Antiarchi

The Antiarchi is an order of heavily armored placoderms. The antiarchs were the second-most successful group of placoderms (after the arthrodires) in terms of numbers of species and range of environments. 
The front part of their bodies were heavily armoured. The rear parts were sometimes scaled, sometimes naked. The pectoral fins were modified. In primitive forms, such as "Yunnanolepis", the limbs were thick and short, while in advanced forms, such as "Bothriolepis", the limbs were long and had elbow-like joints. Probably they helped the fish pull themselves across the substrate, or allow their owners to bury themselves into the substrate.