Editing Protoceratops (section)

===Postcranial skeleton===
[[File:Protoceratops andrewsi skeletal.png|thumb|Skeletal reconstruction of ''P. andrewsi'']]

The [[vertebral column]] of ''Protoceratops'' had nine cervical (neck), 12 dorsal (back), eight sacral (pelvic) and over 40 caudal (tail) vertebrae. The [[centra]] (centrum; body of the vertebrae) of the first three cervicals were coossified together ({{dinogloss|atlas}}, {{dinogloss|axis}} and third cervical respectively) creating a rigid structure. The neck was rather short and had poor flexibility. The atlas was the smallest cervical and consisted mainly of the centrum because the {{dinogloss|neural arch}} (upper, and pointy vertebral region) was a thin, narrow bar of bone that extended upwards and backward to the base of the axis neural {{dinogloss|neural spine|spine}}. The capitular facet (attachment site for [[Haemal arch|chevron]]s; also known as cervical ribs) was formed by a low projection located near the base of the neural arch. The anterior facet of the atlas centrum was highly concave for the articulation of the {{dinogloss|occiput|occipital condyle}} of the skull. The neural arch and spine of the axis were notably larger than the atlas itself and any other cervical. The axial neural spine was broad and backward developed being slightly connected to that of the third cervical. From the fourth to the ninth all cervicals were relatively equal in size and proportions. Their neural spines were smaller than the first three vertebrae and the development of the capitular facet diminished from the fourth cervical onwards.<ref name=Brown1940/><ref name=Tereschenkko2007>{{cite journal|last1=Tereschenko|first1=V. S.|date=2007|title=Key to Protoceratopoid Vertebrae (Ceratopsia, Dinosauria) from Mongolia|journal=Paleontological Journal|volume=41|number=2|pages=175–188|doi=10.1134/S0031030107020086|bibcode=2007PalJ...41..175T |s2cid=84954199 |url=https://www.researchgate.net/publication/226106749}}</ref><ref name=Kuznetsov2010>{{cite journal|last1=Kuznetsov|first1=A. N.|last2=Tereschenko|first2=V. S.|date=2010|title=A Method for Estimation of Lateral and Vertical Mobility of Platycoelous Vertebrae of Tetrapods|journal=Paleontological Journal|volume=44|number=2|pages=209–225|doi=10.1134/S0031030110020139|bibcode=2010PalJ...44..209K |s2cid=84321442 |url=https://www.researchgate.net/publication/225123163}}</ref>
{{multiple image
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|image1 = Protoceratops ZPAL MgD-II 3 left humerus.png

|image2 = Protoceratops ZPAL MgD-II 3 radius & ulna.png

|image3 = Protoceratops ZPAL MgD-II 3 right ilium.png

|image4 = Protoceratops ZPAL MgD-II 3 ischia.png

|image5 = Protoceratops ZPAL MgD-II 3 right femur.png

|image6 = Protoceratops ZPAL MgD-II 3 right fibula & tibia.png

|image7 = Protoceratops hands.png

|image8 = Protoceratops feet.png

|footer = Forelimb (top), pelvic (middle), and hindlimb fossil bones (bottom) of specimen ZPAL Mg D-II/3
}}
The {{dinogloss|dorsals|dorsal vertebrae}} were similar in shape and size. Their neural spines were elongated and sub-rectangular in shape with a tendency to become more elongated in posterior vertebrae. The centra were large and predominantly amphiplatian (flat on both facets) and circular when seen from the front. Sometimes in old individuals the last dorsal vertebra was somewhat coosified to the first sacral. The {{dinogloss|sacrals|sacral vertebrae}} were firmly coosified giving form to the sacrum, which was connected to the inner sides of both ilia. Their neural spines were broad, not coosified, and rather consistent in length. The centra were mainly opisthocoelous (concave on the posterior facet and convex on the anterior one) and their size became smaller towards the end. The {{dinogloss|caudals|caudal vertebrae}} decreased in size progressively towards the end and had very elongated neural spines in the mid-series, forming a [[Neural spine sail|sail]]-like structure. This elongation started from the first to the fourteenth caudal. The centra were {{dinogloss|centrum|heterocoelous}} (saddle-shaped at both facets). On the anterior caudals they were broad, however, from the twenty-fifth onwards the centra became elongated alongside the neural spines. On the underside of the caudal vertebrae a series of chevrons were attached, giving form to the lower part of the tail. The first chevron was located at the union of the third and fourth caudals. Chevrons three to nine were the largest and from the tenth onwards they became smaller.<ref name=Brown1940/><ref name=Tereschenkko2007/><ref name=Kuznetsov2010/><ref name=Tereschhenko20133>{{cite journal|last1=Tereschhenko|first1=V. S.|last2=Singer|first2=T.|date=2013|title=Structural Features of Neural Spines of the Caudal Vertebrae of Protoceratopoids (Ornithischia: Neoceratopsia)|journal=Paleontological Journal|volume=47|issue=6|pages=618–630|doi=10.1134/S0031030113060105|bibcode=2013PalJ...47..618T |s2cid=84639150 |url=https://www.researchgate.net/publication/263677535}}</ref>

All vertebrae of ''Protoceratops'' had ribs attached on the lateral sides, except for the series of caudals. The first five cervical ribs (sometimes called chevrons) were some of the shortest ribs, and among them the first two were longer than the rest. The third to the sixth dorsal (thoracic) ribs were the longest ribs in the skeleton of ''Protoceratops'', the following ribs became smaller in size as they progressed toward the end of the vertebral column. The two last dorsal ribs were the smallest, and the last of them was in contact with the internal surfaces of the ilium. Most of the sacral ribs were fused into the sacrum, and had a rather curved shape.<ref name=Brown1940/>
{{multiple image
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|image1=Protoceratops andrewsi Restoration.png

|image2=Protoceratops hellenikorhinus Restoration.png

|footer=[[Paleoart|Life restorations]] of ''P. andrewsi'' (top) and ''P. hellenikorhinus'' (bottom)
}}
The [[pectoral girdle]] of ''Protoceratops'' was formed by the {{dinogloss|scapulocoracoid}} (fusion of the coracoid and scapula) and clavicle. The {{dinogloss|scapula|scapulae}} (shoulder blades) were relatively large and rounded on their inner sides. At their upper region, the scapulae were wide. At their lower region, the scapulae meet the coracoids. The {{dinogloss|coracoid|coracoids}} were relatively elliptical, and sometimes coosified (fused) to the scapulae. The clavicle of ''Protoceratops'' was an U to slightly V-shaped element that joined to the upper border of the scapulocoracoid. In its general form, the forelimbs of ''Protoceratops'' were shorted than the hindlimbs, and composed by the humerus, radius, and ulna. The {{dinogloss|humerus}} (upper arm bone) was large and slender, and at the lower part it met with both radius and ulna. The {{dinogloss|ulna}} had a slightly recurved shape and was longer than the radius. A concavity was present on its upper part, serving as the connection with the humerus and forming the elbow. The {{dinogloss|radius}} was a rather short bone with a straight shape. The [[Manus (anatomy)|manus]] (hand) of ''Protoceratops'' had five [[Digit (anatomy)|digits]] (fingers). The first three fingers had [[ungual]]s (claw bones) and were the largest digits. The last two were devoid of unguals and had a small size, mostly [[vestigial]] (retained, but without important function). Both hand and feet unguals were flat, blunt and hoof-like.<ref name=Brown1940/><ref name=Justyna2019/>

The [[pelvic girdle]] was formed by the {{dinogloss|ilium}}, {{dinogloss|pubis}}, and {{dinogloss|ischium}}. The ilium was a large element, having a narrow preacetabular process (anterior end) and a wide postacetabular process (posterior end). The pubis was the smallest element of the pelvic girdle and it had an irregular shape, although its lower end was developed into a pointed bony projection downward. The ischium was the longest bone of the pelvic girdle. It had an elongated shaft with a somewhat wide lower end. The hindlimbs of ''Protoceratops'' were rather long, with a slighter longer tibia (lower leg bone) than femur (thigh bone). The {{dinogloss|femur}} (thighbone) was robust and had a rather rounded and pronounced [[greater trochanter]], which was slightly recurved into the inner sides. The {{dinogloss|tibia}} (shinbone) was long and slender with a wide lower end. On its upper region a concavity was developed for the joint with the smaller {{dinogloss|fibula}}. The [[Pes (anatomy)|pes]] (foot) were composed of four {{dinogloss|metatarsal}} and four toes which bore shovel-like pedal unguals. The first metatarsal and toe were the smallest, while the other elements were of similar shape and length.<ref name=Brown1940/><ref name=Justyna2019/>