Reudemannoceratidae
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Reudemanoceratidae Temporal range: Middle Ordovician |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | Nautiloidea |
| Order: | Discosorida |
| Family: |
Reudemannoceratidae Flower 1940 |
The Reudemannoceratidae are the ancestral and most primitive of the Discosorida, an order of cephalopods from the early Paleozoic. The Reudemannoceratidae produced generally medium-sized endogastric and almost straight shells with the siphuncle slightly ventral from the center.
The Reudemannoceratidae first appeared at the beginning of the Middle Ordovician, North American Whiterock stage, (since replaced by the ICS Dapingian), and are restricted to the lower part of that series. (the middle Ordovician). Their origin is unknown. The siphuncles in early members contain features in the early growth stages reminiscent of the siphuncular bulbs found the archaic Plectronoceratae of the Late Cambrian. (Flower and Teichert 1957) but so far no unambiguous Lower Ordovician intermediaries have been found.
Reudemannoceratids are characterized by having short septal necks in the juvenile portion of the siphuncle, toward the apex of the shell, which later in life grow folded back along the back side of the septa in the characteristic fashion of the Discosorida. The connecting ring is bowed out into the camerae and is divided into the characteristic zones, the vinculum, granular zone, conchiolinous (or chitinous) zone offset by amorphous bands, and the layered bullette attached to the previous septal neck. (Flower and Teichert 1957, Teichert 1964)
The Reucenammanoceratidae contain three genera (Teichert 1964). They are Reudemannoceras, Franklinoceras, and Madiganella. Reudemannoceras and Franklinoceras, named by Flower in 1940 and 1957, are found the Champlain Valley in eastern North America. Madiganella, named by Teichert and Glenister in 1952, comes from central Australia.
Reudemannoceras is described (Flower and Teichert 1957) as having a somewhat compressed endogastric shell, such that the width is greater than the height, with the venter slightly flattened. Sutures are closely spaced and slope forward from venter to dorsum with the obliquity increasing as growth progressed. The early part of the shell is essentially straight, but afterward expands and is notably curved. The early segments in the siphuncle (Techert 1964) are bulb shaped and the septal necks are short. In the later part of the shell she segments are expanded and septal necks become recumbent. The connecting rings are thick and have the zoning characteristic of the earlier Discosorids with well-developed bullettes.
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