Temporal range: Givetian
|An artist's illustration of Heterosteus asmussi|
Heterosteus is an extinct genus of placoderm fish. It lived in the Middle Devonian (about 370 million years ago) and his fossil remains were found in eastern Europe, Greenland and Spitsbergen. It is one of the biggest known placoderms having an estimated body length of up to 6 metres (19 ft 8 in).
Heterosteus is considered a primitive representative of arthrodirs, a group of widely spread placoderms and diversified specialties. Although relatively similar to some artroses like Homosteus , it is believed that Heterosteus was a more basic form. Of this animal are known various species, including H. ingens of Estonia and H. groenlandicus of Greenland.
Heterosteus had to reach and perhaps exceed 6 meters in length. The only armor, covering the head and the front of the body, was a couple of feet long. The Heterosteus's cephalic shield was wide and relatively flat; the eyes were placed in the front end. The appearance had to be quite similar to that of another placoderma Homosteus, but unlike the latter, Heterosteus had enormous frontal processes on dorsolateral plaques. Unlike most arthrodid placoderms, Heterosteus had no teeth.
Heterosteus fossils were found in river deposits; the weak jaw-like characteristics of the jaw, together with the rather flat skull, suggest that Heterosteus was a gigantic filtering organism that probably moved slowly into lakes and large rivers feeding on small animals and particles.