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An extinct group of ostracoderms, or armored, jawless vertebrates; armor consisted of bone lacking cavities for bone cells.



a subclass of agnathous fossil vertebrates. Heterostraci were common during the Paleozoic era, from the Ordovician to the end of the Devonian. The shell was made of a varying number of schistoid plates of acellular bone, with a single (caudal) fin, lateral apophyses serving as supporting planes, and dorsal ridges, or spines, for the maintenance of equilibrium. The length of Heterostraci ranged approximately from several cm to 1 m. They inhabited both ocean and fresh waters, feeding on small organisms of the benthic and middle depths. Heterostraci are of great significance in the comparison of continental and marine deposits of the Middle Paleozoic.


Obruchev, D. V. “Vetv’ Agnatha: Bescheliustnye.” In Osnovy paleontologii: Bescheliustnye, ryby. Moscow, 1964.


References in periodicals archive ?
The rostrum was not as highly developed as that of many heterostracans such as Athenaegis Soehn & Wilson, 1990, but it was present.
The utility of the fish biozones varies and depends on the different development stages of fish groups: psammosteid heterostracans, placoderms and acanthodians.
We have not succeeded to identify heterostracans either in Loo Cliff or Kaugatuma Cliff (Kaugatuma Stage, Pridoli) situated nearby, although large samples of several kilograms of rock have been dissolved (for the list of vertebrate fossils found in outcrops see Marss 1986, fig.
Continuous interest in the relationships of Oniscolepis with other heterostracans initiated studies of tessellated forms in the Baltic.
We assumed that the body form of Oniscolepis dentata, as that of other heterostracans who lived just above the bottom of nearshore epicontinental seas, was somewhat flattened dorsoventrally.
It is not possible to speculate whether Oniscolepis had more than one dorsally placed body ridge (= crest) composed of tesserae as some other heterostracans or related taxa did (e.