Based on inserting Mierasaurus into two prior analyses, one by José Carbadillo and Martin Sander in 2013 and another by Philip Mannion and colleagues in 2017, Royo-Torres and colleagues identified a number of synapomorphic traits that allow Mierasaurus to be placed among the Turiasauria.
Asides from limb characteristics noted above, other synapomorphies include the slightly concave profile of the rear surface of the basal tubera; the heart-shaped teeth; the height of the dorsal neural arches below the level of the articular processes known as postzygapophyses being at least equal to that of their corresponding centra; the opisthocoelous condition of the rear dorsals; the slightly procoelous front caudals; the presence of depressions known as pleurocoels in the front caudals; the neural spines of the front caudals being less than 1.2 times the height of their corresponding centra; and the centra of the middle caudals being at least as wide as they are long.
Although not an explicit synapomorphy, the secondary depression on the ulna also unites Mierasaurus with other turiasaurs.

Within the Turiasauria, Royo-Torres and colleagues considered the likewise-Cretaceous Moabosaurus to be the closest relative of Mierasaurus.
They share the L-shaped profile of the basal tubera, and the bifurcating spinodiapophyseal laminae of the dorsal neural spines.
However, they differ from each other by twelve characteristics.
Moabosaurus lacks rounded ridges on its occipital condyle; has vertical ridges on its teeth; has a robust parapophysis; lacks depressions on its atlas intercentrum; has hollows and keels on the bottom of its cervical centra; has convex as opposed to straight centroprezygapophyseal laminae in its front cervicals; has bifurcating cervical ribs; lacks ridges or bulges accompanying the tubercles of its cervical ribs; has prespinal laminae in its middle and rear dorsals; has rectangular as opposed to triangular hyposphenes in its rear dorsals; has uniformly opisthocoelous dorsals; and has a bulge on its femur.
The lack of prominent bifurcation in the cervical ribs also differentiates Mierasaurus from Turiasaurus and potentially other turiasaurs.

The phylogenetic trees recovered by Royo-Torres and colleagues from the two different analyses agreed upon the position of turiasaurs, placing them as a unified group containing Mierasaurus, Moabosaurus, Turiasaurus, Losillasasurus, and Zby outside of the Neosauropoda (thus excluding them from both the Diplodocoidea and the Macronaria).
Below, the tree based on the analysis of Mannion and colleagues is reproduced; it yielded well-resolved relationships within the Turiasauria, as opposed to the tree based on the analysis of Carbadillo and Sander.
The continent-level geographic ranges of various taxa are included in the tree.
Based on inserting Mierasaurus into two prior analyses, one by José Carbadillo and Martin Sander in 2013 and another by Philip Mannion and colleagues in 2017, Royo-Torres and colleagues identified a number of synapomorphic traits that allow Mierasaurus to be placed among the Turiasauria. Asides from limb characteristics noted above, other synapomorphies include the slightly concave profile of the rear surface of the basal tubera; the heart-shaped teeth; the height of the dorsal neural arches below the level of the articular processes known as postzygapophyses being at least equal to that of their corresponding centra; the opisthocoelous condition of the rear dorsals; the slightly procoelous front caudals; the presence of depressions known as pleurocoels in the front caudals; the neural spines of the front caudals being less than 1.2 times the height of their corresponding centra; and the centra of the middle caudals being at least as wide as they are long. Although not an explicit synapomorphy, the secondary depression on the ulna also unites Mierasaurus with other turiasaurs.
Within the Turiasauria, Royo-Torres and colleagues considered the likewise-Cretaceous Moabosaurus to be the closest relative of Mierasaurus. They share the L-shaped profile of the basal tubera, and the bifurcating spinodiapophyseal laminae of the dorsal neural spines. However, they differ from each other by twelve characteristics. Moabosaurus lacks rounded ridges on its occipital condyle; has vertical ridges on its teeth; has a robust parapophysis; lacks depressions on its atlas intercentrum; has hollows and keels on the bottom of its cervical centra; has convex as opposed to straight centroprezygapophyseal laminae in its front cervicals; has bifurcating cervical ribs; lacks ridges or bulges accompanying the tubercles of its cervical ribs; has prespinal laminae in its middle and rear dorsals; has rectangular as opposed to triangular hyposphenes in its rear dorsals; has uniformly opisthocoelous dorsals; and has a bulge on its femur. The lack of prominent bifurcation in the cervical ribs also differentiates Mierasaurus from Turiasaurus and potentially other turiasaurs.
The phylogenetic trees recovered by Royo-Torres and colleagues from the two different analyses agreed upon the position of turiasaurs, placing them as a unified group containing Mierasaurus, Moabosaurus, Turiasaurus, Losillasasurus, and Zby outside of the Neosauropoda (thus excluding them from both the Diplodocoidea and the Macronaria). Below, the tree based on the analysis of Mannion and colleagues is reproduced; it yielded well-resolved relationships within the Turiasauria, as opposed to the tree based on the analysis of Carbadillo and Sander. The continent-level geographic ranges of various taxa are included in the tree.
Mierasaurus