This is the first year I've grown carrots. What gave them legs?
I have a theory that the seedlings merged together. I don't know if that is just silly or if carrots just naturally grow like this.
Carrots often develop forked roots when:
the soil is stony
manure is added to the plot shortly before sowing
the bed is too firm
the soil is very heavy and has not been dug sufficiently - carrots like light, well-drained fertile soil
If your soil is stony - and this is what usually causes the problem -, you should have better luck with a short-rooted variety such as Amsterdam.