Thyreophora

Ankylosaurus magniventris by Todd Marshall (2004)

CHARACTERS Best known for their dermal armour, spines, shields, and clubs found all over their body in various distributions Early forms were bipedal, but later, more derived animals were completely quadrupedal Broad elephantine feet that had toes that would spread to compensate for the heavy weight of the animal and its dermal armour Small interlocking plates in some forms Broad, flattened skull Tibia (shin bone) is shorter than the femur (thigh bone)

Cladogram provided courtesy of T. Holtz Jr 2004 (http://www.geol.umd.edu/~tholtz/G104/10418thyr.htm)

THYREOPHORA "shield bearer" (2)

(1) STEGOSAURIA (2)

Stegosaurs first appeared during the Middle Jurassic and died out during the Early Cretaceous, although Cretaceous forms are rare. Scute size varied in the different forms, and some became huge and very specialized. Stegosaurus, the most famous stegosaur, has rows of huge plates running down its back that have been the focus of debate for years. Some palaeontologists believe they were for sexual display, others for thermoregulation, or even protection.

• Rows of flat plates or spines along either side of the spine
• Basal stegosaurs often had spines emerging from the shoulder region, however this was lost in later forms
• Large spikes were present on the end of the tail called thagomizers, that were used as a form of either defense or attack.

(1) STEGOSAURIDAE The armour on the back was in large flattened plates (example: Stegosaurus stenops) (2) KENTROSAURIDAE The armour on the back was in plates hear the head, but progessively turned into spines going backwards (Examples: Kentrosaurus, Huayangosaurus)

Stegosaurus stenops by Todd Marshall (2004)

(2) ANKYLOSAURS (3)

Like the stegosaurs, ankylosaurs became common during the Jurassic, and they increased in number and thrived right to the end of the Cretaceous. These animals are defined as being more heavily armoured than Scelidosaurus.

CHARACTERISTICS

• Scutes : they were covered in amoured scutes that were fused all over the body including the skull, neck, shoulders, and hips. Unfused scutes were present on almost all other parts of the body including eyelieds, cheeks, and arms.
• Spines : most ankylosaurs had large spines that stuck out horizontally from the body in pairs, and some even had large spikes on their shoulders. The rows of spines were not present in the more advanced ankylosaurs.
• Wide flared hips to support the low, heavy, and wide body

(1) NODOSAURIDAE - Example: Edmontonia (2) POLACANTHIDAE - These Ankylosaurs had head with a downward pointing snout. Example : Hylaeosaurus, Pawpawsaurus, Panoplosaurus (3) ANKYLOSAURIDAE - This group the most derived of all the Ankylosaurs, and contained the largest species Ankylosaurus. They lived from the Middle to Late Cretaceous of North American and Asia Small triagular skulls covered in scutes and tiny horns Nasal passages were extremely well developed Presence of a large defensice club at the end of the tail made of bone

Ankylosaurus without armour, by P. Olsen (2004)

NEXT : ORNITHOPODA

• Characters/ anatomy
• Major subgroups in the phylum
• Fossil record
• Modern forms
• Literature and web links
• Home

Author: Emma Schachner
Last updated: 13 November 2004
Return to Fossil groups home page