| Hemicyclaspis Temporal range: Pridoli–Early Devonian PreꞒ Ꞓ O S D C P T J K Pg N | |
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| H. murchisoni and Thyestes | |
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| Life reconstruction. | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Osteostraci |
| Order: | †Atelaspidiformes |
| Family: | †Ateleaspididae |
| Genus: | †Hemicyclaspis |
Hemicyclaspis (lit. 'half-round shield' or 'semicircle plate') is an extinct genus of primitive jawless fish, closely related to Cephalaspis, that lived in the Late Silurian (Pridoli) to Devonian period in what is now Europe and North America. A typical cephalaspid, Hemicyclaspis had a heavily armored, shovel-shaped headshield. It is thought to have been a better swimmer than most of its relatives because of its powerful tail, stabilizing dorsal fin and the keel-shaped hydrodynamic edges of its head shield. Hemicyclaspis probably foraged the ocean floor for food.
Hemicyclaspis grew to a length of 5 inches (13 centimeters) and would most likely have fed on particles from the muddy sea bed.
H. murchisoni cast. Collected from Ledbury, Herefordshire, England.
1953 plaster reconstruction.
References
- Parker, Steve. Dinosaurus: the complete guide to dinosaurs. Firefly Books Inc, 2003. Pg. 58
- Blieck, Alain; Elliott, David K. (2017-06-01). "Pteraspidomorphs (Vertebrata), the Old Red Sandstone, and the special case of the Brecon Beacons National Park, Wales, U.K." Proceedings of the Geologists' Association. 128 (3): 438–446. doi:10.1016/j.pgeola.2016.07.003. ISSN 0016-7878.
- Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 25. ISBN 1-84028-152-9.
| Taxon identifiers | |
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| Hemicyclaspis | |
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