The time at which the monotreme line diverged from other mammalian lines is uncertain, but one survey of genetic studies gives an estimate of about 220 million years ago. This is in the Upper Triassic. Fossils of a jaw fragment 110 million years old were found at Lightning Ridge, New South Wales. This means they originated up to 100 million years before the Metatheria or Eutheria, so they are definitely 'living fossils'.