Early vertebrate

Early vertebrates are ancient members of the vertebrate lineage, including many extinct jawless forms. Their fossils document the origins and early diversification of vertebrate anatomy.

Vertebrate: An animal in the chordate lineage characterized by a vertebral column or its evolutionary precursors. Early vertebrates belong to this broader lineage, whose defining features evolved incrementally.
Vertebral column: A segmented or partly segmented series of skeletal elements surrounding or replacing the notochord in many vertebrates. Its early forms varied widely and need not have resembled modern backbones.
Haikouichthys: A small Cambrian animal from China commonly interpreted as an early vertebrate or close vertebrate relative. Its fossils preserve features used to investigate vertebrate origins.
Cambrian explosion: A geological interval of rapid animal diversification and expanding fossil visibility beginning about 539 million years ago. Some of the earliest proposed vertebrate fossils come from Cambrian deposits.
Vertebrate paleontology: The study of vertebrate fossils and their evolutionary history. Its methods shape how fragmentary early fossils are identified and interpreted.
Chordate: An animal belonging to the phylum Chordata, whose members develop a notochord, dorsal nerve cord, and other shared traits. Chordates provide the broader evolutionary context for vertebrate origins.
Cranium: The skeletal structure that encloses and protects the brain and supports sensory organs. Cranial anatomy is among the clearest fossil evidence for early vertebrate diversification.
Myllokunmingia: A small Cambrian fossil animal from China often considered among the earliest known vertebrates. It offers a second early Cambrian candidate for vertebrate status.
Burgess Shale: A fossil deposit in British Columbia renowned for exceptionally preserved Cambrian marine animals. Its fossils provide comparative evidence for early chordates and vertebrate relatives.
Stem group: Extinct organisms more closely related to a living group than to its nearest living sister group, but outside the living group itself. Many proposed early vertebrates may instead be stem vertebrates.

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