The dimensions of the preserved foot elements and caudal vertebrae suggest an estimated total length of about 6 or 7 m (20 or 23 ft) for Alierasaurus.

Alierasaurus and Cotylorhynchus both have very wide, barrel-shaped rib cages indicating that they were herbivores that fed primarily on high-fiber plant material.

[3] The paleontologists Marco Romano and Umberto Nicosia have identified several autapomorphies in the feet anatomy of Alierasaurus: metatarsal IV with distinct axial region, length about twice that of the corresponding proximal phalanx, not short and massive as in other large caseids; metatarsal IV proximal head not orthogonal to the bone axis, forming an angle of 120° with the shaft: with this conformation, the proximal and distal heads are much closer along the medial side of the metatarsal; claw-shaped ungual phalanges proportionally shorter than in Cotylorhynchus, with a double ventral flexor tubercle very close to the proximal rim of the phalanx; ungual phalangeal axis bent downward and medially; distal transverse section subtriangular, not spatulate as in Cotylorhynchus.

[2] The known material consist of eight articulated caudal vertebrae, two isolated caudal vertebrae, four distal caudal centra, numerous large fragments referable to at least eight other vertebrae, seven proximal portions of hemal arches, three proximal portions (vertebral segment) of dorsal ribs, ten undetermined fragmentary ribs, poorly preserved right scapula and badly crushed right coracoid plate, distal head of the left ulna, and several autopodial elements represented by a fragmentary calcaneum, three metapodials, five non-ungual phalanges, an almost complete ungual phalanx, and two ungual phalanges lacking distal ends.

Later, despite the absence of the most diagnostic elements (notably the skull) for the comparison with other caseids in general and with Cotylorhynchus in peculiar, the Sardinian specimen was assigned to a new genus named Alierasaurus, on the basis of some differences in feet anatomy.

[2][3] In 2017, Marco Romano and colleagues described other bones belonging to the same individual (some caudal vertebrae and fragments of chevrons and ribs).

[4] More recently, the same levels have yielded remains of an undescribed sphenacodontid pelycosaur, and footprints of a third animal which was only known in the south of France in slightly younger rocks (ichnogenus Merifontichnus from the La Lieude Formation (Wordian) in the Lodève basin).

The bones still in place in the rock were not all on the same bedding plane but were buried at different depths within a 40 cm thick red siltstone layer.

It was roughly C-shaped: its northern (Laurasia) and southern (Gondwana) parts were connected to the west, but separated to the east by the very large Tethys Sea.

[6] A long string of microcontinents, grouped under the name Cimmeria, divided the Tethys in two : the Paleo-Tethys in the north, and the Neo-Tethys in the south.

The south of Sardinia was then located near the east of the Pyrenees (whose mountains did not yet exist), and the north-west of Corsica was positioned in front of the Massif de l'Esterel (the rhyolites of the Scandola peninsula aligning with those of the Esterel, of similar age and composition).

[15] Marc Durand suggests a Wordian age, the erosional gap at the top of the A7 Rhyolite corresponding according to him to a large part of the Roadian.

In the second cladogram, Alierasaurus is positioned above the genus Angelosaurus and forms a polytomy with Cotylorhynchus romeri and a clade containing the species C. bransoni and C.