Camel question...

Rick Toomey 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?
>
>R. Small
>
>

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.

Rick Toomey
Illinois State Museum
toomey at museum.state.il.us


Rick Toomey



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