PERISSODACTYLAMammalogy – EEOB 625 -3 March 2004
• The Origin & Adaptive Radiation of Ungulates
• Order Condylartha: dominant "Ungulates” of the Paleocene
• Ancestral to: Perissodactyla, Artiodactyla,
Subungulates and Cetacea
• Coevolution of Ungulates with:
Food: Woody plants, forbs, and grasses
Predators: Arms race of size & speed
Coevolutionary Factors in the Adaptive Radiation of Ungulates
• Climate Change in the early Cenozoic:
Progressive cooling & drying of continents Loss of forests & expansion of prairies
• Grasses: Origin (Oligocene) and radiation
• Anti-grazing defenses of grasses:
- growth from the base, near the roots
- silica in the cell wall increases the
“cost” of mastication
Adaptations for Cellulose Digestion
• Plant anatomy: Cell wall, cell membrane, and cytoplasm: with protein & carbohydrates
• Dental adaptations for mastication of cell walls and lignified plant structures:
1) the hypsodont (high crowned) molar,
ever growing or “rootless” in some species
2) Selenodont occlusal surface: a rasping,
grinding surface, highly resistant to wear
• Digestive Adaptations: Cecum & rumen
Evolution of the hypsodont molar
bunodont selenodont
hypsodont
Ungulate Adaptations for Locomotion
• Selection for mass, mobility, & speed
• Determinants of speed:
length of stride & rate of striding
• Adaptations for long stride
‑ lengthening of metacarpals & metatarsals
‑ free swing of the scapula
‑ flexible vertebral column
Ungulate Adaptations for Locomotion
• Determinants of running speed:
length of stride & rate of striding
• Adaptations for high stride rate
‑ reduction of mass of distal limb elements
- cannon bone & springing ligament
- short lever arms for “high gear” muscles
- summing velocities of many limb segments
BadgerCheetah
l l
mm
Lever arm ratios (R):m = joint to insertion l = joint to ground
= 15 cm
6 cm10 cm
= 50 cm
Badger: R= 0.4
Cheetah: R = 0.2
Power vs Speed of Movement
Cannon bone & Springing ligament
PERISSODACTYLA: A clade defined by the mesaxony,
• Mesaxonic? Weight-bearing axis through digit 3
• Early descendants of Condylartha
• Eocene radiation, decline in late Oligocene
• Evolution of the horse in N. America: A classic phylogeny, but what is wrong with this picture?
• Trends and misconceptions regarding equid evolution: Compare Text Figs.
MesaxonicFor “meso”i.e., middle
PERISSODACTYLA: Systematics
• Mesaxonic ?
• Early descendants of Condylartha
• Eocene radiation, decline in late Oligocene
• Evolution of the horse in N. America:
• Three Extant families:
• Equidae, Tapiridae & Rhinocerotidae
J.Z. Young
Fig. 19.2, Feldhamer
Fig 19.4,Feldhamer