 However, both families also had accessory articulations in the , which Cope termed the , limiting the motion of vertebrae respective to one another.Amphicoeliidae and "Amphicoelias" were both found to be intermediate and poorly defined by paleontologist Othniel Charles Marsh in 1881, wherein the primary feature-two mildly concave articular faces-was shown to be widespread and also found in sauropods like "Brontosaurus excelsus".