Heterostraci

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Heterostraci

[‚hed·ə′räs·trə‚sī]
(paleontology)
An extinct group of ostracoderms, or armored, jawless vertebrates; armor consisted of bone lacking cavities for bone cells.

Heterostraci

 

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.

REFERENCE

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

D. V. OBRUCHEV

References in periodicals archive ?
Upper Silurian and Devonian heterostracan pteraspidomorphs (Vertebrata) from Severnaya Zemlya (Russia): a preliminary report with biogeographical and biostratigraphical implications.
A psammosteid heterostracan (Vertebrata: Pteraspidomorphi) from the Emsian (Lower Devonian) of the Grand Duchi of Luxembourg.
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.
Randle & Sansom (2016) reanalysed the Pteraspididae, and then (2017) sought to provide an overview of the relationships of all the 'higher' heterostracans with a combined phylogenetic hypothesis, which does not present a clear phylogeny for the Cyathaspididae.
Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stemgnathostomes) using continuous and discrete characters.
All samples contained remains of various vertebrates, including psammosteid heterostracans, placoderms, numerous acanthodians, sarcopterygians and actinopterygians (Marss et al.
We used the same three outgroups as in our earlier study, including 'Athenaegis Tolypelepis' which is a composite of two of the most primitive undoubted heterostracans so far known, Athenaegis being the main source of body-form character states and Tolypelepis being the main source of histological character states.