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, 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. Rose et al. found some skepticism about a eutriconodont identity, and some studies have suggested an identity not even as a mammal, but as a pterosaur, but most recent phylogenetic studies favour a eutriconodont identity.
The most recent phylogenetic studies favour a close relationship with Volaticotherium and Argentoconodon within the triconodontid clade Alticonodontinae.
Ecology[]
Ichthyoconodon's teeth were found in marine deposits, alongside taxa like hybodontidsharks, ornithocheirid pterosaurs, ray-finned fish and sea turtles, as well as several terrestrial taxa like theropods. Unlike other mammal teeth, including other contemporary teeth such as those of Hahnodon, which show some degree of degradation, Ichthyoconodon teeth are not significantly modified, suggesting that the mammal either died in situ or was only carried over for a short distance under water.
Because the teeth of Ichthyoconodon are rather sharp and convergent in some details to the teeth of piscivorous mammals like otters and seals, some researchers have suggested that it may have fed on fish. There is no evidence for an aquatic lifestyle, other than the location the fossil were found. However there were freshwater semi-aquatic mammals in the Mesozoic, including the Jurassic and Cretaceous docodonts like Castorocauda and Haldanodon, Early Cretaceous monotremes and the Late Cretaceous Didelphodon. Ichthyoconodonand Dyskritodon amazighi are the only Mesozoic mammals so far to have been suggested to have possibly foraged in the sea. Researchers such as Zofia Kielan-Jaworowska pointed out lack of functional comparison between eutriconodont teeth and those of marine mammals. Unlike the teeth of seals and cetaceans, eutriconodont molars occlude, creating a shearing motion like carnassials, and unlike the grasping function of marine mammal molars.
It is possible that Ichthyoconodon may have been a gliding mammal, based on its relationship with the other gliding mammals like Volaticotherium. The presence of Argentoconodon in South America, Volaticotherium in Asia and Ichthyoconodonin North Africa in such a relatively close span of time suggests there may have been a widespread clade of Jurassic-Early Cretaceous gliding triconodonts.