Ichthyoconodon

Ichthyoconodon ("fish cone tooth") is an extinct genus of theriimorph mammal from the Lower Cretaceous of Morocco. Usually considered an eutriconodont, it is notable for its oceanic location and atypical shape, indicative of potentially unusual ecological niches; some researchers think that it may be the first marine mammal,[1] or part of a bizarre clade of flying mammals.

Description
Ichthyoconodon is known primarily from isolated teeth from Anoual Syncline sediments of Morocco, in particular strata thought to date to the Berriasian. These teeth, mostly molars, possess many synapomorphies associated with triconodontid eutriconodonts, but its cusps are notoriously sharp for the group's standards and are rather specialised. They belong to animal in life possibly as large as a platypus.

Relationships
Ichthyoconodon has been found to be a eutriconodont, though the degree of speciation has been noted as being difficult to assess its status as such.[1] Rose et al. found some skepticism about a eutriconodont identity,[3] and some studies have suggested an identity not even as a mammal, but as a pterosaur,[4] but most recent phylogenetic studies favour a eutriconodont identity.[5][4][2]

The most recent phylogenetic studies favour a close relationship with Volaticotherium and Argentoconodon within the triconodontid clade Alticonodontinae.