Editing Kentrosaurus (section)

== Description ==
[[Image:Kentrosaurus aethiopicus.png|thumb|[[Life restoration]]]]
''Kentrosaurus'' was a small stegosaur. It had the typical [[dinosaur]]ian body [[Body plan|bauplan]], characterised by a small head, a long neck, short forelimbs and long hindlimbs, and a long, horizontal and muscular tail. Typical [[Stegosauridae|stegosaurid]] traits included the elongation and flatness of the head, the powerful build of the forelimbs, erect and pillar-like hindlimbs and an array of plates and spikes running along both sides of the top mid-line of the animal.<ref name=":3" />

===Size and posture===
[[File:Kentrosaurus_Size_Comparison_by_PaleoGeek.svg|left|thumb|Size compared to a human]]
''Kentrosaurus aethiopicus'' was a relatively small stegosaur, reaching {{cvt|4|-|4.5|m|ft}} in length and {{cvt|700|-|1600|kg|lb}} in body mass.<ref name=Janensch1925/>{{#tag:ref|p. 223 in Paul (2010)<ref name=Paul2010/>|group="upper-alpha"}}<ref name=MallCAE/><ref>{{Cite journal |last1=Benson |first1=Roger B. J. |last2=Campione |first2=Nicolás E. |last3=Carrano |first3=Matthew T. |last4=Mannion |first4=Philip D. |last5=Sullivan |first5=Corwin |last6=Upchurch |first6=Paul |last7=Evans |first7=David C. |date=2014-05-06 |title=Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage |journal=PLOS Biology |language=en |volume=12 |issue=5 |pages=e1001853 |doi=10.1371/journal.pbio.1001853 |issn=1545-7885 |pmc=4011683 |pmid=24802911 |doi-access=free }}</ref> Some specimens suggest that relatively larger individuals could have existed.<ref name=Hennig1915/><ref name=Hennig1925/> These specimens are comparable to some ''[[Stegosaurus]]'' specimens in terms of the olecranon process in development.<ref>{{cite journal|last1=Woodruff|first1=D.C.|last2=Trexler|first2=D.|last3=Maidment|first3=S.C.R.|year=2019|title=Two New Stegosaur Specimens from the Upper Jurassic Morrison Formation of Montana, USA|doi=10.4202/app.00585.2018|journal=Acta Palaeontologica Polonica|volume=64|issue=3|pages=461–480|s2cid=201310639 |doi-access=free}}</ref>

The long tail of ''Kentrosaurus'' results in a position of the [[center of mass]] that is unusually far back for a [[quadrupedalism|quadrupedal]] animal. It rests just in front of the hip, a position usually seen in [[bipedalism|bipedal]] dinosaurs. However, the [[femur|femora]] are straight in ''Kentrosaurus'', as opposed to typical bipeds, indicating a straight and vertical limb position. Thus, the hindlimbs, though powered by massive thigh muscles attached to a long [[Ilium (bone)|ilium]], did not support the animal alone, and the very robust forelimbs took up 10 to 15% of the bodyweight.<ref name=MallROM/> The center of mass was not heavily modified by the [[osteoderm]]s (bony structures in skin) in ''Kentrosaurus'' or ''Stegosaurus'', which allowed the animals to stay mobile despite their armament. The hindlimbs’ thigh muscles were very powerful, allowing ''Kentrosaurus'' to reach a tripod stance on its hindlegs and tail.<ref>{{Cite journal |last=Mallison |first=H. |date=2014-03-07 |title=Osteoderm distribution has low impact on the centre of mass of stegosaurs |url=https://fr.copernicus.org/articles/17/33/2014/ |journal=Fossil Record |language=English |volume=17 |issue=1 |pages=33–39 |doi=10.5194/fr-17-33-2014 |issn=2193-0066|doi-access=free |bibcode=2014FossR..17...33M }}</ref>

=== Skull and dentition ===
Eight specimens from the skull, mandible, and teeth have been collected and described from the Tendaguru Formation, most of them being isolated elements.<ref name=":2">Galton, P. M. (1988). [https://www.researchgate.net/profile/Peter-Galton/publication/272152710_Skull_bones_and_endocranial_casts_of_stegosaurian_dinosaur_Kentrosaurus_Hennig_1915_from_Upper_Jurassic_of_Tanzania_East_Africa/links/554197010cf2b790436be3bf/Skull-bones-and-endocranial-casts-of-stegosaurian-dinosaur-Kentrosaurus-Hennig-1915-from-Upper-Jurassic-of-Tanzania-East-Africa.pdf Skull bones and endocranial casts of stegosaurian dinosaur Kentrosaurus Hennig, 1915 from Upper Jurassic of Tanzania, East Africa.] ''Geologica et Palaeontologica'', ''22'', 123-143.</ref> Two [[Quadrate bone|quadrates]] (bones from the jaw joint) were referred to ''Kentrosaurus'', but they instead belong to a juvenile [[Brachiosauridae|brachiosaurid]].<ref>Maidment, S. C., Norman, D. B., Barrett, P. M., & Upchurch, P. (2008). Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). ''Journal of Systematic Palaeontology'', ''6''(4), 367-407.</ref>
[[File:KentrosaurusBraincase(HMN St 460).jpg|left|thumb|Braincase of ''Kentrosaurus'' in lateral view.]]
The long and narrow [[skull]] was small in proportion to the body. It had a small [[antorbital fenestra]], the hole between the nose and eye common to most [[archosaur]]s, including modern birds, though lost in extant crocodylians. The skull's low position suggests that ''Kentrosaurus'' may have been a browser of low-growing vegetation. This interpretation is supported by the absence of premaxillary teeth and their likely replacement by a horny beak or [[Beak#Anatomy|rhamphotheca]]. The presence of a beak extended along much of the jaws may have precluded the presence of cheeks in stegosaurs.<ref name="czerkas1999">{{cite journal |last1=Czerkas |first1=S |year=1999 |title=The beaked jaws of stegosaurs and their implications for other ornithischians |journal=Miscellaneous Publication of the Utah Geological Survey |volume=99–1 |pages=143–150}}</ref> Due to its phylogenetic position, it is unlikely that ''Kentrosaurus'' had an extensive beak like ''Stegosaurus'' and it instead probably had a beak restricted to the jaw tips.<ref name="knoll2008">{{cite journal |last1=Knoll |first1=F |year=2008 |title=Buccal soft anatomy in ''Lesothosaurus'' (Dinosauria: Ornithischia) |url=https://www.researchgate.net/publication/233720216 |format=PDF |journal=Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen |volume=248 |issue=3 |pages=355–364 |doi=10.1127/0077-7749/2008/0248-0355|bibcode=2008NJGPA.248..355K }}</ref><ref name="barrett2001">Barrett, P.M. (2001). Tooth wear and possible jaw action of ''Scelidosaurus harrisonii'' Owen and a review of feeding mechanisms in other thyreophoran dinosaurs. Pp. 25-52 in Carpenter, K. (ed.): ''The Armored Dinosaurs''. Bloomington: Indiana University Press.</ref> Other researchers have interpreted these ridges as modified versions of similar structures in other ornithischians which might have supported fleshy cheeks, rather than beaks.<ref name="dinosauria04">{{cite book |title=The Dinosauria |vauthors=Galton PM, Upchurch P |publisher=University of California Press |year=2004 |isbn=978-0-520-24209-8 |veditors=Weishampel DB, Dodson P, Osmólska H |edition=2nd |chapter=Stegosauria}}</ref>

There are two nearly complete [[Neurocranium|braincases]] known from ''Kentrosaurus'' though they exhibit some taphonomic distortion.<ref name=":2" /> The [[Frontal bone|frontals]] and [[Parietal bone|parietals]] are flat and broad, with the latter bearing two transversely concave ventral sides with a ridge running down the middle that divides them. The lateral surface of the frontals form part of the [[Orbit (anatomy)|orbit]] (eye socket) and the medial side creates the anterior part of the [[Endocranium|endocranial cavity]] (braincase). [[Basilar part of occipital bone|Basioccipitals]] (where the skull articulated with the cervical vertebrae) form the posterior floor of the brain and the [[Occipital condyles|occipital condyle]], which is large and spherical in ''Kentrosaurus''. The rest of the braincase is formed by the [[Sphenoid bone|presphenoid]] composing the anterior end. The overall braincase morphology is very similar to those of ''[[Tuojiangosaurus]]'', ''[[Huayangosaurus]]'', and ''[[Stegosaurus]]''. However, the occipital condyle is a closer distance to the [[Sphenoid bone|basisphenoid tubera]] (bone at the front of the braincase) in ''Kentrosaurus'' and ''Huayangosaurus'' than in ''Tuojiangosaurus'' and some specimens of ''Stegosaurus''. Due to dinosaurs having more molding in their braincases, [[endocast]]s of ''Kentrosaurus'' can be reconstructed using the preserved fossils. The brain is relatively short, deep, and small, with a strong [[Cerebral cortex|cerebral]] and [[pontine flexures]] and a steeply inclined posterodorsal edge when compared to those of other ornithischians. There is a small dorsal projection in the endocast where an unossified (lacking bone) region between the top of the [[supraoccipital]] (bone at the top-back of the braincase) and overlying parietal that was likely covered in [[cartilage]]. This characteristic is seen in other ornithischians. Because of the prominent flexures, many of the aspects of the brain can only be interpreted by the present structures.<ref name=":2" />

[[File:Fossil Kentrosaurus aethiopicus in Museum für Naturkunde Berlin 002.JPG|thumb|Skull and neck of the Berlin mount]]
In the [[mandible]] (lower jaw), only an incomplete right dentary is known from ''Kentrosaurus''.<ref>Hennig, E. (1936). Ein dentale von Kentrurosaurus aethiopicus Hennig. ''Palaeontographica-Supplementbände'', 309-312.</ref> The deep dentary is almost identical in shape to that of ''Stegosaurus'', albeit much smaller. Similarly, the tooth is a typical stegosaurian tooth, small with a widened base and vertical grooves creating five ridges. The dentary has 13 preserved [[Dental alveolus|alveoli]] on the dorsomedial side and they are slightly convex in lateral and dorsal views. On the surface adjacent to the alveoli, there is a shallow groove bearing small [[Vertebra|foramina]] (small openings in bone) that is similar to grooves on the dentary of the [[Cretaceous]] neornithischian ''[[Hypsilophodon]]'', with one foramina per tooth position. Stegosaurian teeth were small, triangular, and flat; wear facets show that they did grind their food.<ref name="FasWeis04">{{cite book |title=The Evolution and Extinction of the Dinosaurs |vauthors=Fastovsky DE, Weishampel DB |publisher=Cambridge University Press |year=2005 |isbn=978-0-521-81172-9 |veditors=Fastovsky DE, Weishampel DB |edition=2nd |pages=107–30 |chapter=Stegosauria: Hot Plates}}</ref> A single complete cheek tooth is preserved, with a large crown and long root. The crown notably has fewer marginal [[Denticle (tooth feature)|denticles]] and a prominent [[Cingulum (tooth)|cingulum]] compared to ''Stegosaurus'', ''Tuojiangosaurus'', and ''Huayangosaurus''.<ref name=":2" />

===Postcrania===
[[File:KentrosaurusDorsalVertebra.jpg|left|thumb|A dorsal (back) vertebra of ''Kentrosaurus'' in lateral and anterior views.]]
The neck was composed of 13 [[Cervical vertebrae|cervical]] (neck) vertebrae, the first being the [[Atlas (anatomy)|atlas]] which was strongly fused to the occipital region of the skull and followed by the [[Axis (anatomy)|axis]]. The other 11 cervicals had hourglass-shaped [[Vertebra|centra]] (the base of a vertebra) and rounded ventral keels. The [[diapophyses]] are large and strongly angled posteriorily and parallel to each other. The spinous processes got larger towards the posterior end, while the [[Articular processes|postzygapophyses]] became smaller and less horizontal, giving the anterior part of the neck lots of mobility laterally. The dorsal column consists of 13 [[Thoracic vertebrae|dorsal]] (back) vertebrae which are tall and have short centra. They have a [[neural arch]] more than twice as high as the centrum, the vertebral body, and almost completely occupied by the extremely spacious [[neural canal]], a trait unique to ''Kentrosaurus.'' The diapophyses too were laterally elongated, creating a Y-shape in anterior view. The [[sacrum]] (part of pelvis with vertebrae) consists of 6 fused centra, the first being a loose sacrodorsal, while the rest of the centra's [[transverse processes]] (extensions of bone) are fused to the dorsal parts of the [[Rib cage|sacral ribs]] into a solid sacral plate. The ribs also fuse to the [[Ilium (bone)|ilium]] (the upper part of the pelvis) creating a fully ankylosed and solid sacrum. The ilium is notable in that the preacetabular process, front blade, of the [[Ilium (bone)|ilium]] widens laterally, to the front outer side, and does not taper unlike in all other stegosaurs. Another characteristic is that the length of the ilium equals, or is greater than, that of the thigh bone.<ref name="MallisonRealLecto" /> The [[Vertebra|caudal]] (tail) vertebrae are 29 in number, though 27-29 are coossified for attachment to the thagomizers (tail spikes). The caudal vertebrae are unique, as they have a combination of transverse processes up to the 28th vertebra and rod-shaped processes on the posterior caudals. These posterior caudal processes have narrow bases that do not tough the plate formed by the fusion of the processes of the sacral vertebrae. ''Kentrosaurus'' can be distinguished from other members of the [[Stegosauria]] by a number of processes of the vertebrae, which in the tail do not run sub-parallel, as in most dinosaurs. In the front third of the tail, they point backwards, the usual direction. In the middle tail, however, they are almost vertical, and further back they are hook-shaped and point obliquely forward. The [[Chevron (anatomy)|chevrons]], bones pointing to below from the bottom side of the tail vertebrae, have the shape of an inverted T.<ref name="MallisonRealLecto" /> 
[[File:KentrosaurusSacrum(HMNSt439).jpg|thumb|Sacrum of ''Kentrosaurus'' in ventral view.]]
The [[scapula]] (shoulder blade) is sub-rectangular, with a robust blade. Though it is not always perfectly preserved, the [[acromion]] ridge is slightly smaller than in ''Stegosaurus''. The blade is relatively straight, although it curves towards the back. There is a small bump on the back of the blade, that would have served as the base of the [[triceps]] muscle. The [[coracoid]] is sub-circular.<ref>{{Cite journal |last1=Maidment |first1=Susannah Catherine Rose |last2=Brassey |first2=Charlotte |last3=Barrett |first3=Paul Michael |date=2015-10-14 |title=The Postcranial Skeleton of an Exceptionally Complete Individual of the Plated Dinosaur Stegosaurus stenops (Dinosauria: Thyreophora) from the Upper Jurassic Morrison Formation of Wyoming, U.S.A. |journal=PLOS ONE |language=en |volume=10 |issue=10 |pages=e0138352 |doi=10.1371/journal.pone.0138352 |issn=1932-6203 |pmc=4605687 |pmid=26466098|bibcode=2015PLoSO..1038352M |doi-access=free }}</ref> The fore limbs were much shorter than the stocky hind limbs, which resulted in an unusual posture. The [[humerus]] (upper arm bone), like other stegosaurs, has greatly expanded proximal and distal ends that were attachment points between the coracoid and [[ulna]]-[[Radius (bone)|radius]] (forearm bones) respectively. The radius was larger than the ulna and had a wedge-shaped proximal end. The manus (hand) was small and had five toes with 2 toes bearing only a single phalange. The hindlimbs were much larger and too are similar to those of other stegosaurs. The [[femur]] (thigh bone) is the longest element in the body, with the largest known femur measuring 665&nbsp;mm from the proximal to distal end. The [[tibia]] (shin bone) was wide and robust, while the fibula was skinny and thin without a greatly expanded distal end. The [[Pes (anatomy)|pes]] (foot) terminated in 3 toes, all of which had hoof-like [[ungual]]s (claws).<ref name=":3">Hennig, E. (1925). Kentrurosaurus aethiopicus; die Stegosaurierfunde vom Tendaguru, Deutsch-Ostafrika. ''Palaeontographica-Supplementbände'', 101-254.</ref><ref>Galton, P. M. (1982). The postcranial anatomy of stegosaurian dinosaur Kentrosaurus from the Upper Jurassic of Tanzania, East Africa.</ref><ref name=":2" />

===Armour===
[[File:Kentrosaurus aethiopicus 01.jpg|thumb|left|Lectotype, partial individual from excavation 'St' at Kindope, Tendaguru, Tanzania]]
Typically for a stegosaur, ''Kentrosaurus'' had extensive [[osteoderm]] (bony structures in the skin) covering, including small plates (probably located on the neck and anterior trunk), and spikes of various shapes. The spikes of ''Kentrosaurus'' are very elongated, with one specimen having a bone core length of 731 millimetres.<ref name=MallCAE/> The plates have a thickened section in the middle, as if they were modified spines.<ref name=Galton2004/> The spikes and plates were likely covered by [[Horn (anatomy)|horn]]. Aside from a few exceptions they were not found in close association with other skeletal remains. Thus, the exact position of most [[osteoderms]] is uncertain. A pair of closely spaced spikes was found articulated with a tail tip, and a number of spikes were found apparently regularly spaced in pairs along the path of an articulated tail.<ref name=Hennig1925/>
[[File:Kentrosaurus thagomizer.JPG|thumb|[[Thagomizer]] at the Museum of Palaeontology of Tübingen]]
Hennig<ref name=Hennig1925/> and Janensch,<ref name=Janensch1925/> while grouping the dermal armour elements into four distinct types, recognised an apparently continuous change of shape among them, shorter and flatter plates at the front gradually merging into longer and more pointed spikes towards the rear, suggesting an uninterrupted distribution along the entire body, in fifteen pairs.<ref name=Galton2004/> Because each type of osteoderm was found in mirrored left and right versions, it seems probable that all types of osteoderms were distributed in two rows along the back of the animal, a marked contrast to the better-known North American ''Stegosaurus'', which had one row of plates on the neck, trunk and tail, and two rows of spikes on the tail tip. There is one type of spike that differs from all others in being strongly, and not only slightly, asymmetrical, and having a very broad base. Because of bone [[Morphology (biology)|morphology]] classic reconstructions placed it on the hips, at the iliac blade, while many recent reconstructions place it on the shoulder, because a similarly shaped spike is known to have existed on the shoulder in the Chinese stegosaurs ''[[Gigantspinosaurus]]'' and ''[[Huayangosaurus]]''.<ref name=Galton2004/>