The archaeological team had expected to find pottery fragments at the site based on similar excavations nearby. ______, they instead…

The sentence explicitly signals a departure from expectation with "they instead uncovered," and pairing that with the transition instead correctly frames the entire second sentence as a substitution for what was expected, not an addition to it or a result of it. Predictably would mean the outcome matched expectations, directly contradicted by the passage. Furthermore would present the finding as an additional, compatible point. As a result would incorrectly suggest the wooden tools were a consequence of expecting pottery, which makes no logical sense.