Estonioceras is a species of nautiloid from the Ordovician Period in Europe. Unlike most nautiloids, Estonioceras had a spiral shell, which allowed it to live deeper than its straight shelled cousins. It was the ancestor of the Mesozoic Ammonites and the modern chambered nautilus.

In The Land Before Time

An Estonioceras is seen in The Land Before Time IX: Journey to Big Water, where one is resting on the seafloor, until it noticed Littlefoot, who was exploring Mo's Home, and jetted away.