Dravidosaurus Deepest Fossil

Genus

Age

Geographic Location

Chialingosaurus

Middle Jurassic

China

Chunkingosaurus

Late Jurassic

China

Dacentrurus

Late Jurassic

Western Europe

Dravidosaurus

Late Cretaceous

India

Hesperosaurus

Late Jurassic

Western Europe

Huayangosaurus

Middle Jurassic

China

Kentrosaurus

Late Jurassic

Tanzania

Lexovisaurus

Late Jurassic

UK, France

Monokonosaurus

Early Cretaceous

China

Stegosaurus

Late Jurassic

Western USA

Tuojiangosaurus

Late Jurassic

China

Wuerhosaurus

Early Cretaceous

China

loquially known as the "armored dinosaurs" in recognition of their abundant, well-developed external bony parts, such as knobs and spikes. The only other dinosaurs that possessed body armor were titanosaurids (Chapter 10), thus this trait was apparently unusual outside of Thyreophora. Because of their impressive osteodermal accou-terments and the inference that all thyreophorans were herbivores, they are often used as an example of animals that engaged in an evolutionary "arms race" with their potential predators, particularly theropods (Chapter 9). Fossil evidence suggests that defenses by sauropods (Chapter 10) against theropods included extreme size, and those by ornithopods (Chapter 11) included large numbers. In contrast, thyreophorans stayed within relatively small size parameters (by dinosaur standards) and made themselves individually difficult to attack. They not only used body armor for protection, but some also had clubbed and spiked tails. Their body armor probably resulted in sacrificing mobility. Coupled with short limbs, their armor may have kept them close to the ground and their ventral surfaces relatively safe from assault.

Despite the defensive emphasis of such prominent features, thyreophorans probably had multiple purposes for their more visual osteoderms, such as display for sexual attraction, forms of intraspecific competition or, in the case of some stegosaurs, body heat regulation. Unfortunately, little more is known about thyreophoran lifestyles than through their skeletal remains. Some trackways from ankylosaurs and stegosaurs have been identified, but no eggs, nest structures, toothmarks, or coprolites have been tied to thyreophorans. Consequently, an approach that uses multiple lines of evidence must be limited to considering the functional morphology and biomechanics of thyreophorans. Because this information is all that paleontologists have for forming their hypotheses about thyreophorans, much of what is presented in this chapter may change considerably in the future with new discoveries. Regardless, thyreophorans provide an extreme in dermal armor never seen in any other land-dwelling vertebrates. For this reason alone, study of how they evolved to such a unique status should give insights on the evolution of plant-herbivore and predator-prey relationships.

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