Belongs within: Nautilosiphonata.
The Piloceratidae were a family of Lower Ordovician breviconic endocerid cephalopods. They had a large endocone-packed siphuncle occupying a large part of the shell.
Characters (from Teichert 1964): Breviconic, more or less strongly curved, rapidly expanding conches with compressed section; body chamber may have slightly contracted aperture. Siphuncle rapidly expanding, large; septal necks holochoanitic; endocones simple, complex system of endosiphuncular blades and endosiphofunicles occasionally present.
<==Piloceratidae |--Dartonoceras Flower 1964EK12 |--Cassinoceroides Xu & Lai 1987EK12 |--Utoceras Ulrich, Foerste & Miller 1943EK12 | |--*U. coloradoense Ulrich, Foerste & Miller 1943T64 | `--U. gleneyriense Ulrich, Foerste & Miller 1943P68 |--Cassinoceras Ulrich & Foerste 1936T64 | |--*C. explanator (Whitfield 1886) [=Piloceras explanator]T64 | |--C. arkansasense Ulrich, Foerste & Miller 1943P68 | |--C. grande Ulrich & Foerste 1943P68 | `--C. wortheniT64 |--Piloceras Salter in Murchison 1859T64 | |--*P. invaginatum Salter in Murchison 1859T64 | |--P. horneiP68 | |--P. manchuriense Endo 1932P68 | |--P. saffordi Ulrich, Foerste & Miller 1943P68 | `--P. tuvense Balashov 1968K93 `--Allopiloceras Ulrich & Foerste 1936 [incl. Trundleoceras Foerste 1938]T64 |--*A. tennesseense Ulrich & Foerste 1936T64 |--A. affine Ulrich, Foerste & Miller 1943P68 |--A. baylorense Ulrich, Foerste & Miller 1943P68 |--A. breve Ulrich, Foerste & Miller 1943P68 |--A. compressum Ulrich, Foerste & Miller 1943P68 |--A. erectum Ulrich, Foerste & Miller 1943P68 |--A. sevierense Ulrich, Foerste & Miller 1943P68 |--A. subrectum Ulrich, Foerste & Miller 1943P68 |--A. subunguliforme Ulrich, Foerste & Miller 1943P68 `--A. unguliforme Ulrich, Foerste & Miller 1943P68
*Type species of generic name indicated
References
[EK12] Evans, D. H., & A. H. King. 2012. Resolving polyphyly within the Endocerida: the Bisonocerida nov., a new order of early Palaeozoic nautiloids. Geobios 45 (1): 19–28.
[K93] King, A. H. 1993. Mollusca: Cephalopoda (Nautiloidea). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 169–188. Chapman & Hall: London.
[P68] Purnell, L. R. 1968. Catalog of the type specimens of invertebrate fossils. Part I: Paleozoic Cephalopoda. United States National Museum Bulletin 262: 1–198.
[T64] Teichert, C. 1964. Endoceratoidea. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt K. Mollusca 3. Cephalopoda—General Features—Endoceratoidea—Actinoceratoidea—Nautiloidea—Bactritoidea pp. K160–K189. The Geological Society of America and the University of Kansas Press.