As you said yesterday, this definitely looks like a bug. I can just make out the piercing mouthparts in your 3rd photo. I looks similar to Monophlebulus sp., a species we have seen in the area: https://atlasoflife.naturemapr.org/Community/Species/Details/21136
Did it seem to have a fuzzy white coating? Here's a bit more information about mealy bugs on a website called Brisbane Insects. It's one of many different websites we use when we're trying to identify unfamiliar insects. https://www.brisbaneinsects.com/brisbane_softbugs/SnowBallMealybug.htm If it is Monophlbulus, it must be a young one. They reach about 20mm long as adults.
Perhaps it was dead, but it could also be a species that is 'ant-tended'. That is, many bugs and other plant-feeding insects have a mutually-beneficial relationship with ants. The ants get food in the form of left-over sugary syrup from the bug, and the bug is protected because ants chase away potential predators.
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