''Ichthyoconodon'' is an extinct genus of eutriconodont mammal from the Lower Cretaceous of Morocco. It is notable for having been found in a unique marine location, and the shape of its teeth suggests an unusual, potentially fish-eating ecological niche. Analysis suggests it is part of a group of gliding mammals that includes '' Volaticotherium''.

Description

''Ichthyoconodon'' is only known from two molar teeth from Anoual Syncline sediments of Morocco, in the Ksar Metlili Formation which dates to the Berriasian. These teeth possess characteristics associated with volaticotherian eutriconodontan mammals. The molars are only around 4 millimeters long, a size comparable to the related species '' Jugulator''. They are compressed into blade-like shape, and arranged in a line, with a slight recurve, similar to other animals in this group such as '' Argentoconodon''.

Etymology

''Ichthyoconodon'' essentially means "fish cone tooth", from the Greek ιχθυς, "fish", κῶνος, "cone", and ὀδών, "tooth". The type species, ''I. jaworowskorum'', was named "in honour of Zofia Kielan-Jaworowska and Zbigniew Jaworowski for their generous hospitality on many occasions".

Relationships

''Ichthyoconodon'' has been found to be a eutriconodontan mammal, despite there only being two molar teeth. although some authors have been skeptical of this interpretation. Other possibilities for the identity of these teeth have included pterosaur, dinosaur, and shark, but there has been no supporting evidence to date.Kielan-Jaworowska, R. L. Cifelli, and Z.-X. Luo. 2004. Mammals from the age of dinosaurs: Origins, evolution, and structure. Columbia University Press, New York 1–630 . Whatley/R. Whatley/R. Whatley/ref> Phylogenetic analysis favours the interpretation of these teeth as mammalian, and they are similar to the lower teeth of other mammals in Volaticotherini. Phylogenetic studies find a close relationship with '' Volaticotherium'', '' Jugulator'', '' Triconolestes'' and '' Argentoconodon'', within Volaticotheria.Thomas Martin, Jesús Marugán-Lobón, Romain Vullo, Hugo Martín-Abad, Zhe-Xi Luo & Angela D. Buscalioni (2015). A Cretaceous eutriconodont and integument evolution in early mammals. Nature 526, 380–384.

Ecology

''Ichthyoconodons teeth were found in marine deposits, alongside taxa like hybodontid sharks, ornithocheirid

pterosaurs Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...

, ray-finned fish and

sea turtles Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, ...

, as well as several terrestrial taxa like theropods. Unlike other mammal teeth, including other contemporary teeth such as those of ''

Hahnodon ''Hahnodon'' ("Hahn's tooth") is an extinct genus of mammaliaforms from the Early Cretaceous Ksar Metlili Formation in Morocco. Although originally considered to be a relatively early member of the extinct clade Multituberculata, recent studies i ...

'', 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 ''Castorocauda'' is an extinct, semi-aquatic, superficially otter-like genus of docodont mammaliaforms with one species, ''C. lutrasimilis''. It is part of the Yanliao Biota, found in the Daohugou Beds of Inner Mongolia, China dating to the M ...

'' and '' Haldanodon'',

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

monotremes and the Late Cretaceous '' Didelphodon''. ''Ichthyoconodon'' and ''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.Zofia Kielan-Jaworowska, Richard L. Cifelli, Zhe-Xi Luo (2004). "Chapter 7: Eutriconodontans". Mammals from the Age of Dinosaurs: origins, evolution, and structure. New York: Columbia University Press. pp. 216–248. . 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 ''Ichthyoconodon'' in North Africa in such a relatively close span of time suggests there may have been a widespread clade of Jurassic-Early Cretaceous gliding triconodonts.

References

{{Taxonbar, from=Q11682803 Eutriconodonts Cretaceous mammals Mesozoic mammals of Africa Fossil taxa described in 1995 Taxa named by Denise Sigogneau‐Russell Prehistoric mammal genera