Hadrocodium wui (Luo, Crompton and Sun 2001; Early Jurassic; skull length: 1.2cm), known only from a skull. Hadrocodium was originally considered a juvenile basal mammal, due to the emerging teeth and low molar number. The first premolar replaces the lost canine.

Luo Z-X, Crompton AW and Sun A-L 2001. New Mammaliaform from the Early Jurassic and Evolution of Mammalian Characteristics. Science 292 (5521): 1535–1540. Bibcode:2001Sci...292.1535L. doi:10.1126/science.1058476. PMID 11375489.

wiki/Hadrocodium