''Ichthyoconodon'' is an extinct genus of eutriconodont mammal from the

Lower Cretaceous Lower may refer to: * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Н� ...

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to A ...

. 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

, in the

Ksar Metlili Formation The Ksar Metlili Formation is a geological formation in eastern High Atlas of Morocco, it is late Tithonian to Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision ...

which dates to the

Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ag ...

. These teeth possess characteristics associated with volaticotherian eutriconodontan mammals. The molars are only around 4

millimeter 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter. The millimetre (American and British English spelling differences#-re, -er, ...

s long, a size comparable to the related species ''

Jugulator ''Jugulator'' is the thirteenth studio album by English heavy metal band Judas Priest. It was released in Japan on 16 October 1997 and the rest of the world on 28 October 1997. It was their first studio album since ''Painkiller'' in 1990 an ...

''. 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 Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

ιχθυς, "fish", κῶνος, "cone", and ὀδών, "tooth". The type species, ''I. jaworowskorum'', was named "in honour of

Zofia Kielan-Jaworowska Zofia Kielan-Jaworowska (25 April 1925 – 13 March 2015) was a Polish paleobiologist. In the mid-1960s, she led a series of Polish-Mongolian paleontological expeditions to the Gobi Desert. She was the first woman to serve on the executive commit ...

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 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 ...

, 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'', ''

'', '' 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 Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...

ornithocheirid Ornithocheiridae (or ornithocheirids, meaning "bird hands") is a group of pterosaurs within the suborder Pterodactyloidea. These pterosaurs were among the last to possess teeth. Members that belong to this group lived from the Early to Late Cre ...

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 6 ...

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

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, loggerhe ...

, as well as several terrestrial taxa like

theropods Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...

. 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 studie ...

'', 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 The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

, including the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

and

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

docodonts Docodonta is an order of extinct mammaliaforms that lived during the Mesozoic, from the Middle Jurassic to Early Cretaceous. They are distinguished from other early mammaliaforms by their relatively complex molar teeth, from which the order ge ...

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 ''Haldanodon'' is an extinct docodont mammaliaform which lived in the Upper Jurassic (Kimmeridgian, about 145 million years ago). Its fossil remains have been found in Portugal, in the well-known fossil locality of Guimarota, which is in the Al ...

'',

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

monotremes and the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

'' 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

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

carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified f ...

s, 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 South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

, '' Volaticotherium'' in

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

and ''Ichthyoconodon'' in

North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...

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