Freshwater oyster or crocodile eggshell?

One of the beautiful but lesser-known creatures who lives in the Mara is Etheria elliptia, the freshwater oyster. We often find their shells on the river bank, but we've only ever found one alive, despite many hours spent kicknetting and digging around in the river. They are a type of freshwater mussel, which play important roles in river ecosystems as filter feeders and natural filtration devices. They can form a cement-like attachment to rocks or other shells (like the two attached shells in the photo below), which is remarkably strong and difficult to break (a friend broke a wooden rungu trying). They lay down their shells in layers, and I have long been interested in analyzing the elements in the different shell layers as a type of data recorder over time for conditions in the river. However, in order to date the layers, we would have to find live specimens. 

We have been told by several Maasai that they think the shells are crocodile eggshells, a description which I love, as it is exactly what I would imagine a crocodile eggshell would look like if I didn't know that they are actually flexible and almost paper-thin. But couldn't you just imagine a little crocodile, with bony scales and needle-sharp teeth, crawling out of one of these?

Etheria elliptica shells on the bank of the Mara River