what are the causes for it to become threatened?
Dams, irrigation, pollution, netting, and trapping.
Platypus
dams, irrigation, pollution, netting, and trapping. 
when did the duck billed platypus become extinct There is a threat of extinction but they are not completely extinct is this animal classified as a reptile, mammal or amphibian or any other? Mammal does that animal give birth or does it lay eggs? They lay eggs which places are they mainly found in? Australia, New South Wales in which part of the body do they store venom? The male platypus has a spur on the hind foot that delivers a venom how many times does the female reproduce in a year? Females are thought likely to become sexually mature in their second year, with breeding confirmed still to take place in animals over nine years old. how many eggs do they lay each time? UNANSWERABLE what do these animals eat? Annelid worms, insect larvae, freshwater shrimp, and freshwater yabby what is their conservation status tagged as? "Near Threatened"
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Platypus [SEP] Status and threats
The platypus is not considered to be in immediate danger of extinction, because conservation measures have been successful, but it could be adversely affected by habitat disruption caused by dams, irrigation, pollution, netting, and trapping. Reduction of watercourse flows and water levels through excessive droughts and extraction of water for industrial, agricultural, and domestic supplies are also considered a threat. The IUCN lists the platypus on its Red List as "Near Threatened" as assessed in 2016, when it was estimated that numbers had reduced by about 30 percent on average since European settlement. The animal is listed as endangered in South Australia, but it is not covered at all under the federal "EPBC Act".