Editing Diplodocidae (section)

==Description==
[[File:DiplodocusDB.jpg|thumb|left|''[[Diplodocus]]'', depicted with spines limited to the mid-line of the back]]
Diplodocids were generally large animals, even by sauropod standards. Thanks to their long necks and tails, diplodocids were among the longest sauropods, with some species such as ''[[Supersaurus vivianae]]'' and ''[[Diplodocus hallorum]]'' estimated to have reached lengths of {{convert|30|meters|feet|-1}} or more.<ref name="Lovelace2007"/> The heaviest diplodocids, such as ''Supersaurus'' and ''[[Apatosaurus]]'', may have weighed close to 40 tonnes.<ref name="Lovelace2007"/><ref name="Bates2015"/><ref name="Campione2017"/> However, not all diplodocids were so large; the South American species ''[[Leinkupal laticauda]]'' was one of the smallest diplodocids, with an estimated length of only {{convert|9|meters|feet}}.<ref name="Gallina2022"/>

Their heads, like those of other sauropods, were tiny with the nasal openings on the top of the head (though in life the nostrils themselves would have been close to the tip of the snout<ref name="Witmer2001"/>).

The heads of diplodocids have been widely depicted with the nostrils on top due to the position of the nasal openings at the apex of the skull. There has been speculation over whether such a configuration meant that diplodocids may have had a trunk.<ref name="Bakker1986"/> A 2006 study surmised there was no paleoneuroanatomical evidence for a trunk.<ref name="Knoll2006"/> It noted that the [[facial nerve]] in an animal with a trunk, such as an elephant, is large as it innervates the trunk. The evidence suggests that the facial nerve is very small in diplodocids. Studies by Lawrence Witmer (2001) indicated that, while the nasal openings were high on the head, the actual, fleshy nostrils were situated much lower down on the snout.<ref name="Witmer2001"/>

Diplodocids had long necks, which could reach an estimated length of {{convert|15|m|ft|-1}} in the largest, longest-necked species.<ref name="TaylorWedel2013"/> The neck was typically composed of 15 vertebrae, though in ''[[Barosaurus]]'', the neck probably had 16 vertebrae as the result of the incorporation of an additional vertebra from the dorsal series.<ref name="McIntosh2005"/> The habitual [[Sauropod neck posture|neck posture]] of diplodocids is controversial; studies have proposed postures ranging from nearly straight and below horizontal<ref name="StevensParrish1999"/> to an S-curve that reaches vertical.<ref name="Taylor2014"/>

=== 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

===Skin===
[[File:Diplodocus sp. fossil dinosaur skin (Morrison Formation, Upper Jurassic; Mother's Day site, Carbon County, Montana, USA) 2.jpg|thumb|left|Skin impression of a diplodocid, specimen CMC VP 10659]]
Few skin impressions of diplodocids have been found. However, at least one significant find was reported by Stephen Czerkas in 1992. Fossils from the Howe Quarry in [[Shell, Wyoming]] preserved portions of the skin from around the tip of the tail, or "whiplash".<ref name="Czerkas1993A"/> Czerkas noted that the skin preserved a sequence of conical spines, and that other, larger spines were found scattered around larger tail vertebrae. The spines appeared to be oriented in a single row along the mid-line of the tail, and Czerkas speculated that this midline row may have continued over the animal's entire back and neck.<ref name="Czerkas1993B"/>

Skin fossils have been discovered at the Mother's Day Quarry that have been assigned to ''Diplodocus'' sp. These skin fossils exhibit a vast amount of scale diversity, the scales of which vary in shape, size, orientation, and 3-dimensional relief depending on their location on the integument. Some of the scale orientations may indicate where the skin originated on the body. For instance, a scale orientation consisting of arching rows of square scales is noted to look similar to scale orientations seen around crocodilian limbs, so it is hypothesized that this area may have come from around a limb in life. Due to the high diversity of scales seen on a relatively small area of skin, the small size of the scales, and the presence of small and juvenile individuals at the Mother's Day Quarry, it is hypothesized that the skin originated from a small or juvenile individual.<ref name="Gallagher2021"/>