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Origolestes is an ancestor to therian mammals, the group that includes all placentals and marsupials alive today.

It formed convergently, via multiple evolutionary pathways, and, at least in therian mammals, gave rise to myriad new innovations in jaw and ear evolution.

But when the researchers looked at therian mammals alone – that is, the group that contains placental and marsupial mammals – they found that this subgroup quickly responded to the ecological shakeup by evolving more jaw functions.

The acquisition of the auditory bones in euharamiyidans was related to the formation of the dentary-squamosal jaw joint, which allows a posterior chewing movement, and must have evolved independently from the middle ear structures of monotremes and therian mammals.

Now scientists have shed further light on the matter, suggesting that early therian mammals – the predecessors of today’s placental and marsupial mammals – had developed a wide range of diets and ecological roles about 10 to 20 million years before the dinosaurs were wiped out.