Rugosodon

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Rugosodon
Temporal range: Late Jurassic, 160  Ma
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The-paulchoffatiid-Rugosodon-eurasiaticus-Yuan-et-al-2013-BMNH1142A-Daxishan-Site.png
Fossil and interpretive drawing
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Multituberculata
Genus: Rugosodon
Yuan et al., 2013
Species:
R. eurasiaticus
Binomial name
Rugosodon eurasiaticus
Yuan et al., 2013

Rugosodon is an extinct genus of multituberculate (rodent-like) mammals from eastern China that lived 160 million years ago during the Jurassic period. The discovery of its type species and currently only known species Rugosodon eurasiaticus was reported in the 16 August 2013 issue of Science .

Contents

Description

Rugosodon is represented by a nearly complete fossilized skeleton, including a skull, that bears a strong resemblance to a small rat or a chipmunk. The mammal is estimated to have weighed 65–80 g (2.3–2.8 oz), about that of an average chipmunk. The generic name Rugosodon (Latin for "wrinkly tooth") refers to the rugosity, or wrinkliness, of the distinctively shaped teeth. [1] [2] Its teeth indicate that the animal was an omnivore, well-adapted to gnawing both plants and animals, including fruits and seeds, worms, insects and small vertebrates. Its ankle joints were highly mobile at rotation. [3] This means that the ankle is remarkably flexible, allowing the foot to hyper-extend downward—like a ballerina standing on pointed toes—and to rotate through a wide range of motion. This feature, along with highly mobile digits, defines the multituberculates and is not seen in other mammalian lineages of the era. Rugosodon also had a highly flexible spine, which would have allowed it to twist both left to right and front to back. [2] Due to the proportions of its hand bones, it is thought to have been terrestrial rather than arboreal. Its diet was likely omnivorous. [4]

Discovery and taxonomic significance

In 2009, a local fossil hunter unearthed an unusual fossil in the Tiaojishan Formation of China's Liaoning province, dating to 160 million years ago. He turned the fossil over to the Chinese Academy of Geological Sciences, where it was eventually identified as a nearly complete skeleton and given the name Rugosodon eurasiaticus. [5] The fossil was discovered on what was the shore of an ancient lake. [6] It was preserved in two shale slabs and measures about 17 cm (6.5 inches) long from head to rump. The site of the discovery consists of lake sediments with embedded volcanic layers, which also contained fossils of feathered dinosaur Anchiornis and the pterosaur Darwinopterus . [4] [3] The dental features of Rugosodon most resemble those of multituberculates of the Late Jurassic of Western Europe, suggesting that Europe and Asia had extensive mammal faunal interchanges (hence the specific name, eurasia) during the Jurassic. [4] [3] [7]

Prior to the discovery of Rugosodon, scientists knew that multituberculates living 66 million years ago had highly flexible ankles. [6] However, older species were mostly known from small fragments, and it was not proven that the trait was ancestral. Additionally, it was unknown what sort of diet was primitive in the lineage. [5] The presence of the characteristic flexible ankles in Rugosodon demonstrates that the trait is ancestral and provides a strong clue that the trait was a major factor in the lineage's evolutionary success. [6] The animal's diet provides a bridge between very early mammals, which were mostly insectivores, and later multituberculates, which were mostly herbivores. [5]

In the initial description, Rugosodon was attributed to Paulchoffatiidae, a group of multituberculates otherwise known from Western Europe. However, later studies suggested that it lacked key morphological features of the family, and was instead placed as a member of the more inclusive Paulchoffatiid-line outside of any defined family, [8] or possibly even more basally than that. [9]

Related Research Articles

<span class="mw-page-title-main">Multituberculata</span> Extinct order of mammals

Multituberculata is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, and reached a peak diversity during the Late Cretaceous and Paleocene. They eventually declined from the mid-Paleocene onwards, disappearing from the known fossil record in the late Eocene. They are the most diverse order of Mesozoic mammals with more than 200 species known, ranging from mouse-sized to beaver-sized. These species occupied a diversity of ecological niches, ranging from burrow-dwelling to squirrel-like arborealism to jerboa-like hoppers. Multituberculates are usually placed as crown mammals outside either of the two main groups of living mammals—Theria, including placentals and marsupials, and Monotremata—but usually as closer to Theria than to monotremes. They are considered to be closely related to Euharamiyida and Gondwanatheria as part of Allotheria.

<span class="mw-page-title-main">Placentalia</span> Infraclass of mammals in the clade Eutheria

Placental mammals are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished from monotremes and marsupials in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young which are then nurtured for a period inside the mother's pouch.

<span class="mw-page-title-main">Paulchoffatiidae</span> Extinct family of mammals

Paulchoffatiidae is a family of extinct mammals that lived predominantly during the Upper Jurassic period, though a couple of genera are known from the Early Cretaceous. Fossils have been reported from Europe. Paulchoffatiids were members of the order Multituberculata. They were relatively early representatives and are within the informal suborder of "Plagiaulacida". The family was named by G. Hahn in 1969, and it honors the Portuguese geologist Léon Paul Choffat. Two subfamilies are recognized.

<i>Catopsbaatar</i> Extinct species of mammal

Catopsbaatar is a genus of multituberculate, an extinct order of rodent-like mammals. It lived in what is now Mongolia during the late Campanian age of the Late Cretaceous epoch, about 72 million years ago. The first fossils were collected in the early 1970s, and the animal was named as a new species of the genus Djadochtatherium in 1974, D. catopsaloides. The specific name refers to the animal's similarity to the genus Catopsalis. The species was moved to the genus Catopsalis in 1979, and received its own genus in 1994. Five skulls, one molar, and one skeleton with a skull are known; the last is the genus' most complete specimen. Catopsbaatar was a member of the family Djadochtatheriidae.

<span class="mw-page-title-main">Theropoda</span> Clade of dinosaurs

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 carnivorous, although a number of theropod groups evolved to become herbivores and omnivores. Theropods first appeared during the Carnian age of the late Triassic period 231.4 million years ago (Ma) and included all the large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous, about 66 Ma. In the Jurassic, birds evolved from small specialized coelurosaurian theropods, and are today represented by about 10,500 living species.

<span class="mw-page-title-main">Sauropodomorpha</span> Extinct clade of dinosaurs

Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The prosauropods, which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the Late Triassic until their decline and extinction at the end of the Cretaceous.

<i>Barapasaurus</i> Sauropod dinosaur genus from Early Jurassic India

Barapasaurus is a genus of basal sauropod dinosaur from Jurassic rocks of India. The only species is B. tagorei. Barapasaurus comes from the lower part of the Kota Formation, which is of Early to Middle Jurassic age. It is therefore one of the earliest known sauropods. Barapasaurus is known from approximately 300 bones from at least six individuals, so that the skeleton is almost completely known except for the anterior cervical vertebrae and the skull. This makes Barapasaurus one of the most completely known sauropods from the early Jurassic.

Oligokyphus is an extinct genus of herbivorous tritylodontid cynodont known from the Late Triassic to Early Jurassic of Europe, Asia and North America.

<i>Tritylodon</i> Extinct genus of mammaliamorphs

Tritylodon is an extinct genus of tritylodonts, one of the most advanced group of cynodont therapsids. They lived in the Early Jurassic and possibly Late Triassic periods along with dinosaurs. They also shared many characteristics with mammals, and were once considered mammals because of overall skeleton construction. That was changed due to them retaining the vestigial reptilian jawbones and a different skull structure. Tritylodons are now regarded as non-mammalian synapsids.

<i>Castorocauda</i> Jurassic beaver-like animal from China

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 Middle to Late Jurassic. It was part of an explosive Middle Jurassic radiation of Mammaliaformes moving into diverse habitats and niches. Its discovery in 2006, along with the discovery of other unusual mammaliaforms, disproves the previous hypothesis of Mammaliaformes remaining evolutionarily stagnant until the extinction of the non-avian dinosaurs.

<span class="mw-page-title-main">Evolution of mammals</span> Derivation of mammals from a synapsid precursor, and the adaptive radiation of mammal species

The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.

<i>Nigersaurus</i> Genus of reptiles (fossil)

Nigersaurus is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in Niger. Fossils of this dinosaur were first described in 1976, but it was only named Nigersaurus taqueti in 1999, after further and more complete remains were found and described. The genus name means "Niger reptile", and the specific name honours the palaeontologist Philippe Taquet, who discovered the first remains.

<i>Limusaurus</i> Genus of theropod dinosaur

Limusaurus is a genus of theropod dinosaur that lived in what is now China during the Late Jurassic, around 161 to 157 million years ago. The type and only species Limusaurus inextricabilis was described in 2009 from specimens found in the Upper Shishugou Formation in the Junggar Basin of China. The genus name consists of the Latin words for "mud" and "lizard", and the species name means "impossible to extricate", both referring to these specimens possibly dying after being mired. Limusaurus was a small, slender animal, about 1.7 m in length and 15 kg (33 lb) in weight, which had a long neck and legs but very small forelimbs. It underwent a drastic morphological transformation as it aged: while juveniles were toothed, these teeth were completely lost and replaced by a beak with age. Several of these features were convergently similar to the later ornithomimid theropods as well as the earlier non-dinosaurian shuvosaurids.

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<span class="mw-page-title-main">Evolution of reptiles</span> Origin and diversification of reptiles through geologic time

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Coloniatherium is a meridiolestid mammal from the Late Cretaceous of Argentina. The single species, Coloniatherium cilinskii, was a large member of the family Mesungulatidae.

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<i>Laquintasaura</i> Extinct genus of dinosaurs

Laquintasaura is a genus of Venezuelan ornithischian dinosaur containing only the type species Laquintasaura venezuelae. The species was the first dinosaur to have been identified from Venezuela. It is known from extensive remains, all from a singular bonebed locality which has been sampled for specimen blocks over the course of several expeditions, largely led by Marcelo R Sánchez-Villagra. A small, very primitive animal, it is known for its distinct dental anatomy and for being one of the earliest and most primitive ornithischians in the fossil record. Taxonomic uncertainty has led to conflicting theories that it is either as the base of Ornithischia or at the base of the subgroup Thyreophora. In either model, its dating to around 200 million years ago, at the start of the Jurassic, existence in equatorial latitudes, and primitive nature make it a key view into early ornithischian evolution. It's thought that Laquintasaura would've lived in groups and had a possible omnivorous diet, living on a seasonal alluvial plain and being preyed about by the contemporary Tachiraptor.

<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.

Vilevolodon is an extinct, monotypic genus of volant, arboreal euharamiyids from the Oxfordian age of the Late Jurassic of China. The type species is Vilevolodon diplomylos. The genus name Vilevolodon references its gliding capabilities, Vilevol, while don is a common suffix for mammalian taxon titles. The species name diplomylos refers to the dual mortar-and-pestle occlusion of upper and lower molars observed in the holotype; diplo, mylos.

References

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