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Class Osteostraci, once known as "Ostracoderma," was a group of bony-armored jawless fish that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian.
Anatomically speaking, the osteostracans, especially the Devonian species, were among the most advanced of all known agnathans.
This is due to the development of paired fins, and their complicated cranial anatomy. However, the osteostracans were more related to other agnathans than to jawed vertebrates as their inner ears are formed by two pairs of semicircular canals, similar to those of living lampreys, as opposed to the three pairs found in the inner ears of jawed vertebrates.
Osteostraci
| | Name | Osteostraci | | image |  | | Regnum | Animalia | | Phylum | Chordate | | Subphylum | Vertebrate | | Unranked Classis | Cephalaspidomorphi | | Classis | Cephalaspidomorphi | | Subdivision Ranks | Orders | | Subdivision | Orders |
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