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What does it mean when fossils are in stasis?
Stasis is the situation in which evolutionary lineages persist for long periods without change. In the fossil record, stasis is common but it has recently taken on a new importance with the punctuated equilibrium debate. Living fossils such as lungfish are lineages which have experienced a long period of stasis.
How do biologists explain fossils?
A fossil is the preserved remains or traces of a dead organism . Fossils are found in rocks and can be formed from: Hard body parts, such as bones and shells, which do not decay easily or are replaced by other materials as they decay. Parts of organisms that have not decayed.
What causes stasis in evolution?
A period in which no anagenetic processes occur in a particular species is termed evolutionary stasis. Evolutionary stasis is apparently not only a consequence of the absence of selection pressures and the absence of evolution, but is rather a certain type of active evolutionary process.
How are leaf fossils formed?
When the leaf rotted, it would leave a leaf-shaped imprint in the sand. Slowly, the sand would harden into a rock, like sandstone. Then hundreds of millions of years later, someone else might pick up the rock and see the shape of that leaf you dropped: a plant fossil.
What does stasis mean in science?
Stasis: A stoppage or slowdown in the flow of blood or other body fluid, such as lymph.
Is evolution gradual or rapid?
Charles Darwin understood that evolution was a slow and gradual process. By gradual, Darwin did not mean “perfectly smooth,” but rather, “stepwise,” with a species evolving and accumulating small variations over long periods of time until a new species was born.
How are leaves preserved as fossils?
A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. The best fossils of leaves are found preserved in fine layers of sediment that have been compressed in a direction perpendicular to the plane of the deposited sediment.