I found this on the foreshore of a beach on the Jurassic Coast. It looks like a piece of rock with small holes over it, there is something inside, as it rattles.the stone also has empty indents on either side.
From the outside it looks like a fairly unremarkable pebble, with modern animal borings and indentations from adjacent obects such as fossils or stones. In this setting, the indentations are likely to be moulds (in a higher-pressure terrain, they could be caused by selective pressure-solution of one clast on another). The indentations are not regular enough to be from an ammonite.
Can't be sure why it rattles, but it is possible it contains a hollow fossil, inside which there may be either: another part of the fossil that has come loose; or precipitated mineral which has also become loose. Alternatively, the fossil could have dissolved in the solid rock, leaving the internal mould loose in the external mould. You'd need to saw or break it open to find out.
So, to answer your question, I don't think it is a fossil in itself.
But i might contain a fossil or the mould of a fossil.
Unfortunately it is not a fossil but it still has a lot of interest because it rattles.
I recently found a similar nodule and like yours it rattled, so as I do not like to carry things home if I cannot confirm it is a fossil or mineral I tapped it with my hammer and found several bivalves?
I am unsure of there name but they could be called Piddocks and it is there nature to bore into rocks.
What surprised me was the small hole on the outside of the rock leading to a much larger creature inside of its shell.
I usually take a picture but not this time, sorry but I hope this helps.
Came across these fossils today with Piddock holes in them, the first one is a block of Lower Jurassic - Lower Lias limestone with an ammonite inside of it (Arnioceras semicostatum)
The second one is a Lower Jurassic - Lower Lias bivalve (Pleuromya) were the creature has actually burrowed through the fossil.
Hi again Foskin
Had a go at prepping this 'cannon ball' from the Yorkshire coast and noticed it has very similar holes on the outside of it to yours.
It is a pyritic nodule from bed 33 - cannon ball doggers near Whitby and contains an ammonite called Eleganticeras elegantulum from the Upper Lias of the Lower Jurassic of Yorkshire (200myo)
During prepping I noticed the creatures had bored (eaten) right into the rock and only stopped when it came upon the ammonite.
Probably it did not like the tase of it!
Nice job Tabfish!
Also, good observation about the burrows. I don't know what creaturs are responsible for such burrows, but I can't help wondering if they have an interest in the rock for chemical nutrients (as well, potentially, as protection/anchoring). If so, maybe they like a little of a paritcular something in the chemical/mineral gradient/halo around concentrations of pyrite; but may find the pyrte itself distateful/toxic/etc., hence their stopping there. (Many animals seek out chemicals from mineral sources: parrots, butterflies, etc.) ...Unless that's a coincidence in this particular specimen. So, I wonder if the presence of these little burrows on the outside of doggers can be taken as a clue that there is (unharmed) pyrite within?
On one of the images I posted you can see the burrow on the outside of the rock were it started to enter the specimen is a lot narrower than further in were it is a larger chamber, were presumably the creature had grown and needed more room.
As you say many animals seek out chemicals from minerals so i wonder if the animal uses what it finds in the rock for it's shell but still remains a filter feeder?
This Dactylioceras tenuicostatum is over 4in across and probably you won't get a much bigger one, but as you can see those little creatures liked the taste of this ammonite!