Psittacosaurus
by Keri C.
The psittacosaurus is a dinosaur. It’s a plant-eating dinosaur with a beak and a boxed-shaped skull. It’s one of the smallest dinosaurs and has large eyes. Also, the psittacosaurus is the most primitive horned dinosaur. In addition, its nickname is “the parrot-lizard”.
The psittacosaurus evolved eight major traits before it became the psittacosaurus. First, it developed a vertebral column and braincase, which made it a vertebrate. Then, it became a gnathostome by having a jaw, a tetrapod with four legs, and then laid watertight eggs, making it an amniote. After this came a pair of openings in its palate, making it a sauropsid. Then it became a dinosaur by developing a hole in its hip socket. Next, it had an extension of its pubis bone that points backwards, which means it became an ornithischian. Finally, the psittacosaurus evolved a frill at the back of its skull, naming it a marginocephalian.
According to our cladogram, the psittacosaurus is most closely related to the protoceratops and the triceratops. The trait they all share is that they are all marginocephalians. To be a marginocephalian means they have a frill or shelf at the back of their skulls. In order to figure out what the psittacosaurus is most closely related to, and what the closest trait they share is, I had to use our cladogram. I traced down the psittacosaurus’ path to the closet node to figure out what animal it was most closely related to. Whatever branched off of the node is or are the animals that the psittacosaurus is closet related to. Additionally, to figure out what the most advanced trait they shared, I traced down the paths of all three animals until they all met at the same spot. Where they stopped is the most advanced trait they share. Though they share the marginocephalian trait, they are also different in a way. For instance the most important difference between them is that the psittacosaurus walks on two legs and the protoceratops and the triceratops walk on four legs.
According to the cladogram at the American Museum of Natural History, the psittacosaurus is most closely related to many animals. But one of them is the styracosaurus. They share a trait of having a rostral bone on their snouts. This gave them the advantage of having the beginning of a shield so that they could protect themselves. I figured out what animal the psittacosaurus was most closely related to, and the most advanced trait it shared in the similar way I did on our cladogram. I traced their paths until they met up at the common node and knew that was their shared trait. I traced down the psittacosaurus’ path and then went up the path that broke off from the nearest node. Therefore, the psittacosaurus is most closely related to the protoceratops, triceratops, and the styracosaurus.
Last updated April 7, 2007.