Archaeoceti

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iArchaeoceti
Fossil range: Eocene to Miocene (non-Autocetan)

Pakicetus, one of the very first archeocetids

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Cetacea
Suborder:	Archaeoceti

Families and Clades

see text

Archaeocetids, or "ancient whales", are a paraphyletic group of cetaceans that gave rise to Autoceti - the new cetaceans. The archaeoceti once thought to have evolved from the mesonychids. However, recent studies show that the first whales or the archaeoceti might have evolved from the Acreodi - which were ancestral to mesonychids. So, mesonychids and the cetaceans shared a common ancestor. The skulls and teeth of early cetaceans such as Archaeocetes strongly resemble those of certain Acreodi, and the Acreodi ungulates probabaly gave rise to hippopotamuses as well, which are the closest relatives of cetaceans. The ancestors of archaeoceti probably diverged from artiodactyls in the Latest Cretaceous or Early Paleocene. Most archeocetids had hind limbs unlike the cetaceans of today. The very first archaeocetid was probably fully terrestrial. As the Eocene progressed the archaeocetids were becoming less terrestrial and more aquatic. By the Late or latest Eocene the archaeocetids, the basilosaurids gave rise to early modern cetaceans. The Archaeoceti managed to survive the Eocene-Oligocene extinction event, but they suffered a heavy loss of genera. The Archaeoceti were common early in the Oligocene, but not as common as in Eocene. The last archaeoceti became extinct in the Miocene, which was probably a basilosaurid, probably because of competition with the toothed cetaceans and the new sharks appearing in the Miocene (e.g. Megalodon). Another explanation is climate change; as Miocene progressed, the ocean became cooler and cooler. They may have became extinct in the combination of the two factors.

Image:Basilosaurus illustration.jpg

1 Taxonomy and Phylogeny
- 1.1 Phylogeny
2 See also
3 External links

[edit] Taxonomy and Phylogeny

Superorder Cetartiodactyla (or Acreodi)
- Order Cetacea
  - Suborder Archaeoceti
    - - Genus ?Ferecetotherium (the most primitive cetacean)
      - Family Pakicetidae
    - (?unranked) ?Ambulocetoidea
      - Genus Himalayacetus
        Genus Gandakasia
      - Family Ambulocetidae
        Genus Ambulocetus
      - Family Remingtonocetidae
      - Family Protocetidae
      - Subfamily Indocetinae
        Genus Protocetus
        Genus Georgiacetus
      - Family Basilosauridae
        Subfamily Basilosaurinae
        Genus Basilosaurus
        
        Subfamily Dorudontinae
        Genus Dorudon
  - (unranked) Autoceta
  - Suborder Mysticeti
  - Suborder Odontoceti
    - (unranked) Squalodontoidea
      - Genus Squalodon

[edit] Phylogeny

Cetartiodactyla
|--Cetacea
|  |--Pakicetidae 
|  `--+--Ambulocetidae 
|     `--+--Remingtonocetidae 
|        `--Protocetidae
|           |--Georgiacetus
|           `--Basilosauridae
|              |--Basilosaurus
|              `--+--Dorudon 
|                 `--Autoceta
|                    |--Odontoceti 
|                    |  |--Squalodontoidea 
|                    |  |  |--Squalodontidae 
|                    |  |  `--Rhabdosteidae
|                    |  `--Physeteroidea 
|                    `--Mysticeti 
`--Artiodactyla