Galeaspida

Galeaspida is an extinct group of jawless vertebrates that lived during the Silurian and Devonian periods. Its fossils are known chiefly from China and Vietnam.

Vertebrate: An animal with a backbone or a related internal skeleton derived from the notochord. Galeaspids belong to the vertebrate lineage despite lacking jaws.
Galeaspid head shield: The broad, often flattened bony armor covering the head of a galeaspid. Its shape and sensory openings are among the most recognizable galeaspid features.
Silurian: A geological period lasting from about 444 to 419 million years ago. Some galeaspids lived during this period of early jawless-fish diversification.
Galeaspis: A genus of galeaspid jawless vertebrates known from fossils in China. This genus gives Galeaspida its name and exemplifies its distinctive head shield.
Agnatha: A traditional grouping of jawless vertebrates, including living lampreys and hagfishes and extinct forms. Galeaspids are commonly discussed among extinct jawless vertebrates.
Median dorsal opening: A large opening on the top of the galeaspid head shield, associated with water passage and respiration. This distinctive opening helped water reach the gill region.
Devonian: A geological period lasting from about 419 to 359 million years ago, often called the Age of Fishes. Galeaspids persisted into this period of expanding vertebrate diversity.
Hanyangaspis: An extinct genus of galeaspid vertebrate known from Silurian fossils in China. Its fossils contribute to knowledge of galeaspid diversity and anatomy.
Gnathostomata: The vertebrate clade whose members possess jaws, including most living vertebrates. Galeaspids lived before jaws characterized the dominant vertebrate groups.
Galeaspid gill apparatus: The respiratory structures of galeaspids, arranged beneath the head shield and connected to external openings. Its arrangement is reconstructed from the shield and branchial openings preserved in fossils.

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Jawless fishBroader topic: Galeaspids provide a distinctive fossil record of early jawless vertebrate anatomy.