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Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
Thelodonti ('feeble-teeth') are a group of small, extinct jawless fishes with distinctive scales instead of large plates of armour. There is much debate over whether the group of Palaeozoic fish known as the Thelodonti (formerly coelolepids [11]) represent a monophyletic grouping, or disparate stem groups to the major lines of jawless and jawed ...
Arandaspida is a taxon of very early, jawless prehistoric fish which lived during the Ordovician period. Arandaspids represent some of the oldest known vertebrates. The group represents a subclass within the class Pteraspidomorphi, and contains only one order, the Arandaspidiformes.
Thelodonti (from Greek: "nipple teeth") [4] is a class of extinct Palaeozoic jawless fishes with distinctive scales instead of large plates of armor. There is much debate over whether the group represents a monophyletic grouping, or disparate stem groups to the major lines of jawless and jawed fish. Shielia taiti
Furcacauda is a genus of thelodontid agnathan from the Lower Devonian of Canada, and is the type genus of the order Furcacaudiformes. [2] Furcacaudiform thelodontids were deep water jawless vertebrates with symmetrical fork and lobed-finned tails and scales smaller than typical loganellid and nikoliviid thelodonti scales. [1]
The scales of Acanthodii have distinctive ornamentation peculiar to each order. Because of this, the scales are often used in determining relative age of sedimentary rock. The scales are tiny, with a bulbous base, a neck, and a flat or slightly curved diamond-shaped crown. Despite being called "spiny sharks", acanthodians predate sharks.
Lepidaspis serrata ("serrated scaly shield") is an extinct heterostracan jawless fish from Early Devonian Canada. Its scientific name refers to the fact that the armor is composed of hundreds of tiny scales with serrated edges. Lepidaspis serrata cast. Mackenzie Mountains, Northwest Territories . At the Royal Tyrrell Museum of Palaeontology.
Furcacaudiformes is an extinct order of jawless fish in the class Thelodonti. [1]Because the paucity of intact fossils, especially since some families are known entirely from scale fossils, taxonomy of thelodonts is based primarily on scale morphology.