<h2>Sciuromorpha</h2>

<p>
The term Sciuromorpha has referred to numerous groups of rodents, but the only family common to all variations is the 
Sciuridae, the squirrels. Most definitions also include the mountain beaver.
</p>

<p>
Traditionally, the term has been defined on the basis of the shape of the infraorbital canal. A sciuromorphous zygomasseteric 
system is characterized by attachment of the lateral masseter muscle along the side of the rostrum. Unlike hystricomorphous and 
myomorphous rodents, the medial masseter muscle does not pass through the infraorbital canal. Among extant rodents, only the 
families Sciuridae, Castoridae, Heteromyidae, and Geomyidae are truly sciuromorphous. Some authorities would exclude the 
Geomyidae and Heteromyidae from that list due to the attachment of the medial masseter directly behind the zygomatic arch.
</p>

<p>
Carleton and Musser (2005) redefined rodent suborders on the basis of a host of both morphological and molecular reasons. 
They defined the Sciuromorpha as including three families, Sciuridae, Aplodontiidae, and Gliridae. Of these, only the 
Sciuridae are truly sciuromorphous. The Aplodontiidae are protrogomorphous and the Gliridae are myomorphous. 
The connection between Aplodontiidae and Sciuridae has been proposed numerous times in the past. The two 
families have been united into a common infraorder (Sciurida) or superfamily (Sciuroidea). It has long been 
suggested that dormice (Gliridae) are not particularly related to the Myomorpha, and their zygomasseteric 
structure has been termed "pseudomyomorphy". The connection between squirrels and dormice has been almost 
exclusively suggested through genetic studies, and to a lesser degree via the fossil rodent Reithroparamys.
</p>
