Sactoceras [SEP] parent taxon
"siphon becomes approximately reduced . . . with age", which he interpreted as a "degradational senile shrinking". Barrande (according to Foord (1888)) considered this to indicate a reversion to the simple siphuncle of the Orthoceratidae, which might be taken to indicate a relationship to the Proteoceratidae.
Evans (2000) considered "Sactoceras" to be an orthocerid, placing it in the Pseudorthoceratoidea (originally Pseudorthoceratacea) of Flower and Caster, 1935, and in the family Sactoceratidae of Troedsson, 1926. The Pseudorthocerataceae
Sactoceras
Sactoceras is an extinct nautiloid cephalopod that lived during the Ordovician and Silurian in what would become North America, Europe, and Asia.
Taxonomy.
The genus "Sactoceras" was named by Hyatt (1884). The type species is "Orthoceras richteri" Barrande, 1874, which comes from the Upper Silurian Ludlow Series of the Prague Basin, Czech Republic. Hyatt named "Sactoceras" for actinocerid species in which siphuncle segments were much reduced in diameter relative to the diameter of the shell, noting that the