Final answer:
Omomyoids are not mentioned in the provided material, but the evolution of major mammalian groups is outlined. Placental mammals evolved around 110 million years ago, with their diverse family tree stemming from ancestral synapsids and the earliest amniotes.
Step-by-step explanation:
The omomyoids are not directly mentioned in the provided reference material. Usually, when referring to the evolution of mammalian groups, we talk about major groups such as monotremes, marsupials, and placental mammals. According to the information, placental mammals evolved about 110 million years ago. These mammals, which included the now-extinct genus Eomaia, were also small and climbed trees. It is important to understand that the mammalian family tree is diverse and complex, with many branches that have evolved over millions of years from common ancestors.
The evolutionary history of mammals can be traced back to synapsids from about 300 million years ago and further back to the earliest amniotes about 350 million years ago. These later amniotes diverged into synapsids, which eventually evolved into mammals, and sauropsids, which gave rise to reptiles, dinosaurs, and birds.
Considering the context, if the term omomyoids from your question refers to a specific group within the mammalian evolutionary tree, this group likely evolved during a period that was part of the broader evolutionary timeline of mammalian ancestors, possibly during the Mesozoic era when many mammalian groups were diversifying.