Kentrosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Stegosauridae

Genus:Kentrosaurus

Species:Kentrosaurus aethiopicus

Introduction

Kentrosaurus is considered the African cousin of the famous North American dinosaur Stegosaurus. It is characterized by its sharp spines along its back and tail. Some scientists believe that there were additional spikes at the top of either the fore or the hind leg.

In the Triassic period (between 251 and 201 million years ago), there existed a supercontinent called Pangaea. Within this supercontinent, animals were able to move from one area to another, populating various regions. Over a period of approximately 100 million years, during the Late Triassic period and the Jurassic period, the land mass began to break into northern and southern landmasses, named Laurasia and Gondwana, respectively. During the Late Jurassic, further division occurred between east and west. Four distinct biogeographic provinces began to develop: West Laurasia (North America), West Gondwana (Africa and South America), Central Laurasia (Europe), and East Laurasia (Asia), plus East Gondwana (Antarctica, Madagascar, India, and Australia).

While many dinosaurs have the same parent group, diversity within the separated biogeographic provinces developed over time, resulting in species variation within geographic areas. For instance, Stegosaurus of West Laurasia and Kentrosaurus of West Gondwana are generally similar in appearance, yet vary considerably in size, structure, and armor. These differences in dinosaurs within the same family, along with other geologic evidence, have helped paleontologists understand the original composition of the supercontinent Pangaea and how the continents divided and shifted to look as they do today.

Classification

Scientists often disagree as to the most accurate method of classifying living organisms, including dinosaurs. The traditional classification method is Linnaean taxonomy, a rank-based system that separates living things into different hierarchical categories based on shared traits. Dinosaurs have long been divided into two orders based on pelvic structure—Ornithischia (bird-hipped) and Saurischia (lizard-hipped)—and although in the twenty-first century some researchers began to challenge that longstanding distinction, it remained in wide use. Kentrosaurus is placed in the Ornithischian order and the suborder Thyreophora, defined by the presence of armored body plates or body spikes. In the Linnaean system, Kentrosaurus is further classified in the Stegosauridae family, containing dinosaurs related to the famous Stegosaurus. Only one species, Kentrosaurus aethiopicus, has been described in the genus.

Cladistic or phylogenetic classification is an alternate system that paleontologists use to classify dinosaurs according to their common ancestry and shared physical characteristics. In a cladistic analysis, Kentrosaurus falls under the larger Thyreophora group (or clade) of armored dinosaurs, and then under the subgroup Stegosauria, as it featured rows of plates and spikes. Close relatives of Kentrosaurus include Lexovisaurus and Tuojiangosaurus, as both had double rows of boney plates along their neck to midsection and double rows of spikes from their midsection to tail.

The cladistics method of classification seeks to draw relationships between species. Considered a somewhat fluid system, discoveries can often cause differences in opinion between paleontologists based on how they read the data. However, cladistics helps scientists to understand the similarities and differences between and among species, as well as to develop theories about how different species evolved.

Anatomy

Although it shared traits with similarly classed dinosaurs, Kentrosaurus was unique in that its pairs of spikes, as many as seven, extended from its tail through the middle portion of its back. From the mid-back to its neck were pairs of boney plates. A pair of spikes was also positioned on either the dinosaur's hip or shoulder region, with one spike on either side. (There is still some debate surrounding the arrangement of the dinosaur's dermal armor.) Two large, sharp spikes on the tail (50–60 cm/2 ft long) were likely used for defensive purposes. Because of the large number of vertebrae, it is also believed that Kentrosaurus would have been highly flexible, allowing for a powerful lateral swing of its tail to ward off an attack. In addition to protection, it is believed that the spikes also served to help regulate body temperature and perhaps to attract mates.

The front legs of Kentrosaurus were shorter and less powerful than the hind legs. All four legs had hoof-like claws on the toes. It is believed that the hind legs could have allowed the animal to stand up for short periods of time to reach high vegetation.

Intelligence

Kentrosaurus had an elongated, small head and brain, suggesting a low level of intelligence. Although the actual size of its brain in cubic centimeters has not been determined, it is estimated to have been around the size of a walnut.

Scientists can estimate animal intelligence using the encephalization quotient (EQ). An animal's brain and body size are compared and given a value; most dinosaurs fall between 0.1 and 5.8 on this scale. A higher number reflects a higher level of intelligence. Creatures in the Stegosauria branch, which includes Kentrosaurus, have been charted at 0.6, on the lower end of the EQ scale. Despite this low intelligence rating, the creature's olfactory ability, or sense of smell, was well developed. This characteristic likely helped the dinosaur find edible vegetation and avoid predators.

Reproduction and Population

Fossil evidence offers little information regarding population numbers, gender differences, and mating and reproduction for Kentrosaurus. Paleontologists have analyzed dinosaur hip anatomy and have concluded that females, regardless of species, tended to have a wider frame for producing and hatching eggs. As such, it is likely that the female Kentrosaurus had a wider hip structure than the male. Some fossils have been interpreted as potential evidence of particularly distinct sexual dimorphism in Kentrosaurus.

Other evidence indicates that most dinosaurs, including the Kentrosaurus, were oviparous, meaning that they laid eggs (normally several eggs at a time). Some dinosaurs laid their eggs in nests that were eventually abandoned, leaving the eggs vulnerable to predators. Some species’ nests and eggs were safely hidden or buried, while fossil evidence proves that other species’ eggs were covered and kept warm by both mother and father. Scientists assume that Kentrosaurus was oviparous, though fossils proving this assumption have not been found. Scientists also have applied more detailed findings from other similar creatures in the same class to make assumptions about the reproductive system and nesting behavior of the Kentrosaurus. Until fossil evidence is found, these assumptions will provide some foundation for our understanding of the Kentrosaurus.

Diet

Climate conditions in Africa during the Jurassic period were somewhat tropical, with warm temperatures and occasional droughts. Low-lying forest areas provided a plant diet of cycads, mosses, and fern leaves. Kentrosaurus's long and narrow head was low to the ground and perfectly suited for this diet. It had a small head with a toothless beak and small teeth in its cheeks. The front beak probably pulled and tore plant matter, while the side and rear teeth did the grinding and chewing. The dinosaur's spikes and plates offered it protection from predators while it ate low-lying vegetation.

Because this dinosaur weighed approximately two tons, it needed to spend the majority of each day seeking and ingesting food. Plant materials are low in calories, so more of this type of food would have been needed to sustain such a large creature.

Behavior

Because of its size, Kentrosaurus walked slowly. There is some evidence that Kentrosaurus was a herding animal (although this has been questioned by some scientists). Herding dinosaurs were docile and nonaggressive compared to the solitary carnivores that lived in the same environment. Travelling together protected the group as a whole, especially the young.

Paleontologists have found the bones of dinosaurs of various sizes alongside Kentrosaurus fossils. These findings have led to assumptions that dinosaurs like Brachiosaurus, Tendaguria, and Diplodocus may have travelled in herds with Kentrosaurus. These types of dinosaurs were giant sauropods. They had long necks and tails and feasted on the vegetation of the North American and African forests.

Habitat and Other Life Forms

The habitat of the Late Jurassic period was characterized by lush jungles of gymnosperms (non-flowering, seed-bearing plants). Some relatives of these plants are still in abundance today. For the Kentrosaurus, though, low-lying vegetation would have been the major source of its diet.

Many dinosaurs populated the earth during the Jurassic period in what is now East Africa. Some examples include Allosaurus, Ceratosaurus, Janenschia, and Tendaguria. Scientists believe that in the Late Jurassic period, many of the largest dinosaurs, the sauropods, began to both flourish and diversify. Additionally, the Late Jurassic period was characterized by diversification within genera. For instance, dinosaurs unique to West Gondwana included Dicraeosaurus, Torniera, and Elaphrosaurus.

Ceratosaurus and Allosaurus may have been predators of Kentrosaurus, though any predator would have had a difficult time attacking the spiked dinosaur. Its long tail with double rows of spikes could lash out when threats arose. The single spikes on the hips or shoulders of the dinosaur offered added protection from lateral attacks.

Research

German paleontologists discovered the first Kentrosaurus fossil during expeditions in Africa in the early 1900s. Edwin Henning was part of that expedition and is credited with first describing Kentrosaurus in 1915. A reconstruction of the Kentrosaurus fossils was mounted in the Humboldt Museum at the University of Berlin until it was destroyed during World War II.

In that same area of Tendaguru Hill, Tanzania, paleontologists unearthed Brachiosaurus brancai, one of the largest dinosaurs that ever lived. Fossils of the very similar species Brachiosaurus altithorax have been found in the western United States, providing further evidence for the theory of a prehistoric supercontinent (Pangaea).

Scientists continue to debate whether dinosaurs were warm- or cold-blooded creatures. The evolutionary link with reptiles suggests that dinosaurs were ectothermic, relying on external sources to regulate their relatively cold body temperature. However, evidence exists proving some dinosaurs had feathers, which may have provided insulation. This would suggest that at least some dinosaurs were endothermic, or warm-blooded.

Research on Kentrosaurus specifically continued into the twenty-first century. One study published in 2013 suggested that Kentrosaurus grew faster than Stegosaurus and other larger relatives. Classification efforts have also increasingly recognized Kentrosaurus as a relatively basal member of the Stegosauridae family or clade.

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