method is to scale up the fraction of unknown species estimated in a specific sample or region. Other methods rely on our system of taxonomic classification the way we name and group different species. We can use the rate of discovery of new families and orders or the rate at which new species are described to estimate the total number of species there must be.

According to a study from , the average time between the discovery of a new species and its description is 21 years. Because each method relies on assumptions and particular datasets, they have resulted in wide variations in estimates. The very high estimates any larger than 10m are now thought unlikely by many, but current common estimates still vary between around 0. This means that, after years of describing, naming and cataloguing the species we share our planet with, we are still a long way off achieving a complete census.

Smart cookie preferences. Change cookie preferences Accept all cookies. Skip to content. Read later. You don't have any saved articles. By Katie Pavid. These extinct sea creatures are relatives of today's squid and nautilus. But what was the water like when these cephalopods were common under the waves? Tropical predators The sea around the land mass which is now Britain was the home of marine reptiles, large snails, ancient crustaceans and sea urchins.

Evolution Climate change Feature Prehistoric Oceans. Explore prehistoric seas Visit the Fossil Marine Reptiles gallery to see what was going on in the oceans while dinosaurs dominated the land. Read the news story Museum scientists were called in to help rescue an ammonite graveyard. Dive deeper Find out more about marine science at the Museum. Discover oceans. Related posts.