Help Identify Black Coconut Shaped Pod Found In Michigan

Question From: L. Monks - MICHIGAN
Q: I live on a large pond in Oakland County. There are several places that have marshy wetlands along the coast of the pond. During a canoe ride recently, we found a strange looking, large, black, coconut shaped pod and would like to know exactly what it is. Since it was early in the spring, there were no leaves on the trees that we found in near. It resembles a black walnut but is not nearly as large as this one is. Any ideas would be appreciated!
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A: My guess would be a black walnut that had been sitting in water a good while. Google photos of black walnut and see what you think. Best And Happy Yardening, Nancy