Kentrosaurus

Kentrosaurus Temporal range: Late Jurassic, 156–151 Ma PreЄ Є O S D C P T J K Pg N ↓
Mounted skeleton in Museum für Naturkunde, Berlin
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Ornithischia
Suborder:	Thyreophora
Infraorder:	Stegosauria
Family:	Stegosauridae
Genus:	Kentrosaurus Hennig, 1915
Species
K. aethiopicus Hennig, 1915 (type)
Synonyms
Doryphorosaurus Nopcsa, 1916 Kentrurosaurus Hennig, 1916

Kentrosaurus is a genus of stegosaurid dinosaur from the Late Jurassic of Tanzania. Its fossils have been found only in the Tendaguru Formation of Tanzania, dated to the Kimmeridgian stage, between about 155.7 ± 4 Ma and 150.8 ± 4 Ma (million years ago). Apparently, all finds belong to one species, K. aethiopicus Hennig 1915.

Kentrosaurus was described by German palaeontologist Edwin Hennig in 1915. Often thought to be a primitive member of the Stegosauria, several recent cladistic analyses find it to be derived, and a close relative to Stegosaurus from the North American Morrison Formation.

Kentrosaurus generally measured around 4.5 metres (15 ft) in length as an adult, probably had a double row of small plates and spikes running down its back, and could use its tail as a "thagomizer" for defense.

Description

Body size and posture

Restoration of Kentrosaurus aethiopicus

Size compared to a human.

Kentrosaurus aethiopicus was a small stegosaur, smaller than Stegosaurus armatus, Hesperosaurus mjosi, Dacentrurus armatus and Tuojiangosaurus multispinus, and about as large as Huayangosaurus taibaii. The total length of a composite skeletal mount in the Museum für Naturkunde Berlin, Germany, from the tip of the snout to the tip of the tail is 4.5 m (15 ft). Slightly more than half of this length is made up by the tail.^[1] Larger single elements were found,^[2] so that the animal could probably attain a total length of 5.5 m (18 ft).

The long tail of Kentrosaurus results in a position of the center of mass that is unusually far back for a quadrupedal animal. It rests just in front of the hip, a position usually seen in bipedal dinosaurs. However, the femora are straight in Kentrosaurus, as opposed to typical bipeds, indicating a straight and vertical limb position. Thus, the hind feet did not support the animal alone, and the fore feet took up 10 to 15% of the bodyweight. The posterior position of the center of mass may not have been advantageous for rapid locomotion, but meant that the animal could quickly rotate around the hips by pushing sideways with the arms, keeping the tail pointing at threats.

Autapomorphies

Kentrosaurus can be distinguished from other members of the Stegosauria by a number of osteological characters. Most notably, the neural spines in the tail are not sub-parallel, as in most dinosaurs. In the anterior 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 forward. Also typical are, among other features, that the dorsal vertebrae have a neural arch more than twice as high as the centrum, and completely occupied by the extremely spacious neural canal. The preacetabular process of the ilium widens laterally, and does not taper.

Armor

Mounted skeleton

The elements of the dermal armour of Kentrosaurus were, aside from a few exceptions, 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.^[2] Hennig and Janensch, while grouping the dermal armour elements into four distinct types, recognized an apparently continuous change of shape among them, suggesting an uninterrupted distribution along the entire body. Because all elements were found in two symmetrical forms, the dermal armour appears to have been placed in at least two parallel rows, although an altenating placement is theoretically possible.

Discovery and species

Kentrosaurus aethiopicus skeletal mount (lectotype and paralectotpyes) at the Museum für Naturkunde Berlin, Germany. This version of the mount was erected in 1925 and taken down in 2006. Since 2007 a new version with a slightly altered posture is on exhibit.

The first fossils of Kentrosaurus were discovered by the German Tendaguru Expedition in 1909, recognized as belonging to a stegosaur by expedition leader Werner Janensch on 24 July 1910, and described by German palaeontologist Edwin Hennig in 1915.^[3] During four field seasons, the German Expedition found over 1200 bones of Kentrosaurus,^[2] many of which were destroyed during the Second World War.^[4] Today, almost all remaining material is housed in the Museum für Naturkunde Berlin (roughly 350 remaining specimens), while the museum of the Institute for Geosciences of the Eberhard-Karls-University Tübingen houses a composite mount, roughly 50% of it being original bones.^[5] Although no complete individuals were found, some material was found in association, including a nearly complete tail, hip, several dorsal vertebrae and some limb elements of one individual. These form the core of a mount in the Museum für Naturkunde by Janensch.^[1] The mount was dismantled during the museum renovation in 2006/2007, and re-mounted in an improved pose by Research Casting International. Some other material, including a braincase and spine, was thought to have been misplaced or destroyed during World War II.^[6] However, all the supposedly lost cranial material was later found in a drawer of a basement cupboard.^[7] The British Tendaguru Expedition also found material, but it is unclear how much, in what state of preservation, and where it is today. The type and sole species of Kentrosaurus is K. aethiopicus. Fragmentary fossil material from Wyoming, named Stegosaurus longispinus by Charles Gilmore in 1914,^[8] has been suggested to belong to a North American species of Kentrosaurus. However, this notion has not found any support in the professional community.

Etymology

When Hennig named his new stegosaur, he chose to highlight the extensive dermal armour in the generic name. From the Greek kentron/κεντρον, meaning "point" or "prickle", and sauros/σαυρος meaning "lizard",^[9] Hennig created Kentrosaurus ( /ˌkɛtrɵˈsɔrəs/ ken-tro-sawr-əs), adding the species name aethiopicus to denote the provenance.

Naming controversy

Kentrosaurus was described by Edwin Hennig in 1915,^[3] but soon after its description, a controversy arose over its name, which is very similar to the ceratopsian dinosaur Centrosaurus. Under the rules of biological nomenclature, two animals may not be given the same name. Hennig renamed his stegosaur Kentrurosaurus,^[10] while Hungarian paleontologist Franz Nopcsa renamed the genus Doryphorosaurus.^[11] If a renaming had been necessary, Hennig's would have had priority.^[12] However, because both the spellings are different (Centrosaurus is pronounced with a soft C), both Doryphorosaurus and Kentrurosaurus are unneeded replacement names; Kentrosaurus remains the valid name for the genus.

Type specimens and type locality

In the original description, Hennig did not define a holotype specimen. However, in a detailed monography on the osteology, systematic position and palaeobiology of Kentrosaurus in 1925, Hennig picked the most complete partial skeleton as a lectotype (see syntype).^[2] This material includes a nearly complete series of tail vertebrae, several vertebrae of the back, a sacrum with five sacral vertebrae and both ilia, both femora and an ulna, and is included in the mounted skeleton at the Museum für Naturkunde in Berlin, Germany. The type locality is Kindope, Tanzania, near the Tendaguru hill. Unaware that Hennig had already defined a lectotype, Peter Galton^[13] selected two dorsal vertebrae from the material figured in Hennig's 1915 description as 'holotypes'. This definition of a holotype is not valid, because Hennig's selection has priority.^[5]

Paleobiology

Dentition and diet

Close up of skull and neck

Like all ornithischians, Kentrosaurus was a herbivore. Only a single complete tooth was known when Hennig published his monography in 1925.^[2] Later, a part of a dentary was found, which bears a just emerging tooth,^[14] and some tooth fragments were recovered from matrix sticking to other bones. The dentary is almost identical in shape to that of Stegosaurus, albeit much smaller. Similarly, the tooth is a typical stegosaurian tooth, with a widened base and vertical grooves creating five ridges. It indicates a herbivorous diet. The fodder was barely chewed and swallowed in large chunks. One theory on stegosaurid diet holds that they were low-level browsers, eating foliage and low-growing fruit from various non-flowering plants.^[15] It may also have been possible for Kentrosaurus to rear up on its hind legs to reach vegetation higher in trees.

Defense

Because the tail had at least 40 caudal vertebrae,^[2] it was highly mobile.^[16] Probably, it could flex as much as the tails of modern crocodiles, which are almost able to touch the tips of their tails to the body side. This made the tail a dangerous weapon, able to cover a large arc when swinging quickly. Swing speeds may have been as high as 50 km/h, causing lethal strikes against e.g. theropod skulls, and significant harm when other body parts were hit.^[17]

References

1. ^ ^{a b} Janensch, W. (1925). "Ein aufgestelltes Skelett des Stegosauriers Kentrurosaurus aethiopicus HENNIG 1915 aus den Tendaguru-Schichten Deutsch-Ostafrikas." ("A mounted skeleton of the Stegosaur Kentrurosaurus aethiopicus HENNIG 1915 from the Tendaguru layers of German East Africa.") Palaeontographica Supplement 7:257-276.[German]
2. ^ ^{a b c d e f} Hennig, E. (1925). "Kentrurosaurus aethiopicus. Die Stegosaurier-Funde vom Tendaguru, Deutsch-Ostafrika." ("Kentrurosaurus aethiopicus. The Stegosaur find from Tendaguru, German East-Africa") Palaeontographica Supplement 7:101-254German
3. ^ ^{a b} Hennig, E. (1915). "Kentrosaurus aethiopicus, der Stegosauride des Tendaguru." ("Kentrosaurus aethiopicus, the stegosaur of Tendaguru") Sitzungsberichte der Gesellschaft naturforschender Freunde zu Berlin 1915:219-247 German
4. ^ Maier, G. African Dinosaurs Unearthed. The Tendaguru Expeditions. Indiana University Press, Bloomington, Indiana.
5. ^ ^{a b} Mallison, H. (2011). "The real lectotype of Kentrosaurus aethiopicus HENNIG 1915". Neues Jahrbuch für Geologie und Paläontologie 259(2):197-206
6. ^ Glut, Donald F. (1997). "Kentrosaurus". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. pp. 516–519. ISBN 0-89950-917-7. 
7. ^ Galton, P.M. (1988). "Skull bones and endocranial casts of stegosaurian dinosaur Kentrosaurus HENNIG, 1915 from Upper Jurassic of Tanzania, East Africa". Geologica et Palaeontologica 22:123-143.
8. ^ Gilmore, C.W. (1914). "Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus Stegosaurus". United States National Museum Bulletin 89:1–136
9. ^ Liddell, Henry George and Robert Scott (1980). A Greek-English Lexicon (Abridged Edition). United Kingdom: Oxford University Press. ISBN 0-19-910207-4. 
10. ^ Hennig, E. (1916). "Zweite Mitteilung über den Stegosauriden vom Tendaguru" ("Second report on the stegosaurid of Tendaguru"). Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin 1916(6):175–182 German
11. ^ Nopcsa, F. (1915). "Die Dinosaurier der Siebenbürgischen Landesteile Ungarns." ("The dinosaurs of the Siebenbürgen part of the Hungarian Empire"). Mitteilungen aus dem Jahrbuche der Königlich Ungarischen Geologischen Reichsanstalt 23:1–26 German
12. ^ Hennig, E. (1916). "Kentrurosaurus, non Dorypphorosaurus. Centralblatt für Mineralogie, Geologie und Paläontologie, Stuttgart 1916:578. German
13. ^ Galton, P.M. (1982). "The postcranial anatomy of stegosaurian dinosaur Kentrosaurus from the Upper Jurassic of Tanzania, East Africa". Geologica et Palaeontologica 15:139-165
14. ^ Hennig, E. (1936). "Ein Dentale von Kentrurosaurus aethiopicus HENNIG" ("A dentary of Kentrurosaurus aethiopcius HENNIG"). Palaeontographica Supplement 7 Part II':311-312 German
15. ^ Weishampel DB (1984). "Interactions between Mesozoic Plants and Vertebrates: Fructifications and seed predation". N. Jb. Geol. Paläontol. Abhandl. 167: 224–250. 
16. ^ Mallison, H. (2010). "CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus HENNIG 1915" Swiss Journal of Geosciences online first: [1]
17. ^ Mallison, H. (subm.). "Defense capabilities of Kentrosaurus aethiopicus HENNIG 1915. Palaeontologia Electronica

External links

Dinosaurs portal

• Kentrosaurus in The Dinosaur Encyclopaedia at Dino Russ's Lair
• Stegosauria from Thescelosaurus.com (Includes details on Kentrosaurus, its junior synonyms, and other material)
• Kentrosaurus from DinoData.org