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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).
Chondrichthyes (/ k ɒ n ˈ d r ɪ k θ i iː z /; from Ancient Greek χόνδρος (khóndros) 'cartilage' and ἰχθύς (ikhthús) 'fish') is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage.
Other ways of classifying the vertebrates have been devised, particularly with emphasis on the phylogeny of early amphibians and reptiles. An example based on work by M.J. Benton in 2004 [47] is given here († = extinct): Subphylum Vertebrata †Palaeospondylus; Infraphylum Agnatha or Cephalaspidomorphi (lampreys and other jawless fishes)
Jawless fish belong to the superclass Agnatha in the phylum Chordata, subphylum Vertebrata. Agnatha means 'un-jawed, without jaws' (from Ancient Greek). [11] It excludes all vertebrates with jaws, known as gnathostomes. Although a minor element of modern marine fauna, jawless fish were prominent among the early fish in the early Paleozoic.
The appearance of the early vertebrate jaw has been described as "a crucial innovation" [25] and "perhaps the most profound and radical evolutionary step in the vertebrate history". [ 26 ] [ 27 ] Fish without jaws had more difficulty surviving than fish with jaws, and most jawless fish became extinct during the Triassic period.
The first identifiable placoderms appear in the fossil record during the late Llandovery epoch of the early Silurian. [6] They eventually outcompeted the previously dominant marine arthropods (e.g. eurypterids ) and cephalopod molluscs (e.g. orthocones ), producing some of the first and most infamous vertebrate apex predators such as ...
The hierarchy of biological classification's eight major taxonomic ranks.A domain contains one or more kingdoms. Intermediate minor rankings are not shown. In biology, a kingdom is the second highest taxonomic rank, just below domain.
Nuucichthys (meaning "Núu-ci fish") is an extinct genus of stem-group vertebrates known from the Cambrian (Miaolingian series) Marjum Formation of Utah, United States. The genus contains a single species, N. rhynchocephalus, known from a single individual, representing the first Cambrian vertebrate from the Great Basin region of North America.