A small, wormlike creature called Pikaia is thought to be the ancestor of all backboned animals.
Its fossil remains were found in the 530- million-year-old mudstone deposits of the Burgess Shale in Canada.
Pikaia was the first known chordate. All backboned animals belong to this group as well as marine animals called tunicates and acraniates.
Pikaia was 2 inches long, with a notochord running around its body-- a kind of primitive spine that gave its body flexibility.
The notochord also allowed the animal's simple muscles to work against it, and the animal's body organs to hang from it.
Pikaia is very similar to a modern creature called Branchiostoma, a small, transparent creature that lives in the sand at the bottom of the sea.
As it lacks a bony skeleton, paired fins, and jaws, Pikaia is not really
a fish.
Pikaia is a more complex creature than many other animals found in the Burgess Shale. It suggests that other complex creatures must have lived before it, although there is no fossil evidence for this.
The head of Pikaia was very primitive with a pair of tentacles, a mouth, and a simple brain for processing information.
Pikaia swam in a zigzag fashion similar to a sea snake.
Its fossil remains were found in the 530- million-year-old mudstone deposits of the Burgess Shale in Canada.
Pikaia was the first known chordate. All backboned animals belong to this group as well as marine animals called tunicates and acraniates.
Pikaia was 2 inches long, with a notochord running around its body-- a kind of primitive spine that gave its body flexibility.
The notochord also allowed the animal's simple muscles to work against it, and the animal's body organs to hang from it.
Pikaia is very similar to a modern creature called Branchiostoma, a small, transparent creature that lives in the sand at the bottom of the sea.
As it lacks a bony skeleton, paired fins, and jaws, Pikaia is not really
a fish.
Pikaia is a more complex creature than many other animals found in the Burgess Shale. It suggests that other complex creatures must have lived before it, although there is no fossil evidence for this.
The head of Pikaia was very primitive with a pair of tentacles, a mouth, and a simple brain for processing information.
Pikaia swam in a zigzag fashion similar to a sea snake.
Pachycephalosaurs were among some of the last Dinosaur groups to appear. They lived 75-65 mya.
They are named after one of the best-known members of the group, Pachycephalosaurus.
Pachycephalosaurus means "thick-headed reptile," due to the domed and hugely thickened bone on the top of its skull--like a cyclist's crash helmet.
About 15 feet long from nose to tail, Pachycephalosaurus lived in Montana, South Dakota, and Wyoming.
Stegoceras, which also lived in North America, was about 8 feet long, with a body the size of a goat.
Homalocephale was about 10 feet long and had a flatter skull. It lived in East Asia.
Pachycephalosaurs may have defended themselves by loweringtheir heads and charging at their enemies.
At breeding time, the males may have engaged in head-butting contests, as some sheep and goats do today.
They are named after one of the best-known members of the group, Pachycephalosaurus.
Pachycephalosaurus means "thick-headed reptile," due to the domed and hugely thickened bone on the top of its skull--like a cyclist's crash helmet.
About 15 feet long from nose to tail, Pachycephalosaurus lived in Montana, South Dakota, and Wyoming.
Stegoceras, which also lived in North America, was about 8 feet long, with a body the size of a goat.
Homalocephale was about 10 feet long and had a flatter skull. It lived in East Asia.
Pachycephalosaurs may have defended themselves by loweringtheir heads and charging at their enemies.
At breeding time, the males may have engaged in head-butting contests, as some sheep and goats do today.
