Why do scientists disagree about the evolutionary position of osteoglossomorph fishes?

Scientists generally consider osteoglossomorphs to be the most primitive group of teleost fishes, a reputation based on their rudimentary caudal skeleton and the absence of certain intermuscular bones.1

However, their evolutionary position remains a subject of scientific debate for several reasons:

• Challenged Basal Status: Some researchers, such as American ichthyologist Gloria Arratia, have challenged the view that osteoglossomorphs are the most basal teleosts. Arratia argues that the caudal skeleton of certain elopomorphs, such as the genus Elops, is actually more primitive.2
• Fossil Relationships: While various fossil groups—including the Mesozoic families Cladocyclidae and Ichthyodectidae and the Eocene genus Brychaetus—are classified as osteoglossomorphs, their specific evolutionary relationships to living members of the superorder remain obscure.2
• Intragroup Classification: There is also ongoing discussion regarding the internal classification of the group, specifically whether hiodontiforms should be treated as a distinct order or demoted to a family (Hiodontidae) within the order Osteoglossiformes.2