Xiphodolamia
Xiphodolamia is a rare extinct genus of mackerel shark which lived during the Eocene epoch. It is only known from isolated teeth, but has been found in Europe, Africa, and Asia. It is assumed to be pelagic, occurring more frequently in deeper water deposits, most notably the London Clay and Eocene deposits in Denmark. It is distinguished by its rectangular root and twisted blade, unique among Mackerel sharks. It is unclear what niche this specialized dentition helped exploit. Taxonomy and Affinities. The following species have been attributed to "Xiphodolamia": "X. barbadica" was described from the Lutetian-aged Scotland Formation  of the West Indies, and "X eocaena" was treated as the Ypresian-aged North American and European representative. "X. ensis" was originally described out of the early-middle Eocene of Central Asia and Jordan. However, "X. barbadica" and "X. eocaeana" are not easily discernable from the type species "X. ensis", and most recent authors have treated them as junior synonyms. "X. serrata" is a serrated variety known from the Upper Eocene of Africa and Arabia. It appears to be the culmination of a singular evolving lineage, and thus "Xiphodolamia" is an example of anagensis. The development of serrations in "Xiphodolamia  mirrors that of Otodus" in the Ypresian, and thus is an example of convergent evolution. This genus is not known to have survived into the Oligocene. Though in the past the genus has been placed in many orders, it is now the consensus "Xiphodolamia" is an unusual member of the order Lamniformes. However, its placement within Lamniformes is uncertain, especially its relationship to Lamnidae and "Isurus". Some have placed it in its own family, Xiphidolamnidae. It is unlikely this matter will be resolved until associated material or transitional fossils are found and described. Paleobiogeography. "Xiphodolamia" is widely but thinly spread . The following places have produced "Xiphodolamia" teeth: