What criteria likely determined the placement of Xiphactinus within Family Ichthyodectidae?
Answer
Specific skeletal features beyond those shared across the entire order.
Moving from the Order Ichthyodectiformes to the Family Ichthyodectidae involves refinement based on shared, more specific morphological traits. The placement within *Ichthyodectidae* indicates that *Xiphactinus* shared unique structural characteristics with its closest relatives that were not necessarily present in all other members of the broader order. These distinguishing features are generally focused on detailed skeletal morphology, likely involving the precise structure of the skull, the articulation and complexity of the jaw apparatus, and potentially identifiable differences in scale types, allowing for a closer phylogenetic grouping.
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