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Saurischian Dinosaurs: The Lizard-Hipped Lineage

Saurischian dinosaurs are one of the two major groups of dinosaurs, along with ornithischian dinosaurs. The name saurischian means “lizard-hipped” and refers to the shape of their pelvis, which resembles that of modern reptiles. Saurischian dinosaurs include some of the most well-known and diverse dinosaurs, such as birds, theropods, and sauropods.

Birds: The Living Saurischians

Birds are the only living descendants of saurischian dinosaurs. They evolved from a group of small, feathered theropods during the Jurassic Period, about 150 million years ago. Birds share many features with their saurischian ancestors, such as a three-toed foot, a furcula (wishbone), and a reversed pubis. Birds are also the only living animals with a keeled sternum (breastbone) that supports the flight muscles.

Theropods: The Meat-Eating Saurischians

Theropods were bipedal carnivores that ranged in size from the chicken-sized Compsognathus to the gigantic Tyrannosaurus. Theropods had sharp teeth, claws, and often horns or crests on their heads. Some theropods, such as Deinonychus and Velociraptor, had a large sickle-shaped claw on their second toe that they used to slash their prey. Theropods were also the first dinosaurs to evolve feathers, which may have been used for insulation, display, or flight.

Sauropods: The Long-Necked Saurischians

Sauropods were quadrupedal herbivores that had long necks and tails, small heads, and massive bodies. Sauropods included some of the largest land animals ever, such as Apatosaurus and Brachiosaurus. Sauropods had columnar legs and heavy, solid limb bones to support their weight. They also had adaptations for feeding on plants, such as peg-like teeth, elongated jaws, and gastroliths (stones swallowed to help digest food).

References:

• Saurischia – Wikipedia
• Saurischian | dinosaur order | Britannica
• The Saurischian Dinosaurs – University of California Museum of Paleontology

Evolution: The Saurischian Success Story

Saurischian dinosaurs originated in the Late Triassic Period, about 230 million years ago, from a common ancestor with ornithischian dinosaurs. The earliest saurischians were small and bipedal, such as Herrerasaurus and Eodromaeus. They diversified into two main branches: the theropods and the sauropodomorphs.

The theropods evolved into a variety of forms and sizes, adapting to different environments and prey. Some theropods became specialized for running, such as Ornithomimus and Gallimimus, while others developed powerful jaws and arms, such as Allosaurus and Spinosaurus. Some theropods also evolved feathers, which may have had various functions, such as insulation, display, or flight. The most advanced theropods were the maniraptorans, which gave rise to the first birds in the Jurassic Period.

The sauropodomorphs evolved into large and long-necked herbivores that fed on high vegetation. The earliest sauropodomorphs were still bipedal, such as Plateosaurus, but they gradually became quadrupedal and increased in size. The most derived sauropodomorphs were the sauropods, which reached enormous proportions and dominated the land ecosystems for millions of years. Some sauropods had distinctive features, such as armor plates (Saltasaurus), spines (Amargasaurus), or crests (Shunosaurus).

Saurischian dinosaurs survived two major mass extinctions that wiped out many other groups of animals. The first one occurred at the end of the Triassic Period, about 200 million years ago, and may have been caused by volcanic eruptions or climate change. The second one occurred at the end of the Cretaceous Period, about 66 million years ago, and was likely caused by an asteroid impact or volcanic activity. The only saurischians that survived this event were the birds, which diversified into many modern groups in the following Paleogene Period.

References:

• Saurischia – Wikipedia
• Saurischian | dinosaur order | Britannica
• The Saurischian Dinosaurs – University of California Museum of Paleontology
• Évolution Origine et évolution des saurischiens
• Origine et évolution des saurischiens – ScienceDirect
• Origine et évolution des Saurischiens | Request PDF – ResearchGate