Which posterior locomotor structure was significantly elongated in *Xenacanthus*, suggesting optimization for agility?
Answer
The anal fin
The arrangement of the fins in *Xenacanthus* shows a marked departure from standard shark morphology, especially concerning the lower posterior fins. While the caudal fin provided thrust, the anal fin was particularly notable for being significantly elongated, running along a substantial portion of the rear underside of the body. This extensive fin, working in concert with the tail fin, would have functioned to provide powerful thrust and enhanced maneuverability, allowing the shark to execute short bursts of speed or precise steering necessary for navigating confined, cluttered freshwater environments.
Related Questions
What is the direct translation of the genus name *Xenacanthus*?From which specific anatomical area does the defining nuchal spine of *Xenacanthus* extend backward?Which morphology best describes the overall body shape of *Xenacanthus* compared to modern open-ocean sharks?How does the configuration of the dorsal fins in *Xenacanthus* differ from the familiar shark body plan?What specific structural characteristic defines the dentition of *Xenacanthus*?What specialized ecological niche did *Xenacanthus* occupy during the late Paleozoic era?*Xenacanthus* is the most famous genus within which distinct, extinct order of specialized freshwater sharks?Which posterior locomotor structure was significantly elongated in *Xenacanthus*, suggesting optimization for agility?During which periods of the late Paleozoic era did the freshwater shark *Xenacanthus* thrive?Regarding the cranial details, how were the jaws of *Xenacanthus* situated on the head structure?What is the generally hypothesized primary defensive function attributed to the prominent, sharp nuchal spine?