Old Earth Ministries Online Dinosaur Curriculum
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Lesson 46 - Thyreophora Overview
The Thyreophora ("shield bearers", often known simply as "armored dinosaurs") were a subgroup of the ornithischian dinosaurs. They were armored herbivorous dinosaurs, living from the early Jurassic until the end of the Cretaceous.
Thyreophorans are characterized by
the presence of body armor lined up in longitudinal rows along the body.
Primitive forms had simple, low, keeled scutes or
osteoderms whereas more
derived forms developed more elaborate structures including spikes and
plates. Most thyreophorans had relatively small brains for their body size.
Date Range: 190 - 65.5 Ma
|Mymoorapelta (Picture Source)|
Thyreophorans include well-known suborders such as the Ankylosauria and Stegosauria as well as lesser-known groups. Among the Ankylosauria, the two main groups are the Ankylosaurids and Nodosaurids. In both groups, the forelimbs were much shorter than the hindlimbs, and this was particularly exaggerated in stegosaurs. The clade has been defined as the group consisting of all species more closely related to Ankylosaurus than to Triceratops. Thyreophora is the sister group of the Cerapoda within the Genasauria.
Ankylosaurids are noted by the presence of a large tail club composed of distended vertebrae that have fused into a single mass. They were heavy-set and heavily armored from head to tail in bony armor, even down to minor features such as the eyelids. Spikes and nodules, often of horn, were set into the armor. The head was flat, stocky, with little or no "neck", roughly shovel-shaped and characterized by two spikes on either side of the head approximately where the ears and cheeks were. Euoplocephalus tutus is perhaps the best-known ankylosaurid.
Nodosaurids, the other family in the Ankylosauria, may actually include the ancestors of the ankylosaurids. They lived during the middle Jurassic (approx 170 mya) on up through the late Cretaceous (65 mya) and, while armored as the ankylosaurids, did not have a tail club. Instead, the bony bumps and spikes that covered the rest of their body continued out to the tail and/or were augmented with sharp spines. Two examples of nodosaurs are Sauropelta and Edmontonia, the latter most notable for its formidable forward-pointing shoulder spikes.
The Stegosauria suborder comprises the Stegosauridae and Huayangosauridae. These dinosaurs lived mostly from the Middle to Late Jurassic, although some fossils have been found in the Early Cretaceous. Stegosaurs had very small heads with simple, leaf-like teeth. Stegosaurs possessed rows of plates and/or spikes running down the dorsal midline and elongated dorsal vertebra. It has been suggested that stegosaur plates functioned in control of body temperature (thermoregulation) and/or were used as a display to identify members of a species, as well as to attract mates and intimidate rivals. Well known stegosaurs are Stegosaurus and Kentrosaurus.
While ranked taxonomy has largely fallen out of favor among dinosaur paleontologists, a few 21st century publications have retained the use of ranks, though sources have differed on what its rank should be. Most have listed Thyreophora as an unranked taxon containing the traditional suborders Stegosauria and Ankylosauria, though Thyreophora is also sometimes classified as a suborder, with Ankylosauria and Stegosauria as infraorders.
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