I may have cuckoo marans, dominiques, and barred rocks. I called the hatchery and they confirmed all three hatched well on the day of my assortment and they had included marans as the possible rare breed bonus. My chicks are 22 days old. I can see baby combs on some, but not others. Some have bold, defined barring, others barely have any. Some look to be turning more white and others are staying mostly black. At what age will i know whos who? (Im super excited to maybe have a marans!)
Did you order sexed or straight run? The marans as the rare breed bonus, is that one chick or several? Marans are supposed to have white legs. Rocks and Dominiques have yellow legs, usually with a dark wash of color on the front for females. Rocks have straight combs, you'll see a little ridge of points sticking up. Dominiques have rose combs, so you'll mostly see a wider, flat spot for the comb right now. Hope that helps a little. It will be easier when they feather out. Marans are cuckoo, not barred, so the pattern often looks "messier" than the barred birds.
The leg color definately helps! The way i was told is there could ve one or even six marans since i got an assortment. I have a few messy birds (which leg color will be checked). I ordered sexed (and think i got a "whoopsy roo", but i like him).