Often thought to be a "primitive" member of the Stegosauria, several recent cladistic analyses find it as more derived than many other stegosaurs, and a close relative of Stegosaurus from the North American Morrison Formation within the Stegosauridae.

Fossils of K. aethiopicus have been found only in the Tendaguru Formation, dated to the late Kimmeridgian and early Tithonian ages, about 152 million years ago.

In the Tendaguru Formation, it coexisted with a variety of dinosaurs such as the carnivorous theropods Elaphrosaurus and Veterupristisaurus, giant herbivorous sauropods Giraffatitan and Tornieria, and the dryosaurid Dysalotosaurus.

[12] During four field seasons, the German Expedition found over 1200 bones of Kentrosaurus, belonging to about fifty individuals,[13] many of which were destroyed during the Second World War.

However, in a detailed monography on the osteology, systematic position and palaeobiology of Kentrosaurus in 1925, Hennig picked the most complete partial skeleton, today inventorised as MB.R.4800.1 through MB.R.4800.37, as a lectotype (see syntype).

In 2011, Heinrich Mallison clarified that all the material known to Hennig in 1915, i.e. all the bones discovered before 1912, when Hermann Heck concluded the last German excavations, are paralectotypes, and that MB.R.4800 is the correct lectotype.

Typical 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.

Thus, the hindlimbs, though powered by massive thigh muscles attached to a long ilium, did not support the animal alone, and the very robust forelimbs took up 10 to 15% of the bodyweight.

[9] The center of mass was not heavily modified by the osteoderms (bony structures in skin) in Kentrosaurus or Stegosaurus, which allowed the animals to stay mobile despite their armament.

It had a small antorbital fenestra, the hole between the nose and eye common to most archosaurs, including modern birds, though lost in extant crocodylians.

[24] The frontals and parietals are flat and broad, with the latter bearing two transversely concave ventral sides with a ridge running down the middle that divides them.

Basioccipitals (where the skull articulated with the cervical vertebrae) form the posterior floor of the brain and the occipital condyle, which is large and spherical in Kentrosaurus.

However, the occipital condyle is a closer distance to the basisphenoid tubera (bone at the front of the braincase) in Kentrosaurus and Huayangosaurus than in Tuojiangosaurus and some specimens of Stegosaurus.

The brain is relatively short, deep, and small, with a strong cerebral and pontine flexures and a steeply inclined posterodorsal edge when compared to those of other ornithischians.

The spinous processes got larger towards the posterior end, while the postzygapophyses became smaller and less horizontal, giving the anterior part of the neck lots of mobility laterally.

[15][32][24] 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.

[13] Hennig[13] and Janensch,[8] 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.

[33] Like the spikes and shields of ankylosaurs, the bony plates and spines of stegosaurians evolved from the low-keeled osteoderms characteristic of basal thyreophorans.

[37] 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.

A consecutive narrowing down of this concept caused Kentrosaurus, until the 1980s to be seen as a typical "primitive" stegosaurian,[38] to be placed in a more derived, higher, position in the stegosaur evolutionary tree.

Fragmentary fossil material from Wyoming, named Stegosaurus longispinus by Charles Gilmore in 1914,[42] was in 1993 classified as a North American species of Kentrosaurus, as K.

[43] However, this action was not accepted by the paleontological community, and S. longispinus has been assigned to its own genus, Alcovasaurus, differing from Kentrosaurus in having more elongated tail spikes and the structure of the pelvis and vertebrae.

[9] 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.

[48] 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.

[48] 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.

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.

[20] 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.

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.

[54] Kentrosaurus would have coexisted with fellow ornithischians like Dysalotosaurus lettowvorbecki; the sauropods Giraffatitan brancai, Dicraeosaurus hansemanni and D. sattleri, Janenschia africana, Tendaguria tanzaniensis and Tornieria africanus; theropods "Allosaurus" tendagurensis, "Ceratosaurus" roechlingi, "Torvosaurus" ingens, Elaphrosaurus bambergi, Veterupristisaurus milneri and Ostafrikasaurus crassiserratus; and the pterosaur Tendaguripterus recki.

[55][56][57][58] Other organisms that inhabited the Tendaguru included corals, echinoderms, cephalopods, bivalves, gastropods, decapods, sharks, neopterygian fish, crocodilians and small mammals like Brancatherulum tendagurensis.