Quenstedtoceras (Hyatt, 1877) is a genus of ammonites from Cardioceratidae family, Quenstedtoceratinae subfamily. Quenstedtoceras were common in the seas of the boreal and sub-boreal zones of the northern hemisphere at the end of the Middle Jurassic (Late Callovian).
At the Early Oxfordian time Quenstedtoceras not died out, they gave rise to a new ammonoid genus - Cardioceras. The transformation from one genus to another was gradual and this fact complicates the definition of transitional forms - they combine the features of both genre, Quenstedtoceras, and Cardioceras.
Ammonites from Longaeviceras genus were ancestors of Quenstedtoceras.The volume of Quenstedtoceras genus different researchers understand differently. Some of them describe in it dozens of species, other scientists reduces the whole genus to three or four species. In any case, the "main" specie, recognized by all researchers, is Quenstedtoceras lamberti. It is acknowledged by all paleontologists, but the volume of this spicie also understand all their own way.
Also, many of the authors included to the Quenstedtoceras two other Quenstedtoceratinae genera: Vertumniceras and Eboraciceras. These ammonites - close relatives of Quenstedtoceras, "the side branches", diverged from the main trunk of the family. However, their morphological differences are sufficient to separate them into different genera.
Typically in modern literature, these genre are separated, but in books published over 30 years ago, most often they all considered to Quenstedticeras. In the older literature can be found and obsolete genus name - Quenstedticeras - with the letter "i" in the place where now decided to write "o".
In Quenstedtoceras known aptychi (jaw apparatus), muscle attachment scars and probably lifetime color pattern.