17 - Perissodactyla

Annotations:

• large, hoofed, terrestrial herbivores 
• walk around on tips of toes 
• hard, KERATINIZED hooves
• limbs move in single plane because of pulley-like ASTRAGALUS in ankle 
• cursorial locomotion 
• usually HYPSODONT dentition 
• morphology and life histories typically suited for open habitats 
• efficient feeding and outrunning predators 
• ungulate distribution limited by forage 
• morphology of forage the result of pressures of ungulates over evolutionary time 
• ungulates = the most IMPORTANT group of mammals to humans for commerce and economics 
• domestication, sport hunting, ecotourism 
• perissodactyls today much LESS diverse than artiodactyls 
• a switch from 50 mya, when they far outnumbered smaller, less diverse artiodactyles 
• MONOPHYLETIC group
• 3 families, 6 genera, 16 species 
• horses, asses, zebras, tapirs, rhinos 
• formerly much more DIVERSE 
• oldest identifiable perissodactyl fossils from late Paleocene (55 mya) 

1. characteristics

   Annotations:

   • adapted to UNGULIGRADE (hoofs) CURSORIAL locomotion
   • clavicle ABSENT 
   • group defined by FOOT structure 
   • odd-toed ungulates 
   • only ONE functional digit on each foot, weight borne on middle digit - the LARGEST 
   • tapirs with 4 digits on front, 3 on hind, 3 on each in rhinos, 3rd digit the only one on HORSES 
   • cannot bend hindlimbs enough to get up hindfeet first when laying on ground 
   • elongate skull with long ROSTRUM
   • large molars and premolars, typically HYPSODONT and LOPHODONT for grazing lifestyle 
   • diastema between incisors and cheekteeth 
   • no true HORNS or ANTLERS 
   • rhino "horn" lacks bony core and keratinized sheath; a dermal mass of agglutinised, keratinized fibers (fused hairs) 
2. evolutionary/fossil history

   Annotations:

   • arose in late PALEOCENE in Asia
   • Rhinos evolved in Eurasia and North America in early Eocene 
   • largest known land mammal = PARACERATHERIUM (5 meters tall, 11,000 kg)
   • tapirs evolved in North America in EOCENE
   • dominant browsers of Eocene 
   • began to decline in Miocene (climatic changes, competition with artiodactyls) 
   • horses evolved in North America in early EOCENE
3. cursorial locomotion adaptations

   Annotations:

   • integrated LOCOMOTOR and RESPIRATORY functions
   • synchronize breathing with stride cycles 
   • tracheal valving shunts air from side to side between lungs
   • slim, elongate legs 
   • muscles positioned near body 
   • tendons DISTALLY 
   • long legs
   • metacarpals and metatarsals elongate 
   • LOSS or REDUCTION of clavicle 
   • FLEXION and EXTENSION of spine
   • increase number of moveable joints in limb
   • only hoof-bearing TIPS of digits contact ground
   • ASTRAGALUS rests on distal tarsal bones 
   • tarsals modified by loss or fusion of elements 
   • weight transferred to central digits 
   • SPRINGING ligament in feet 
   • NUCHAL ligament supports weight of head 
4. feeding specializations

   Annotations:

   • herbivorous
   • simple stomach, but large CECUM for microorganism-facilitated breakdown of cellulose 
   • molariform cheek teeth with large complex occlusal surfaces 
   • food retained shorter period than for ruminant artiodactyls 
   • less efficient and must consume LARGER amounts than ruminants 
5. economics & conservation

   Annotations:

   • horses domesticated ~4,500 years ago in Central Asia 
   • second only to CATTLE in importance to human development or cultural and economic systems 
   • travel, exploration, warfare, agriculture 
   • domestic horses doing VERY WELL (introductions)
   • other perissodactyls in trouble (human interference, poaching rhino horns, habitat destruction)
   • African ass and quagga recently extinct
   • Onager, Przewalski's horse, Grevy's and mountain zebra endangered 
   • mountain tapir endangered 
   • all rhinos endangered or vulnerable 
6. families
   1. Equidae

      Annotations:

      • most species are HIGHLY social
      • form herds and/or clans
      • polygynous mating system
      • social hierarchy - led by DOMINANT stallion 
      • HAREMS formed in some species 
      • bachelor species 
      • complex behavior and vocal communication 
      • fission-fusion social system common 
   2. Tapiridae

      Annotations:

      • Stocky build (weigh up to 320 kilograms) 
      • short, flexible (proboscis)
      • limbs short and stout 
      • 4 toes on front, 3 toes on hind feet 
      • brachyodont cheek teeth 
      • nasal bones of skull RETRACTED - above orbits 
   3. Rhinocerotidae

      Annotations:

      • large, heavy-bodied, short-legged
      • graviportal limbs 
      • weigh up to 2,800 kg
      • 3 or 4 toes on front foot, 3 toes on hind foot 
      • nasal bones THICKENED and enlarged 
      • supported horn of dermal material 
      • use of horns in traditional Eastern "medicine" and more recently sprinkled in alcoholic cocktails 
      • $75,000 per kg (twice the value of gold) 
      • 90% decrease in number of wild rhinos today compared to 1970
      • critically threatened - 35 Javan rhinos, ~100 Sumatran, and <5,000 black rhinos 
      • near threatened - ~20,000 white rhinos 
      • vulnerable - as few as 600 greater one-horned rhinos in 1976, increased since then