GeologyRocks

I'm curious on the fotos. Don't forget to add a scale to them by the way. If you found it while digging in lose soil I already doubt it is a fossilised egg though...

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Your local rock guy was probably right to sound skeptical. Fossil eggs (or at least intact ones) are extremely rare. I know people who have found small fragments of them before, but even a half intact one really would be something special.

Though very often nature can create things that look a lot like eggs in some ways, but really aren't. The devil, as always, will be in the details ~

I would agree that finding a fossil of any kind loose in soil is highly unlikely. Sedimentary layers are the best places for fossils, and for it to be a bird egg (as in oval - I know of no fish that lay anything but spherical eggs) the sediment would have been deposited in a non-marine environment. From my own modern observations, most eggs crack when they hit the ground. Assuming a perfect scenario, where a nest landed upright on the ground with an egg still intact, we next have the potential for predators to consume the egg, and then a LONG time of deposition to occur, thousands of years after the egg would have rotted and likely collapsed from the chemical changes going on inside due to decay. Deposition can occur much more quickly in marine environments, where fossils can be preserved very well, but that would make it unlikely to have an oval shaped egg. Next, there would need to be some mechanism to separate the fossilized egg from the sediment and transport it in the mix of your soil.

It is likely a rock that has weathered to look like an egg, probably from a prior fluvial source.