Rantamäki (Ingrian) comes from Ingrian ranta, from Proto-Finnic ranta, from Proto-Germanic strandō, from Proto-Indo-European (s)trAnt-, from Proto-Indo-European sterh₃-, from Proto-Indo-European ster- — sterile, infertile.
Ancestry of “Rantamäki”, step by step
Rantamäki traces back through two separate lines of ancestry.