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Rhenanida
Rhenanida ("Rhine (fish)") is an order of scaly placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles. The patterns and components of this "mosaic" correspond to the plates of armor in other, more advanced placoderms, suggesting that the ancestral placoderm had armor made of unfused components, as well. All rhenanids were flattened, ray-like, bottom-dwelling predators that lived in marine environments. Evolution The rhenanids were once presumed to be the most primitive, or at least the closest to the ancestral placoderm, as their armor was made up of a mosaic of tubercles, as opposed to the solidified plates of "advanced" placoderms, such as antiarchs and arthrodires. However, comparing the skull anatomies of ''Jagorina pandora'' with those of antiarchs, the rhenanids are considered to be the sister group of the antiarchs (together with their respective Acanthothoracid relatives). Presence in the fossil record ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Placoderm
Placoderms (from Ancient Greek πλάξ [''plax'', ''plakos''] 'Plate (animal anatomy), plate' and δέρμα [''derma''] 'skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the Devonian geological period, periods. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armour (zoology), armoured plates (hence the name), and the rest of the body was scale (zoology), scaled or naked depending on the species. Placoderms were among the first jawed fish (their fish jaw, jaws likely Evolution, evolved from the first pair of gill arches), as well as the first vertebrates to have true tooth, teeth. They were also the first fish clade to develop pelvic fins, the second set of paired fins and the homology (biology), homologous precursor to hindlimbs in tetrapods. 380-million-year-old fossils of three other genera, ''Incisoscutum'', ''M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
