Mollusca		Nautiloidea
CYRTOSOMA		TarphyceriNa

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Tarphycerina

Cephalopoda
|--NAUTILOIDEA
|  |--TARPHYCERIDA
|  |  |--Tarphycerina  
|  |  `--BARRANDEOCERINA
|  `--ONCOCERIDA 
|     |--Oncoceratidae  
|     `--NAUTILIDA    
|        |--NAUTILIDA i.s.
|        `--NAUTILINA
`--Neocephalopoda
   |--Ammonoidea
   `--Coleoidea

Introduction
Families & Genera

Tragoceras falcatum (Schlotheim, 1820)
family: Tarphyceratidae
Middle Ordovician (Darriwilian)
Mochty, Poland
graphic from Jerzy Dzik, Phylogeny of the Nautiloidea, p.38

Introduction

Coiled cephalopods, having a thick complex connecting ring, like the Ellesmeroceratida. Siphuncle ventral in young, may become central or dorsal in adult. Evolved from the Bassleroceratidae

Campbelloceras sp.
family: Tarphyceratidae
Middle Ordovician (?Dapingian)
USA
graphic from Teichert 1988 p.32, from Teichert 1967

Families and Genera

The following list is in no way definitive, up to date, or comprehensive. It is mostly from on Flower and Kummel, p.606-8. The dates are from The Fossil Record II

Family TARPHYCERATIDAE Hyatt

Aphetoceras americanum Hyatt
height about 13 cm
Early Ordovician (?Floian) of Newfoundland
image from Moore, Lalicker and Fischer, Invertebrate Fossils p.355
Shell gyroconic or tightly coiled, siphuncle ventral or central, but ventral in young. Evolved from the Bassleroceratidae. Aphetoceras is almost identical to Bassleroceras, except that it is a gyrocone whereas Bassleroceras is a cyrtocone. Probably ancestral to the Trocholitidae and the Barrandeoceratidae.
Early to Late Ordovician (Tremadoc to Hirnantian)
Aphetoceras, Clytoceras, Pycnoceras, Shumardoceras, Cycloplectoceras, Alaskoceras, Campbelloceras, Centrotorphyceras, Eurystomites, Pionoceras, Pilotoceras, Seclyoceras (?), Tragoceras.

Family TROCHOLITIDAE Chapman

Cyclopectoceras miseri Ulrich
height about 13 mm
Early Ordovician (?Floian) of Arkansas and Oklahoma
image from Moore, Lalicker and Fischer, Invertebrate Fossils p.355
Siphuncle in adult dorsad of center, may be ventral in young or central as in more advanced types.
Early Ordovician: Arkoceras, Curioceras, Jasperoceras, Litoceras, Trocholitoceras, Wichitoceras.
Mid to Late Ordovician: Trocholites, Discoceras
Silurian: Graftonoceras.

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page uploaded 26 September 2002
last revised ATW060102
checked ATW050615
(originally uploaded on Kheper Site 1998)
text © M. Alan Kazlev 1998-2002
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this material may be freely used for non-commercial purposes