How did Charles Darwin's fossil record provide evidence for evolution?

When Charles Darwin, a young graduate of Cambridge University, joined the HMS Beagle as a naturalist, he had just finished reading two of the most influential books on geology and palaeontology, written by Charles Lyell and Georges Cuvier.

Darwin was already familiar with the concept of species "transmutation" prior to setting out on his journey; this term was eventually superseded by the word "evolution."

Remember that Darwin was more than just your average palaeontologist. He discovered some fossils in Argentina while traveling to gather specimens (he was also a hunter!).

He was shocked to discover that only tiny armadillos lived in the region despite having discovered a massive fossilized structure that resembled the outer shell of an animal resembling an armadillo.

Darwin observed only smaller but related sloths residing in South America, but he also discovered enormous fossilized ground sloth bones there.

He was led to believe in the appearance of more recent forms of life descended from extinct ones by these two discoveries.

After returning from his expedition in 1836, Darwin's theory of evolution was nearly complete by 1839, but he had to wait nearly 20 years to publish his theory of natural selection.

Charles Darwin's fossil record provided evidence for evolution by showing a sequence of increasingly complex life forms over time, indicating the gradual change of species over generations, supporting the idea of descent with modification and the concept of common ancestry.