Saurischia

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   The **Saurischians** (Lizard-hipped) were a group of dinosaurs that were comprised of mainly *carnivorous* species, though some dinos such as the "Therizinosaurus" were plant-eaters (Theropod). Although the charismatic ones died out during the **K-T extinction event**, a group of Saurischians known as the "*Theropods*" (Beast-Foot) evolved into Birds over the past tens of millions of years. Theropods can be distinguished from other dinosaurs by their bipedal stance, which is not seen in any other dinosaur group. The second main group of Saurischians were known as the "*Sauropods*" were some of the largest animals to have ever existed, characterized by their long necks and tails as well as their quadrupedal stance. Other physical and biological features of Saurischians that distinguish them from other dinosaurs (among other major characteristics; including a grasping hand (Theropods), asymmetrical fingers, and a long, mobile neck) is the **pubis** that points downward and forward at an angle to the ischium. The Saurischians and Ornithischians separated as lineages perhaps 235 million to 240 million years ago during the Middle Triassic Period (242-227 million years ago). The first dinosaurs were small and bipedal; only later did they evolve immense size and a variety of adaptations for feeding and other functions.

## Subgroups

* **Tyrannosauridae: T***yrannosaurinae* (Tyrannosaurus and more) and *Albertosaurinae* (Albertasaurus and more)
* **Carcharodontosauridae** (Dinosaur enthuasists refer to it as "Gigantosauridae"): Carcharodontosaurus, Giganotosaurus, Mapusaurus, Tyrannotitan and Acrocanthrasaurus

* **Allosauridae** (ancestors of the Carcharodontosauridae): Allosaurus and Saurophaganax (possibly a subspecies)
* **Cetiosauridae**
* **Brachiosauridae:** Brachiosaurus
* **Camarasauridae:** Camarasaurus
* **Diplodocidae:** Diplodocus and Apatosaurus
* **Titanosauridae:** Dreadnoughtus, Patagotitan, Argentinasaurus (largest animal ever), Paralititan and Antarcticasaurus
* **Sauropodomorpha** (ancestors of Sauropods): *Unaysauridae*, *Plateosauria*,

* **Tyrannosauridae:** *Tyrannosaurinae* (Tyrannosaurus and more) and *Albertosaurinae* (Albertasaurus and more)
* **Carcharodontosauridae** (Dinosaur enthuasists refer to it as "Gigantosauridae"): Carcharodontosaurus, Giganotosaurus, Mapusaurus, Tyrannotitan and Acrocanthrasaurus

* **Allosauridae** (ancestors of the Carcharodontosauridae): Allosaurus and Saurophaganax (possibly a subspecies)

## "Theropoda" and "Sauropoda"

The **Saurischians** form two major groups. The Sauropoda were large herbivores such as *Apatosaurus* and *Diplodocus*. The Theropoda were bipedal carnivores (meat eaters), ranging from the chicken-sized *Compsognathus* and the fearsome *Deinonychus* and *Velociraptor* to the crested *Dilophosaurus* and the gigantic Tyrannosaurus. The oldest known dinosaurs, from the middle Triassic of South America, were saurischians.

Living **Birds** had common ancestors on the *Theropod* lineage. Oddly, birds are derived from the "Lizard-hipped" dinosaurs and not from the "Bird-hipped" *Ornithischian* dinosaurs. The "bird-hipped" condition of a pubis pointing toward the back of the animal occurred twice independently, once in the ornithischians and once in the lineage leading to birds, an example of *convergent evolution*. Thus "Ornithischia," taken literally, is a misnomer, since the Ornithischians have **Ornithischian**-like pelves, not bird-like. Only birds (and their immediate ancestors) have Bird-like pelves.