Genus: Microsphenodon CHAMBI-TROWELL, MARTINELLI, WHITESIDE, de VIVAR, SOARES, SCHULTZ, GILL, BENTON, & RAYFIELD, 2021
Etymology: Greek, micro, "small" + Sphenodon; refering to the sole extant genus of rhynchocephalian. Like Sphenodon, the animal has caniniforms and pronounced differentiation of its teeth, but is itself a much smaller animal, therefore "small Sphenodon."

Species: bonapartei CHAMBI-TROWELL, MARTINELLI, WHITESIDE, de VIVAR, SOARES, SCHULTZ, GILL, BENTON, & RAYFIELD, 2021
Etymology: In honor of the late Argentina paleontologist Jose F. Bonaparte (1928-2020), who led the main collections of fossil vertebraes from the linha Sao Luis outcrop until 2005, deposited at the UFRGS, including the discovery of the holotype specimen.

Holotype: UFRGS-PV-0972-T

Locality: Linha Sao Luiz Locality, an abandoned quarry located 1.5 km northwest of downtown do Soturno Faxinal, 53°30'23"E, 29°34'08"S, near Barrio Santo Antonino, Faxinal do Soturno, Rio Grande do Sul State, Brazil.

Horizon: Caturrita Formation.

Biostratigraphy: Icidosaur Assemblage Zone.

Age: Adamanian, Lower Coloradian age, Late Carnian-Early Norian Stage, Late Triassic Epoch, Late Triassic.

Material: A nearly complete skull with some damage to its rostrum and missing the premaxillae and vomers.

Referred material:

UFRGS-PV-613T: Incomplete, obliquely dorsoventrally and laterally crushed skull and mandible of a juvenile with attached anterior cervical vertebrae. (Note: orignally paratype to Clevenosaurus braziliensis BONAPARTE & SUSE, 2006).

UFRGS-PV-0848-T: Isolated right mandible.

UFRGS-PV-0827-T: Isolated right palatine.