Work Step by Step
In examining the cladogram, we look at the characteristic that arose before any of those species arose. Option A is incorrect. The placenta arose right before the evolution of humans. Option C is incorrect. Four limbs evolved after the appearance of the trout. Option D is incorrect. Mammary glands appeared right before the appearance of the wallaby and human. Option B is correct. The notochord appeared before the appearance of the trout, wallaby, and human; this means that these species share this characteristic.