The placement of Squalicorax within the shark evolutionary lineage has been debated for over a hundred years (1). After years of various paleontologists attempting to classify Squalicorax, they were placed in a newly erected family, Anacoracidae. Originally defined for Squalicorax, Anacoracidae now includes many other taxa with similar teeth (2). However, the evolutionary relationships within Anacoracidae remain unclear (3, 4).
Anacoracidae is generally placed within the order Lamniformes, the mackerel sharks. This order contains a wide variety of species, such as the great white shark, basking sharks, and mako sharks (1, 5). Other paleontologists categorize Anacoracidae within Hexanchiformes instead, a more primitive group of sharks that include frilled sharks and a small number of other extant species (1, 2). Reanalysis of anatomical data, however, suggests that Squalicorax is not a hexanchiform, and that this cateogorization of Anacoracidae is inaccurate (1).
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