Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct taxon of rodent-like allotherian mammals that existed for approximately 166 million years, the longest fossil history of any mammal lineage. They eventually declined from the late Palaeocene onwards, disappearing in the late Eocene, though they might have lived even longer into the Miocene, if gondwanatheres are part of this group. More than 200 species are 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 closer to Theria than to monotremes.
|Skeleton of Catopsbaatar|
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. 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). 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 aren't 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, and in several taxa like gondwanatherians and taeniolabidoideans the plagiaulacoid disappeared entirely or was reconverted into a molariform tooth.
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. Palinal jaw strokes are almost entirely absent in modern mammals (with the possible exception of the dugong), 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.
At least two lineages developed hypsodonty, in which tooth enamel extends up beyond the gumline: lambdopsalid taeniolabidoideans and sudamericid gondwanatheres. The latter, having been around already during the Cretaceous, are the earliest known lineage of grazing mammals. A species from the Katsuyama Dinosaur Forest Geopark may offer an even earlier example of grass-eating adaptations as it dates from the Lower Cretaceous at about 120 million years.
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 example is Rugosodon, a rodent-like omnivore living 160 million years ago in what would someday be China.
During the Cretaceous, the multituberculates radiated into a wide variety of morphotypes, including the squirrel-like arboreal ptilodonts. Like all categories of life on earth, most species of multituberculata appear to have been wiped out during the K-T event (the extinction of the dinosaurs), but they seem to have been among the first to recover and diversify again. 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. Tooth marks attributed to multituberculates are known on Champsosaurus fossils, indicating that at least some of these mammals were scavengers.
A ptilodont that throve 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.
In Europe, another family of multituberculates were equally successful—the Kogaionidae, first discovered in Haţeg, Romania. They also developed an enlarged blade-like lower premolar. The Hainina, the most successful genus, was originally believed to be a ptilodont. However, more detailed analysis of this genus revealed a smaller number of dental cusps and a retained fifth premolar—a unique combination of primitive and advanced features indicating that Hainina were related to some Jurassic genera and that enlarged, blade-like premolars were acquired independently in Europe and North America.
Another group of multituberculates, the taeniolabids, were heavier and more massively built, indicating that they lived a fully terrestrial life. The largest specimens weighted probably as much as 100 kg, making them comparable in size to large rodents like Castoroides. They reached their highest diversity in Asia during the late Cretaceous and Paleocene, which suggests that they originated from there.
About 80 genera of Multituberculata are known, including Lambdopsalis, Ptilodus and Meniscoessus. In the northern hemisphere, during the late Cretaceous, more than half of typical land mammalian species were multituberculates. While most mammals — along with birds and other dinosaurs and most other types of life — were wiped out during the K-T event (the extinction of the dinosaurs 65 million years ago), a large proportion of the mammals that show up in the fossil record after the extinction are multituberculates.
The group went on to dominate land in the next twenty million years of the paleocene, but it appears that increasing competition from placental mammals drove them to extinction by the end of the eocene, about 40 million years ago.
Recent studies demonstrate that multituberculates had relatively complex brains, some braincase regions even absent in therian mammals.
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 and possibly the more derived Gondwanatheria. Its members are the more basal Multituberculata, though gondwanatherians are rather derived. Chronologically, they ranged from perhaps the middle Jurassic (unnamed material), until the lower Cretaceous. This group is further subdivided into three informal groupings: the allodontid line, the paulchoffatiid line, and the plagiaulacid line.
Gondwanatheria is a monophyletic group that was diverse in the Late Cretaceous of South America, India, Madagascar and possibly Africa and occurs onwards into the Cenozoic of South America and Antarctica. Though their identity as multituberculates has been disputed, most recent phylogenetic studies recover them as the sister group to cimolodonts. There are two major families, Ferugliotheriidae and Sudamericidae, with a few taxa like Greniodon and Groeberia being uncertainly placed. Patagonia is the youngest multituberculate known, occurring in the Miocene of Argentina.
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.
Suborder †Plagiaulacida Simpson 1925
The multituberculates existed for about 166 or 183 million years, and are often considered the most successful, diversified, and long-lasting mammals in natural history. They first appeared in the Jurassic, or perhaps even the Triassic, survived the mass extinction in the Cretaceous, and became extinct in the early Oligocene epoch, some 35 million years ago. The oldest known species in the group is Indobaatar zofiae from the Jurassic of India, some 183 million years ago, and the youngest are two species, Ectypodus lovei and an unnamed possible neoplagiaulacid, from the late Eocene/Oligocene Medicine Pole Hills deposits of North Dakota. If gondwanatheres are multituberculates, then the clade might have survived even longer into the Colhuehuapian Miocene in South America, in the form of Patagonia peregrina.
The extinction of multituberculates has been a topic of controversy for several decades. 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 (mid-Miocene if gondwanatherians are multituberculates). 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.
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.
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. A recent study seems to indeed indicate that eutherians recovered more quickly from the KT event than multituberculates.
Competition between gondwanatherians and rodents and/or other Glires is untested, with a wide span of time between the youngest representatives of the former in India, Africa and Madagascar in the Maastrichtian and the first representatives of the latter in the Palaeocene, Eocene and Oligocene respectively. Co-existence between both groups is currently confirmed only in South America, Patagonia peregrina is thought to have been forced into a specialised fossorial niche by competition with rodents and argyrolagoidean paucituberculate marsupials, but another clade, Groeberiidae, attained its peak diversity in the mid-Oligocene, after the arrival of rodents.
Multituberculates are mostly known from the northern continents (Laurasia), but there are various records from the southern continents (Gondwana). The group Gondwanatheria, known from Argentina, Antarctica, Madagascar, India, and possibly Tanzania, has been referred to the order in the past and, while this placement remains controversial, most recent phylogenetic studies recover them as multituberculates outside but close to Cimolodonta. Two genera, Hahnodon and Denisodon, are known from the Early Cretaceous of Morocco, but they may instead be haramiyidans. Multituberculates have also been recorded from the Late Cretaceous of Madagascar and Argentina. An Australian multituberculate, Corriebaatar, is known from a single tooth. Indobaatar is known from the Kota Formation of India - then part of eastern Gondwanna - and is the oldest known multituberculate.
In the late Cretaceous, multituberculates were widespread and diverse in the northern hemisphere, and possibly across most southern landsmasses as well, making up more than half of the mammal species of typical faunas. Although several lineages became extinct during the faunal turnover at the end of the Cretaceous, multituberculates as a whole managed very successfully to cross the Cretaceous–Paleogene boundary and reached their peak of diversity during the Paleocene. They were an important component of nearly all Paleocene faunas of Europe and North America, and of some late Paleocene faunas of Asia. Multituberculates were also most diverse in size during the Paleocene, ranging from the size of a very small mouse to that of a panda. However, in Asia, Palaeocene and Eocene multituberculates compose a very small percentage of the overall local mammalian fauna, having never managed to recover from the KT event in the same way that their North American and European counterparts did. Gondwanatheres are common in the Late Cretaceous of Madagascar and India, the Paleocene and Eocene of Seymour Island, and occur in South America from the Late Cretaceous to the Miocene.
Taeniolabidoids underwent a modest taxonomic radiation during the early Palaeocene of North America and underwent a dramatic increase in body size, with Taeniolabis taoensis possibly exceeding 100 kg
Allotheria (meaning "other beasts", from the Greek αλλός, allos–other and θήριον, therion–wild animal) is an extinct branch of successful Mesozoic mammals. The most important characteristic was the presence of lower molariform teeth equipped with two longitudinal rows of cusps. Allotheria includes Multituberculata, Gondwanatheria (which may be part of Multituberculata, as the sister group to Cimolodonta), and probably Haramiyida, although some studies show them to be more basal mammaliaforms rather than true mammals, therefore differing from true allotheres significantly.Allotheres also had a narrow pelvis, indicating that they gave birth to tiny helpless young like marsupials or laid eggs and gave milk to feed their young like monotremes do. This is a feature of all non-placental mammals.Cimolodon
Cimolodon is a genus of the extinct mammal order of Multituberculata within the suborder Cimolodonta and the family Cimolodontidae. Specimens are known from the Late Cretaceous of North America.Cimolodonta
The Cimolodonta are a taxon of extinct mammals that lived from the Cretaceous to the Eocene. They were some of the more derived members of the extinct order Multituberculata. They probably lived something of a rodent-like existence until their ecological niche was assumed by true rodents. The more basal multituberculates are found in a different suborder, "Plagiaulacida".
Cimolodonta is apparently a natural (monophyletic) suborder. Remains have been identified from across the Northern Hemisphere. The taxon is recognized as the informal Paracimexomys group and the superfamilies Djadochtatherioidea, Taeniolabidoidea, and Ptilodontoidea. Additionally, and of uncertain affinities, 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.Cimolodontidae
Cimolodontidae is a family of fossil mammals within the extinct order Multituberculata. Representatives are known from the Upper Cretaceous and Paleocene of North America. The family Cimolodontidae was named by Othniel Charles Marsh in 1889 and is part of the suborder Cimolodonta within the superfamily Ptilodontoidea.Cimolomyidae
Cimolomyidae is a family of fossil mammal within the extinct order Multituberculata. Representatives are known from the Upper Cretaceous and the Paleocene of North America and perhaps Mongolia. The family is part of the suborder Cimolodonta. Other than that, their systematic relationships are hard to define. Some authors have placed the taxon within Taeniolabidoidea. Kielan-Jaworowska and Hurum (2001) expressly don't.
The family Cimolomyidae was named by Othniel Charles Marsh in 1889.Cimolomys
Cimolomys is a mammal genus from the Upper Cretaceous of North America. It was a member of the extinct order Multituberculata within the suborder Cimolodonta and family Cimolomyidae.
The genus Cimolomys was named by Othniel Charles Marsh in 1889.Eobaataridae
Eobaataridae is a family of fossil mammal within the order Multituberculata. Remains are known from the Lower Cretaceous of Europe and Asia. These herbivores thus lived during the Mesozoic era, also known as the "age of the dinosaurs". They were among the most derived representatives of the informal suborder "Plagiaulacida".
In this case of one taxon, remains are reasonably well known. This refers to Sinobaatar from the extraordinary Chinese locality of Liaoning. They were close relatives of the Plagiaulacidae, while the second upper molar has similarities to ones known from the informal Paracimexomys group within the more derived suborder, Cimolodonta.
The recently described Indobaatar from the Early Jurassic Kota Formation is the earliest known multituberculate, let alone the earliest eobaatarid, and may stretch the eobaatarid-cimolodontan group much earlier than previously thought.Genus Teutonodon is the first Jurassic mammal discovered in Germany.Hahnodon
Hahnodon ("Hahn's tooth") is a genus of extinct mammal 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 indicate that it instead is a haramiyid.Kryptobaatar
Kryptobaatar ("hidden hero," from Greek: kryptos, "hidden," and Mongolian: baatar, "hero" or "athlete") and also known as Gobiaatar, Gobibaatar ("Gobi hero") or Tugrigbaatar is an extinct mammalian genus dating from the Upper Cretaceous Period and identified in Central Asia. This animal was a member of the extinct order of Multituberculata within the suborder Cimolodonta, and was a member of the family Djadochtatheriidae. It lived contemporaneously with some of the dinosaurs. Its skull had a length of perhaps 3 cm.Mesodma
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.Meteuthria multituberculata
Meteuthria multituberculata is a species of sea snail, a marine gastropod mollusk in the family Buccinidae, the true whelks.Mexichromis multituberculata
Mexichromis multituberculata is a species of sea slug, a dorid nudibranch, a shell-less marine gastropod mollusk in the family Chromodorididae.Microcosmodontidae
Microcosmodontidae is a poorly preserved family of fossil mammals within the extinct order Multituberculata. Representatives are known from the Lower Paleocene of North America. The family is part of the suborder Cimolodonta. Other than that, their systematic relationships are hard to define.
These microcosmodontids were rather small and had a "large lower incisor with a restricted enamel band, (Kielan-Jaworowska & Hurum 2001, p.417). This grouping has also be seen as Microcosmodontinae Holtzman & Wolberg, 1977, within Eucosmodontidae. However, "Microcosmodontidae (new rank assigned by Fox to the subfamily Microcosmodontinae)," (Kielan-Jaworowska & Hurum, 2001).Paulchoffatiidae
Paulchoffatiidae is a family of extinct mammals that lived predominantly during the Upper Jurassic period, though a couple of genera are known from the earliest Cretaceous. Some undescribed fossils from the Middle Jurassic of England may represent earlier versions. Remains have been reported from Portugal, Spain and England. 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.
The most productive fossil site for Paulchoffatiids has been Guimarota, Portugal. Remains from this locality are generally diagnosed on the basis of lower or upper jaws. In only one instance, that of Kuehneodon, has it been possible to match the two up. Some of the lower jaws probably represent the same animals as some of the upper, so the diversity of Paulchoffatiids is very possibly exaggerated. As the site is now a flooded, disused coalmine, further excavations are highly unlikely. However, other locations may yet provide more clarity.
The Paulchoffatiids have been further arranged into two subfamilies and a couple of other genera.Pinheirodontidae
Pinheirodontidae is a poorly known family of fossil mammals within the order Multituberculata. Remains are known from the Late Jurassic to earliest Cretaceous of Europe, (predominantly Portugal and Spain), but are so far restricted to teeth. These small plant-eaters lived during the "age of the dinosaurs". They're part of the informal suborder "Plagiaulacida".
The family Pinheirodontidae was named by Hahn G. and Hahn R. in 1999, after the locality of Porto Dinheiro, in central west Portugal.Plagiaulacidae
Plagiaulacidae is a family of fossil mammals within the order Multituberculata. Remains are known from the Upper Jurassic of North America through the Lower Cretaceous of Europe. They were among the more derived representatives of the informal suborder of "Plagiaulacida".
The taxon Plagiaulacidae was named by Gill T.N. in 1872. It is also known as Bolodontidae, a name developed by Osborn H.F. in 1887.Plesiochoffatia
Plesiochoffatia is an extinct mammal of the Upper Jurassic. It was a relatively early member of the also extinct order Multituberculata. It was a resident of Portugal during the "age of the dinosaurs." It's in the suborder "Plagiaulacida" and family Paulchoffatiidae.
The genus Plesiochoffatia ("near Choffatia") was named by Hahn G. and Hahn R. in 1999. It has also been known as Parachoffatia ("beside Choffatia") Hahn & Hahn, 1998 (preoccupied).
Remains have been found in the Kimmeridgian (Upper Jurassic)-age strata of Guimarota, Portugal. Three species were described in the same study under the name of Parachoffatia; (P. peparethos, P. staphylos and P. thoas). As something else had already been given that name, the genus was rechristened a year later.Sloanbaataridae
Sloanbaataridae is a family of fossil mammals within the extinct order Multituberculata. Remains are known from the Upper Cretaceous of Mongolia. These small herbivores lived during the "age of the dinosaurs". This family is part of the suborder Cimolodonta. The family Sloanbaataridae was named by Kielan-Jaworowska, Z. in 1974.West Usambara two-horned chameleon
The West Usambara two-horned chameleon or West Usambara blade-horned chameleon (Kinyongia multituberculata) is a chameleon endemic to the West Usambara Mountains of Tanzania. Until 2008, it was generally confused with Fischer's chameleon (K. fischeri), which is not found in the Usambara Mountains. Another related species, K. vosseleri, occurs in the same range as K. multituberculata, while K. matschiei is restricted to the East Usambaras.