Trocholitidae
| Trocholitidae Temporal range: LOrdovician(Jeffersonian)-USilurian(Niagaran) |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | Nautiloidea |
| Order: | Tarphycerida |
| Family: |
Trocholitidae Chapman (1857) |
The Trocholitidae are Tarphycerida with whorls in close contact as with the Tarphyceratidae, but in which the siphuncle, similar in structure, becomes dorsal. The Trocholitidae are derived from the Tarphyceratidae, perhaps from different tarphyceratids.
Members of the Trocholitidae vary in whorl section and siphuncle position. Most are tightly coiled with the dorsum impressed to some degree. As exceptions Arkoceras and Wichitoceras have their whorls touching but without a dorsal impression. Discoceras and have somewhat subquadrate whorl sections and are moderately impressed. In Graftonoceras and Jasperoceras the venter is rounded and continues smoothly through the flanks to a broad dorsum which in each is moderately impressed. The siphuncle in Graftonoceras is on the dorsal margin, in Jasperoceras it is between the center and dorsum. Whorls in Trocholites have a wide cross section and low profile, in Wichitoceras they are laterally compressed resulting in a high profile. Litoceras has a broad cross section and a deeply impressed dorsum. As with Discoceras and Curtoceras the siphuncle is between the center and dorsum.
Arkoceras, Trocholitoceras, and Wichitoceras are limited to the upper Lower Ordovician, along with the enigmatic Beekmanoceras which may or may not belong. Curtoceras, Litoceras, and Hardmanoceras begin in the Lower Ordovician and continue into the middle of the Period, Hardmanoceras questionably. Jasperoceras is known only from the Middle Ordovician; Trocholites and Discoceras from the Middle and Upper. Graftonoceras comes from the Upper Silurian. Hardmanoceras which is strongly ribbed may be the ancestor of the Ophidioceratidae of the Upper Silurian
Genera assigned to the Trocholitidae are found in three principal realms: North America, Australia, and Northern Europe (Balto-Scandia).
Genera known only from North America
Genera known from North America and Europe ---
Genera known from North America and Australia. ---
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Wikipedia