Damn - bjorns beat me to it with a flippant remark!
The answer is yes, you may take it as accompanied luggage, and as it is below 32kgs (even when in the crate), it falls within the Club World baggage allowance, and the size is fine too. The fossil should be treated as an "Out of Gauge" item and, if it is marked in several clearly visible places as fragile, should be treated with respect.
I would, however, take precautions to protect the surfaces with copious quantities of bubble-wrap as if the loaders think it is merely a "lump of rock", they may place it in a position where suitcases etc may put pressure on it. If the aeroplane encounters turbulence, cases and boxes may become dislodged and fall on it.
Out of curiosity, what creature does the fossil contain?