PERISSODACTYLA Mammalogy – 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

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

Power vs Speed of Movement Cheetah Badger Lever arm ratios (R): m = joint to insertion l = joint to ground m 10 cm m 6 cm Badger: R= 0.4 l = 15 cm l = 50 cm Cheetah: R = 0.2

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.

Mesaxonic For “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