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Why do scientists debate whether Chondrostei is a natural evolutionary group?
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chondrostean
Russian sturgeon (Acipenser gueldenstaedtii) swimming along the seafloor of the Black Sea.
Scientists debate whether the subclass Chondrostei is a natural evolutionary group primarily because it is widely considered to be paraphyletic. In biological classification, a paraphyletic group is one that does not include all the descendants of a common ancestor, failing to represent a single, complete evolutionary lineage.12
The debate is further complicated by the following factors:
- Genealogical Relationships: Evidence suggests that the order Acipenseriformes—which includes sturgeons and paddlefishes—is more closely related to holosteans than it is to the polypteriforms (bichirs and reedfish), which are sometimes grouped within the Chondrostei.12
- Unclear Taxonomy: Because the relationships between living and fossil forms remain poorly understood, the classification of chondrosteans is considered unsettled.23
- Inconsistent Grouping: While some taxonomies include polypteriforms within the subclass, others exclude them due to these unclear evolutionary connections.12
Ultimately, because the group does not reflect a single, exclusive branch of the evolutionary tree, many taxonomists argue that it is not a "natural" or monophyletic group.12