Pakicetidae
| Pakicetidae | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Skull of Pakicetus |
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| Temporal occurrence | ||||||||||||
| Eocene | ||||||||||||
| 50 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pakicetidae | ||||||||||||
| Gingerich & Russell , 1990 | ||||||||||||
The Pakicetidae are a group of extinct early representatives of the whales that still had limbs that allowed them to live on land. They lived in South Asia in the Eocene and allow important conclusions to be drawn about evolution. There are three known genera: Pakicetus , Nalacetus and Ichthyolestes .
See also: Basilosaurus , Ambulocetidae , Dorudontidae
General
The Pakicetidae were very similar in physique and were about the size of a fox to wolf , which outwardly showed little resemblance to today's whales. They had four mammalian limbs that were suitable for locomotion on land. However, some adjustments showed that the animals could have lived in shallow water at least for a time, for example a thickening of the bones, which could have reduced buoyancy. The eye sockets were high on the head, the nostrils were above the front teeth. The affiliation to the whales can be recognized by the construction of the ears , the cranial cavity and the molars (in the arrangement of the cusps).
The Pakicetidae lived in the Eocene about 50 million years ago. Fossil finds are known from Pakistan and India , and it is believed that the development of whales took place in this region.
Systematics
Apart from the poorly preserved Himalayan acetus , the Pakicetidae are the oldest whale finds. Groups that emerged later, such as the Ambulocetidae , Rodhocetus or the Remingtonocetidae, show significantly stronger adaptations to aquatic life.
Importance for research
The discovery of the Pakicetidae has helped to better understand the relationships between whales. A descent of the whales from the Mesonychia , which was sometimes assumed in the past, has now been refuted. Rather, it could be seen that the early whales still had an ankle joint with a double-rolled joint surface. This feature was previously considered to be the exclusive feature of the ungulate , so the close relationship between the two taxa could be morphologically substantiated. Molecular genetic studies had already shown this close relationship earlier, according to today's most common theory, even-toed ungulates and whales are grouped together as cetartiodactyla , as some even- toed ungulates, like hippos, are more closely related to whales than to other mammals.
literature
- TS Kemp: The Origin & Evolution of Mammals. Oxford University Press, Oxford 2005, ISBN 0-198-50761-5 .
Web links
- Information on palaeos.com
- Information on The Thewissen Lab ( Memento from October 12, 2011 in the Internet Archive )