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Scientific Classification
Kingdom: Animalia
Phylum: Chordata
SuperOrder: Dinosauria
Order: Ornithischia
Family: Ceratopsidae
Genus: Monoclonius
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The Monoclonius was ceratopsian dinosaur that walked the earth in the late Cretaceous period. The ceratopsids were distinguished by their large skull frills. One of the most well-known dinosaurs of this group is the Triceratops, but it belonged to a different subfamily as compared to the Monoclonius. The timeline of its existence is placed at 79 to 73 million years ago. This lies in the Campanian age of the Cretaceous.
The validity if the Monoclonius as a separate genus is questioned by many scientists. It bears a striking resemblance to the Centrosaurus and some paleontologists believe that the fossils ascribed to the Monoclonius could belong to a juvenile Centrosaurus. And the Monoclonius was discovered at such a time when family Ceratopsidae was not defined. Due to this, the genus has been used as a ‘wastebasket’ group where all similar looking fossils were classified. Hence, sorting out the mess and properly defining it had been difficult.

The size of this dinosaur was intermediately large. Its length was about 5 meters and it weighed a little above 2 tons. These dimensions are only slightly smaller as compared to the Centrosaurus, which reinforces the theory that it could have been a sub-adult. It was herbivorous and had a rectangular frill with small spokes on it.


The Monoclonius was named by Edward Drinker Cope, one of the two participants of the infamous Bone Wars. In fact he found its fossils while trying to best O. C. Marsh.

The name Monoclonius has two parts, ‘mono’ which means ‘one’ and ‘klonion’ which is the Greek word for ‘shoot’ or ‘sprout’. Thus, the name means ‘a single shoot’. This was in contrast to another dinosaur describe by Cope, the Diclonius. The former had only one row of teeth at a given point of its life, and the latter grew permanent teeth before the temporary set fell off. For a long time, the name Monoclonius was thought to mean ‘single horn’, due to the prominent nasal boss that this dinosaur showed; but this isn’t so.

The specific name M. crassus has Latin origins. ‘Crassus’ translates to ‘thick’ or ‘fat’ in English. This alluded to the expanded skull of the Monoclonius and its stocky build. The genus was named and defined in the year 1876.

Discovery of fossils

  • The holotype of the Monoclonius was discovered by Edward Drinker Cope in 1876 near the Judith River in Montana, in the Chouteau County area. He was assisted by Charles Sternberg.


  • A single, articulated skeleton was not discovered, but various bones were found from different locations at that time. Most of the skull, axial and appendicular were found in Montana; only the feet were missing. Cope hurriedly described these remains in the same year, and believed frills to be part of the sternum.


  • Sternberg had discovered another set of remains from the Cow Island in Missouri in the same year. This specimen was named the M. sphenocerus, based on the structure of the nasal horn.


  • A few bones have also been excavated from the Dinosaur Provincial Park of Canada that may be ascribed to the Monoclonius. They were found by Charles M. Sternberg and he named them the M. lowei.


When E. D. Cope had first examined the remains of the Monoclonius, he had thought it to be a hadrosaurid dinosaur. He misinterpreted much of the frills and the skull projections as a complete skeleton was never found by him. But in 1989, O. C. Marsh described the Triceratops and when Cope saw this dinosaur, he reevaluated the Monoclonius.

Cope then classified the Monoclonius and the Agathaumus, a dinosaur grouped as a hadrosaur by him earlier, with the Triceratops in family Ceratopsidae.

He also named various subspecies of the Monoclonius, the M. recurvicornis and the M. fissus from the bones he had discovered in Montana.

After this, any ceratopsid fossil recovered from Montana was classified under the Monoclonius. At one point or another, the remains of the Aveceratops, Eoceratops, Brachyceratops, Chasmosaurus and the Styracosaurus were grouped with it.

The relationship between the Monoclonius and the Centrosaurus

In the year 1902, Lawrence Lambe discovered three new Monoclonius species, the M. belli, M. canadensis and the M. dawsoni. Upon further research, he reclassified the first two as the Chasmosaurus belli and canadensis. The third he assigned a completely new name and genus, the Centrosaurus apertus. Subsequently, the Centrosaurus has been well represented by fossils discovered in Canada.

This discovery led to paleontologists reexamining the remains of the Monoclonius to determine their validity.

Barnum Brown in 1914 was of the opinion that Monoclonius was synonymous with the Centrosaurus, thus giving the genus Monoclonius seniority as it was named first.

Lawrence Lambe believed that the Monoclonius was a nomen dubium, as he believed that the fossils retained within the genus were too indistinct to define a separate genus.

Peter Dodson in 1990 deemed that both the genera were valid and disparate. The Monoclonius could have been the predecessor of the Centrosaurus.

The final possibility is that the Monoclonius is a developmental stage of the Centrosaurus or of a yet unknown dinosaur.

Physical features

The Monoclonius was very similar to the Centrosaurus physically. It was just slightly smaller at 15 feet and 4700 pounds. It had a rectangular frill with small spikes at its periphery. It also has a long and curved nasal horn. Its jaw was modified to form a parrot like beak and its legs were short and muscular.

Habits and habitat

The Monoclonius was a quadrupedal dinosaur which had a slow gait.

Its diet consisted of low lying vegetation, as it could not move its neck much.

The frills and horns were likely for display during courtship or they could be used interspecific or intraspecific combat.

Some ceratopsids may have displayed sexual dimorphism, but there is no evidence that the Monoclonius did.

Related species

It is clear that the Monoclonius was related to the Centrosaurus. If it indeed was a separate genus, it was related to the Coronosaurus and Sinops too.

The final notes

The position of the Monoclonius in the taxonomic tree is still a matter of contention among paleontologists. Unless more fossil evidence is unearthed, this debate may never be laid to rest.

The Dinosaur had a large head, a spike on its nose like a rhinoceros, and heavily armored body, and was 9feet tall, and 20 feet long at an adult full grown age. It was a herbivore as well like many of the other dinosaurs in its group (Ceratopsidae).