Introduction and Description

Allotrioceras is a tubular fossil from the middle Chazyan (Mid Ordovician) of New York state, collected by Rousseau Flower and included by him in the Endocerida and placed in a new family the Allotrioceratidae. (Flower 1955). Allotrioceras is characterized by a lateral pair of subequal endocones separated by a straight partition that extends more than half way across from either the dorsal or vental side, as perceived, and runs along the length. What remains is thought to represent the siphuncle which ranges from about 8mm to about 15 mm in diameter.


Some endocerids, derived from the Proterocameroceratidae, Najaceras, Cacheoceras, and Williamsoceras, (Flower 1976a)have a longitudinal dorsal or ventral process, or both about which the endocones are formed, which the partitian of Allotrioceras has somewhat of a resemblance. In the Chihliocreratidae, also derived from the Proterocameroceratidae, (Flower 1958. 1976b) the main endocones are flanked by two smaller endocones, one on each side. Longitudinal partitians and multiple endocones are not unknown in the order. Simply on the basis of either, Allotrioceras can not be excluded.


The holotype of Allotrioceras, Attotrioceras bifercatum Flower 1955, rests in the collection of the New Mexico Museum of Natural History and Science in Albuquerque, NM.


  • Flower, R H 1955; Status of Endoceroid Classification; Journal of Paleontology Vol 29, no3,pp 329-371; May 1955
  • _____1958; Some Chazyan and Mohawkian Endoceratida; Journal of Paleontology Vol 32, no3, pp 433-458; May 1958
  • ­­_____ 1976A; Some Whterock and Chazy Endoceroids, Part II, Memoir 28, New Mexico Bureaur of Mines and Mineral Resources, Socorro, NM.
  • ­­­______ 1976b; Ordovician Cephalopod Faunas And Their Role in Correlation, in The Ordovician System: proceedings of a Paleontological Association Symposium, Bermingham 1974; Bassett, M.G. (ed) 1976.

Other sources

  • Curt Teichert 1964, Encoceratoidea, K160 -- __ in Vol K Treatise on Invertebrate Paleontology , Teichert C and Moore, R, C, eds, GSA and Univ Kansas Press.
  • Collections of the New Mexico Museum of Natural History and Science,Albuquerque, NM.

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