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The first vertebrates ("fish") appear: the Agnathans. They were jawless, had seven pairs of pharyngeal arches like their descendants today, and their endoskeletons were cartilaginous (then only consisting of the chondro cranium/braincase and vertebrae). The jawless Cyclostomata diverge at this stage.
The first known footprints on land date to 530 Ma. [74] 520 Ma Earliest graptolites. [75] 511 Ma Earliest crustaceans. [76] 505 Ma Fossilization of the Burgess Shale: 500 Ma Jellyfish have existed since at least this time. 485 Ma First vertebrates with true bones (jawless fishes). 450 Ma First complete conodonts and echinoids appear. 440 Ma
The first jawed vertebrates may have appeared in the late Ordovician (~445 mya) and became common in the Devonian period, often known as the "Age of Fishes". [33] The two groups of bony fishes, Actinopterygii and Sarcopterygii, evolved and became common. [34]
While tunicate fossils predate the Cambrian explosion, [194] the Chengjiang fossils Haikouichthys and Myllokunmingia appear to be true vertebrates, [24] and Haikouichthys had distinct vertebrae, which may have been slightly mineralized. [195] Vertebrates with jaws, such as the acanthodians, first appeared in the Late Ordovician. [196]
Ordovician (485–443 Ma): Fish, the world's first true vertebrates, continued to evolve, and those with jaws (Gnathostomata) may have first appeared late in this period. Life had yet to diversify on land. Arandaspis: Arandaspis are jawless fish that lived in the early Ordovician period, about 480–470 Ma.
The vertebrate land invasion refers to the transition of vertebrate animals from being aquatic/semiaquatic to predominantly terrestrial during the Late Devonian period. This transition allowed some vertebrates to escape competitive pressure from other aquatic animals and explore niches on land, [1] which eventually established the vertebrates as the dominant terrestrial phylum.
The first tetrapodomorphs, which included the gigantic rhizodonts, had the same general anatomy as the lungfish, who were their closest kin, but they appear not to have left their water habitat until the Late Devonian epoch (385–359 Mya), with the appearance of tetrapods (four-legged vertebrates).
The first fully terrestrial vertebrates were reptilian amniotes — their eggs had internal membranes that allowed the developing embryo to breathe but kept water in. This allowed amniotes to lay eggs on dry land, while amphibians generally need to lay their eggs in water (a few amphibians, such as the common Suriname toad, have evolved other ways of getting around this limitation).