toomey at denr1.igis.uiuc.edu
Fri May 20 12:53:44 EST 1994
eang95 at castle.ed.ac.uk (J R Small) writes:
>NO: Camels are artiodactyls because they have two toes, etc. Does anyone
>have any ideas why this kind of 'footware' may be of selective advantage
>to these kinds of animals?
Actually, the thing that makes camels artiodactyls is a more recent
common ancestry with pigs, deer, cows, hippos, giraffes, and
peccaries than with any other living vertebrates. (This
would be a phylogenetic definition of Artiodactyla).
If this definition is used, one of the shared derived features
uniting Artiodactyla would be a mesaxonic foot (the axis passing
between digits 3 and 4). Other characters would be a characteristic
shape of the astragalus (one of the ankle bones), digestive
system modifications, and a host of other soft anatomy characters.
The mesaxonic foot tends to lead to animals with 2 or 4 toes;
however, it does vary considerably:
2: Camels, deer, cows sheep
3: peccaries (hind foot)
4: peccaries (hind foot), pigs, hippos
5: some fossil forms
Perissodactyls also have varying numbers of toes
1: living horses
3: rhinos (hind foot) tapir (rear foot)
3-4: rhinos (front foot)
For this reason it is not possible to identify something as
an artiodactyl based on the number of toes.
Illinois State Museum
toomey at museum.state.il.us
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