Archaeoceti

Taxobox
name = Archaeoceti
fossil_range = Eocene to Miocene (non-Autocetan)


image_width = 250px
image_caption = Pakicetus, one of the very first archeocetids
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Cetacea
subordo = Archaeoceti
subdivision_ranks = Families and Clades
subdivision = see text

Archaeocetes, or "ancient whales", are a paraphyletic group of cetaceans that gave rise to the modern cetaceans. The Archaeocetes were once thought to have evolved from the mesonychids based on dental characteristics. However, recent studies in molecular genetics and non-dental morphology show that the first whales or the archaeoceti most likely evolved from artiodactyls (perhaps of the family Hippopotamidae which includes the modern Hippopotamus). The ancestors of archaeocetes probably diverged from the artiodactyls around the time of the Cretaceous–Tertiary extinction event. Most archeocetes had hind limbs, suggesting that they were likely fully terrestrial. As the Eocene epoch progressed the archaeocetes were becoming less terrestrial and more aquatic. Before the Eocene epoch came to an end, one group of archaeocetes, the basilosaurids, gave rise to early modern cetaceans. The Archaeocetes suffered a heavy loss of genera during the Eocene-Oligocene extinction event, but some species survived into the Oligocene. The last archaeocetes became extinct in the Oligocene, which was probably a basilosaurid. Another explanation is climate change; as Miocene progressed, the ocean became cooler and cooler. They may have become extinct in the combination of the two factors: competition and climate change.

Taxonomy and Phylogeny

* Superorder Cetartiodactyla
** Order Cetacea
*** Suborder Archaeoceti
***** Family Pakicetidae
****** Genus "Pakicetus"
****** Genus "Nalacetus"
****** Genus "Ichthyolestes"
***** Family Ambulocetidae
****** Genus "Ambulocetus"
****** Genus "Gandakasia"
****** Genus "Himalayacetus"
***** Family Remingtonocetidae
****** Genus "Andrewsiphius"
****** Genus "Attockicetus"
****** Genus "Dalanistes"
****** Genus "Kutchicetus"
****** Genus "Remingtonocetus"
***** Family Protocetidae
****** Genus "Rodhocetus"
***** Subfamily Indocetinae
****** Genus "Protocetus"
****** Genus "Georgiacetus"
***** Family Basilosauridae
****** Subfamily Basilosaurinae
******* Genus "Basilosaurus"
****** Subfamily Dorudontinae
******* Genus "Zygorhiza"
******* Genus "Dorudon
*** Suborder Mysticeti
*** Suborder Odontoceti
**** (unranked) Squalodontoidea
***** Genus "Squalodon"

Phylogeny

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

ee also

* Evolution of cetaceans
* Cetaceans
* Mesonychid
* Cetartiodactyla

References

External links

* [http://www.palaeos.com/Vertebrates/Units/520Cetartiodactyla/520.100.html#Pakicetidae Archaeoceti]
* [http://members.tripod.com/Dolphinity/archaeocetitekst.htm Archaeoceti and Basilosaurus]