Kentrosaurus

Kentrosaurus is a stegosaurian genus, which occurred in Africa during the Late Jurassic. The type species, Kentrosaurus aethiopicus was discovered by the German Tendaguru Expedition in 1909, and it was described by Edward Hennig in 1915[1], and up to now this is the only one scientifically accepted species of the genus. Unfortunately, a large part of its fossils were lost during World War II. The meaning of the name Kentrosaurus is ”sharp-pointed lizard”. The waste majority of fossil Kentrosaurus remains are stored in the Museum für Naturkunde Berlin, and there is also a specimen exhibited in the Institute for Geosciences of the University of Tübingen, which is constructed from original bones and composite elements. Kentrosaurus is a close relative of the North-American Stegosaurus. Its only known locality is the Tendaguru Formation in Tanzania, which is approximately 152 million years old. The Late Jurassic Tendaguru ecosistem consisted of shallow marine lagoons, low coastal regions and vegetated inland environments, where coniferous trees were predominant. This ecosystem had a climate subtropical to tropical, with dry and rainy periods[2].

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Known occurrences of Kentrosaurus fossils.

Description and anatomy

Kentrosaurus was smaller than its North-American relative Stegosaurus - the length of an adult was around 4.5 meters, and it weighed about 1–1.5 tonnes. These herbivorous dinosaurs walked on four legs, had a small and elongated head, and a long tail. Just like all other stegosaurs, Kentrosaurus had extensive bony structures in the skin (osteoderm), covering a variety of plates and spikes. These dinosaurs beared a double row of small, concave plates from their head to the mid of the back, from where they turned into spikes towards the end of the tail, and there was one further spike above each shoulder. These long spikes on the tail played an important role in the defence agains predators. Probably the plates and spines were originally covered by horn, so they were even bigger and more spectacular when these animals have been living.

Important distinguishing features between Kentrosaurus and other members of Stegosauria are a number of extensions on the vertebrae, which do not run sub-parallel in case of the tail like in most of the dinosaurs. While they are positioned backwards in the front third of the tail, which is the usual direction, they are nearly vertical in the middle, and in the last third they point slantwise forward and are hook-shaped. The neural arch of dorsal vertebrae is positioned somewhat more than twice as high as the center, the vertebral body, and it is almost completely filled by the neural canal[3].


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Kentrosaurus, in size comparison with a human. Source: By Dinosaur Zoo - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15709796

Paleobiology

Kentrosaurus was herbivorous, and used its beak to bite off leafs and other parts of plants, then scantily scewed the plant material with its typical stegosaurid teeth. Kentrosaurus usually browsed the low-level foliages and low-growing plants and fruits, but it might be also capable of rear up on its hind-limbs in order to reach higher for leafs, buds and fruits[4]. The main defense tool of Kentrosaurus was its highly mobile tail, which probably could sway at an arc of 180 degrees, and the speed of these movements could even reach 50 km/h, causing very serious bone or soft tissue injuries for the attackers[5]. It is supposed that this dinosaur positioned its forelegs into sprawling pose, and due to the relatively posterior position of center of the body mass, the animal could fast turn around its hips by using the forelegs. This allowed the Kentrosaurus to keep its tail pointed at the predator, additionally, its neck was long and flexible enough to keep the animals sight on the attacker. However, the anterior part of the body was much less protected, and predators which hunted in packs definitely meant a serious threat for these dinosaurs[6]. Some paleontological evidences show that Kentrosaurus likely showed some degree of sexual dimorphism, and it is hypothesised that there were fewer males than females, which allowed to males to mate with several females[7]. As the spines and plates might have caused serious difficulties during the copulation process, it is likely that the male and the female mated in a back-to-back position.

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Kentrosaurus skeleton. Source: By Etemenanki3 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=72404325


Scientific references

[1] Hennig, E. (1915): Kentrosaurus aethiopicus, der Stegosauride des Tendaguru [Kentrosaurus aethiopicus, the stegosaur of the Tendaguru]". Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin. 1915: 219–247.

[2] Aberhan, M.; Bussert, R.; Heinrich, Wolf-Dieter; Schrank, E.; Schultka, S.; Sames, B; Kriwet, J.; Kapilima, S. (2002): Palaeoecology and depositional environments of the Tendaguru Beds (Late Jurassic to Early Cretaceous, Tanzania). Fossil Record. 5 (1): 19–44. doi:10.1002/mmng.20020050103

[3] Mallison, H. (2011): The real lectotype of Kentrosaurus aethiopicus HENNIG 1915. Neues Jahrbuch für Geologie und Paläontologie. 259 (2): 197–206. doi:10.1127/0077-7749/2011/0114

[4] Weishampel, D.B. (1984): Interactions between Mesozoic Plants and Vertebrates: Fructifications and seed predation. N. Jb. Geol. Paläontol. Abhandl. 167: 224–250.

[5] Mallison, H. (2011): Defense capabilities of Kentrosaurus aethiopicus HENNIG 1915. Palaeontologia Electronica. 14 (2): 10.

[6] Mallison, H. (2010): CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus HENNIG 1915. Swiss Journal of Geosciences. 103 (2): 211–233. doi:10.1007/s00015-010-0024-2.

[7] Barden, H.E. & Maidment, S.C.R. (2011): Evidence for sexual dimorphism in the stegosaurian dinosaur Kentrosaurus aethiopicus from the Upper Jurassic of Tanzania. Journal of Vertebrate Paleontology. 31 (3): 641–651. doi:10.1080/02724634.2011.557112.