Brasilitherium, Chaoyangodens, Akidolestes and Kuehneotherium

Brasilitherium riograndensis (Bonaparte et al., 2003; Early Norian, Late Triassic, 208 mya) was considered a stem mammal, but here nests at the base of the monotreme mammals despite the not-quite mammalian jaw joint. This may explain why monotreme ear bones are below and medial to the jawline, but in other mammals they are posterior to the jaw joint. The long rostrum includes as many as seven premolars and 4 molars.

Chaoyangodens lii (Hou and Meng 2014; early Cretaceous, 120mya) was considered a eutriconodont mammal with a reduced post-canine tooth formula and five incisors. Here it nests in the monotreme clade between Brasilitherium and Akidolestes. The teeth are large for the skull. The scapula is perforated. The pelvis is unfused and simple.

Akidolestes cifellii (Li and Luo 2006; Yixian Formation, Early Cretraceous. 124 mya; NIGPAS 139381A, B) nests as a basal toothed platypus in the large reptile tree, contra the original interpretation that considered the many similarities convergent. Akidolestes was derived from a sister to Kuehneotherium (see below) with long jaws containing many more teeth than is typical for mammals.

As a monotreme, Akidolestes was an egg-layer, yet providing nourishment for its hatchlings with an early form of milk secreting from ventral glands in its skin.

It probably was a fish and tadpole eater and had a thick, probably waterproof, furry coat.

Teeth Prior to the toothless condition found in Ornithorhynchus, phylogenetic predecessors developed more teeth. Akidolestes is one example. Keuhneotherium is yet another (see below).

Akidolestes

Bonaparte JF, Martinelli AG, Schultz CL and Rubert R 2003. The sister group of mammals: small cynodonts from the Late Triassic of Southern Brazil. Revista Brasileira de Paleontologia 5:5-27.

Kermack Dm, Kermack KA, Mussett F 1968. The Welsh pantothere Kuehneotherium praecursoris. Journal of the Linnean Society of London, Zoology. 47 (312): 407–423.

Li G and Luo Z-X. 2006. A Cretaceous symmetrodont therian with some monotreme-like postcranial features. Nature, 439:195–200.

Patterson B and Olson EC 1961. A triconodont mammal from the Triassic of Yunnan. In Vandebroek G (ed.), International Colloquium on the Evolution of Lower and Non Specialized Mammals. Koninklijke Vlaamse Academir voor Wetenschappen, Letteren en Schone Kunsten can Belgie 129-191.

Shaw G 1799. The Naturalist's Miscellany.

wiki/Akidolestes
wiki/Kuehneotherium

Pre-Mammals

Mammalia

Akidolestes

Ornithorhynchus

Juramaia

Acristatherium - Cronopio