Q.39Arrange the following evolutionary events in the history of horse evolution chronologically –
- (A) Miohippus
- (B) Orohippus
- (C) Hyracotherium (Eohippus)
- (D) Merychippus
Choose the correct answer from the options given below:
- (A), (B), (C), (D)
- (C), (B), (D), (A)
- (B), (A), (D), (C)
- (C), (B), (A), (D)
The correct chronological order is (C), (B), (A), (D): Hyracotherium (Eohippus) → Orohippus → Miohippus → Merychippus. This traces horse evolution from ~55 million years ago (Eocene) through increasing size, toe reduction, and grassland adaptations.
Question Breakdown
This matching question requires arranging horse evolutionary ancestors by geological age. Hyracotherium starts as a small, multi-toed browser; later forms develop single toes and grazing teeth for open plains. Key for GATE Life Sciences evolution sections.
Option Analysis
Option 1: (A), (B), (C), (D)
Wrong: Miohippus (Oligocene, ~34 mya) predates Orohippus (~50 mya) and Hyracotherium (~55 mya).
Option 2: (C), (B), (D), (A) Correct
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(C) Hyracotherium/Eohippus: Eocene (~55-45 mya), dog-sized, 4-toed front/3-toed back.
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(B) Orohippus: Early Eocene-Mesozoric (~50 mya), slight size increase, better teeth.
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(A) Miohippus: Oligocene (~34 mya), three-toed, larger, forest-grassland transition.
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(D) Merychippus: Miocene (~15 mya), single-toed precursor, high-crowned teeth for grass.
Option 3: (B), (A), (D), (C)
Wrong: Orohippus after Hyracotherium; places earliest last.
Option 4: (C), (B), (A), (D)
Wrong: Miohippus (~34 mya) before Merychippus (~15 mya); reverses late sequence.
Horse evolution chronological order reveals a 55-million-year progression from forest browsers to grassland runners, starting with Hyracotherium and advancing through Orohippus, Miohippus, to Merychippus—crucial for competitive biology exams like GATE Life Sciences.
Timeline Breakdown
Hyracotherium (Eohippus) kicked off in Eocene forests: small, multi-toed, fruit-eater. Orohippus refined teeth for tougher forage. Miohippus grew larger amid grasslands, reducing toes. Merychippus revolutionized speed with springy legs and grinding molars.
Trends: Size doubled repeatedly; toes fused to one; legs lengthened; brain enlarged; teeth hypsodont for silica-rich grass.
Stage Era (mya) Key Traits Hyracotherium Eocene (55-45) Dog-sized, 4 toes front Orohippus Eocene (50) Improved molars Miohippus Oligocene (34) 3 functional toes Merychippus Miocene (15) High-crowned teeth, speed Exam Relevance
GATE questions test this sequence to assess macroevolution grasp. Note: Modern view shows branching, not linear—Equus arose from multiple Miocene lines.
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