The one dollar coin denomination (written as $1) was introduced in Australia in 1984, replacing the earlier banknotes. The original reverse design by Stuart Devlin featuring five kangaroos - known in Australia as the "Mob of Roos" design - has not been changed since its introduction.
Some of these coins were released in October 2018 and due to their date which was then in the future were known for a while as the "time traveller" coins. These were the special issue coins with privy marks - incorrectly called mint marks - of A, U or S incuse in a square above the AR of DOLLAR, and a tiny (microtext) number 35 between the three kangaroos on the left, to mark the 35th anniversary of the denomination. The Royal Australian Mint announced these (after they had been in circulation for some time) as a "coin hunt" and distributed albums for collectors, with three slots for the three coins with different privy marks, and a magnifying glass to help see the tiny 35 marking.
Coins with this design were not included in this year's uncirculated and proof sets, which featured instead a Non-Circulating Legal Tender $1 design marking the 50th Anniversary of the Moon Landing .
Coins issued in 2019 have now been in circulation for less than one year.