Antiarchi

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Antiarchi were an ancient order of heavily armored placoderms (jawed fishes) that lived from about 425 to 359 million years ago, spanning the Late Silurian to Late Devonian periods.

Body and armor
- The front part of their bodies was covered in thick armor, forming a box-like shield around the head and chest.
- The rear part of their bodies could be scaled or bare and often became wavy in later species.
- Their pectoral fins were transformed into paired, claw-like limbs, similar to arthropod legs.

Limb variation
- In early forms like Yunnanolepis, the limbs were short and thick.
- In later forms like Bothriolepis, the limbs were longer and had elbow-like joints.
- The limbs likely helped them crawl along the substrate and possibly bury themselves in sediment.

Classification and relationships
- Antiarchi are among the most primitive placoderms and are more closely related to other jawed vertebrates than to jawless fishes.

Name origin
- The name Antiarchi means "opposite anus." It comes from the ideas of paleontologist Edward Drinker Cope, who misinterpreted the openings in the head shield and the position of the anal opening.

Overall
- They were one of the most diverse and widespread placoderm groups, second only to the arthrodires in the number of species and the variety of environments they inhabited.