This video says about itself:
Monotremes seem to have branched off from placental and marsupial mammals way back on the tree of life, and possess some reptilian and avian attributes that no other mammals have.
From British daily The Independent:
Rediscovered: Attenborough’s ‘extinct’ egg-laying mammal
By Steve Connor, Science Editor
Published: 16 July 2007
A species of mammal that lays eggs and suckles its young in a pouch has been rediscovered in the jungles of Papua New Guinea, nearly 50 years after it was seen for the first and last time.
Attenborough’s long-beaked echidna – which was named after Sir David Attenborough – was known only from a single museum specimen caught in 1961. Its subsequent disappearance led scientists to believe that it had become extinct.
However, a scientific expedition to the remote Cyclops Mountains has found that the endangered creature is still alive and continues to use its long, toothless beak to poke exploratory holes in the ground in its endless search for earthworms.
“We’ve not found a live one yet, but we’ve found the areas where they feed – they leave very distinctive imprints in the soil with their beaks,” said Jonathan Baillie of the Zoological Society of London, who led the expedition.
See also here.
Echidnas and ants: here.
Echidnas’ sex lives in Australia: here.