David S. Berman and McIntosh in 1978 referred "Cetiosauriscus" to the family Diplodocidae along with multiple other genera; "Diplodocus", "Apatosaurus", "Barosaurus", "Mamenchisaurus" "Dicraeosaurus" and "Nemegtosaurus". Like other members of the family, "Cetiosauriscus" possesses wing-like transverse processes, divided chevrons with forward and backward projections, the tail is "whiplash"-like, the humerus is 2/3 the length of the femur, the calcaneum is absent, metatarsal III and IV are the longest, and metatarsal I has a process on the bottom back corner. This referral would make "Cetiosauriscus", known from the Callovian, the oldest diplodocid, millions of years older than "Diplodocus", "Barosaurus" or "Apatosaurus". In the paper naming "Cetiosauriscus stewarti", Charig also described the chevrons of a new specimen and created the term "diplodociform" to describe them. This meant they were robust and double-beamed, as in "Diplodocus" and its relatives like "Mamenchisaurus". Because of the similarly "diplodociform" chevrons, Charig referred "Cetiosauriscus" to the Diplodocidae along with the new specimen. Elaborating upon his earlier paper, McIntosh (1990) weakly referred "Cetiosauriscus" to the subfamily Diplodocinae, characterised by more cervicals and fewer dorsals, tall sacrum neural spines, short forelimbs, no calcaneum, metatarsals III and IV being the longest, and a small process on the distal end of metatarsal I. The subfamily also included "Diplodocus", "Barosaurus" and "Apatosaurus". In 2004 this placement was followed by Weishampel "et al." without comment.