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The term paraphyly, or paraphyletic, derives from the two Ancient Greek words παρά (pará), meaning "beside, near", and φῦλον (phûlon), meaning "genus, species", [2] [3] and refers to the situation in which one or several monophyletic subgroups of organisms (e.g., genera, species) are left apart from all other descendants of a unique common ancestor.
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish.
Fishes are a paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal taxonomy.Traditional classification divides fish into three extant classes (Agnatha, Chondrichthyes, and Osteichthyes), and with extinct forms sometimes classified within those groups, sometimes as their own classes: [1]
Actinopterygii. Actinopterygii (/ ˌæktɪnɒptəˈrɪdʒiaɪ /; from actino- 'having rays' and Ancient Greek πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish [ 2 ] that comprise over 50% of living vertebrate species. [ 3 ]
Psarolepis. Achoania. Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish, including tetrapods) Osteichthyes (/ ˌɒstiːˈɪkθi.iːz /), also known as osteichthyans or commonly referred to as the bony fish, is a diverse superclass of vertebrate animals that have endoskeletons primarily composed of bone tissue.
Ostracoderm. Cardipeltis bryanti, a lower Devonian ostracoderm from the Bighorn Mountains of Wyoming. Ventral (underside) exposed. Ostracoderms (lit. 'shell-skins') are the armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes) (may also be ...
Synonyms. Placodermata. Placoderms (from Greek πλάξ (plax, plakos) ' plate ' and δέρμα (derma) 'skin') [1] are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the Devonian periods. While their endoskeletons are mainly cartilaginous, their head and ...
The term monophyly, or monophyletic, derives from the two Ancient Greek words μόνος (mónos), meaning "alone, only, unique", and φῦλον (phûlon), meaning "genus, species", [4][5] and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a unique common ancestor.