Question

background
when charles darwin first proposed the idea that all new species descend from an ancestor, he performed an exhaustive amount of research to provide as much evidence as possible. today, the major pieces of evidence for this theory can be broken down into the fossil record, embryology, comparative anatomy, and molecular biology.
fossils
this is a series of skulls and front leg fossils of organisms believed to be ancestors of the modern-day horse.
source: http://www.iq.poquoson.org

1. give two similarities between each of the skulls that might lead to the conclusion that these are all related species.
2. what is the biggest change in skull anatomy that occurred from the dawn horse to the modern horse?

Explanation:

1. For skull similarities: All skulls share a basic jaw and skull cavity structure that houses the brain, and each has a tooth-bearing jaw adapted for feeding, indicating a shared evolutionary origin.
2. For the largest skull change: Comparing the dawn horse (Eohippus) to the modern horse (Equus), the overall skull size and length increased significantly, and the snout/face portion elongated dramatically to accommodate larger teeth and a more specialized feeding structure.

Answer:

1. Two similarities across all skulls:

• All have a defined brain cavity and jaw structure.
• All possess teeth within a jawbone for feeding.

1. The biggest change in skull anatomy is a dramatic increase in overall skull size and a significant elongation of the snout/face region from the small, compact skull of Eohippus to the large, elongated skull of the modern Equus.