Tarphycerida

Taxobox
name = Ellesmerocerida
fossil_range = L-Ordovician - Devonian


regnum = Animalia
phylum = Mollusca
classis = Cephalopoda
subclassis = Nautiloidea
ordo = Tarphycerida
ordo_authority = Flower 1950

The Tarphycerida were the first of the coiled cephalopods. They are found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some like "Aphetoceras" and "Estonioceras" are loosely coiled, gyroconic, others like "Campbelloceras", "Tarphyceras", and "Trocholites" are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular (Furnish and Glenister 1964), as much as half the length of the containing whorl in most, greater than in the Silurian Ophidioceratidae.

The Tarphycerida evolved from the elongate, compressed, exogastric Bassleroceratidae, probably "Bassleroceras", around the end of the Gasconadian through forms like "Aphetoceras". Close coiling developed rather quickly and both gyroconic and evolute forms are found in the early middle Canadian.

Tarphycerids tend to uncoil in the late mature stage of their growth, indicating they settled into a benthic lifestyle as they became older. Younger, wholly coiled forms were probably more active, nekto-benthic, certainly more maneuverable

Composition and Taxonomy

The Estonioceratidae, Tarphyceratidae, Trocholitidae, Ophidioceratidae are included in the original Tarphycerida (Furnish and Glenister 1964), since incorporated into a suborder, the Tarphycerina (Teichert 1988) . A slightly later and overlapping group of coiled cephalopods, the [Barrandeocerids|Barrandeocerida ( Sweet 1964) has been included, referred to as the Barrandeocerina (Teichert 1988), now recognized as containing two separate lineages (Flower 1984) derived from different tarphyceratids. One is based on Plectoceras, derived from Campbelloceras. The other is based on "Barrandeoceras", derived from "Centrotarhyceras"

Broader Relationships

Tarphycerids are more closely related to the diverse Oncocerida, through the ancestral Bassleroceratidae in the Lower Ordovician, than to the other nautiloid orders. The Oncocerida in tern gave rise to the Nautilida which includes the recent "Nautilus" and "Allonautilus". The puts the Tarphycerida on the broad group that includes the nautilids. It makes them also separate from the groups that include the Discosorida, Actinocerida , Endocerida, and Orthocerida, and from the superficially similar Ammonoidea .( Teichert and Moore 1964, Wade 1988)

Tarphycerid Biology

The tarphycerid animal must have been rather elongate, like squid, although no close relationship is implied. Either that or it was able to retreat deep into its portable lair. As for what ever arms or tentacles they may have had, there is no indication. What may be surmised is that they went through two stages, first a younger more active and swimming stage with simple coiled shells, followed by a less active bottom dwelling stage with shells that diverge during which they mated and produced , probably, a single litter of young, like the modern but unrelated Coleoids.

References

*Flower R.H. 1984, Bodeiceras A New Mohawkian Oxycone, with revision of the Older Barrandeocerida and Discussion of the Status of the Order; Journal of Paleontology V 58, no.6 , pp1372-1379, Nov 1984
* Flower R.H. 1988; Progress and Changing Concepts in Cephalopod and Particularly Nautiloid Phylogeny and Distribution, in Cephalopods – Present and Past pp 17-24, Wiedmann & Kullman (Eds), Stuttgart.
* Furnish and Glenister 1964; Nautiloidea - Tarphycerida; In the Treatise on Invertebrate Paleontology Vol K; Teichert and Moore, (eds) GSA and U of Kansas Press 1964
* Sweet W. 1964; Nautiloidea - Barrandeocerida; In the Treatise on Invertebrate Paleontology Vol K; Teichert and Moore, (eds) GSA and U of Kansas Press 1964
*Teichert, C 1988; Main Features of Cephalopod Evolution, Ch 2 in The Mollusca, Vol 12 Paleontology and Neontology of Cephalopods, M.R. Clarke and E.R Trueman Eds.
* Teichert, C and Moore, R.C 1964; Classification and Stratigraphic Distribution; Treatise on Invertebrate Paleontology Vol K; Teichert and Moore, (eds) GSA and U of Kansas Press 1964
* Wade, M, 1988; Nautiloids and their descendants: cephalopod classification in 1986; New Mexico Bureau of Mines and Mineral Resources Memoir 44, Oct 1988.