Smithsonian Digital Archive / Exhibit 04

Evolution of Whales

Tracing the morphological shift from terrestrial quadrupeds to the titans of the abyssal deep.

Fossil Record

~50 MILLION YEARS AGO
Pakicetus
Pakicetus Skeleton
Early four-walking legs. Large teeth adapted for eating meat. The terrestrial dawn of the cetacean lineage.
~38 MILLION YEARS AGO
Dorudon
Dorudon Skeleton
Fully aquatic but retained vestigial hind limbs. Evolution of the tail fluke for propulsion.
PRESENT ERA
Blue Whale
Blue Whale Tail
The largest known animal. Complete loss of external hind limbs; nostrils migrated to the blowhole.

Phylogenetic Cladogram

Tracing the common ancestor shared among Artiodactyla (even-toed ungulates) and Cetacea.

  • 🦒 Giraffe Diverged
  • 🐄 Cow Diverged
  • 🦛 Hippopotamus Sister Clade
  • 🐋 Blue Whale Crown
Cladogram

Embryological Evidence

Dolphin and whale embryos initially develop hind limb buds, which are later reabsorbed before birth—a genetic echo of their walking ancestors.

Mammal Embryo
Cow Embryo
Dolphin Embryo
Dolphin Embryo

Anatomical Homology

Sister Taxa Comparison
Hippopotamus
Hippopotamus

Closest living terrestrial relative. Shares common traits such as multi-chambered stomachs, internal testicles, and lack of hair/sweat glands. Primarily amphibious lifestyle.

Crown Species
Blue Whale
Whale Underwater

Pelagic adaptation. Forelimbs modified into flippers with homologous skeletal structures. Hindlimbs reduced to internal floating pelvic bones.