Evolutionary Biology

Step 1: Understanding Equidae Evolution.
The evolution of Equidae (horses) is marked by several changes, including changes to the number of digits, hypsodonty (tooth structure), and limb length. One of the most prominent changes is the lengthening of the skull in front of the orbit, a feature that distinguishes modern horses.
Step 2: Analyzing the options.
(A) Number of lateral digits or toes increases: Incorrect — The number of digits decreased over time in the evolution of Equidae, from multiple toes to a single digit.
(B) Decrease in hypsodonty: Incorrect — Hypsodonty, or high-crowned teeth, actually increased in horses as they adapted to grazing on tougher vegetation.
(C) Lengthening of skull in front of the orbit: Correct — This is a key feature of equid evolution, contributing to their distinctive head shape.
(D) Limb ratios remained constant: Incorrect — Limb proportions changed over time, with an increase in limb length relative to body size.
Step 3: Conclusion.
The correct answer is (C) Lengthening of skull in front of the orbit, a significant feature in the evolution of Equidae.