Plesiadapis

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Plesiadapis Fossil range: Late Paleocene–Early Eocene PreЄ Є O S D C P T J K Pg N [1]
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: †Plesiadapiformes Superfamily: †Plesiadapoidea Family: †Plesiadapidae Genus: †Plesiadapis Gervais, 1877
Type species
†Plesiadapis tricuspidens
Paleospecies[2][3]
†Plesiadapis walbeckensis Russell, 1964 †Plesiadapis remensis Lemoine, 1887 †Plesiadapis tricuspidens Gervais, 1877 †Plesiadapis russelli Gingerich, 1976 †Plesiadapis insignis (Piton, 1940) †Plesiadapis praecursor Gingerich, 1975 †Plesiadapis anceps Simpson, 1936 †Plesiadapis rex (Gidley, 1923) †Plesiadapis gingerichi Rose, 1981 †Plesiadapis churchilli Gingerich, 1975 †Plesiadapis fodinatus Jepsen, 1930 †Plesiadapis dubius (Matthew, 1915) †Plesiadapis simonsi Gingerich, 1975 †Plesiadapis cookei Jepsen, 1930

Plesiadapis is one of the oldest known primate-like mammal species which existed about 58-55 mya in North America and Europe.^[2] It looked a little like a squirrel. Plesiadapis still had claws and its eyes were located on each side of the head, making them faster on the ground than on the top of the trees, but they begin to spend long times on lower branches of trees, feeding on fruits and leaves.

This genus probably arose in North America and colonized Europe on a landbridge via Greenland. Thanks to the abundance of the genus and to its rapid evolution, species of Plesiadapis play an important role in the zonation of Late Paleocene continental sediments and in the correlation of faunas on both sides of the Atlantic. Two remarkable skeletons of Plesiadapis, one of them nearly complete, have been found in lake deposits at Menat, France ^[2]. Although the preservation of the hard parts is poor, these skeletons still show remains of skin and hair as a carbonaceous film - something unique among Paleocene mammals. Details of the bones are better preserved in fossils from Cernay, also in France, where Plesiadapis is one of the most common mammals. The skull of Plesiadapis is relatively broad and flat, with a long snout with rodentlike jaws and teeth and long, gnawing incisors separated by a gap from its molars. Orbits are still directed to the side, unlike the forward facing eyes of modern primates that enable three-dimensional vision ^[4]. Although its braincase was small according to today's standards, it was larger than in the contemporary hoofed mammals, for instance. Plesiadapis had mobile limbs that terminated in strongly curved claws, and it sported a long bushy tail which is beautifully preserved in the Menat skeletons. The way of life of Plesiadapis has been much debated in the past. Climbing habits could be expected in a relative of the primates, but tree-dwelling animals are rarely found in such high numbers. Based on this and other evidence, some paleontologists have concluded that these animals were mainly living on the ground, like today's marmots and ground squirrels ^[2]. However, more recent investigations have confirmed that the skeleton of Plesiadapis is that of an adept climber, which can be best compared to tree squirrels or to tree-dwelling marsupials such as possums ^[4].

[edit] References

[edit] External links

• Mikko's Phylogeny Archive

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