Named By: Louis Agassiz - 1835/39/43?
Classification: Chordata, Sarcopterygii, Porolepiformes, Holoptychiidae.
Species: H. americanus, H. flemingi, H. giganteus, H. halli, H. hopkinsii, H. nobilissimus.
Size: About 50 centimetres long, some variation between species.
Known locations: Possibly worldwide with some known locations including Belgium, Russia and the United Kingdom.
Time period: Givetian of the Devonian through to the Bashkirian of the Carboniferous.
Fossil representation: Many individuals.
Holoptychius seems to have been a particularly widespread genus of lobe-finned fish. Like relative genera, the body was streamlined with most of the fins in a more rearward placement on the body. The scales were fairly large and round, and the tail was asymmetrical with an upper lobe far more greatly developed than the lower. Because fish are driven by a rearward propulsion of the tail they have a tendency to nosedive into the depths, but the effect is magnified far greater if the upper lobe of the tail is more strongly developed. To counter this effect, the pectoral fins (the forward pair near the head) are angled to act as hydroplanes to counter this down pitching. The pectoral fins of Holoptychius are particularly large suggesting that Holoptychius were particularly fast swimmers.
- A synopsis of the classification of the British Palaeozoic rocks, with a systematic description of the British Palaeozoic fossils.Fasciculus 3, Mollusca and Palaeozoic fishes - F. M'Coy - 1855.