Why is the early evolutionary history of Acipenseriformes uncertain?

The early evolutionary history of the order Acipenseriformes—which includes sturgeons and paddlefishes—is considered uncertain for several reasons:

• Poor Documentation: While these fishes are clearly derived from palaeonisciform groups, the fossil record documenting their early history is both confused and poorly documented.1
• Early Specialization: Both sturgeons and paddlefishes became highly specialized early in their history, which has limited their diversification over time and made it difficult to draw direct comparisons between living forms and their ancient ancestors.1
• Classification Challenges: Because living members have differentiated so markedly from their Paleozoic ancestors, significant problems have arisen in classification and in understanding the precise interrelationships between past and present forms.1

While definitive fossils related to these groups date back to the Middle Jurassic Epoch, the lack of a clear, continuous fossil trail from their ancestral origins contributes to the ongoing uncertainty regarding their evolutionary lineage.12