<Tr> <Td> Allotheria </Td> <Td> <P> Multituberculates † </P> </Td> </Tr> <Tr> <Td> Trechnotheria </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Spalacotheroidea † </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Cladotheria </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Dryolestoidea † </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Theria </Td> <Td> <Table> <Tr> <Td> Metatheria </Td> <Td> <P> Marsupials </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Eutheria </Td> <Td> <P> Placentals </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Table> <Tr> <Td> </Td> <Td> <P> Spalacotheroidea † </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Cladotheria </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> Dryolestoidea † </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Theria </Td> <Td> <Table> <Tr> <Td> Metatheria </Td> <Td> <P> Marsupials </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> Eutheria </Td> <Td> <P> Placentals </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> <P> Spalacotheroidea † </P> </Td> </Tr>

Mammals had their greatest development in which of the following ages