Thirty-three remarkable species that once ruled the ancient world, some extinct, some with living descendants, and a few that are still here today. A reference database of prehistoric life, from the Ediacaran to the present.
Order Notostraca, Tadpole Shrimp
The star of this site. Triops has existed for roughly 220 million years with virtually no morphological change. Found on every continent except Antarctica, they inhabit temporary rainwater pools and can survive drought for decades via their resilient eggs.
~220 Ma, Present
Phylum Arthropoda, Extinct
One of the most successful groups in Earth history, trilobites thrived for nearly 300 million years. Over 20,000 species are known. Their compound eyes were the first known visual systems in the animal kingdom, built from calcite crystals, literally mineral eyes.
~521–252 Ma
Order Radiodonta, Apex Predator
The largest animal of the Cambrian, reaching up to 1 meter in length. Anomalocaris was a fearsome marine predator with a circular mouth lined with plates and two large, spiny frontal appendages for grasping prey. Its fossils from the Burgess Shale revolutionized our understanding of early animal evolution.
~508–480 Ma
Phylum Mollusca, Extinct
Spiral-shelled cephalopods that dominated marine ecosystems for over 300 million years. Related to modern nautiluses, ammonites ranged from a few millimeters to over 2 meters across. Their fossils are so common they are used as index fossils for dating geological layers.
~400–66 Ma
Order Eurypterida, Sea Scorpion
Eurypterus is the most well-known of the sea scorpions, aquatic arthropods that were once the largest predators in the ocean. Growing up to 1.5 meters, they used paddle-like rear legs for swimming and powerful chelicerae for crushing prey. Modern horseshoe crabs are their closest living relatives.
~460–252 Ma
Phylum Onychophora (?), Cambrian Worm
So bizarre it was originally reconstructed upside-down. Hallucigenia was a tiny (1–5 cm) worm-like creature with rows of spines on its back and stubby legs beneath. First discovered in the Burgess Shale, it is now considered a relative of modern velvet worms, linking the Cambrian explosion to living species.
~508–505 Ma
Order Opabiniidae, Five-Eyed Predator
A 5-centimeter Cambrian oddity with five eyes on stalks, a forward-facing flexible proboscis, and a segmented body with lateral lobes for swimming. When first presented at a geological conference, it reportedly made the audience laugh. Its unique anatomy defies easy classification and remains one of the Cambrian's most enigmatic organisms.
~508–505 Ma
Phylum incertae sedis, Cambrian Enigma
A soft-bodied oval creature covered in protective scale-like sclerites and two rows of long dorsal spines. Wiwaxia crawled across the Cambrian seafloor roughly 508 million years ago, grazing on bacteria. Its strange mix of mollusk-like and annelid-like features has kept paleontologists debating its classification for over a century.
~508–505 Ma
Phylum Mollusca (?), Ediacaran Grazer
One of the earliest known bilaterian animals, Kimberella lived roughly 555 million years ago in the Ediacaran period, before the Cambrian explosion. This oval, soft-bodied creature moved across microbial mats, scraping food into its mouth with a radula-like structure, some of the earliest evidence of complex animal behavior in the fossil record.
~558–555 Ma
Order Coelacanthiformes, Living Fossil Fish
Thought extinct for 66 million years until a living specimen was discovered off South Africa in 1938. Coelacanths are lobe-finned fish more closely related to lungfish and tetrapods than to modern ray-finned fish. They can reach 2 meters in length and live for up to 100 years in deep underwater caves.
~410 Ma, Present
Order Xiphosura, Living Fossil Arthropod
Not a true crab at all, horseshoe crabs are more closely related to spiders and scorpions. They have existed for over 445 million years with minimal change. Their blue, copper-based blood is harvested for biomedical testing because it clots in the presence of bacterial toxins, a property that has saved countless human lives.
~445 Ma, Present
Order Therapsida, Great Dying Survivor
A pig-sized herbivore that survived the Permian-Triassic extinction, the worst mass extinction in Earth's history. Lystrosaurus made up roughly 95% of land vertebrates in the early Triassic. Its burrowing lifestyle, wide geographic range, and generalist diet helped it endure while 90% of all species vanished.
~255–248 Ma
Order Arthrodira, Armored Placoderm
One of the most terrifying fish ever to swim, Dunkleosteus was an armored predator of the Devonian seas reaching up to 6 meters. Instead of teeth, it had massive bony jaw plates that could crush almost anything, with a bite force rivaling that of a crocodile. It was the apex predator of its time, before sharks rose to dominance.
~382–358 Ma
Order Eugeneodontida, Buzzsaw Fish
Famous for its bizarre spiral of teeth, Helicoprion lived in the Permian seas. The tooth whorl sat in the lower jaw, and scientists long debated its function. Modern research suggests the spiral of serrated teeth worked like a circular saw to slice through soft-bodied prey. It survived into the Triassic before vanishing.
~290–270 Ma
Order Elpistostegalia, Fishapod
The famous fishapod that bridges fish and land vertebrates. Tiktaalik had fish-like scales and fins, but also a flat head, a neck, and robust fins with wrist-like bones that could support its weight. Discovered in the Canadian Arctic, it represents a crucial step in the evolution of tetrapods, the ancestors of all land vertebrates.
~375 Ma
Order Therapsida, Saber-Toothed Rulers
The saber-toothed apex predators of the late Permian. Gorgonopsids like Inostrancevia and Rubidgea were mammal-like reptiles with long canine teeth, capable of taking down prey larger than themselves. They were the top predators of their ecosystems until the Permian-Triassic extinction wiped them out roughly 252 million years ago.
~265–252 Ma
Water Bears, Extreme Survivors
The indestructible water bears. These microscopic animals, 0.1 to 1.5 millimeters long, can survive vacuum, extreme radiation, boiling, freezing, and decades without water. They enter cryptobiosis, a state of suspended animation, and have survived exposure to space. They are among the most resilient life forms ever discovered.
~500 Ma, Present
Class Diplopoda, Giant Millipede
The largest land arthropod ever to exist, Arthropleura was a millipede-like creature that grew up to 2.5 meters long during the Carboniferous. It thrived in the oxygen-rich swamp forests 300 million years ago. Its massive size was possible because atmospheric oxygen levels were much higher than today.
~345–290 Ma
Order Isopoda, Deep Sea Living Fossil
A deep-sea giant that resembles a massive woodlouse, reaching up to 50 centimeters. Giant isopods live in the dark depths of the ocean, scavenging on carcasses that sink to the seafloor. Their lineage dates back over 300 million years, making them true living fossils of the abyss. They can survive months without food.
~300 Ma, Present
Pterygotus, Jaekelopterus and relatives
The eurypterids were aquatic arthropods that ruled the seas before fish took over. Some, like Jaekelopterus, reached lengths of 2.5 meters, making them the largest arthropods ever to live. They hunted with grasping claws and swam with paddle-like appendages. Their closest living relatives are horseshoe crabs.
~467–252 Ma
Earth's First Complex Animals
The mysterious life forms of the Ediacaran period, roughly 575 to 541 million years ago, were Earth's first complex multicellular organisms. Dickinsonia was a flat, oval creature that may have been an early animal, while Charnia and Spriggina were frond-like or segmented forms. They represent life before the Cambrian explosion.
~575–541 Ma
Order Protorosauria, Long-Necked Reptile
One of the strangest reptiles of the Triassic, Tanystropheus had a neck longer than its body and tail combined, made of elongated vertebrae. It likely used its long neck to hunt fish and squid while keeping its body hidden or anchored on the shore. It lived alongside early dinosaurs and Triops in the Triassic.
~245–228 Ma
First Bird, Late Jurassic
The famous first bird, Archaeopteryx lived roughly 150 million years ago and bridged the gap between dinosaurs and birds. It had feathers and wings like a bird, but teeth, a long bony tail, and claws on its wings like a dinosaur. Its fossils from the Solnhofen limestone are among the most famous in paleontology.
~150 Ma
Early Vertebrates, Index Fossils
Small, jawless, eel-like animals whose tiny tooth-like elements are among the most abundant fossils on Earth. Conodonts lived from the Cambrian to the Triassic and are used as index fossils to date rock layers with remarkable precision. Their eyes were some of the earliest vertebrate eyes known.
~500–200 Ma
Order Crocodylia, Terror Croc
A giant crocodilian of the late Cretaceous, Deinosuchus could reach 10 meters in length, dwarfing modern crocodiles. It lived alongside dinosaurs and likely preyed on them, ambushing from the water like modern crocodiles do. Its massive skull and bone-crushing bite made it one of the largest predators of its time.
~82–73 Ma
Order Synapsida, Sail-Backed Predator
Often mistaken for a dinosaur, Dimetrodon was actually a synapsid, more closely related to mammals than to reptiles. It lived in the Permian and is famous for its large sail, likely used for temperature regulation. It was the apex predator of its ecosystem, hunting amphibians and other early tetrapods.
~295–272 Ma
Order Plesiosauria, Long-Necked Marine Reptile
A plesiosaur with one of the longest necks relative to body size, containing up to 72 vertebrae. Elasmosaurus swam through the Cretaceous seas hunting fish and squid. Its neck allowed it to strike at prey from a distance while keeping its body hidden. It was discovered in Kansas during the famous Bone Wars.
~86–66 Ma
Order Meganisoptera, Giant Dragonfly
A giant dragonfly of the Carboniferous with a wingspan of up to 70 centimeters, the largest flying insect ever known. Meganeura dominated the skies of the swamp forests 300 million years ago. Its enormous size was possible due to the higher oxygen levels in the Carboniferous atmosphere, which allowed insects to grow beyond today's limits.
~300–290 Ma
Order Squamata, Apex Marine Predator
A giant marine lizard that ruled the late Cretaceous seas, reaching up to 17 meters. Mosasaurus had a powerful tail, flipper-like limbs, and jaws lined with conical teeth for seizing prey. It was one of the last great marine reptiles before the asteroid impact that ended the age of dinosaurs.
~82–66 Ma
Order Pterosauria, Largest Flying Animal
The largest animal ever to fly, Quetzalcoatlus was a pterosaur with a wingspan of up to 12 meters, roughly the size of a small airplane. It lived in the late Cretaceous and likely soared over plains hunting small animals. Despite its size, its bones were hollow and light, allowing it to take flight.
~70–66 Ma
Phylum Chordata, Early Chordate
A small, eel-like creature from the Burgess Shale, Pikaia is one of the earliest known chordates, the group that includes all vertebrates. It had a primitive notochord, a flexible rod that would evolve into the backbone. Pikaia represents a crucial early step in the lineage that eventually led to fish, amphibians, and humans.
~508 Ma
Order Lamniformes, Giant Shark
The largest shark ever to live, Megalodon reached lengths of up to 18 meters, with teeth over 17 centimeters long. It dominated the oceans for 20 million years, preying on whales and other large marine animals. It went extinct roughly 3.6 million years ago, possibly due to cooling oceans and competition with great white sharks.
~23–3.6 Ma
Genus incertae sedis, State Fossil of Illinois
One of the most mysterious fossils ever found, the Tully Monster had a soft, segmented body, a long proboscis tipped with a jaw, and eyes on stalks. It lived roughly 300 million years ago in the swamps of Illinois. Its classification remains debated, with theories placing it as a vertebrate, a mollusk, or something entirely extinct.
~309–300 MaEach of these species tells a story about evolution, adaptation, and the history of life on Earth. Some, like Triops, demonstrate that "staying the course" can be a winning strategy. Others, like trilobites and ammonites, show that even the most successful lineages can eventually go extinct.
The Cambrian explosion (roughly 540–500 Ma) produced many of the body plans we see today, and a few we have since lost. Species like Anomalocaris, Hallucigenia, and Opabinia remind us that evolution is not a neat, linear march toward complexity. It is messy, experimental, and full of forms we can barely imagine.
The survival stories are just as remarkable: Coelacanths hiding in deep ocean caves for 66 million years undetected, horseshoe crabs donating their blue blood to modern medicine, and Lystrosaurus inheriting a devastated planet and thriving. Understanding these creatures is not just about the past. It helps us comprehend biodiversity today, predict how ecosystems might change, and appreciate the sheer tenacity of life.
Triops are one of the prehistoric creatures on this list that you can actually keep in your home. They are easy to raise, fascinating to watch, and they will connect you to 220 million years of evolutionary history.
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