A placenta-specific boundary element near an ancient conserved element. Color codes: blue: placental poeciliids alignment; orange: nonplacental poeciliids alignment; green: “ancient” teleost alignment. (A) Average nucleotide diversity for each alignment, 20-bp sliding window. (B) Per-base conservation scores, representing the estimated likelihood of the base belonging to a conserved element according to PhastCons. (C) Conserved elements predicted by PhastCons.