Perhaps it has not been found yet.
There are species of dinosaurs known only from a single find. For example, Minotaurasaurus ramachandrani, whose skull was acquired by American-Indian scientist Vilayanur Ramachandran from a fossil dealer, remains a mystery as it is unknown where and when this ankylosaur lived. Also among the rare specimens is the six-meter Shaochilong maortuensis from China and the small Pegomastax africana, which measures about 60 cm and is known only from a single lower jawbone.
The fate of Amphicoelias fragillimus is particularly tragic; it was described in 1878 by American paleontologist Edward Cope based on fossilized vertebrae. These vertebrae have been lost (apparently disintegrated), and no other bones of this dinosaur have been found in the 140 years since.
It is important to note that the rarity of a species in the deposits does not necessarily indicate its low numbers, as remains are preserved only under specific conditions, such as swamps, quicksand, or tar lakes.
