Mammals Fish Birds Reptiles Amphibians

Vertebrate animals accept come up a long way since their tiny, translucent ancestors swam the world's seas over 500 million years ago. The following is a roughly chronological survey of the major vertebrate animal groups, ranging from fish to amphibians to mammals, with some notable extinct reptile lineages (including archosaurs, dinosaurs, and pterosaurs) in between.

Fish and Sharks

Diplomystus fossil — Paul Kay / Getty Images

Between 500 and 400 million years ago, vertebrate life on earth was dominated by prehistoric fish. With their bilaterally symmetric torso plans, V-shaped muscles, and notochords (protected nerve chords) running downwardly the lengths of their bodies, bounding main dwellers like Pikaia and Myllokunmingia established the template for later vertebrate evolution It also didn't hurt that the heads of these fish were singled-out from their tails, another surprisingly bones innovation that arose during the Cambrian menstruation. The first prehistoric sharks evolved from their fish forebears most 420 million years ago and quickly swam to the apex of the undersea food chain.

Tetrapods

Model reconstruction of Acanthostega at State Museum of Natural History in Stuttgart (Germany) — Dr. Günter Bechly / Wikimedia Commons / CC BY-SA 3.0

The proverbial "fish out of h2o," tetrapods were the starting time vertebrate animals to climb out of the sea and colonize dry out (or at least swampy) land, a central evolutionary transition that occurred somewhere betwixt 400 and 350 one thousand thousand years ago, during the Devonian catamenia. Crucially, the first tetrapods descended from lobe-finned, rather than ray-finned fish, which possessed the characteristic skeletal structure that morphed into the fingers, claws, and paws of later vertebrates. Oddly plenty, some of the first tetrapods had seven or eight toes on their hands and feet instead of the usual five, and thus wound upwardly every bit evolutionary "dead ends."

Amphibians

Solenodonsaurus janenschi — Dmitry Bogdanov / Wikimedia Commons / CC BY three.0

During the Carboniferous flow, dating from about 360 to 300 one thousand thousand years ago, terrestrial vertebrate life on earth was dominated by prehistoric amphibians. Unfairly considered a mere evolutionary way-station between earlier tetrapods and later reptiles, amphibians were crucially important in their own right, since they were the first vertebrates to figure out a fashion to colonize dry country. However, these animals still needed to lay their eggs in h2o, which severely limited their power to penetrate to the interior of the world's continents. Today, amphibians are represented past frogs, toads, and salamanders, and their populations are rapidly dwindling under environmental stress.

Terrestrial Reptiles

Hylonomus lyelli — Matteo De Stefano/MUSE / Wikimedia Commons / CC Past-SA 3.0

About 320 one thousand thousand years ago, give or take a few one thousand thousand years, the first true reptiles evolved from amphibians. With their scaly skin and semi-permeable eggs, these ancestral reptiles were free to go out rivers, lakes, and oceans backside and venture deep into dry out country. The globe's landmasses were quickly populated past pelycosaurs, archosaurs (including prehistoric crocodiles), anapsids (including prehistoric turtles), prehistoric snakes, and therapsids (the "mammal-like reptiles" that later evolved into the first mammals). During the tardily Triassic menstruum, two-legged archosaurs spawned the first dinosaurs, the descendants of which ruled the planet until the end of the Mesozoic Era 175 meg years later.

Marine Reptiles

Plesiosaurus dolichodeirus — Dmitry Bogdanov / Wikimedia Commons / CC BY 3.0

At least some of the ancestral reptiles of the Carboniferous period led partly (or by and large) aquatic lifestyles, merely the truthful historic period of marine reptiles didn't begin until the appearance of the ichthyosaurs ("fish lizards") during the early to centre Triassic period. These ichthyosaurs, which evolved from state-dwelling house ancestors, overlapped with, and were then succeeded past long-necked plesiosaurs and pliosaurs, which themselves overlapped with, and were then succeeded by the exceptionally sleek, vicious mosasaurs of the belatedly Cretaceous period. All of these marine reptiles went extinct 65 million years ago, along with their terrestrial dinosaur and pterosaur cousins, in the wake of the 1000/T falling star impact.

Pterosaurs

Pteranodon dinosaurs flying - 3D render — Elenarts / Getty Images

Oftentimes mistakenly referred to equally dinosaurs, pterosaurs ("winged lizards") were actually a singled-out family of pare-winged reptiles that evolved from a population of archosaurs during the early to middle Triassic period. The pterosaurs of the early Mesozoic Era were fairly small, but some truly gigantic genera (such equally the 200-pound Quetzalcoatlus) dominated the late Cretaceous skies. Like their dinosaur and marine reptile cousins, the pterosaurs went extinct 65 million years ago. Opposite to popular belief, they didn't evolve into birds, an honour that belonged to the small, feathered theropod dinosaurs of the Jurassic and Cretaceous periods.

Birds

Hesperornis regalis skeleton at the Smithsonian museum of Natural History — Quadell / Wikimedia Eatables / CC BY-SA 3.0

Information technology's difficult to pin down the exact moment when the first true prehistoric birds evolved from their feathered dinosaur forebears. Most paleontologists point to the tardily Jurassic period, about 150 million years ago, on the evidence of distinctly bird-similar dinosaurs similar Archaeopteryx and Epidexipteryx. However, it's possible that birds evolved multiple times during the Mesozoic Era, near recently from the pocket-sized, feathered theropods (sometimes called "dino-birds") of the eye to late Cretaceous menstruation. By the way, following the evolutionary classification organisation known as "cladistics," information technology's perfectly legitimate to refer to modern birds as dinosaurs!

Mesozoic Mammals

Reconstruction of a Megazostrodon species, in the Natural History Museum, London. — Theklan / Wikimedia Eatables / CC BY-SA 4.0

As with most such evolutionary transitions, there wasn't a bright line separating the most advanced therapsids ("mammal-like reptiles") of the tardily Triassic period from the first true mammals that appeared around the aforementioned fourth dimension. All we know for sure is that pocket-size, furry, warm-blooded, mammal-similar creatures skittered beyond the high branches of trees about 230 million years ago, and coexisted on diff terms with much bigger dinosaurs right upward to the cusp of the K/T Extinction. Considering they were so pocket-size and fragile, most Mesozoic mammals are represented in the fossil tape only past their teeth, though some individuals left surprisingly complete skeletons.

Cenozoic Mammals

hydracodon nebraskensis running rhino hooved Natural History Museum Los Angeles — Dawn Pedersen / Flickr / CC BY 2.0

Later on dinosaurs, pterosaurs and marine reptiles vanished off the face of the earth 65 million years agone, the big theme in vertebrate evolution was the rapid progression of mammals from small, timid, mouse-sized creatures to the giant megafauna of the middle to late Cenozoic Era, including oversized wombats, rhinoceroses, camels, and beavers. Among the mammals that ruled the planet in the absence of dinosaurs and mosasaurs were prehistoric cats, prehistoric dogs, prehistoric elephants, prehistoric horse, prehistoric marsupials and prehistoric whales, most species of which went extinct by the end of the Pleistocene epoch (often at the easily of early humans).

Primates

Plesiadapis — Matteo De Stefano/MUSE / Wikimedia Commons / CC BY-SA 3.0

Technically speaking, in that location'southward no adept reason to separate prehistoric primates from the other mammalian megafauna that succeeded the dinosaurs, but it's natural (if a scrap egotistic) to want to distinguish our man ancestors from the mainstream of vertebrate evolution. The first primates appear in the fossil record as far dorsum as the late Cretaceous menstruum and diversified in the course of the Cenozoic Era into a bewildering array of lemurs, monkeys, apes, and anthropoids (the last the direct ancestors of modern humans). Paleontologists are still trying to sort out the evolutionary relationships of these fossil primates because new "missing link" species are constantly beingness discovered.