Could do with seeing it from some other angles,
but it gives the impression of being an internal mould of a bivalve (fossil, not modern).
Have a look at this for comparison - http://www.hullcc.gov.uk/museumcollections/collections/search-results/display.php?irn=121803&keywordsorig=belemnite&titleorig=&personorig=&placeorig=&dateorig=&materialorig=&accessionnumberorig=&collectionorig=&museumorig=&keywords=bivalve&newsearch=new&title=&person=&place=&date=&material=&accessionnumber=&collectionall=all&museumall=all&location=any&SearchSubmit_x=28&SearchSubmit_y=8&Sender=List&Page=109
Could I be even more demanding? The two photos are from the front and back, could I ask for one from the side and one from each end? Was the bone found on or near a beach? At the moment I am considering a chevron bone from a whale tail but further photos could exclude that.
There are two things that make me think this is NOT a chevron. The first is the odd holes at the one end which I have not seen on a chevron and the second is that it is very flat, a chevron is, well, chevron shaped ie. a V shape. I have never really had an interest in fish but looking at the internet then I can see that a Tilly Bone is a possibility. I know that the department of archeology at Sydney University has a special interest in fish skeletons, may be they could help?