Multituberculata

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Multituberculates
Catopsbaatar catopsaloides.jpg
Skeleton of Catopsbaatar
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Allotheria
Order: Multituberculata
Cope, 1884
Suborders

Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) 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. [1] 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. [2] [3] Multituberculates are usually placed as crown mammals outside either of the two main groups of living mammals Theria, including placentals and marsupials, and Monotremata [4] but usually as closer to Theria than to monotremes. [5] [6] They are considered to be closely related to Euharamiyida and Gondwanatheria as part of Allotheria.

Contents

Description

Restoration of Taeniolabis, the largest multituberculate at approximately 100 kg (220 lb). Taeniolabis NT small.jpg
Restoration of Taeniolabis , the largest multituberculate at approximately 100 kg (220 lb).

The multituberculates had a cranial and dental anatomy superficially similar to rodents such as mice and rats, with cheek-teeth separated from the chisel-like front teeth by a wide tooth-less gap (the diasteme). Each cheek-tooth displayed several rows of small cusps (or tubercles, hence the name) that operated against similar rows in the teeth of the jaw; the exact homology of these cusps to therian ones is still a matter of debate.[ citation needed ] Unlike rodents, which have ever-growing teeth, multituberculates underwent dental replacement patterns typical to most mammals (though in at least some species the lower incisors continued to erupt long after the root's closure). [7] Multituberculates are notable for the presence of a massive fourth lower premolar, the plagiaulacoid; other mammals, like Plesiadapiformes and diprotodontian marsupials, also have similar premolars in both upper and lower jaws, but in multituberculates this tooth is massive and the upper premolars are not modified this way. In basal multituberculates all three lower premolars were plagiaulacoids, increasing in size posteriorly, but in Cimolodonta only the fourth lower premolar remained, with the third one remaining only as a vestigial peg-like tooth, [7] and in several taxa like taeniolabidoideans, the plagiaulacoid disappeared entirely or was reconverted into a molariform tooth. [8] [9] [10]

Skull of Ptilodus. Notice the massive blade-like lower premolar. Ptilodus skull BW.jpg
Skull of Ptilodus . Notice the massive blade-like lower premolar.

Unlike rodents and similar therians, multituberculates had a palinal jaw stroke (front-to-back), instead of a propalinal (back-to-front) or transverse (side-to-side) one; as a consequence, their jaw musculature and cusp orientation is radically different. [4] [7] Palinal jaw strokes are almost entirely absent in modern mammals (with the possible exception of the dugong [11] ), but are also present in haramiyidans, argyrolagoideans and tritylodontids, the former historically united with multituberculates on that basis. Multituberculate mastication is thought to have operated in a two stroke cycle: first, food held in place by the last upper premolar was sliced by the bladelike lower pre-molars as the dentary moved orthally (upward). Then the lower jaw moved palinally, grinding the food between the molar cusp rows. [4] [7]

Lower jaws and teeth of allodontid multituberculates American Jurassic Mammals plate VII.jpg
Lower jaws and teeth of allodontid multituberculates

The structure of the pelvis in the Multituberculata suggests that they gave birth to tiny helpless, underdeveloped young, similar to modern marsupials, such as kangaroos. [2] [7] However, a 2022 study reveals that they might actually have had long gestation periods like placentals. [12]

At least two lineages developed hypsodonty, in which tooth enamel extends beyond the gumline: lambdopsalid taeniolabidoideans [13] and sudamericid gondwanatheres. [14]

Studies published in 2018 demonstrated that multituberculates had relatively complex brains, some braincase regions even absent in therian mammals. [15]

Evolution

Multituberculates first appear in the fossil record during the Jurassic period, and then survived and even dominated for over one hundred million years, longer than any other order of mammaliforms, including placental mammals. The earliest known multituberculates are from the Middle Jurassic (Bathonian ~166-168 million years ago) of England and Russia, including Hahnotherium and Kermackodon from the Forest Marble Formation of England, and Tashtykia and Tagaria from the Itat Formation of Russia. These forms are only known from isolated teeth, which bear close similarity to those of euharamyidans, which they are suspected to be closely related. [16] During the Late Jurassic and Early Cretaceous, primitive multituberculates, collectively grouped into the paraphyletic "Plagiaulacida" were abundant and widespread across Laurasia (including Europe, Asia and North America). During the Aptian stage of the Early Cretaceous, the advanced subgroup Cimolodonta appeared in North America, characterised by a reduced number of lower premolars, with a blade-like lower fourth premolar. By the early Late Cretaceous (Cenomanian) Cimolodonta had replaced all other multituberculate lineages. [17]

During the Late Cretaceous, multituberculates experienced an adaptive radiation, corresponding with a shift towards herbivory. [18] Multituberculates reached their peak diversity during the early Paleocene, shortly after the Cretaceous–Paleogene extinction event, but declined from the mid Paleocene onwards, likely due to competition with placental mammals such as rodents and ungulates, the group finally became extinct in the Late Eocene. [19] [20] There are some isolated records of multituberculates from the Southern Hemisphere, including the cimolodontan Corriebaatar from the Early Cretaceous of Australia, [21] and fragmentary remains from the Late Cretaceous Maevarano Formation of Madagascar. [22] The family Ferugliotheriidae from the Late Cretaceous of South America, traditionally considered gondwanatherians, may actually be cimolodontan multituberculates. [21]

During the Late Cretaceous and Paleocene the multituberculates radiated into a wide variety of morphotypes, including the squirrel-like arboreal ptilodonts. The peculiar shape of their last lower premolar is their most outstanding feature. These teeth were larger and more elongated than the other cheek-teeth and had an occlusive surface forming a serrated slicing blade. Though it can be assumed that this was used for crushing seeds and nuts, it is believed that most small multituberculates also supplemented their diet with insects, worms, and fruits. [4] Tooth marks attributed to multituberculates are known on Champsosaurus fossils, indicating that at least some of these mammals were scavengers. [23] A ptilodont that thrived in North America was Ptilodus . Thanks to the well-preserved Ptilodus specimens found in the Bighorn Basin, Wyoming, we know that these multituberculates were able to abduct and adduct their big toes, and thus that their foot mobility was similar to that of modern squirrels, which descend trees head first. [4]

Restoration of Catopsbaatar Catopsbaatar.jpg
Restoration of Catopsbaatar

Another group of multituberculates, the taeniolabids, were heavier and more massively built, indicating that they lived a fully terrestrial life. The largest specimens weighed probably as much as 100 kg (220 lb), making them comparable in size to large rodents like Castoroides . [24]

Classification

Multituberculate is generally placed in the Allotheria alongside Euharamiyida, a clade of mammals known from the Middle Jurassic to Early Cretaceous of the Asia and possibly Europe that several morphological similarities to multituberculates. [16] [25]

Gondwanatheria is a monophyletic group of allotherians that was diverse in the Late Cretaceous of South America, India, Madagascar and possibly Africa and occurs onwards into the Paleogene of South America and Antarctica. Their placement within Allotheria is highly controversial, with some phylogenies recovering the group as deeply nested within multituberculates, while others recover them as a distinct branch of allotherians separate from multituberculates. [25]

Restoration of Taeniolabis taoensis Taeniolabis taoensis.jpg
Restoration of Taeniolabis taoensis

In their 2001 study, Kielan-Jaworowska and Hurum found that most multituberculates could be referred to two suborders: "Plagiaulacida" and Cimolodonta. The exception is the genus Arginbaatar , which shares characteristics with both groups.

"Plagiaulacida" is paraphyletic, representing the more primitive evolutionary grade. Its members are the more basal Multituberculata. Chronologically, they ranged from perhaps the Middle Jurassic until the mid-Cretaceous. This group is further subdivided into three informal groupings: the allodontid line, the paulchoffatiid line, and the plagiaulacid line.

Cimolodonta is, apparently, a natural (monophyletic) suborder. This includes the more derived Multituberculata, which have been identified from the lower Cretaceous to the Eocene. The superfamilies Djadochtatherioidea, Taeniolabidoidea, Ptilodontoidea are recognized, as is the Paracimexomys group. Additionally, there are the families Cimolomyidae, Boffiidae, Eucosmodontidae, Kogaionidae, Microcosmodontidae and the two genera Uzbekbaatar and Viridomys . More precise placement of these types awaits further discoveries and analysis. [26] [ better source needed ]

Taxonomy

Subgroups
Multituberculate phylogenetic tree Multituberculata.png
Multituberculate phylogenetic tree

Based on the combined works of Mikko's Phylogeny Archive [28] and Paleofile.com.[ citation needed ]

Suborder † Plagiaulacida Simpson 1925

Phylogeny [27]

Multituberculata

Paulchoffatiidae

Plagiaulacidae

Eobaataridae

Gondwanatheria

Ferugliotheriidae

Groeberiidae

Sudamericidae

Cimolodonta

Cimolodontidae

Ptilodontoidea

Cimexomys

Cimolomyidae

Boffius

Buginbaatar

Eucosmodontidae

Microcosmodontidae

Djadochtatherioidea

Bulganbaatar

Chulsanbaatar

Sloanbaataridae

Nemegtbaatar

Djadochtatheriidae

Kogaionidae

Taeniolabidoidea

Yubaatar

Bubodens

Valenopsalis

Lambdopsalidae

Taeniolabididae

Paleoecology

Behaviour

Multituberculates are some of the earliest mammals to display complex social behaviours. One species, Filikomys, from the Late Cretaceous of North America, engaged in multi-generational group nesting and burrowing. [29]

Extinction

The extinction of multituberculates has been a topic of controversy for several decades. [30] After at least 88 million years of dominance over most mammalian assemblies, multituberculates reached the peak of their diversity in the early Palaeocene, before gradually declining across the final stages of the epoch and the Eocene, finally disappearing in the early Oligocene. [31]

The last multituberculate species, Ectypodus childei , went extinct near the end of the Eocene in North America. It is unclear why this particular species persisted for so long when all of its counterparts succumbed to replacement by rodents. [32] :43

Traditionally, the extinction of multituberculates has been linked to the rise of rodents (and, to a lesser degree, earlier placental competitors like hyopsodonts and Plesiadapiformes), which supposedly competitively excluded multituberculates from most mammalian faunas. [1]

However, the idea that multituberculates were replaced by rodents and other placentals has been criticised by several authors. For one thing, it relies on the assumption that these mammals are "inferior" to more derived placentals, and ignores the fact that rodents and multituberculates had co-existed for at least 15 million years. According to some researchers, multituberculate "decline" is shaped by sharp extinction events, most notably after the Tiffanian, where a sudden drop in diversity occurs. Finally, the youngest known multituberculates do not exemplify patterns of competitive exclusion; the Oligocene Ectypodus is a rather generalistic species, rather than a specialist. This combination of factors suggests that, rather than gradually declining due to pressure from rodents and similar placentals, multituberculates simply could not cope with climatic and vegetation changes, as well as the rise of new predatory eutherians, such as miacids. [31]

More recent studies show a mixed effect. Multituberculate faunas in North America and Europe do indeed decline in correlation to the introduction of rodents in these areas. However, Asian multituberculate faunas co-existed with rodents with minimal extinction events, implying that competition was not the main cause for the extinction of Asiatic multituberculates. As a whole, it seems that Asian multituberculates, unlike North American and European species, never recovered from the KT event, which allowed the evolution and propagation of rodents in the first place. [30] A recent study seems to indeed indicate that eutherians recovered more quickly from the KT event than multituberculates. [33] Conversely, another study has shown that placental radiation did not start significantly until after the decline of multituberculates. [20]

Related Research Articles

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

Eobaataridae is a family of fossil mammals within the order Multituberculata. Remains are known from the Lower Cretaceous of Europe and Asia. They are among the most derived representatives of the informal suborder "Plagiaulacida", and closely related to Cimolodonta. Most eobaatarids are only known from isolated teeth, though several reasonably complete members are known, including Sinobaatar and Jeholbaatar. The body of Sinobaatar is generalised, while Jeholbaatar displays clear adaptations for scansoriality (climbing) due to its elongated digits. Due to the morphology of the cheek teeth, Eobaatar and Jeholbaatar are inferred to be omnivorous, likely feeding on plants and invertebrates.

<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.

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

Catopsalis is a genus of extinct mammal from the Paleocene of North America. This animal was a relatively large member of the extinct order of Multituberculata. Most Multituberculates were much smaller.

<i>Taeniolabis</i> Extinct genus of rodent-like mammals from the Paleocene epoch

Taeniolabis is a genus of extinct multituberculate mammal from the Paleocene of North America.

Mesodma is an extinct genus of mammal, a member of the extinct order Multituberculata within the suborder Cimolodonta, family Neoplagiaulacidae. It lived during the upper Cretaceous and Paleocene Periods of what is now North America. The earliest definitive record is from the late Santonian stage strata of the Straight Cliffs Formation. A single premolar tooth from the lower Cenomanian stage strata of the Cedar Mountain Formation has been tentatively assigned to this genus based on its similarity, but its describers noted that it is unlikely that Mesodma lived during that time.

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

Kogaionidae is a family of fossil mammals within the extinct order Multituberculata. Representatives are known from the Upper Cretaceous and the Paleocene of Europe. Having started as island endemics on Hateg Island during the Upper Cretaceous, where they were in fact the dominant mammal group and diverged into rather unique ecological niches, they expanded across Europe in the Paleocene, where they briefly became a major component of its mammal fauna before their extinction. They are considered to be basal members of Cimolodonta.

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

Barbatodon is a mammal genus from the Upper Cretaceous period. It lived in Transylvania at the same time as some of the last dinosaurs and was a member of the extinct order of Multituberculata. It is within the suborder of Cimolodonta, and the family Kogaionidae. The genus Barbatodon was named by Constantin Rădulescu and Petre Mihai Samson in 1986.

Ferugliotherium is a genus of fossil mammals in the family Ferugliotheriidae from the Campanian and/or Maastrichtian period of Argentina. It contains a single species, Ferugliotherium windhauseni, which was first described in 1986. Although originally interpreted on the basis of a single brachydont (low-crowned) molar as a member of Multituberculata, an extinct group of small, rodent-like mammals, it was recognized as related to the hypsodont (high-crowned) Sudamericidae following the discovery of additional material in the early 1990s. After a jaw of the sudamericid Sudamerica was described in 1999, these animals were no longer considered to be multituberculates and a few fossils that were previously considered to be Ferugliotherium were assigned to unspecified multituberculates instead. Since 2005, a relationship between gondwanatheres and multituberculates has again received support. A closely related animal, Trapalcotherium, was described in 2009 on the basis of a single tooth.

Ferugliotheriidae is one of three known families in the order Gondwanatheria, an enigmatic group of extinct mammals. Gondwanatheres have been classified as a group of uncertain affinities or as members of Multituberculata, a major extinct mammalian order. The best-known representative of Ferugliotheriidae is the genus Ferugliotherium from the Late Cretaceous epoch in Argentina. A second genus, Trapalcotherium, is known from a single tooth, a first lower molariform, from a different Late Cretaceous Argentinean locality. Another genus known from a single tooth, Argentodites, was first described as an unrelated multituberculate, but later identified as possibly related to Ferugliotherium. Finally, a single tooth from the Paleogene of Peru, LACM 149371, perhaps a last upper molariform, and a recent specimen from Mexico, may represent related animals.

<span class="mw-page-title-main">Allotheria</span> Extinct subclass of mammals

Allotheria is an extinct clade of mammals known from the Mesozoic and early Cenozoic. Shared characteristics of the group are the presence of lower molariform teeth equipped with longitudinal rows of cusps and enlarged incisors. Typically, the canine teeth are also lost. Allotheria includes Multituberculata, Gondwanatheria, and probably Haramiyida, although some studies have recovered haramiyidans to be basal mammaliaforms unrelated to multituberculates. Allotherians are often placed as crown group mammals, more closely related to living marsupials and placentals (Theria) than to monotremes or eutriconodonts.

<span class="mw-page-title-main">Haramiyida</span> Extinct order of mammaliaforms

Haramiyida is a possibly polyphyletic order of mammaliaform cynodonts or mammals of controversial taxonomic affinites. Their teeth, which are by far the most common remains, resemble those of the multituberculates. However, based on Haramiyavia, the jaw is less derived; and at the level of evolution of earlier basal mammals like Morganucodon and Kuehneotherium, with a groove for ear ossicles on the dentary. Some authors have placed them in a clade with Multituberculata dubbed Allotheria within Mammalia. Other studies have disputed this and suggested the Haramiyida were not crown mammals, but were part of an earlier offshoot of mammaliaformes instead. It is also disputed whether the Late Triassic species are closely related to the Jurassic and Cretaceous members belonging to Euharamiyida/Eleutherodontida, as some phylogenetic studies recover the two groups as unrelated, recovering the Triassic haramiyidians as non-mammalian cynodonts, while recovering the Euharamiyida as crown-group mammals closely related to multituberculates.

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

Amphitheriidae is a family of Mesozoic mammals restricted to the Middle Jurassic of Britain, with indeterminate members also possibly known from the equivalently aged Itat Formation in Siberia and the Anoual Formation of Morocco. They were members of Cladotheria, more derived than members of Dryolestida, and forming a close relationship with Peramuridae. Amphitheriidae is the only family of the order Amphitheriida.

Several mammals are known from the Mesozoic of Madagascar. The Bathonian Ambondro, known from a piece of jaw with three teeth, is the earliest known mammal with molars showing the modern, tribosphenic pattern that is characteristic of marsupial and placental mammals. Interpretations of its affinities have differed; one proposal places it in a group known as Australosphenida with other Mesozoic tribosphenic mammals from the southern continents (Gondwana) as well as the monotremes, while others favor closer affinities with northern (Laurasian) tribosphenic mammals or specifically with placentals. At least five species are known from the Maastrichtian, including a yet undescribed species known from a nearly complete skeleton that may represent a completely new group of mammals. The gondwanathere Lavanify, known from two teeth, is most closely related to other gondwanatheres found in India and Argentina. Two other teeth may represent another gondwanathere or a different kind of mammal. One molar fragment is one of the few known remains of a multituberculate mammal from Gondwana and another has been interpreted as either a marsupial or a placental.

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

<span class="mw-page-title-main">Paratheria (mammals)</span> Former taxonomic group including xenarthran and similar mammals

Paratheria is an obsolete term for a taxonomic group including the xenarthran mammals and various groups thought to be related to them. It was proposed by Oldfield Thomas in 1887 to set apart the sloths, anteaters, armadillos, and pangolins, usually classified as placentals, from both marsupial and placental mammals, an arrangement that received little support from other workers. When teeth of the extinct gondwanathere mammals were first discovered in Argentina in the 1980s, they were thought to be related to xenarthrans, leading to renewed attention for the hypothesis that xenarthrans are not placentals. However, by the early 1990s, gondwanatheres were shown to be unrelated to xenarthrans, and xenarthrans are still considered to be placentals.

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

Megaconus is an extinct genus of allotherian mammal from the Middle Jurassic Tiaojishan Formation of Inner Mongolia, China. The type and only species, Megaconus mammaliaformis was first described in the journal Nature in 2013. Megaconus is thought to have been a herbivore that lived on the ground, having a similar posture to modern-day armadillos and rock hyraxes. Megaconus was in its initial description found to be member of a group called Haramiyida. A phylogenetic analysis published along its description suggested that haramiyidans originated before the appearance of true mammals, but in contrast, the later description of the haramiyidan Arboroharamiya in the same issue of Nature indicated that haramyidans were true mammals. If haramiyidans are not mammals, Megaconus would be one of the most basal ("primitive") mammaliaforms to possess fur, and an indicator that fur evolved in the ancestors of mammals and not the mammals themselves. However, later studies cast doubt on the euharamiyidan intrepretation, instead finding it to be a basal allotherian mammal.

<span class="mw-page-title-main">Euharamiyida</span> Extinct clade of mammaliaforms

Euharamiyida also known as Eleutherodontida, is clade of early mammals or mammal-like cynodonts from the Middle Jurassic to Early Cretaceous of Eurasia and possibly North America. The group is sometimes considered a sister group to Multituberculata, or part of an earlier divergence within the synapsid line. It is disputed whether or not they are related to the Haramiyids from the Late Triassic, such as Haramiyavia. The morphology of their teeth indicates that they were herbivorous or omnivorous. Some members of the group are known to be arboreal, including gliding forms similar to modern flying squirrels or colugos.

<span class="mw-page-title-main">Plagiaulacoid</span> Mammalian tooth

A plagiaulacoid is a type of blade-like, most often serrated, tooth present in various mammal groups, usually a premolar. Among modern species it is present chiefly on diprotodontian marsupials, which have both the upper and lower first premolars converted into serrated blades. However, various other extinct groups also possessed plagiaulacoids. These would be multituberculates, some "Plesiadapiformes" such as Carpolestes and various metatherians such as Epidolops and various early diprotodontians. In many of these only a lower premolar became converted into a blade, while the upper premolars showed less specialisation.

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.

Cifelliodon is an extinct genus of mammaliaforms from the Lower Cretaceous of North America. In the describing paper, it was considered one of the latest surviving haramiyids yet known, belonging to the family Hahnodontidae. Its discovery led to the proposal to remove hahnodontids from the larger well-known group, the multituberculates. However, later papers have considered it to be a basal allotherian outside of Haramiyida.

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