Miragaia was placed in the Stegosauridae in 2009. Mateus and colleagues performed a phylogenetic analysis and found Miragaia to group with Dacentrurus in a cladeDacentrurinae, newly named for the occasion, the sister group to Stegosaurus (the latter genus was in the cladistic analysis considered to include Hesperosaurus and Wuerhosaurus).[1]

The position of Miragaia in the stegosaurid evolutionary tree is shown by this cladogram:[1]

Stegosauridae
 

Kentrosaurus

 
 
 

Loricatosaurus

 
 
 
 

Dacentrurus

 
 

Miragaia

 
 
 
 

Stegosaurus

 
 
 

Wuerhosaurus (=Stegosaurus homheni Maidment et al. 2008)

 
 

Hesperosaurus (=Stegosaurus mjosi Maidment et al. 2008)

 
 
 
 
 
 

The authors stressed that the only synapomorphy, shared derived trait, supporting the Dacentrurus-Stegosaurus clade was the possession of the long cervical postzygapophyses, and that these are in fact unknown for Decentrurus itself, so that its close position to Stegosaurus was merely based on the new data provided by the description of Miragaia.[1]

Source: en.wikipedia.org/wiki/Miragaia_longicollum