Heintzichthys

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Heintzichthys is an extinct, single‑species placoderm that lived during the Late Devonian period, roughly 371 to 359 million years ago. Its fossils have been found in what is now Europe and North America, with the type specimen discovered in the Cleveland Shale near Cleveland, Ohio. The only species in this genus is Heintzichthys gouldii.

What it was like:
- A member of the armored jawed fish group known as placoderms
- Part of the family Selenosteidae, within a larger group called Eubrachythorachi

Relation to other fishes:
- Heintzichthys is considered closely related to other placoderms like Gorgonichthys
- A 2022 study found Heintzichthys to be a sister taxon to Gorgonichthys, meaning they are each other’s closest known relatives within their group

In short, Heintzichthys is a small, well‑defined lineage of armored fishes from the Late Devonian, known from a single species found in North America and Europe.