Re: the difference between gazelles and impalas

A number of different genera (the plural of genus) make up a family.  The 
llama (for example) belongs to the camel family.  Three different genera 
make up the camel family.  Several different families make up an order.  
Llamas share the artiodactyl order with pigs, peccaries, hippopotamuses, 
deer, giraffes, and cattle.  The members of all nine families in the order 
have three main things in common.  First, they have an even number of toes 
on their feet.  Second, their toes are covered with hoofs.  Third, they 
have more than one chamber in their stomachs.
The order of even-toed hoofed animals shares an even larger group, called 
a class, with many other orders.  Carnivores, bats, elephannts, rodents, 
and even hoofed animals with an odd number of toes, make up some of the 
other orders I the class of animals called mammals.  All mammals have body 
hair and feed their young with milk from the mothers’ bodies.  Most of 
them give birth to living young, but a few are so primitive that they lay 
eggs.
The animal kingdom is easily divided into animals with backbones (called 
vertebrates) and animals without backbones (called invertebrates).  
Mammals, birds, fish, reptiles, and amphibians are all vertebrates.  But 
all of these animals are only part of one of the big groups in which the 
animal kingdom is divided.  Such a big group is called a phylum.  All 
vertebrates and a few other creatures belong to the chordate phylum.  
Chordates have a special elastic rod inside the body that acts as an 
internal skeleton.  In the vertebrates, that rod has hardened into a 
backbone.

The impala and the gazelle are mammals belonging to the Artiodactyla order 
in the bovidae family.  There has been debate over which antilopes are 
more closely related.  Recently, Alan Gentry has suggested, on a study of 
the skull, teeth and horn-cores, that the impala is more nearly related to 
the hartebeest and gnu!


Reference:
Young Students Learning Library: Weekly Reader Books, Middletown, 
Connecticut.
The International Wildlife Encyclopedia: Marshall Cavendish Corporation, 
New York.