Bilaterally symmetrical animals
INFRACLASS: Eutherians
Eutherians are distinguished by their unique development of the bone structure of the lower part of their legs and their jaws.
Eutheria have prominent malleolus. The malleolus is best recognised in humans as the bone which protrudes outwards either side of the ankle.
There are also differences in the foot bone structure and the jaws and teeth of eutherians which distinguish them from other therians.
Fossilised extinct eutherians have been named as bobolestes, montanalestes, murtoilestes and prokennalestes. However, eomaia is considered the oldest dating back 125 million years.
The extant eutherians belong to four subgroups. The subgroups are euarchontoglires, laurasiatheria, xenarthra and afrotheria.
The euarchontoglires are closely related to the laurasiatheria and this has been based on DNA analysis.
In fact, DNA evidence has played a major part in categorising today's mammals into all of these four subgroups.
Rodents, rabbits and primates all belong to the euarchontoglires.
Hedgehogs, moles, whales, dolphins, bats, giraffes, hippopotami, camels and many farm animals belong to the laurasiatheria.
Xenarthra are extant throughout the Americas and contain animals such as the anteater and the armadillo. The members of xenertha have unique vertebral development.
Afrotheria are considered to have developed earlier than euarchontoglires, xenarthra and laurasiatheria.
Afrotheria were originally considered solely resident to the African continent, although fossil evidence shows that at least over time, this is not strictly true.
Afrotheria are believed to share similar characteristics in regard to have a large number of vertebra, anklebone shape and the fact that their adult teeth develop quite late.
Afrotheria contain animals such as the aardvark, elephant and manatee.
Humans are euarchontoglires.
|
Primates and all other DNA proven relatives. |
LAURASIATHERIA DNA related Laurasian based mammals. |
XENARTHRA Uniquely backboned American based mammals. |
AFROTHERIA Bone structure and dentally unique mammals. |
|
BOBOLESTES |
MONTANALESTES |
MURTOILESTES |
PROKENNALESTES |
EOMAIA Extinct 10cm long eutherian. |
