Diplocaulidae
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The Diplocaulidae ("double cauls") is an extinct family of "nectridean" tetrapodomorphs that arose during the Late Carboniferous and died out in the Late Permian. They are distinguished by the presence of strange, horn-like protrusions jutting out from the rear of their skulls; in some genera said protrusions gave their heads an almost boomerang-like outline.
Phylogeny
Below is a cladogram modified from Germain (2010):