Middle Ordovician – Devonian
Treptoceras is an extinct genus of nektobenthic carnivores
Identification in Hand Sample:
- Orthocones depressed with closely spaced septa
- Two siphuncles, one being a large marginal subcylindrical tube, the other a small moniliform structure
- Some individuals show darker markings on the lighter ground of the shell interior, interpreted to be remnants of coloring that may have served as camouflage
- Conch longiconic
- Specimens of Treptoceras are very abundant in certain rock layers. For example, Frey (1989) referred to the “Treptoceras duseri shale” layer within the Waynesville Formation of southwestern Ohio. This layer includes three species of the genus, one of which is a new species, as yet unnamed.
- In fossil specimens in which the shell wall is preserved, some individuals show darker markings on the lighter ground of the shell interior. For example, in specimens the Ordovician species Treptoceras duseri, there may be longitudinal dark lines. These lines are the remains of color bands on the living animal. Such color patterns commonly are interpreted as having served as camouflage, although they may have had a function in mating.
Treatise on Invertebrate Paleontology, Part K, Mollusca 3 (1964):
- Depressed orthocones with closed spaced septa and 2 siphuncles, one a large marginal subcylindrical tube, the other a small moniliform structure about halfway between center and venter. Neither surface nor interior nor real nature of ?2 siphuncles well known. (Foerste 1928 suspected symbiotic relationship between this cephalopod and an organism that is responsible for the internal feeding tube. Flower 1952 admitted Foerste’s view is possible, but noted that 4 species with similar internal structure are known. He regarded Treptoceras as a probably valid genus deserving of recognition as a distinct family or even higher nautiloid group, although he mistakenly believed that all 4 species were of the same age.)