Evolutionary Development of the Equine

• The earliest animal to bear recognizably horse-like anatomy was the Hyracotherium or Eohippus

• Over his 55 million year history, the horse has evolved into an animal whose specialized anatomical adaptations to the musculoskeletal system facilitate extremely efficient locomotor characteristics.

Eohippus

Equus

Relevance of Mammalian Stance to Comparative Vertebrate Anatomy

• A mammal's stance affects many aspects of their lives and is, therefore, a very good way to compare mammals.

• By comparing two different species stances, it would be possible to predict which animal would be faster or stronger.

• Stance can tell how well an animal can grasp things, balance on two feet, or leap great distances.

• It is a structural difference that benefits the animal in its particular lifestyle and way of survival.

Zoological Axiom“The degree of specialization of a structure is directly

correlated to the survival of the species”

Types of mammalian postures

• Plantigrade- In terrestrial animals Plantigrade locomotion means walking with the metatarsals and phalanges flat on the ground.

Examples: human, bear, squirrels, coons, opossums

• Digitgrade- Is a posture that allows animals to stand or walk on its digits, or toes. Digitigrade animals walk on their distal and intermediate phalanges.

Examples: walking birds, cats, dogs, and most other mammals

• Unguligrade- hoofed animals that sustain the whole body weight on the tips of the most distal phalanx’s

Examples: horses, cows, llamas, rhino’s, hippo’s, camels

Examples of postural stance

Postural development from “Digitgrade” to “Unguligrade”

EohippusMiohippus

Merychippus

Equus

• Changes in weather patterns and environment have resulted in a much larger, heavier animal with well developed locomotor capabilities– Athletic potential– Speed + endurance

• In order for the modern horse to be successful, bio-engineering has resulted in many unique specialty adaptations

• The earliest animal to bear recognizably horse-like anatomy was the Hyracotherium or Eohippus

Overview of the modern equine musculoskeletal design and function

*Elongation of distal bones: ‘s leverage and use of power = speed + endurance

*Migration of distal muscles proximally results in ligamentous support and a degree of automacity

*Rear wheel drive

Specialty adaptations of the equine distal limb that conserve energy and dissipate shock

The Fetlock Joint -sesamoid bones-SL, DFT, SFT and distal check ligs

Front half of foot Back half of foot

Specialty adaptations of the equine distal limb that conserve energy and dissipate shock

The footThick hoof wall, concave sole, well developed fibro fatty cushions, navicular bone, bars, frog, dermal epidermal lamellae, bars, specialized vasculature