Hemiphragmoceratidae
Encyclopedia
The Hemiphragmoceratidae is a family of endogastrically brevconic oncocerids
characterized by elaborately visored apertures in which the hyponomic sinus in mature specimens is on a spout-like process and there may be lateral and dorsal salients. (Sweet 1964, Flower 1950). Shells are compressed with the apical portion curved and the anterior straight. Siphucles are nummuloideal with expanded spheroidal segments and continuously actinosiphonate interiors.
The Hemiphragmoceratidae are probably descended from the Oncoceratidae and are known from the middle and upper Silurian
but may range into the middle Devonian
(Sweet 1964). They are similar with regards to their constricted and ornate apertures to the middle Silurian exograstric Trimeroceratidae and the Siluro-devonian discosorid
Phragmoceratidae (Teichert 1964)
Some five genera have been described; Hemiphragmocers, Contradoceras, Hexameroceras, Octamerella, and Tetrameraoceras.
Oncocerida
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...
characterized by elaborately visored apertures in which the hyponomic sinus in mature specimens is on a spout-like process and there may be lateral and dorsal salients. (Sweet 1964, Flower 1950). Shells are compressed with the apical portion curved and the anterior straight. Siphucles are nummuloideal with expanded spheroidal segments and continuously actinosiphonate interiors.
The Hemiphragmoceratidae are probably descended from the Oncoceratidae and are known from the middle and upper Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
but may range into the middle Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
(Sweet 1964). They are similar with regards to their constricted and ornate apertures to the middle Silurian exograstric Trimeroceratidae and the Siluro-devonian discosorid
Discosorida
Discosorida is a unique order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the chambers in cephalopods, which unlike...
Phragmoceratidae (Teichert 1964)
Some five genera have been described; Hemiphragmocers, Contradoceras, Hexameroceras, Octamerella, and Tetrameraoceras.
References
- Sweet, W. C. 1964; Nautiloidea-Oncocerida, in the Treatise on Invertebrate Paleontology; Geological Society of America and University of Kansas Press.
- Flower, R. H. and Kummel B, 1950; A Classification of the Nautiloidea; Journal of Paleontology V24 n.5 Sept 1950
- Teichert, C. 1964; Nautiloidea-Discosorida, in the Treatise on Invertebrate Paleontology; Geological Society of America and University of Kansas Press.