Saurischia

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Saurischia is one of the two primary divisions of Dinosauria, the other being Ornithischia. The term "Saurischia" is derived from the Greek words "sauros" (meaning "lizard") and "ischion" (meaning "hip joint"), referring to the lizard-like configuration of the pelvis. This group includes all the theropods, which are primarily carnivorous dinosaurs, and the sauropodomorphs, which are primarily herbivorous.

Classification

Saurischians are traditionally divided into two main suborders:

• Theropoda: This suborder includes bipedal carnivorous dinosaurs such as Tyrannosaurus rex, Velociraptor, and modern birds. Theropods are characterized by hollow bones and three-toed limbs.

• Sauropodomorpha: This suborder includes long-necked herbivorous dinosaurs such as Brachiosaurus, Diplodocus, and Apatosaurus. Sauropodomorphs are known for their massive size, long necks, and tails.

Evolutionary History

Saurischians first appeared in the late Triassic period, approximately 230 million years ago. They diversified rapidly during the Jurassic and Cretaceous periods. The evolutionary success of saurischians is attributed to their diverse range of body sizes, feeding strategies, and ecological niches.

The theropods, which include the ancestors of modern birds, are particularly notable for their evolutionary adaptations such as feathers, which were initially used for insulation and later for flight in some lineages.

Anatomy

The defining characteristic of saurischians is their pelvic structure. Unlike the Ornithischia, which have a "bird-hipped" pelvic structure, saurischians have a "lizard-hipped" configuration where the pubis points down and forward. This anatomical feature is a key factor in their classification.

Theropods typically have a lightweight, agile build with adaptations for bipedal locomotion, while sauropodomorphs have a more robust skeletal structure to support their massive size.

Extinction

Most saurischians, like other non-avian dinosaurs, went extinct at the end of the Cretaceous period, approximately 66 million years ago, likely due to a combination of volcanic activity, climate change, and the impact of a large asteroid.

However, the lineage of theropods that led to modern birds survived this mass extinction event, making birds the only extant representatives of the Saurischia.

Also see

• Ornithischia
• Theropoda
• Sauropodomorpha
• Dinosauria
• Mesozoic Era