Kentrosaurus

Kentrosaurus; Temporal range: Late Jurassic PreЄ Є O S D C P T J K Pg N ↓
	A restoration of Kentrosaurus aethiopicus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	†Ornithischia
Suborder:	†Stegosauria
Family:	†Stegosauridae
Genus:	†Kentrosaurus; Hennig, 1915
Binomial name
	†Kentrosaurus aethiopicus; Hennig, 1915
Synonyms
	Doryphorosaurus Nopcsa, 1916; Kentrurosaurus Hennig, 1916;

Kentrosaurus (meaning prickle lizard) 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. The type species is K. aethiopicus. 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. The extra-long shoulder spikes protected it from side attacks.

Description[]

Kentrosaurus 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 4.5m (15ft). Slightly more than half of this length is made up by the tail. Larger single elements were found, so that the animal could probably attain a total length of 5.5m (18ft). 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.

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.

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. 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.

Armor[]

Kentrosaurus aethiopicus 01 — Lectotype, partial individual from excavation 'St' at Kindope, Tendaguru, Tanzania

The spikes and plates of Kentrosaurus were likely covered by 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.

File:Kentrosaurus thagomizer.jpg

Thagomizer at the Museum of Palaeontology of Tübingen

[2] Hennig[2] and Janensch,[1] 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 each type of osteoderm was found in two handed versions, it seems probably 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. Because of bone morphology classic reconstructions placed it on the hips, while many recent reconstructions place it on the shoulder, because a similarly shaped spike is known to have existed on the should in the Chinese stegosaur Gigantspinosaurus.

History[]

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. During four field seasons, the German Expedition found over 1200 bones of Kentrosaurus, many of which were destroyed during the Second World War. 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. 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.

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. However, all the supposedly lost cranial material was later found in a drawer of a basement cupboard. 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, has been suggested to belong to a North American species of Kentrosaurus. However, this notion has not found any support in the professional community.

Paleobiology[]

Kentrosaurus vs ceratosaurus — A Kentrosaurus fighting a Ceratosaurus with its tail

Like all ornithischians, Kentrosaurus was a herbivore. Only a single complete tooth was known when Hennig published his monography in 1925. Later, a part of a dentary was found, which bears a just emerging tooth, 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. It may also have been possible for Kentrosaurus to rear up on its hind legs to reach vegetation higher in trees. Because the tail had at least 40 caudal vertebrae, it was highly mobile. 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 for example theropod skulls, and significant harm when other body parts were hit.

Sexual dimorphism[]

Differences in the proportions, not the size, of the femurs (thighbones) led Holly Barden and Susannah Maidment to realize that Kentrosaurus probably showed sexual dimorphism. This dimorphism of the femurs consisted in them being either more or less robust than the other. The occurrence ratio of the robust morph to the gracile one was 2:1, and it is likely that the higher percentage of animals were females. Because of this ratio, it was considered reasonable to assume that in their society, Kentrosaurus males mated with more than one female, a behaviour also found in other vertebrates. The problem posed by the ratio is that the multiple specimens studied, died in the same place, but probably not in a sudden mass-death and so do not represent a single herd or contemporary population. The results may have been distorted by a greater chance for robust animals of getting fossilised or discovered. In an earlier study by Galton in 1982, it was suggested that individual difference in the sacral rib count of both Kentrosaurus and Dacentrurus might be an indication of dimorphism: females would have had an extra pair of sacral ribs, having also the first sacral vertebra connected to the ilium, in addition to the subsequent four sacrals.

Reproduction and growth[]

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 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. In 2013, a study by Ragna Redelstorff e.a. concluded that the bone histology of Kentrosaurus indicated that it had a higher growth rate than reported for Stegosaurus and Scutellosaurus, in view of the relatively rapid deposition of highly vascularised fibrolamellar bone. As Stegosaurus was larger than Kentrosaurus, this contradicts the general rule that larger dinosaurs grew quicker than smaller ones.

Defence[]

Because the tail had at least forty caudal vertebrae, it was highly mobile. It could possibly swing at an arc of 180 degrees, covering the entire half circle behind it. Swing speeds at the tail end may have been as high as 50 km/h. Continuous rapid swings would have allowed the spikes to slash open the skin of its attacker or to stab the soft tissues and break the ribs or facial bones. More directed blows would have resulted in the sides of the spikes fracturing even sturdy longbones of the legs by blunt trauma. These attacks would have crippled small and medium-sized theropods and may even have done some damage to large ones. Earlier interpretations of the defensive behaviour of Kentrosaurus included the suggestion that the animal might have charged to the rear, to run through attackers with its spines, in the way of modern porcupines.

Though Kentrosaurus likely stood with forelimbs erect like in other dinosaurs, it is hypothesised that the animal adopted a sprawling posture when defending itself. Its neck was flexible enough to allow it to keep sight of predators, as it could reach the sides of its body with its snout and look over the back. In addition, 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 pointed at the attacker. Kentrosaurus was nevertheless not invulnerable. A quick predator could have made it to the tail base (where the impact speed would be much lower) when the tail passed and the neck and upper-part of the body would have been unprotected by the tail swings. A successful predation of Kentrosaurus may have required group hunting. Compared to the more robust spikes of Stegosaurus, the thinner spikes of Kentrosaurus were at greater risk of bending.

Kentrosaurus3 — Jurassic Park Operation Genesis Kentrosaurus

In the media[]

Kentrosaurus appears in Jurassic Park: Operation Genesis as a 2-stars dinosaur which can be found on the Tengaduru Beds.
Kentrosaurus also appears in Dinosaur King, with the Earth attribute alongside other stegosaurs. Despite being a popular dinosaur, it did not appear in the anime.
Kentrosaurus appears in the movie Ice Age: Dawn of the Dinosaurs and the video game adaption.
Kentrosaurus made its debut in the Jurassic Park franchise canon in the fourth season of Jurassic World: Camp Cretaceous, where an individual named Pierce is subject to experiments on Mantah Corp Island. The dinosaur was later free from experiments alongside the rest of the dinosaurs.
Kentrosaurus appears in Jurassic World: The Game, where it is a legendary tournament herbivore.
Kentrosaurus made an appearance in Jurassic World: Evolution and its sequel as well as Jurassic World: Alive.
Kentrosaurus is one of the many prehistoric creatures that appeared in ARK: Survival Evolved.
Kentrosaurus appeared on Dinosaur Train.
Kentrosaurus appears in the game Parkasaurus.
Kentrosaurus appears in the third season of Dino Dan (or Dino Dana) as a rival to its cousin Stegosaurus.
Kentrosaurus appears in Prior Extinction.