Or that's the conclusion I came across when translating the original description by Lapparent (1960). This taxon comes from the Aptian-Albian Continental Intercalaire of Niger. Here's the material-
Holotype- cervical vertebra (80 mm), two dorsal vertebrae (70 mm, 80 mm), posterior dorsal vertebra (50 mm), three sacral vertebrae, three caudal vertebrae (80-85 mm), humerus (200 mm), distal pubis, distal femur, partial tibia, partial fibula, four metatarsal ends, partial pedal phalanx
Referred- ulna (300 mm)
And here's why I think it's an alvarezsaurid.
The cervical vertebrae are opisthocoelous, like a wide variety of neotheropods, excluding most coelurosaurs (Compsognathus, Calamosaurus and Mononykus being the exceptions). Alvarezsaurus is more basal, as it has amphicoelous cervicals.
The dorsal neural canal is very deep. And I mean VERY deep, over 50% of the centrum height. Neural canals over 40% of the centrum height are only found in Patagonykus, mononykines and pygostylians. The condition in Alvarezsaurus is unknown.
The caudal vertebrae are procoelous. This is restricted to alvarezsaurids and some pygostylians. The vertebra is obviously too long for a pygostylian.
The distal caudal centra are keeled ventrally. This is only seen in alvarezsaurids and "Capita..... uh, USNM 3049 (must not get into another discussion about that :-) ).
The humerus, though missing its middle portion, is quite short (10 cm wide proximally by 20 cm long). This is uniquely alvarezsaurid, though unknown in Alvarezsaurus itself.
A few other comments- The posterior dorsal doesn't look very procoelous to me, perhaps indicating "E." gautieri is more primitive than Patagonykus and mononykines. The caudal centra have lateral fossae or pleurocoels, resembling Patagonykus. The humerus lacks the highly divergent internal tuberosity of Patagonykus and mononykines, also suggesting it is more primitive than these taxa. Though the pubis could be propubic as Lapparent presumedly interpreted it, reverse which way is anterior and it is similar to Patagonykus'. Either way, it doesn't matter, as the condition in basal alvarezsaurids is unknown and the boot otherwise resembles a good plesiomorphic type such as ornithomimosaurs. The pubic symphysis is said to be oval, perhaps indicating it's reduced as much as Patagonykus. The presence of any symphysis shows it is not a mononykine. The hindlimb elements are very slender, and the greatly expanded distal tibia seem to be an apomorphy of the taxon.