Ichthyoconodon

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Ichthyoconodon
Temporal range: Early Cretaceous, Berriasian
Ichthyoconodon jaworowskorum.jpg
Holotype lower right molar seen from four different angles
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Eutriconodonta
Clade: Volaticotherini
Genus: Ichthyoconodon
Sigogneau-Russell, 1995
Species:
I. jaworowskorum
Binomial name
Ichthyoconodon jaworowskorum
Sigogneau-Russell, 1995

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 . [1]

Contents

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 . [2] [1]

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". [2]

Relationships

Ichthyoconodon has been found to be a eutriconodontan mammal, despite there only being two molar teeth. [2] although some authors have been skeptical of this interpretation. [3] Other possibilities for the identity of these teeth have included pterosaur, dinosaur, and shark, but there has been no supporting evidence to date. [4] Phylogenetic analysis favours the interpretation of these teeth as mammalian, and they are similar to the lower teeth of other mammals in Volaticotherini. [5] [4] [1]

Phylogenetic studies find a close relationship with Volaticotherium , Jugulator , Triconolestes and Argentoconodon , within Volaticotheria. [1] [6] [7]

Ecology

Ichthyoconodon's teeth were found in marine deposits, alongside taxa like hybodontid sharks, ornithocheirid pterosaurs, [8] ray-finned fish and sea turtles, as well as several terrestrial taxa like theropods. [9] 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. [2]

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 . 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. [10]

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. [1]

Related Research Articles

<i>Morganucodon</i> An early mammaliaform genus of the Triassic and Jurassic periods

Morganucodon is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, Morganucodon is well represented by abundant and well preserved material. Most of this comes from Glamorgan in Wales, but fossils have also been found in Yunnan Province in China and various parts of Europe and North America. Some closely related animals (Megazostrodon) are known from exquisite fossils from South Africa.

<i>Repenomamus</i> Extinct family of mammals

Repenomamus is a genus of opossum-sized to badger-sized gobiconodontid mammal containing two species, Repenomamus robustus and Repenomamus giganticus. Both species are known from fossils found in China that date to the early Cretaceous period, about 125-123.2 million years ago. R. robustus is one of several Mesozoic mammals for which there is good evidence that it fed on vertebrates, including dinosaurs, though it is not possible to determine if it actively hunted live dinosaurs or scavenged dead ones. R. giganticus is among the largest mammals known from the Mesozoic era.

<i>Jeholodens</i> Extinct family of mammals

Jeholodens was a primitive mammal belonging to the order Eutriconodonta, and which lived in present-day China during the Middle Cretaceous about 125 million years ago.

<i>Volaticotherium</i> Extinct family of mammals

Volaticotherium antiquum is an extinct, gliding, insectivorous mammal that lived in what would become Asia during the Jurassic period, around 164 mya. It is the only member of the genus Volaticotherium.

Volaticotherini Extinct clade of mammals

Volaticotherini is a clade of eutriconodont mammals from the Mesozoic. In addition to the type genus Volaticotherium, it includes the genera Argentoconodon, Ichthyoconodon, and potentially Triconolestes.

Eutriconodonta Extinct order of mammals

Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack et al. in 1973 as a replacement name for the paraphyletic Triconodonta.

<i>Gobiconodon</i> Extinct genus of mammals

Gobiconodon is an extinct genus of carnivorous mammal from the early Cretaceous. It weighed 10–12 pounds (4.5–5.4 kg) and measured 18–20 inches (460–510 mm). It was one of the largest mammals known from the Mesozoic. Like other gobiconodontids, it possesses several speciations towards carnivory, such as shearing molar teeth, large canine-like incisors and powerful jaw and forelimb musculature, indicating that it probably fed on vertebrate prey; rather uniquely among predatory mammals and other eutriconodonts, the lower canines were vestigial, with the first lower incisor pair having become massive and canine-like. Like the larger Repenomamus there might be some evidence of scavenging.

Deltatheroida is an extinct group of basal metatherians that were distantly related to modern marsupials. The majority of known members of the group lived in the Cretaceous; one species, Gurbanodelta kara, is known from the late Paleocene (Gashatan) of China. Their fossils are restricted to Central Asia and North America. This order can be defined as all metatherians closer to Deltatheridium than to Marsupialia.

Trechnotheria Extinct clade of mammals

Trechnotheria is a group of mammals that includes the therians and some fossil mammals from the Mesozoic Era. In the Jurassic through Cretaceous periods, the group was endemic to what would be Asia and Africa.

Shuotherium is a fossil mammal known from Middle-Late Jurassic of the Forest Marble Formation of England, and the Shaximiao Formation of Sichuan, China.

<i>Kuehneotherium</i> Extinct genus of mammaliaforms

Kuehneotherium is an early mammaliaform genus that lived during the late Triassic period and is characterized by reversed-triangle pattern of molar cusps. Although many fossils have been found, the fossils are limited to teeth, dental fragments, and mandible fragments. The genus includes Kuehneotherium praecursoris and all related species. It was first named and described by Doris M. Kermack, K. A. Kermack, and Frances Mussett in November 1967. The family Kuehneotheriidae and the genus Kuehneotherium were created to house the single species Kuehneotherium praecursoris. Modeling based upon a comparison of the Kuehneotherium jaw with other mammaliaforms indicates it was about the size of a modern-day shrew between 4 and 5.5 g at adulthood.

Triconodontidae Extinct family of mammals

Triconodontidae is an extinct family of actively mobile mammal, endemic to what would be North America, Europe, Africa and probably also South America and Asia during the Jurassic through Cretaceous periods at least from 190–70.6 mya. They are distinguished from amphilestids and gobiconodontids due to their occlusion patterns: instead of interlocking molars, triconodontids fit their teeth more directly, with lower cusp "a" occluding anteriorly to upper cusp "A", between "A" and "B". However, a study on Priacodon suggests that they had embrasure occlusion.

Gobiconodontidae Extinct family of mammals

Gobiconodontidae is a family of extinct mammals that ranged from the mid-Jurassic to the early Late Cretaceous, though most common during the Early Cretaceous. The Gobiconodontids form a diverse lineage of carnivorous non-therian mammals, and include some of the best preserved Mesozoic mammal specimens.

Gobiconodonta Extinct order of mammals

Gobiconodonta is an order of extinct mammals known from the Early Jurassic to early Late Cretaceous. They are generally held to be part of Eutriconodonta.

Argentoconodon is an extinct genus of theriimorph mammal from the Cañadón Asfalto Formation of the Cañadón Asfalto Basin in Patagonia. When originally described, it was known only from a single molariform tooth, which possessed a combination of primitive and derived features. The tooth is currently held in the Museo Paleontológico Egidio Feruglio, where it was given the specimen number MPEF-PV 1877. New material described in 2011 show that Argentoconodon was similar to Ichthyoconodon, Jugulator and Volaticotherium within the family Triconodontidae, and possibly also Triconolestes.

Jugulator is a genus of extinct mammal from the Cretaceous of North America. A eutriconodont, it is known from the Cedar Mountain Formation, and is both a large sized and possibly ecologically specialised taxon, showcasing the diversity of mammals in the Mesozoic.

<i>Dyskritodon</i> Extinct family of mammals

Dyskritodon is a genus of extinct mammal from the Early Cretaceous of Morocco, and possibly the Early Jurassic of India. Of uncertain affinities, it is tentatively described as a eutriconodont.

Astroconodon is an extinct genus of mammal from the Cretaceous of North America. Part of Eutriconodonta, it was a small sized predator, either a terrestrial insectivore and carnivore, or a semi-aquatic piscivore.

<i>Triconodon</i> Extinct family of mammals

Triconodon is a genus of extinct mammal from the Early Cretaceous of England and France with two known species: T. mordax and T. averianovi. First described in 1859 by Richard Owen, it is the type genus for the order Triconodonta, a group of mammals characterised by their three-cusped (triconodont) molar teeth. Since then, this "simplistic" type of dentition has been understood to be either ancestral for mammals or else to have evolved multiple times, rendering "triconodonts" a paraphyletic or polyphyletic assemblage respectively, but several lineages of "triconodont" mammals do form a natural, monophyletic group, known as Eutriconodonta, of which Triconodon is indeed part of.

Alticonodon is a genus of extinct mammal from the Late Cretaceous of North America. It is the geologically youngest known eutriconodont, and is a fairly more specialised animal than earlier representatives of this clade.

References

  1. 1 2 3 4 5 Gaetano, Leandro C.; Rougier, Guillermo W. (2011). "New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4): 829–843. doi:10.1080/02724634.2011.589877.
  2. 1 2 3 4 Sigogneau-Russell, Denise (1995). "Two possibly aquatic triconodont mammals from the Early Cretaceous of Morocco" (PDF). Acta Palaeontologica Polonica. 40 (2): 149–162.
  3. Rose, K.D., Cifelli, R.L. & Lipka, T.R. (2001) Second triconodont dentary from the Early Cretaceous of Maryland. Journal of Vertebrate Paleontology Volume 21. pp. 628–632.
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  7. Percy M. Butler; Denise Sigogneau-Russell (2016). "Diversity of triconodonts in the Middle Jurassic of Great Britain" (PDF). Palaeontologia Polonica 67: 35–65. doi : 10.4202/pp.2016.67_035.
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