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 is today 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
Cedaromys ("Cedar mouse") is an extinct mammal which lived during the Upper Cretaceous, at the same time as many dinosaurs. It was a member of the also extinct order of Multituberculata. It's within the suborder of Cimolodonta, and a possible member of the Paracimexomys group.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.Djadochtatheriidae
Djadochtatheriidae is a family of fossil mammals within the extinct order Multituberculata. Remains are known from the Upper Cretaceous of Central Asia. These animals lived during the Mesozoic, also known as the "age of the dinosaurs". This family is part of the suborder of Cimolodonta. The taxon Djadochtatheriidae was named by Z. Kielan-Jaworowska and J. H. Hurum in 1997.
Multituberculates are a rather diverse group in terms of locomotion and diet. Forms like Kryptobaatar and Catopsbaatar were hopping, gerboa-like omnivores (and this is probably the ancestral condition for the group, given that Nemegtbaatar also had this lifestyle), while Mangasbaatar was a robust, digging herbivore.Ecprepaulax
Ecprepaulax is a Lower Cretaceous mammal from Portugal. It was a member of the also extinct order Multituberculata and shared the world with dinosaurs. It lies within the suborder "Plagiaulacida" and family Pinheirodontidae.
The genus Ecprepaulax was named by Hahn G. and Hahn R. in 1999 based on a single species Ecprepaulax anomala Fossil remains were found in Berriasian (Lower Cretaceous) strata in Portugal. The species is a multituberculate mammal within the informal suborder of "Plagiaulacida".Gerhardodon
Gerhardodon is an extinct genus of mammal from the Lower Cretaceous of southern England. It was a member of the also extinct order of Multituberculata, and lived with such dinosaurs as Iguanodon. It lies within the suborder "Plagiaulacida" and family Pinheirodontidae.
The genus Gerhardodon ("Gerhard’s tooth") was named by Kielan-Jaworowska Z. and Ensom P.C. in 1992 based on a single species, Gerhardodon purbeckensis. It is known from the Berriasian (Lower Cretaceous) strata of Durlston Bay in Dorset, England. It is a multituberculate mammal from the Isle of Purbeck, Dorset. This formation is sometimes considered to be partly Upper Jurassic.Glirodon
Glirodon is a genus of extinct mammal from the Upper Jurassic. It was a relatively early member of the also-extinct order of Multituberculata, suborder "Plagiaulacida". These mammals lived in North America during the Mesozoic, also known as the "age of the dinosaurs".
The genus Glirodon has been described by Engelmann G.F. and Callison G. (1999) from a 'gliriform tooth'.
The species Glirodon grandis, also described by Engelmann and Callison, has been found in the Upper Jurassic formations of Dinosaur National Monument in Utah (United States). Other than being a large, early American Multituberculate, (see Multituberculata), the nature of this beast is somewhat unclear. It is an "allodontid (two families and the genus Glirodon)", (Kielan-Jaworowska and Hurum, 2001). It had gliriform incisors; incisors with the "enamel reduced to a stripe on the front side." Apparently, this condition evolved several times among Multituberculates.
It is based on a portion of snout. "Glirodon retains the plesiomorphic 'plagiaulacidan' ("Plagiaulacida") dental formula and shares with Allodontidae the structure of the upper premolars (Pl.1 fis 2-4). It differs from the Paulchoffatiidae and Plagiaulacidae in having a single-cusped I3," (Kielan-Jaworowska & Hurum, 2001, p. 401-402). I3 refers to an upper incisor and 'plesiomorphic' means 'basal'.
Present in stratigraphic zones 4 and 6.Guimarotodon
Guimarotodon is an extinct mammal of the Upper Jurassic. It was a relatively early member of the also extinct order of Multituberculata. It made its living nibbling plants as great big, and small, dinosaurs roamed the world. (For the technically minded, suborder Plagiaulacida, family Paulchoffatiidae.)
Guimarotodon ("Guimarota tooth") Hahn G, 1969. "Guimarotodon Hahn 1969 exhibits a more slender Corpus mandibulae than either Paulchoffatia or Meketibolodon. The most conspicuous character of this genus is the morphology of the P3-4 and the M1.". The Corpus mandibulae is the part of the jaw below the tooth row. P3-4 are upper premolars, whilst M1 is an upper molar tooth.
"The incisor is relatively little curved and its root is of similar length as that of Meketibolodon and extends to underneath the posterior premolars." (Both quotations from Hahn & Hahn 2000, p. 105-106).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.Hahnodontidae
Hahnodontidae is a family of extinct mammals from Early Cretaceous deposits in Morocco and the Western US. Although originally considered to belong to the extinct clade Multituberculata, recent work indicates that hahnodontids belong to the more primitive clade Haramiyida.Henkelodon
Henkelodon was a small mammal of the Upper Jurassic. It was a relatively early member of the extinct order Multituberculata. Henkelodon was a European herbivore that lived during the "age of the dinosaurs". It lies within the suborder "Plagiaulacida" and family Paulchoffatiidae.
The genus Henkelodon ("Henkel's tooth") was named by Hahn G. in 1977 based on a single species.
Fossil remains of the species Henkelodon naias were discovered in the Kimmeridgian (Upper Jurassic)-age strata of Guimarota, Portugal. The remains consisted of one upper jaw. According to Kielan-Jaworowska and Hurum, 2001, (p. 413), this genus was named in 1987. However, Hahn and Hahn 2000 (p. 105) supports 1977.Iberodon
Iberodon is a small, extinct mammal of the Lower Cretaceous from Portugal. It was a member of the also extinct order Multituberculata, and led its obscure and plant-eating existence in the company of dinosaurs. It lies within the suborder "Plagiaulacida" and family Pinheirodontidae.
The genus Iberodon was named by Hahn G. and Hahn R. in 1999 based on a single species. The species, known as Iberodon quadrituberculatus, is known from teeth found in Berriasian (Lower Cretaceous)-age strata of Portugal.Kielanodon
Kielanodon is an extinct mammal of the Portuguese Upper Jurassic. It was a relatively early member of the also extinct order of Multituberculata. It eked out a living during the Mesozoic era, also known as the "Age of the Dinosaurs." It is in the suborder Plagiaulacida, family Paulchoffatiidae.
The genus Kielanodon, meaning "Kielan’s tooth" after Zofia Kielan-Jaworowska, was named by Hahn G. in 1987. The main species, Kielanodon hopsoni, also named by Hahn, is known from fossils found in the Kimmeridgian (Upper Jurassic)-age strata of Guimarota, Portugal. The identification is based on three upper jaws.Lavocatia
Lavocatia is a genus of extinct mammal from the Lower Cretaceous of Spain. It was a member of the also extinct order Multituberculata, and lived alongside of dinosaurs. Like most Mesozoic mammals, it was a shrewish-sized animal. It's in the suborder "Plagiaulacida" and family Pinheirodontidae. The genus Lavocatia was named by J. I. Canudo and G. Cuenca in 1996 based on a single tooth, with the generic epithet in honor of French paleontologist René Lavocat and the specific epithet a reference to the town of Alfambra.
The species Lavocatia alfambrensis is known from the Barremian (Lower Cretaceous)-age strata of Galve, Spain. This genus is apparently differentiated by the number of cusps on the tooth; 15. Also referred to in the reference is Peramura. This was a more "advanced" group of mammals, possibly ancestral to ourselves (see Peramus).Meketichoffatia
Meketichoffatia was a small mammal from the Upper Jurassic of Portugal. It was a relatively early member of the extinct order Multituberculata. It lived at the same time as dinosaurs such as Allosaurus. It's within the suborder "Plagiaulacida" and family Paulchoffatiidae.
The genus Meketichoffatia ("no longer for Choffat"?) was named by Hahn G. in 1993 based on a single species. Fossil remains of the species Meketichoffatia krausei consisting of two upper jaws were found in Kimmeridgian (Upper Jurassic)-age Camadas de Guimarota of Guimarota, Portugal.Pinheirodon
Pinheirodon is a genus of extinct mammal from Portugal. It is a member of the also extinct order of Multituberculata, and shared the world with dinosaurs. It is placed in the suborder "Plagiaulacida" and family Pinheirodontidae.
The species on which the genus is based has been designated as Pinheirodon sp. It is known from isolated fossil teeth.
Initially considered Early Cretaceous, Pinheirodon is from the locality of Porto Dinheiro (Lourinhã, Portugal) which is Late Jurassic (Tithonian).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.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 renamed a year later.Sinobaatar
Sinobaatar is a genus of extinct mammal from the Lower Cretaceous of China. It is categorized within the also extinct order Multituberculata and among these it belongs to the plagiaulacid lineage (a possible infraorder). Sinobaatar was a small herbivore during the Mesozoic era, commonly called "the age of the dinosaurs". The genus was named by Hu Y. and Wang Y. in 2002. Three species have been described.
It has been found in Lower Cretaceous strata of the Yixian Formation in Liaoning, China. According to Hu & Wang (2002),
"[t]he dental features of Sinobaatar show again that eobaatarids are obviously intermediate between Late Jurassic multituberculates and the later forms".
Many Multituberculata are only known from teeth, but the type specimen of Sinobaatar is a reasonably complete skeleton.
Sinobaatar was eaten, at least on occasion, by the feathered dinosaur Sinosauropteryx prima (Hurum et al. 2006).Xenachoffatia
Xenachoffatia is a small Jurassic mammal from Portugal. It was a relatively early member of the also extinct order of Multituberculata. It lived during "the age of the dinosaurs" and belongs to the suborder Plagiaulacida, family Paulchoffatiidae.
The genus Xenachoffatia ("for Xena Choffat") was named by Hahn G. and Hahn R. in 1998. The primary species Xenachoffatia oinopion (Hahn & Hahn, 1998) was found in Kimmeridgian (Upper Jurassic) Camadas de Guimarota of Guimarota, Portugal. The classification is based on three upper molars.