Author's note: these pages were written some years ago. I am not planning to update them. For a more current coverage, see the link to palaeos com Palaeos website (to which many links on these pages point to anyway. More info here

Suborder Stegosauria

Plated Dinosaurs

Stegosaurus as it appeared in life
Stegosaurus stenops - image by  Brenner Fishman

The Stegosaurs are a distinctive component of the Jurassic megafauna. These striking dinosaurs are characterised by pairs of bony plates along the back (presumably for the purpose of thermoregulation) and varying numbers of pairs of spikes along the tail and, in some species the back, hips, and even shoulders.  Despite their protective spikes, they were never a very diverse group.  Reasonably common during the middle and late Jurassic, the stegosaurs were almost wiped out by the Tithonian extinction event.  A few stragglers continued on to the early or middle Cretaceous.


The following taxonomic arrangement is a tentative presentation of Stegosaurid systematics, based on Linnean/Evolutionary Systematic classification of the Stegosaurs. (note - the following is unofficial and should not be taken as authoritative!) Some of these groupings are not formally named and in fact future discoveries may reveal a completely different picture. As most Wikipedia link biologists and Wikipedia link paleontologists now advocate the Cladistic stance, the following is therefore suggested to complement (but not replace) the current paradigm.


Superorder: Dinosauria
   Order: Predentata (= Ornithischia)
      Suborder: Stegosauria
            Family: Huayangosauridae
            Family: Stegosauridae
               Subfamily: Dacentrurinae
               Subfamily: Kentrosaurinae
               Subfamily: Stegosaurinae
                  
tribe Tuojiangosaurini
                  tribe Stegosaurini


Genasauria cladogram 1. cheeks
2. armor
3. armor as plates or spines on back
4. armor as plates
5. armor as spines
6. armor as covering or small plates over back
7. uneven enamel on teeth
8. jaw joint below tooth rows
9. bony shelf on back of head

diagram by Paul E. Olsen

Note that this cladogram only includes the external link  link to palaeos com Genasauria and not some more primitive forms like the Fabrosauria.


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family Huayangosauridae

Huayangosaurus taibaii

Huayangosaurus taibaii, artwork © M. Shiraishi, reproduced with permission

The Huayangosaurs were early ancestral forms that lived during the early to the middle Jurassic. They are mostly a lot smaller than the later stegosaurs. The skull is short and high relative to later stegosaurs, and retains the archosaurian antorbital fenestra (opening in front of the eyes). Although Huayangosaurus is the only certain form, it is likely that other earlier types like Tatisaurus and Emausaurus also belong here. An early Cretaceous jaw of uncertain affinites called Regnosaurus northamptoni has been placed in this group, on the basis of its strong resemblance to the lower jaw of Huayangosaurus, but in view of the incomplete nature of the specimen and its much later date (contemporary with the latest advanced stegosaurines) I remain sceptical.

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Guild/Ecological niche: small to large diurnal terrestrial herbivores
Modern equivalent: none
Known Time-range: link to palaeos com Sinemurian to link to palaeos com Bathonian- link to palaeos com Callovian
Distribution: world-wide?
Evolved from: basal Scelidosaur?
Replaced: ?Aetosaurs
Replaced by: Stegosauridae
Extinction because of: Competition from Stegosaurids and small ornithopods?
Descendents: none
Linnean status: Subfamily (in some books) or Family (preferred ranking)
Cladistic status: ?Paraphyletic clade
Parent clades: Stegosauria, Thyreophora, Ornithischia
Adult length: 1 to 4 meters
Adult weight: 5 to 400 kg
Activity period: diurnal
Intelligence: probably low reptilian equivalent
food source: low-level (to 1 metre) browsers
Food Processing: soft fruits and leaves nipped off using beak, very little oral processing
Community structure: social - small herds of adults and ?juveniles.  Pattern of plates and spines served as intraspecific recognition, and also as sexual display devices.
Predators: Dilophosaurs, Ceratosaurs, Megalosaurs, early Allosaurs
Defense against Predators: tail spikes, spikes on back, shoulder and hips, some armour on flanks.
Weaknesses: slow moving, head close to the ground, making it hard to see preditors approach, neck and much of flanks unprotected



Huayangosaurus taibaii - scale bar equals 50 cm

Huayangosaurus taibaii Dong, Tang, and Zhou, 1982

Horizon:
Age: link to palaeos com Bathonian- link to palaeos com Callovian
Place: north-east link to palaeos com Pangea
Remains: complete skeleton, skull, fragmentary postcrania
Length: 4.3 meters
Weight: 400 kg

Huayangosaurus skull Comments: Huayangosaurus is one of the best-known stegosauroids, with remains belonging to over a half dozen individuals. The skull (left) is deep with a relatively short snout, and has what may be little "horns," which may be a gender-related character. It is also unique for having armor scutes, something like those of scelidosaurs and ankylosaurs, in a row down its sides. This is one of the things that indicate that these three groups may be combined in a single clade, the Thyreophora. (I have not given the Thyreophora a linnean ranking here). Huayangosaurus is protected by two pairs of tail spikes and a pair of spines on the shoulders


Tatisaurus oehleri Simmons, 1965

Horizon: Dark Red Beds, Lower Lufeng Series, of Yunnan, China
Age: ? link to palaeos com Sinemurian
Place: north-east link to palaeos com Pangea
Remains: dentary
Length: 1 or 2 meters

Comments: It is still controversial whether or not Tatisaurus is a proper stegosaurian, but it is the earliest known (but not the most primitive) member of the dinosaurian clade Thyreophora, a group that included various types of armoured dinosaurs.  It is still not very far removed from its Fabrosaur ancestors, but within a few million years Tatisaurus, or a form like it, evolved into large armoured quadrepeds. This poorly-known ornithischian has been related to Scelidosaurus, but seems to be more closely related to the stegosauria. Possibly it represents a form transitional between or ancestral to the two groups.


Emausaurus ernsti Haubold, 1991

Horizon: Upper Lias of Germany
Age: early link to palaeos com Toarcian
Place: European islands, central north link to palaeos com Pangea
Remains: complete skull

Comments: This animal has been compared to a miniature version of Huayangosaurus, the skull of which is very similiar.


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family Stegosauridae

The most diverse and advanced of the Stegosauria, the family Stegosauridae included two subfamilies and it would seem several tribes.  The more advanced genera, such as Stegosaurus, had large bony plates aranged in alternating pairs along the back.  These would have been very efficent heat regulation devices.  Other more primitive types had smaller plates and pairs of spikes along the tail and, in some species the back, hips, and even shoulders.   The unusually large hind limbs and high hips served a double purpose: for rearing up to browse on trees and to swing the spiked tail more efficently

info panel

Guild/Ecological niche: Large to very large diurnal terrestrial herbivores
Modern equivalent: none
Time: link to palaeos com Bathonian to link to palaeos com Albian
Distribution: world-wide
Evolved from: Huayangosauridae
Replaced: Huayangosauridae
Replaced by: none
Extinction because of: Tithonian and Cenomonian turnovers? Decline of food source? Competition from ornithopods?
Descendents: none
Linnean status: Family
Cladistic status: Monophyletic clade
Parent clades: Stegosauria, Thyreophora, Ornithischia
Adult length: 4 to 10 meters
Adult weight: 400 kg to 6 tonnes
Preferred environment: lowland (floodplain) to upland.  Seem to have inhabited different environments to those frequented by sauropods.
Activity period: diurnal
Metabolism: partially endothermic? gigantotherms, plates used for heat-exchange (mostly cooling)
Intelligence: probably lower reptilian equivalent, most functions handled by large pelvic ganglion
food source: low-level (to 1 metre) browsers, possibly on bennettitalian, Nilssoriale, and Caytoniale fruits.  Also able to rear up on hind legs to browse on lower-level trees
Food Processing: soft fruits and leaves nipped off using beak, very little oral processing
Community structure: social - small herds of adults and ?juveniles.  Pattern of plates and spines served as intraspecific recognition, and also as sexual display devices.
Movement: mostly slow walking, the small forelegs make for an ungainlt gait
Maximum speed: about 7 kph
Predators: Ceratosaurs, Megalosaurs, and Allosaurs
Defense against Predators: large size, tail spikes, spikes on back, shoulder and hips. Probably backed tail first towards a predator, like a porcupine.  Could swing on hips to face tail against preditor, making the stegosaur almost impossible for a single animal to out-circle
Weaknesses: slow moving, head close to the ground, making it hard to see preditors approach, neck and flanks unprotected


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external linkPaul E. Olsen divides the stegosauria into two families, Kentrosauridae and Stegosauridae.  More usually however Kentrosaurus is included within the Stegosauridae.  Perhaps a compromise would be to have the Kentrosaurs and Stegosaurs as two subfamilies of the family Stegosauridae.  The more primitive Kentrosaurines would then be transitional betweneen the very primitive Dacentrurinae and the more advanced Stegosaurinae.


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subfamily Dacentrurinae

These were late persisting primitive types, that seem to have characteristics indicating a type ancestral to other stegosaurids (even if they themselves are too late in time to be an actual ancestor). The vertebrae are more primitive and the forelimbs longer in comparison to the hind-limbs. Although Dacentrurus armatus is the only certain species, an early femur has been compared top that species.


Dacentrurus armatus  - scale bar equals 50 cm

Dacentrurus armatus Lucas, 1902b

synonym: Omosaurus armatus Owen, 1875 Horizon: Lower Kimmeridge Clay of England, Argiles d'Octeville of France, unnamed unit of Portugal
Age: link to palaeos com Oxfordian / early link to palaeos com Kimmeridgian-late early link to palaeos com Tithonian
Place: European islands - middle link to palaeos com Laurasia
Remains: two skeletons and assorted postcrania
Length: 7 to 10 meters
Weight: upto 6 tonnes

Comments: This is the first stegosaur described by science, although the original name, Omosaurus, had to be changed to Dacentrurus, (as it was already applied to another animal). It is the most primitive known stegosaurid, with primitive vertebrae and long forelimbs, and some researchers have suggested it deserves to be put in a separate family. It is also among the largest of the stegosaurs. There are also a number of specilised features in the vertebrae and hip that prevent from being an actual ancestor. As with many early-named European dinosaurs, the species seems to be something of a garbage taxon for fragmentary remains of a generally similiar type, as it is unlikely that one species would persist for a period of some 10 or 12 million years or so. Some remains suggest individuals of 10 meters in length, larger than the biggest Stegosaurus.


?Dacentrurus phillipsi (Seeley, 1893)

synonym: Omosaurus phillipsi Seeley, 1893 Horizon: of England
Age: early-mid link to palaeos com Oxfordian
Place: European islands - middle link to palaeos com Laurasia
Remains: femur

Comments: "O." phillipsi is based, like "O." vetustus, on the femur from a juvenile stegosaurid. In may be a very primitive stegosaurid, possibly a species of Dacentrurus.



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Subfamily Kentrosaurinae

Kentrosaurus life-reconstruction

Kentrosaurus aethiopicus, artwork © M. Shiraishi, reproduced with permission

These are primitive stegosaurids, small to large in size, with generally small spikey plates and numerous spikes along the tail, and sometimes the hips and shoulders as well.  A paraphyletic group

, they are transitional between the Dacentrurines and the Stegosaurines.

Kentrosaurus aethiopicus - scale bar equals 50 cm

Kentrosaurus aethiopicus Hennig, 1915

Horizon: Tendaguru formation, Tanzania
Age: middle to late link to palaeos com Kimmeridgian
Place: central link to palaeos com Gondwana
Remains: remains of several individuals
Length: 2.5 to 5 meters
Weight: 450kg

Comments: Kentrosaurus is the best known of the primitive spiny stegosaurs. The six pairs of plates are small and located on the neck to the mid back, with the sixth pair transitional between plate and spine. Beyond this are five large pairs of spines along the back and tail, as well as a pair of prominent shoulder spines. Most specimens known are juveniles. The skull contains a number of primitive features. This animal lived at the same time as the larger and more advanced Stegosaurus.


Chialingosaurus kuani Young, 1959

Horizon: Upper Shaximiao Formation, Sichuan, China
Age: link to palaeos com Oxfordian
Place: north-east link to palaeos com Pangea / east link to palaeos com Laurasia
Remains: skull and skeletal fragments
Length: 4 metres
Weight: about 400 kg?

Comments: High narrow skull, slender limb-bones, small plate-like spines


skull of Chungkingosaurus laminaplacodus

Chungkingosaurus laminaplacodus Dong, Zhou, & Zhang,1983

Horizon: Upper Shaximiao Formation, Sichuan Province,China
Age: link to palaeos com Oxfordian
Place: north-east link to palaeos com Pangea / east link to palaeos com Laurasia
Remains: partial skeleton
Length: 3 to 4 metres
Weight: about 400 kg

Comments: The skull is high and narrow skull, and the sacrum and humerous primitive, all indicating a less-specialised form then Stegosaurus or Tuojungosaurus. There are large thick spine-like bony plates (intermediate between spines and plates) and apparently four or five pairs of tail spines. May be transitional between Kentrosaurines and Stegosaurines


Craterosaurus pottonensis Seeley, 1874

Horizon: Wealden Formation, England
Age: link to palaeos com Valanginian/ link to palaeos com Hauterivian/ link to palaeos com Barremian
Place: European islands - middle link to palaeos com Laurasia
Remains: back vertebra
Length: 4 metres?
Weight: about 500 kg

Comments: fragmentary remains - relationships uncertain; tentatively assigned to this group



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subfamily Stegosaurinae

These are advanced stegosaurids, with generally larger plates and spikes that tend to be limited to the end of the tail, although primitive forms still retain additional spines. One could distinguish two tribes, the paraphyletic or ancestral Tuojiangosaurini, and the specialised Stegosaurini


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tribe "Tuojiangosaurini"

A paraphyletic taxon; intermediate between the Kentrosaurs (which they resemble) and the Stegosaurini, Generally retain the Kentrosaurine pattern of back and hip spines


Lexovisaurus durobrivensis - scale bar equals 50 cm

Lexovisaurus durobrivensis (Hulke, 1887)

Horizon: Lower Oxford Clay and Kimmeridge Clay of England, Marnes d'Arences of France
Age: Middle link to palaeos com Callovian to early link to palaeos com Kimmeridgian
Place: European islands - middle link to palaeos com Laurasia
Remains: skeletal elements, 3 partial postcrania,
Length: 5 to 6 metres
Weight: upto 1.5 tonnes

Comments: Superficially quite similar to Kentrosaurus, this early stegosaurine is a more closely related to Stegosaurus. It has large thin plates, and spines on the hip. In view of the time difference i is unlikely that the fragmentary Kimmeridgian material belongs to the same species as the Callovian material


Lexovisaurus? vetustus (Huene, 1910)

Horizon: England
Age: Late link to palaeos com Bathonian
Place: European islands - middle link to palaeos com Laurasia
Remains: juvenile femur

Comments: tentatively assigned to the genus Lexovisaurus, although the material is too incomplete to be sure. The oldest known stegosaurid


Monkonosaurus lawulacus Zhao, 1983

Horizon: Loe-ein Formation of Tibet
Age: link to palaeos com Kimmeridgian
Place: east link to palaeos com Laurasia
Remains: some skeletal elements (2 vertebrae, sacrum, 3 plates)
Length: 5 metres
Weight: about one tonne

Comments: Dermal plates much like Stegosaurus. Sacral neural spines broad and lower than other stegosaurs. However the large thin bony plates and closed sacral fenestrae are progressive features, this poorly known animal is therefore very tentatively assigned to this group


Paranthodon africanus partial skull

Paranthodon africanus (Broom, 1910)

Horizon: Kirkwood Formation, South Africa
Age: mid link to palaeos com Tithonian to early link to palaeos com Valanginian
Place: southern link to palaeos com Gondwana
Remains: partial skull
Length: ?5 metres

Comments: tentatively assigned to this group


Yingshanosaurus jichuanensis Zhou, 1984

Horizon: Upper Jurassic of China
Age: link to palaeos com Oxfordian / link to palaeos com Kimmeridgian / link to palaeos com Tithonian
Place: north-east link to palaeos com Pangea / east link to palaeos com Laurasia

Comments: broad spikes on shoulders; seems to be closely related to Tuojiangosaurus.


Tuojiangosaurus multispinus  - scale bar equals 50 cm

Tuojiangosaurus multispinus Dong, Li, Zhou, & Zhang,1973

Horizon: Upper Shaximiao Formation, Sichuan, China
Age: link to palaeos com Oxfordian
Place: north-east link to palaeos com Pangea / east link to palaeos com Laurasia
Remains: 2 partial skeletons
Length: 7 metres
Weight: 2 tonnes

Tuojiangosaurus skull Comments: Tthe largest known Jurassic Asian stegosaur. The skull (left) is similiar to that of Stegosaurus. There 17 pairs of small spiny plates, as well as spines on the shoulders, hips, and tail



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tribe Stegosaurini

Stegosaurines are distinguished by large size, no spines on hips or shoulders, only two (or rarely 4) pairs of tail spines, relatively short forelimbs, small elongate head, large plates in life covered with skin and blood vessels. This tribe includes only two genera, Stegosaurus and Wuerhosaurus

Stegosaurus skull
The skull of Stegosaurus. Key to abbreviations

Note on Stegosaurus species: The controversial dinosaurologist Bob Bakker distinguishes between two types of Stegosaurs - those with long legs and relatively smaller plates (Stegosaurus proper) and a more primitive form with shorter legs and larger plates (Diracodon).  Dinogeorge however is critical of proposing a new stegosaur genus on this basis.  (seeexternal linkDinosaur Genera List corrections #63).  See alsoexternal linkcomments by Stanley Friesen (external linkDinosaur Reference Center).  Also, different sources (both in print and on the Web) give different lists of species; e.g. some are synonymised with others.   It may be that spme of these species are only subspecies or local variants.  However, for the sake of completeness (and with the risk of further muddling the issue.... ) I have listed all the types here.



Stegosaurus armatus armatus Marsh,1887

Horizon: Upper Morrison formation, Colorado,Wyoming and Utah, USA
Age: early link to palaeos com Tithonian
Place: west link to palaeos com Laurasia
Remains: large amount of skeletal elements
Length: 6 metres
Weight: 2 tonnes

Comments: The type species of the genus. Has longer legs and relatively smaller plates than S. stenops; 2 pairs of tail spines


Stegosaurus armatus ungulatus Marsh, 1879

Horizon: Upper Morrison formation, Wyoming and Utah, USA
Age: early link to palaeos com Tithonian
Place: west link to palaeos com Laurasia
Remains: large amount of skeletal elements
Length: upto 9 metres
Weight: 5 tonnes

Comments: Along with Dacentrurus armatus, this is the largest known stegosaurid. The limbs are long and slender. It has four pairs of tail spines, and the middle part of the tail bears paired spine-plates. The sacral centra are broad and rounded and lack a ventral keel. This may be variant of S. armatus, rather than a distinct species.


Stegosaurus skeleton

Stegosaurus stenops stenops Marsh, 1877

Horizon: Morrison formation, Colorado,Wyoming and Utah, USA
Age: link to palaeos com Kimmeridgian to early link to palaeos com Tithonian
Place: west link to palaeos com Laurasia
Remains: large amount of skeletal elements
Length: 6 to 7 metres
Weight: 2 tonnes

Comments: S. stenops has very large plates and relatively shorter legs. The sacral centra have a ventral keel. There are two pairs of tail spines. Bob Bakker sugests this species should be relocated under its original genus Diracodon


Stegosaurus stenops laticeps Marsh, 1881

Horizon: Morrison formation, Wyoming , USA
Age: late link to palaeos com Kimmeridgian
Place: west link to palaeos com Laurasia
Remains: large amount of skeletal elements
Length: 6 metres
Weight: 2 tonnes

Comments: This form may be same as S. stenops


Stegosaurus longispinus Gilmore,1914

Horizon: Morrison formation of Utah, USA
Age: Early Tithonian
Place: west link to palaeos com Laurasia
Remains: fragmentary skeleton
Length: 7 metres
Weight: 2 tonnes

Comments: This species is distinguished by two pairs of very elongate (a meter in length) tail spines


Wuerhosaurus homheni Dong,1973

Horizon: Lianmuging Formation, Xinjiang Uygur Zizhiqu,China
Age: link to palaeos com Valanginian/ link to palaeos com Hauterivian/ link to palaeos com Barremian/ link to palaeos com Aptian/ link to palaeos com Albian
Place: east link to palaeos com Laurasia
Remains: partial skeletons
Length: 6 to 8 metres
Weight: 2 to 3 tonnes

Comments: Among the last of the stegosaurs, Wuerhosaurus is closely related to Stegosaurus, with a similiar arrangement of plates and spines. It differs in that Wuerhosaurus's plates are long and low, unlike the tall lozenge-shaped plates of Stegosaurus.


Wuerhosaurus ordosensis Dong,19p3

Horizon: Lianmuging Formation, Xinjiang Uygur Zizhiqu,China
Age: ? link to palaeos com Barremian
Place: east link to palaeos com Laurasia
Remains: partial skeletons
Length: 4 metres
Weight: about 500 kg

Comments: A small species of this genus


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Stegosaurid brains

Kentrosaurus brain and pelvic nerve ganglionStegosaurids had small brains by Dinosaurian standards, although not so small as to fall below the average range of reptilian brain to body weight ratio (the dim-witted dinosaur - all brawn and no brain is in fact a myth).  Stegosaurus is famous for its "second brain" - actually an enlarged pelvic nerve plexus situated in the hip region.  In fact all dinosaurs and birds and many other Sauropsids have such organs (so do mammals, but not developed to such an extent).

This figure shows the Kentrosaurus brain (a) next to the much larger and pelvic nerve ganglion (b)

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Stegosaurid thermoregulation

Stegosaurus plateThe photograph shows the side and top-bottom view of the large plates on the back of the Stegosaurus.  Originally thought to have been a form of armour-plating, the plates of advanced stegosaurs were, as can be seen here, actually quite thin and full of holes for the accomodation of blood vessels.  For all large animals heat disipation is a big problem (that is why African elephants have such large ears for example), and the Stegosaur plates clearly served this purpose.  The plates tend to be small and poorly developed (or even absent) in primitive Stegosaurids, but more developed in more advanced forms, indicating that they conferred an adaptive advantage.



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Web links Links Web links

cladogram Stegosauroidea - Thescelosaurus!

Dinosauricon Stegosauria cladogram, short essay, and list of all known genera.

drawingsphotoscladogram The Real Jurassic Park - Morrison and Tendaguru Formations - part of Professor Paul Eric Olsen's superb coverage of dinosaurs and their predecessors in the DINOSAURS AND THE HISTORY OF LIFE - GEOLOGY V1001x site

cladogram Stegosauria Mikko's phylogeny site

Jurassic Gallery Jurassic Gallery - fantastic artwork by M. Shiraishi. In Japanese and English

printed referenceGalton, P. M., 1990: Stegosauria. 435-455, in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.), The Dinosauria University of California Press, Berkley, Los Angeles, Oxford, 1990. A number of images from this chapter have been used to illustrate various species listed in the present page


internal link cautionary note (please read before using this page as reference material!)


up one node (internal link) back to Predentata (Ornithischia)



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page history

page uploaded 21 August 1998
revised 1 & 18 November
further modified 24 July 1999
converted to Style Sheet and a very large amount of new material added 7 January 2001

content and html by M.Alan Kazlev