Kentrosaurus: Difference between revisions

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>

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|alvelovialveoli]] on the dorsomedial side and it 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" />

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 [[Keel (anatomy)|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 very 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" />

The vast majority of stegosaurian dinosaurs thus far recovered belong to the [[Stegosauridae]], which lived in the later part of the Jurassic and early Cretaceous, and which were defined by [[Paul Sereno]] as all stegosaurians more closely related to ''Stegosaurus'' than to ''Huayangosaurus''.<ref>Sereno, P.C., 1998, "A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria", ''Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen'' '''210''': 41-83</ref> This group is widespread, with members across the Northern Hemisphere, [[Africa]] and possibly [[South America]].<ref name=":0">{{Cite journal |last1=Rauhut |first1=Oliver W. M. |last2=Carballido |first2=José Luis |last3=Pol |first3=Diego |date=2020-12-10 |title=First osteological record of a stegosaur (Dinosauria, Ornithischia) from the Upper Jurassic of South America |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1862133 |journal=Journal of Vertebrate Paleontology |language=en |volume=40 |issue=6 |pages=e1862133 |doi=10.1080/02724634.2020.1862133 |bibcode=2020JVPal..40E2133R |s2cid=234161169 |issn=0272-4634}}</ref> The South American remains come from [[Chubut Province|Chubut]], [[Argentina]] and consist only of a partial humerus, but the anatomy of the humerus is very similar to that of ''Kentrosaurus'' and both date to the Late Jurassic. In a phylogenetic analysis, the Chubut stegosaurid was recovered in polytomy with ''Kentrosaurus'' as basal stegosaurids, further suggesting that they are closely related.<ref name=":0" />

In Hennig's 1915 description, ''Kentrosaurus'' was assigned to the family [[Stegosauridae]] due to the preservation of dermal armor and features like posterodorsally angled neural spines on the caudal vertebrae.<ref name="Hennig1915" /> This is confirmed by modern [[cladistic]] analyses, although in 1915 Stegosauridae was a far more inclusive concept that included some taxa now classified as ankylosaurs. A consecutive narrowing down of this concept caused ''Kentrosaurus'', until the 1980s to be seen as a typical "primitive" stegosaurian,<ref name="Norman1985" /> to be placed in a more derived, higher, position in the stegosaur evolutionary tree. However, recent analyses have consistently found ''Kentrosaurus'' to be in Stegosauridae, though typically as one of the most basal genera in the family.<ref>{{Cite journal |last1=Hui |first1=Dai |last2=Ning |first2=Li |last3=Maidment |first3=Susannah C. R. |last4=Guangbiao |first4=Wei |last5=Yuxuan |first5=Zhou |last6=Xufeng |first6=Hu |last7=Qingyu |first7=Ma |last8=Xunqian |first8=Wang |last9=Haiqian |first9=Hu |last10=Guangzhao |first10=Peng |date=2022-03-30 |title=New stegosaurs from the Middle Jurassic Lower Member of the Shaximiao Formation of Chongqing, China |journal=Journal of Vertebrate Paleontology |volume=41 |issue=5 |pages=e1995737 |doi=10.1080/02724634.2021.1995737 |s2cid=247267743 |issn=0272-4634|doi-access=free }}</ref><ref name=":0" /><ref name=":1">{{Cite journal |last1=Raven |first1=Thomas J. |last2=Maidment |first2=Susannah C. R. |date=2017 |title=A new phylogeny of Stegosauria (Dinosauria, Ornithischia) |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12291 |journal=Palaeontology |language=en |volume=60 |issue=3 |pages=401–408 |doi=10.1111/pala.12291|bibcode=2017Palgy..60..401R |hdl=10044/1/45349 |s2cid=55613546 |hdl-access=free }}</ref> ''Kentrosaurus'' has many traits not seen in other stegosaurids but seen in basal stegosaurians, such as the presence of a parascapular spine and maxillary teeth with only seven denticles at the margin.<ref name="Galton1982" /><ref name="Galton1990" /> Cladogram of Stegosauria below that includes nearly every known stegosaur genus, recovering ''Kentrosaurus'' as a basal stegosaurid:<ref name=":1" />

|2=''[[Miragaia longicollum|Miragaia]]'' }} }}

As the plates and spikes would have been obstacles during copulation, it is possible that pairs mated back-to-back with the female staying still in a [[Lordosis behavior|lordosis posture]] as the male maneuvers his penis into her [[cloaca]]. The shoulder spikes would have made the female unable to lie on her side during mating as is proposed for ''Stegosaurus''.<ref>{{cite journal|author=Isles, T.|year=2009|title=The socio-sexual behaviour of extant archosaurs: Implications for understanding dinosaur behaviour|journal=Historical Biology|volume=21|issue=3–4|pages=139–214|doi=10.1080/08912960903450505|bibcode=2009HBio...21..139I |s2cid=85417112|url=http://doc.rero.ch/record/232923/files/PAL_E4545.pdf}}</ref>

===DefenceDefense===

<ref name=BardenMaidment2011>{{cite journal|author1=Barden, H.E. |author2=Maidment, S.C.R. |year=2011|title=Evidence for sexual dimorphism in the stegosaurian dinosaur ''Kentrosaurus aethiopicus'' from the Upper Jurassic of Tanzania|journal=Journal of Vertebrate Paleontology|volume=31|issue=3|pages=641–651|url=https://www.academia.edu/1477960|doi=10.1080/02724634.2011.557112|bibcode=2011JVPal..31..641B |s2cid=83521877}}</ref>

<ref name=Heinrich2001>{{cite journal|author=Heinrich, Wolf-Dieter|year=2001|title=The German‐TanzanianGerman-Tanzanian Tendaguru Expedition 2000|journal=Fossil Record|volume=4|issue=1|pages=223–237|doi=10.1002/mmng.20010040113|url=https://www.researchgate.net/publication/230461199|display-authors=etal|doi-access=free}}</ref>

<ref name=MallROM>{{cite journal|last=Mallison|first=H.|year=2010|title=CAD assessment of the posture and range of motion of ''Kentrosaurus aethiopicus'' HENNIG 1915|journal=[[Swiss Journal of Geosciences]]|volume=103|issue=2|pages=211–233|doi=10.1007/s00015-010-0024-2|s2cid=132746786|doi-access=free|bibcode=2010SwJG..103..211M }}</ref>

<ref name =Weishampel984>{{cite journal|author=Weishampel DB|year=1984|title=Interactions between Mesozoic Plants and Vertebrates: Fructifications and seed predation|journal=N. Jb. Geol. Paläontol. Abhandl.|pages=224–250|volume=167|issue=2 |doi=10.1127/njgpa/167/1984/224 }}</ref>

{{ThyreophoraStegosauria|S.}}