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. A close relative is the living Dromiciops.

Dromiciops gliroides, (Thomas 1894, Marshall 1978) is the extant, monito del monte or colocolo opossum, a tiny living basal marsupial from South America. The middle ear (endotympanic + alisphenoid (epiterygoid) is greatly inflated. Note the canine-like premolar 1. The canine is absent in this clade.

Dianoconodon youngi (Mao et al 2024b, Early Jurassic, IVPP-V4257) is a tiny member of the flathead marsupial clade. Note the anterior position of the orbit.

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.

Mao F et al. (8 co-authors) 2024b. Fossils document evolutiionary changes of jaw joint to mammalian middle ear. Nature 1759(266): onlline

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