Cetacean Evolution When did whales evolove? –First recognizable cetacean 50 mya From whom did whales evolve? –Suborder Archaeoceti (‘first’-‘whale’) Up to 21m with reduced hindlimbs and strong snouts, long tail, short neck, reduced hindlimbs, paddle-shaped front limbs, and vertebrae that allowed up and down movement. adapted to life in shallow coastal fringes as well as open seas

Cool Whale Evoluton Webpage whalekiosk.html

Precursor to Archaeoceti Terrestrial Mesonychid Condylarthra gave rise to archaeocetes –Mesonychid- large-bodied creatures, some carnivorous, some herbivorous, –Many of their fossils are found in sediments deposited in estuaries and therefore they may have been aquatic. –Condylarthra- primitive ungulates (cows, hippos, etc.).

Artiodactyls ORDER ARTIODACTYLA – Means “even-toed” Suborder Suina –Family Suidae: pigsSuidae –Family Hippopotamidae: hipposHippopotamidae –Family Tayassuidae: peccariesTayassuidae Suborder Tylopoda –Family Camelidae: camels and llamasCamelidaellamas Suborder RuminantiaRuminantia –Family Tragulidae: chevrotainsTragulidae –Family Moschidae: musk deerMoschidae –Family Cervidae: deerCervidaedeer –Family Giraffidae: Giraffe and OkapiGiraffidaeGiraffeOkapi –Family Antilocapridae: pronghornAntilocapridae –Family Bovidae: cattle, goats, sheep, and antelopeBovidaesheepantelope

From Cows to Whales Cetaceans thus share common ancestry with Artiodactyla, that gave rise to modern ungulates –Supported by the following evidence Blood composition Fetal blood sugar Chromosomes Insulin Uterine morphology Tooth enamel microstructure

Where did whales evolve

More Aquatic Meant A backwards shift of the external nostrils More streamlined form A dorsal fin A horizontal tail fluke Teeth became sharp uniform, typical of many present-day odontocetes Lost –Long, mobile neck –Functional hindlimbs –Most of the pelvic girdle

Mysticetes from Odontocetes Mid-Oligocene, some mysticetes lost their teeth for rows of baleen plates. –Baleen is epidermal in origin, growing as fibres embedded in a softer matrix –As the softer material is rubbed away by the tongue, the fibres become exposed –Most present-day baleen whales still have teeth during the early stages of fetal development

Other Adaptations Telescoping of the front of the skull occurred along with The development of acoustic scanning –Echolocation may have been practiced by the earliest odontocetes, because their ear bones were isolated by fat bodies and air saces allowing directional hearing. Specialized Organs –The mellon –Nasal passages –The spermaceti organ (in sperm whales)