The white bones at the front are the leg bones of an extant Eastern Grey Kangaroo (Macropus giganteus).
The bones in the centre are the leg bones and jaw from an extinct "giant forest wallaby" named Protemnodon found at Nebo in Queensland - and this is thought to be the leg from a juvenile (the sign calls it a "joey").
The bones at the back are the leg bones of an unnamed giant kangaroo (on the sign just called Macropus sp.) which also was not yet full-grown! This one was also found at Nebo and would be the largest macropod species known.
