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