What physical characteristic defines membership in Class Actinopterygii for Xiphactinus?
Answer
Its fins were supported by bony spines or rays.
Membership in the Class Actinopterygii, which translates to 'ray-finned fishes,' signifies a crucial anatomical distinction within the hierarchy of fishes. The defining feature of this group is that their fins are supported internally by bony spines or rays. This characteristic separates them sharply from other major fish groups, such as the lobe-finned fishes, whose fins are supported by fleshy, bone-filled structures that eventually led to terrestrial tetrapods, and cartilaginous fishes like sharks, which lack true bony skeletons supporting their fins. This feature is shared by the majority of extant bony fish species today.
Related Questions
What physical characteristic defines membership in Class Actinopterygii for Xiphactinus?How did Xiphactinus compare in size to its contemporaries in the Order Ichthyodectiformes?Who formally established the genus name Xiphactinus in 1870?Which family did Joseph Leidy initially suspect Xiphactinus belonged to?What does the Greek derivation of the name Xiphactinus roughly reference?Which species discovery in 1997 expanded the known temporal distribution of the genus?What characteristic confirms Xiphactinus's placement within Phylum Chordata?What synonym, used by Cope in the 1870s, was eventually superseded by Xiphactinus?What ecological niche did the Order Ichthyodectiformes primarily dominate during the Mesozoic?What criteria likely determined the placement of Xiphactinus within Family Ichthyodectidae?When did Xiphactinus cease to exist following the K–Pg extinction event?