Pterichthyodes

Pterichthyodes are a genus of placoderm fishes from the Devonian period, now all extinct. They were one of the first species recognized for what they were, as they are common in the Old Red Sandstone formation studied by geologists in the early 1800s. Due to their extreme divergence from modern-day fishes, they were a puzzle unsolved until Charles Darwin brought forward his theories on evolution.

The pterichthyodes had heavily armored heads and front bodies, while their tail ends were uncovered. As placoderms they were members of one of the first group of animals to possess jaws, though they had griding plates rather tham teeth. The pterichthyodes are distinguished easily from other placoderms by their odd wing-like appendage where fins would be found on a modern fish ("pterichthys" is Ancient Greek for "wing-fish") -- strictly speaking, these are not fins as we normally think of them, which evolved in another group of fishes the Actinopterygii.

The appearance of pterichthyodes is sufficiently reminiscent of a modern animal that they are one of the few extinct species to have a popular name: "sea scorpions". They are, however, completely unrelated to modern-day sea scorpions, which are modern fish, or the other fossil animal class with the same popular name and similar appearance, the Eurypterids (which are believed to be ancestors of actual scorpions).

External Links

A page devoted to Asterolepidoidei, the parent group of the pterichthyodes according to cladistics