A scientist is studying three different layers of sedimentary rock to learn how a particular mammal species has changed over time. In the rock layer that is closest to the Earth's surface, fossilized individuals of this species have hooves on both their front feet and their back feet. In the layer below, fossilized individuals have three padded toes on both their front feet and their back feet. In the bottom layer, fossilized individuals have four padded toes on their front feet and three padded toes on their back feet.

Question

Based on this information, individuals of this species today most likely have
A.
four padded toes on their front feet and three padded toes on their back feet.
B.
three padded toes on both their front feet and their back feet.
C.
hooves on both their front feet and their back feet.
D.
four padded toes on both their front feet and their back feet.

Answer 1

Based on the information provided, we can infer the evolutionary progression of the mammal species based on the fossilized remains found in the different sedimentary rock layers.

• In the top layer (closest to the surface), the species has hooves on both their front feet and back feet.
• In the middle layer, the species has three padded toes on both their front feet and back feet.
• In the bottom layer, the species has four padded toes on their front feet and three padded toes on their back feet.

The trend shows a progression from four padded toes to three padded toes, and then to hooves, which indicates a potential evolutionary adaptation over time.

Given this trend, the description of the most recent fossils suggests that the living species most likely has the adaptations seen in the most recent layer, which is the one with hooves. Therefore, today’s individuals of this species most likely have:

C. hooves on both their front feet and their back feet.