Editing Apatosaurus (section)

==Description==
[[File:Apatosaurus scale mmartyniuk wiki.png|thumb|left|Comparison of ''A. ajax'' (orange) and ''A.{{nbsp}}louisae'' (red) with a human (blue) and ''[[Brontosaurus parvus]]'' (green)]]
''Apatosaurus'' was a large, long-necked, [[quadruped]]al animal with a long, whip-like tail. Its [[forelimb]]s were slightly shorter than its [[hindlimb]]s. Most size estimates are based on specimen [[Carnegie Museum of Natural History|CM]]{{nbsp}}3018, the [[type (biology)|type specimen]] of ''A.{{nbsp}}louisae'', reaching {{convert|21|-|23|m|ft|abbr=on}} in length and {{convert|16.4|-|22.4|t|LT ST|abbr=on}} in body mass.<ref>{{Cite book|last=Paul|first=Gregory S.|url=http://worldcat.org/oclc/985402380|title=The Princeton Field Guide to Dinosaurs|year=2016|publisher=Princeton University Press|isbn=978-1-78684-190-2|oclc=985402380|pages=217}}</ref><ref name=Seebacher01/><ref name="mazzettaetal2004"/><ref name=henderson/> A 2015 study that estimated the mass of volumetric models of ''[[Dreadnoughtus]]'', ''Apatosaurus'', and ''[[Giraffatitan]]'' estimates CM{{nbsp}}3018 at {{convert|21.8|-|38.2|t|LT ST|abbr=on}}, similar in mass to ''Dreadnoughtus''.<ref name="bates&falkingham2015"/> Some specimens of ''A.{{nbsp}}ajax'' (such as [[Oklahoma Museum of Natural History|OMNH]]{{nbsp}}1670) represent individuals 11{{ndash}}30% longer, suggesting masses twice that of CM{{nbsp}}3018 or {{convert|32.7|-|72.6|t|LT ST|abbr=on}}, potentially rivaling the largest [[titanosaur]]s.<ref name="wedel2013"/> However, the upper size estimate of OMNH{{nbsp}}1670 is likely an exaggeration, with the size estimates revised in 2020 at {{cvt|30|m|ft}} in length and {{cvt|33|MT|ST}} in body mass based on volumetric analysis.<ref>{{cite book|last1=Molina-Pérez|first1=R.|last2=Larramendi|first2=A.|year=2020|title=Dinosaur Facts and Figures: The Sauropods and Other Sauropodomorphs|pages=256|publisher=Princeton University Press|isbn=978-0691190693}}</ref>
[[File:Apatosaurus ajax skull.jpg|thumb|''A. ajax'' skull, specimen CMC VP 7180]]
The skull is small in relation to the size of the animal. The jaws are lined with spatulate (chisel-like) teeth suited to an [[herbivore|herbivorous]] diet.<ref name="fastovsky"/> The snout of ''Apatosaurus'' and similar [[diplodocoidea|diplodocoids]] is squared, with only ''[[Nigersaurus]]'' having a squarer skull.<ref name="whitlock11"/> The braincase of ''Apatosaurus'' is well preserved in specimen BYU{{nbsp}}17096, which also preserved much of the skeleton. A phylogenetic analysis found that the braincase had a morphology similar to those of other diplodocoids.<ref name="balanoff2010"/> Some skulls of ''Apatosaurus'' have been found still in articulation with their teeth. Those teeth that have the [[tooth enamel|enamel]] surface exposed do not show any scratches on the surface; instead, they display a sugary texture and little wear.<ref name="whitlock11"/>
[[File:Apatosaurus ajax holotype cervical.png|thumb|left|Cervical vertebra of ''A. ajax'' (holotype, [[Peabody Museum of Natural History|YPM]] 1860) in side and anterior view]]
Like those of other sauropods, the neck vertebrae are deeply bifurcated; they carried neural spines with a large trough in the middle, resulting in a wide, deep neck.<ref name="fastovsky"/> The vertebral formula for the holotype of ''A.{{nbsp}}louisae'' is 15{{nbsp}}cervicals, 10{{nbsp}}[[thoracic vertebrae|dorsals]], 5{{nbsp}}[[Sacrum#Other animals|sacrals]], and 82{{nbsp}}[[Vertebra#Other animals|caudals]]. The caudal vertebra number may vary, even within species.<ref name="gilmore36"/> The cervical vertebrae of ''Apatosaurus'' and ''Brontosaurus'' are stouter and more robust than those of other [[diplodocid]]s and were found to be most similar to ''Camarasaurus'' by [[Charles Whitney Gilmore]].<ref name="gilmore36"/><ref name="twne15"/> In addition, they support [[Cervical rib#Other animals|cervical ribs]] that extend farther towards the ground than in diplodocines, and have vertebrae and ribs that are narrower towards the top of the neck, making the neck nearly triangular in cross-section.<ref name="twne15"/> In ''Apatosaurus louisae'', the [[atlas (anatomy)|atlas]]-[[axis (anatomy)|axis]] complex of the first cervicals is nearly fused. The dorsal ribs are not fused or tightly attached to their vertebrae and are instead loosely articulated.<ref name="gilmore36"/> ''Apatosaurus'' has ten dorsal ribs on either side of the body.<ref name="riggs-1903"/> The large neck was filled with an extensive system of weight-saving air sacs. ''Apatosaurus'', like its close relative ''[[Supersaurus]]'', has tall neural spines, which make up more than half the height of the individual bones of its vertebrae. The shape of the tail is unusual for a diplodocid; it is comparatively slender because of the rapidly decreasing height of the vertebral spines with increasing distance from the hips. ''Apatosaurus'' also had very long ribs compared to most other diplodocids, giving it an unusually deep chest.<ref name=LHW07/> As in other diplodocids, the tail transformed into a whip-like structure towards the end.<ref name="gilmore36"/>
[[File:Apatosaurus louisae by durbed.jpg|thumb|[[Paleoart|Artistic interpretation]] of ''A. louisae'']]
The limb bones are also very robust.<ref name=LHW07/> Within [[Apatosaurinae]], the [[scapula]] of ''Apatosaurus louisae'' is intermediate in morphology between those of ''A.{{nbsp}}ajax'' and ''Brontosaurus excelsus''. The arm bones are stout, so the [[humerus]] of ''Apatosaurus'' resembles that of ''Camarasaurus'', as well as ''Brontosaurus''. However, the humeri of ''Brontosaurus'' and ''A.{{nbsp}}ajax'' are more similar to each other than they are to ''A.{{nbsp}}louisae''. In 1936, [[Charles W. Gilmore|Charles Gilmore]] noted that previous reconstructions of ''Apatosaurus'' forelimbs erroneously proposed that the [[Radius (bone)|radius]] and [[ulna]] could cross; in life they would have remained parallel.<ref name="gilmore36"/> ''Apatosaurus'' had a single large claw on each forelimb, a feature shared by all sauropods more derived than ''[[Shunosaurus]]''.<ref name="gilmore36"/><ref name="upchurchmanus"/> The first three toes had claws on each hindlimb. The phalangeal formula is 2-1-1-1-1, meaning the innermost finger (phalanx) on the forelimb has two bones and the next has one.<ref name="martin06"/> The single manual claw bone ([[ungual]]) is slightly curved and squarely [[:wikt:truncated|truncated]] on the anterior end. The pelvic girdle includes the robust [[ilium bone|ilia]], and the fused (co-ossified) [[pubic bone|pubes]] and [[ischium|ischia]]. The femora of ''Apatosaurus'' are very stout and represent some of the most robust femora of any member of Sauropoda. The tibia and fibula bones are different from the slender bones of ''Diplodocus'' but are nearly indistinguishable from those of ''Camarasaurus''. The fibula is longer and slenderer than the tibia. The foot of ''Apatosaurus'' has three claws on the innermost digits; the digit formula is 3-4-5-3-2. The first metatarsal is the stoutest, a feature shared among diplodocids.<ref name="gilmore36"/><ref name="Upchurch05"/>