The history and etymology of this word are a gorgeous half-cup-of-coffee exploration. OED tells me that the past participle “shapen” is archaic, entirely replaced by “shaped”… yet I know I have seen “shapen” and heard it and said it plenty in my own experience.

• 1.075 They shaped and wrought, and light they caught
• 2.043 and the shape of their legs,
• 2.073 That’s about the shape of it!”
• 2.113 of various makes, shapes, and sizes.
• 3.042 it must be a moon of the same shape
• 7.107 in enchanted shape,
• 7.116 changing them into all sorts of different shapes
• 7.122 in bear’s shape at any rate.
• 8.029 Out of the gloom came suddenly the shape of a flying deer.
• 8.133 for the elf-king had bargained with them to shape his raw gold
• 12.012 and shape
• 13.018 They saw the little dark shape of the hobbit
• 13.023 when a black shape swooped at him,
• 17.062 dark shapes small yet majestic against the distant glow.
• 18.022 and in bear’s shape;
• 18.043 in man’s shape,
• 18.051 the men of his line had the power of taking bear’s shape,
• 19.028 where the shapes of the land