Phylogeny and Evolution
Cladistic studies have consistently found that the closest relatives of the kitefin shark are the cookiecutter sharks (Isistius), with which they share several dentitional, skeletal, and muscular similarities. Dalatias and Isistius are believed to have evolutionarily diverged shortly after the transition between the Cretaceous and Tertiary periods (65.5 Ma), as part of a larger adaptive radiation of dogfish sharks from the deep sea into relatively shallower habitats.
The oldest fossil teeth that definitively belong to the kitefin shark date to the Middle Eocene epoch, such as those recovered from Bortonian-stage deposits (43.0–37.0 Ma) in New Zealand. Dalatias fossil teeth dating to various ages have also been discovered in Europe, the former USSR, Japan, and western India. The fossil material now recognized as belonging to this species were historically described under a multitude of different names.
Read more about this topic: Kitefin Shark
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