BIOL 3626: Day 3

Indohyus

• closest known relative to cetaceans

• small hoofed animal

  • already adapted for semi-aquatic lifestyle, with dense bones to reduce buoyancy

  • fed terrestrially

Closest living relative to cetaceans?

• Hippo!

• both apart of Artiodactyla

Pakicetus

• first cetacean

• degree of aquaticness debated but at the very least semiaquatic lifestyle

Ambulocetus

• definitely aquatic

  • swimming like an otter

  • feeding like a crocodile

  • webbed digits

Adaptations to get to water

• fatty pad in the lower jaw

• copy the rest

Basilosaurus

• first group of fully aquatic cetaceans with flexible tails, flukes, and nonfunctional hindlimbs

• likely eel-like in movement

Dorudon

• true ocean-going lifestyle

• typical to what we think of as modern cetaceans

Retained but not expressed ancestral features

• dolphin embryos show evidence of:

  • whiskers

  • hindlimb

Pinniped Evolution

• part of carnivora

• evolved from otter-like ancestors

• debate as to whether mono or diphyletic

  • however, now seen as monophyletic

Enaliarctos

• appears to have used both fore and hindlimbs for swimming, unlike

  • sea lions and fur seals (which just use forelimbs)

  • true seals (use hindlimbs)

  • note: only walruses use both

Puijila

• closest non-true pinniped relative to modern pinnipeds

• superficially resembles an otter much more than a modern pinnipeds

Evolution of Sirenia

• closest living relatives are elephants

Prorastomus

• oldest known sirenian ancestor

Desmostylia

• marine mystery

  • seem to be on the path of what sirenians might have became

• only known extinct order of marine mammals

  • may have been outcompeted by sirenians

Thalassocnus

• a seafaring sloth

• likely fed on macroalgae and seagrasses, akin to sirenians and desmostylians