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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).
Myllokunmingiidae is a group of very early, jawless prehistoric fish which lived during the Cambrian period. [2] The Myllokunmingiids are the earliest known group of craniates . The group contains only three known genera, Haikouichthys , Myllokunmingia , and Zhongjianichthys .
"A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23; Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23
A newfound fossil of a jawless fish is the oldest known vertebrate cranium preserved in 3D. The 455 million-year-old find could illuminate how vertebrate heads evolved.
Cyclostomi, often referred to as Cyclostomata / s ɪ k l oʊ ˈ s t ɒ m ə t ə /, is a group of vertebrates that comprises the living jawless fishes: the lampreys and hagfishes.Both groups have jawless mouths with horny epidermal structures that function as teeth called ceratodontes, and branchial arches that are internally positioned instead of external as in the related jawed fishes. [1]
In those days, placoderms were thought to be shelled jawless fish akin to ostracoderms. Some naturalists even suggested that they were shelled invertebrates or even turtle -like vertebrates. In the late 1920s, Dr. Erik Stensiö , at the Swedish Museum of Natural History in Stockholm , established the details of placoderm anatomy and identified ...
After the appearance of jawed fish (placoderms, acanthodians, sharks, etc.) about 420 million years ago, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian period. More recent research indicates that fish with jaws had far less to do with the extinction of the ostracoderms than ...
Haikouichthys / ˌ h aɪ k u ˈ ɪ k θ ɪ s / is an extinct genus of craniate (animals with notochords and distinct heads) that lived 518 million years ago, during the Cambrian explosion of multicellular life. The type species, Haikouichthys ercaicunensis, was first described in 1999. [2]