Editing Diplodocidae (section)

=== Distinguishing anatomical features===
[[File:diploheads.jpg|thumb|Diplodocid heads have historically been restored in various ways: a) skull, b) classic rendering of the head with nostrils on top, c) with speculative trunk, d) modern depiction with nostrils low on the snout and a possible [[Resonating chamber (anatomy)|resonating chamber]]]]
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies - distinctive anatomical features that are unique to a given organism or group.

The clade Diplodocidae is distinguished based on the following characteristics:<ref name="Upchurch2004"/>
* [[nares]]: the external nares face dorsally; and the internarial bar is absent
* [[jugal]]: the jugal forms a substantial part of the caudoventral margin of the [[antorbital fenestra]]
* [[quadratojugal]] processes: the angle between the rostral quadratojugal process and the dorsal quadratojugal process is approximately 130°
* paroccipital process: the distal end of the paroccipital process is rounded and tongue-like in shape
* [[parasphenoid]]: the parasphenoid rostrum is a laterally compressed, thin spike and is lacking the longitudinal dorsal groove
* [[Pterygoid bone|pterygoid]]: the ectopterygoid process of the pterygoid is located below the antorbital fenestra, and is reduced, such that it is not visible below the ventral margin of the skull when examined in lateral view; also the breadth of the main body of the pterygoid at least 33% of the length of the pterygoid
* [[teeth]]: at least 5-6 replacement teeth occur per alveolus (as observed in ''[[Nigersaurus]]'')
* [[dorsal vertebrae]]: no more than 10 dorsal vertebrae are present
* [[caudal vertebrae]]: 70-80 caudal vertebrae are present
* [[Pes (anatomy)|pedal]] [[phalanges]]: pedal phalanx I-1 has a proximoventral margin drawn out into a thin plate or heel that underlies the distal end of metatarsal I; also pedal phalanx II-2 is reduced in craniocaudal length and has an irregular shape