Clade Stegosauria

Clade Stegosauria is named on the basis of the shingle-like appearance of the dermal plates on its back (stegos = "roofed" and sauros = "lizard"). Two overt characteristics help to distinguish them from other thyreophorans:

1 parascapular spines, which are osteoderms evident as spikes on the shoulder regions; and

2 parasagittal plates, which are the dermal armor restricted to two rows of vertically-oriented plates, parallel to but also lateral to the axial skeleton.

Spikes also normally occur toward the posterior of stegosaurs and are often seen as additions to the caudal vertebrae. In contrast, the plates are typical of the anterior portion of the body but are still postcranial.

Stegosaurs are also identifiable by their small skulls relative to their body sizes, similar to sauropods (Chapter 10). In these small skulls were correspondingly diminutive brains, constituting some of the smallest EQs known for dinosaurs. Despite this shortcoming, stegosaurs as a clade lived minimally from the Middle Jurassic through to the Early Cretaceous, a span of about 70 million years. Stegosaurus, by far the most popularly known and best-studied thyreophoran and stegosaur, was first discovered near Morrison,

Perhaps the simplest way to be introduced to stegosaurs as a group is to look at their star member, the Late Jurassic Stegosaurus stenops (Fig. 12.8A).

FIGURE 12.8 Stegosaurus stenops, the most famous of thyreophorans and stegosaurs.

(A) Juvenile specimen (a rare find), Denver Museum of Science and Nature, Denver, Colorado.

(B) Cast of adult S. stenops, Fernbank Museum of Natural History, Atlanta, Georgia.

FIGURE 12.8 Stegosaurus stenops, the most famous of thyreophorans and stegosaurs.

(A) Juvenile specimen (a rare find), Denver Museum of Science and Nature, Denver, Colorado.

(B) Cast of adult S. stenops, Fernbank Museum of Natural History, Atlanta, Georgia.

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