Thanks, and will do if possible. I'll have to see if I can locate them in situ and then leave them there with a marker. They are a few centimetres below surface so I can't easily see them.
I have, at last, realised what this is: a long defunct and desiccated base of Asparagus asparagoides. I saw a 'live' one today and I'm quite confident this is it. Apologies for it being so difficult to see with just a photo. I have only seen them under trees, presumably from bird droppings, these defunct and dessicated ones were in the open.
I don't think it is the base of Asparagus asparagoides as it looks much too rounded (see also the photo at https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&photo=30&file=49/521/Asparagus%20asparagoides%20-%20same%20species%20and%20location%20as%20JRHosking%20s.n.%20collected%20Sep%201988,%20Oxley%20Park,%20Tamworth%20-%20image%2018%20July%202008.JPG)