Multituberculata

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Multituberculata
Skull of Taeniolabis

Skull of Taeniolabis

Temporal occurrence
Jurassic to Eocene
165 to 34 million years
Locations
  • Eurasia, North America
Systematics
Amniotes (Amniota)
Synapsids (Synapsida)
Mammals (mammalia)
Theriiformes
Allotheria
Multituberculata
Scientific name
Multituberculata
Cope , 1884

The Multituberculata are a group of extinct mammals , which showed parallels to rodents in their dimensions, diversity and assumed way of life .

They appeared in the Middle Jurassic (around 165 million years ago) and had their heyday in the Cretaceous and Paleocene - so they survived the extinction of the dinosaurs and became extinct at the end of the Eocene (around 34 million years ago).

They are not closely related to any modern mammal group, but represent a specialized side branch.

anatomy

Multituberculata were all small animals. Most of them varied in size between a small mouse and a rat and even the largest representatives, the Taeniolabidae only reached the size of a marmot (up to 60 centimeters in length).

Head and teeth

The head was built broad, the muzzle short and blunt and the eyes were arranged sideways. The most striking feature were the teeth. In the lower jaw these animals had only one pair of incisors that were enlarged and protruding forward, in the upper jaw there were one to three incisors per half of the jaw. As with rodents, only the front of the incisors was partially covered with tooth enamel and the teeth were sharpened by mutual abrasion. The lower incisors were at best suited for a gnawing activity, although they were certainly not as effective as those of the rodents.

There is a gap ( diastema ) between the incisors and molars . The canines were mostly missing, only in the more primitive species an upper canine was still present. The lower premolars had jagged, sharp cusps that worked against the multi-cusped upper premolars. There were only two molars per half of the jaw , each of which had two (in some younger species, three) rows of up to eight cusps ( tubercles ) arranged one behind the other . The animals owe the name Multituberculata to these many humps. When chewing, the cusps and valleys of the opposing teeth fitted into one another, thus ensuring effective grinding.

The lower jaw was large and must have been moved by powerful muscles of mastication. A sideways movement of the lower jaw was not possible, instead the food was ground by a strong back and forth movement.

Remaining physique

As with many fossil mammals, only teeth or parts of the skull have survived, but some completely preserved skeletons have also been found. The narrow shoulder blade is characteristic in the construction of the shoulder , the raven bone is reduced as in the Theria , however, as in the monotremes, there is an interclavicula ("intermediate collarbone "). The pelvis has pouch bones , which is probably an original mammalian feature.

Multituberculata are among the few fossil mammals that have been shown to have hair. Remains of lambdopsalis were discovered in fossil coprolites , which clearly showed traces of a fur.

Investigations of the cranial cavity of various species showed that the brain was significantly smaller than that of today's mammals of comparable size. The olfactory bulb , however, was well developed.

Way of life

Much about the way of life of these extinct animals remains of course speculative. From the structure of the brain it can be concluded that the sense of smell was well developed, which could possibly speak for a nocturnal lifestyle.

The analogy to rodents mentioned at the beginning can also be seen in the fact that these animals colonized a large number of habitats and developed different modes of locomotion. In Ptilodus very flexible feet and presumably a prehensile tail can be seen, which indicates a tree-dwelling way of life. Bulganbaatar, on the other hand, had limbs arranged under the body and should have been a fast runner in a dry habitat. In the case of Nemegtbaatar, it can be assumed that the genus moved in a jumping manner - possibly similar to the jerboa . Lambdopsalis had a broad, flat skull and massive humerus bones, which could perhaps speak for a burrowing way of life similar to the moles . However, the majority of the genera is only known from skulls or teeth finds, so that the Multituberculata probably had an even wider range of modes of locomotion and habitats than previously known.

The diet of the Multituberculata has not been completely clarified. Some of them ate plant material such as seeds and tubers, but the extent to which they also ate small animals is a matter of dispute. Presumably some representatives were omnivores, which supplemented their diet with insects , worms and other invertebrates, while other species were probably pure herbivores.

An examination of the pelvis gave the speculative conclusion that the Multituberculata had given birth to live young. The narrowness of the birth canal (3.4 millimeters for Kryptobaatar ) was too small for eggs, so the newborns could have been comparable in size to newborn marsupials .

Tribal History and External Systematics

Tribal history

The oldest finds of the Multituberculata come from the Middle Jurassic and are around 165 million years old. The animals soon spread over Laurasia (today's Eurasia and North America ), but they never came to Gondwana . (Finds from South America are now viewed as a separate group, Gondwanatheria .) They continued to develop in the Cretaceous period . In terms of both the number of individuals and the number of species, they represent the most common mammal group of this epoch, up to 75% of all mammals found in the Upper Cretaceous are Multituberculata. Although some groups, such as the Djadochtatherioidea, probably died out at the end of the Cretaceous period , they still represent a considerable part of the mammalian fauna in the Paleocene .

The decline of this group in the Eocene and its extinction at the end of this epoch (around 34 million years ago) is likely to be related to the development and worldwide distribution of rodents that occupy similar ecological niches . The exact reasons for the extinction of the Multituberculata are unclear, however, possibly the rodents were superior to them in the construction of the locomotor and chewing apparatus.

Nevertheless, the Multituberculata existed for around 130 million years, making them one of the longest-lived groups of mammals.

External system

How the Multituberculata are related to other groups of mammals is still a matter of debate. One theory sees them as descendants of the Haramiyida , an early group of mammals known almost exclusively from their teeth. Although similarities in the structure of the teeth suggest this relationship - the common taxon is called Allotheria and possibly also includes the Gondwanatheria . In the structure of the jaw, however, the Multituberculata show similarities with other mammals, which speaks against this ancestry. Another theory sees the multituberculata close relatives of the monotons . This view is supported by similarities in the construction of the skull and the ear, but other features contradict this, so that this is only a minority opinion.

A third theory presents them as close relatives of the Trechnotheria , a taxon which, in addition to some extinct relatives, also includes today's Theria . Thus, the Multituberculata are more closely related to the sacs and higher mammals than they are to the monastery. A detailed cladistic analysis sees a little more support for this than for the Allotheria theory, but the difference is hardly meaningful. The question of the origin of the Multituberculata cannot be answered at the present time.

Internal system

The most comprehensive study on the internal systematics of the Multituberculata comes from Zofia Kielan-Jaworowska and Jørn H. Hurum in 2001. They distinguished two groups, the more primitive Plagiaulacida, which lived from the Middle Jurassic to the Middle Cretaceous, and the more developed Cimolodonta, the existed from the Lower Cretaceous to the end of the Eocene.

Plagiaulacida

The Plagiaulacida are the older and more primitive of the two subtaxas. Since the cimolodonta evolved from them, they are paraphyletic . The representatives of this group are not yet as differentiated in the structure of their teeth as the later species. They can be divided into three lines of development, the Allodontid line, the Paulchoffatiid line and the Plagiaulacid line, to which there are some genera that have not yet been discovered.

Plagiaulacida incertae sedis

These genera are incertae sedis , that is, their systematic classification is unclear.

  • Hahnotherium and Kermackodon are only known from molarsthat were foundin England in 2005. They come from the middle Jurassic and are the oldest known representatives of the Multituberculata.
  • Ameribaatar and Janumys were discovered in the Utah Central Cretaceous North America and are dated to the Middle Cretaceous. Their assignment is controversial; they may also belong to the Cimolodonta.

Allodontid line

The types of the allodontid line have an ancient structure of the teeth (five upper and four lower premolars, small third incisors) and are among the oldest, better-known multituberculata. So far teeth and individual jaw and skull bones have been found. All representatives come from the Upper Jurassic and were found in North America. They are divided into the family of the Allodontidae ( Ctenacodon , Morrisodon and Psalodon ) as well as into the isolated genera Glirodon and Zofiabataar .

Paulchoffatiid line

The species of the Paulchoffatiid line are also characterized by a primeval tooth structure. You still have one canine and five premolars in the upper jaw, and the enamel of the incisors is not prismatic. Apart from teeth and jaw parts, little is known about them. Representatives of this group were widespread from the Middle Jurassic to the Lower Cretaceous, finds are known from Western Europe and North Africa. Three families can be distinguished:

Plagiaulacid line

The representatives of the Plagiaulacid line were widespread from the Upper Jurassic to the Lower Cretaceous and lived in North America and Eurasia. At least the lower canine was lost and the number of premolars reduced. Presumably the later Multituberculata, the Cimolodonta, developed from this group. Four families can be distinguished:

  • The Plagiaulacidae are known from the Upper Jurassic North America and the Lower Cretaceous England and include the genera Bolodon , Parabolodon and Plagiaulax .
  • The Albionbaataridae (genera Albionbaatar and Proalbionbaatar ) are only known from individual teeth from the Upper Jurassic and the Lower Cretaceous from Western Europe and possibly also from East Asia.
  • The Eobataaridae (genera Eobaatar , Loxaulax , Monobaatar , Parendotherium and Sinobaatar ) lived in the Lower Cretaceous and are known from Western Europe and East Asia. From Sinobaatar also the body is known. It was an animal the size of a shrew with fifteen feet, which was not very specialized in comparison to later multituberculata.
  • Arginbaatar is placed in its own family, Arginbaataridae. The genus is only known through individual teeth, which show a transition stage between the Plagiaulacida and the Cimolodonta and make the systematic classification difficult. The genus lived in the Lower Cretaceous in Mongolia.

Cimolodonta

The more developed Multituberculata are summarized as Cimolodonta . They are believed to be a monophyletic group that evolved from an ancestor in the Plagiaulacid line. They appear in the Lower Cretaceous, had their heyday in the Upper Cretaceous and the Paleocene, and are probably extinct at the end of the Eocene. Cimolodonta are known from North America and Eurasia. They can be divided into a basal group, three superfamilies ( Ptilodontoidea , Djadochtatherioidea and Taeniolabioidea ) and several families of unclear affiliation.

Basal cimolodonta

The most primitive representatives of the Cimolodonta are grouped together in the so-called Paracimexomys group. It is not a natural group as several lines are believed to have evolved from them. They were mouse-sized animals whose weight is estimated at 20 to 100 grams. Finds of the genus Cimexomys were made in dinosaur nests (from Maiasaura ) - whether this allows conclusions about their diet is disputed. These animals are documented from the Lower Cretaceous to the Paleocene and mostly come from North America. To Paracimexomys group the genera are Bryceomys , Cedaromys , Cimexomys , Dakotamys and Paracimexomys . The systematic position of the genus Uzbekbaatar (Upper Cretaceous Central Asia) and Viridomys (Upper Cretaceous North America) is still unclear.

Cimolodonta incertae sedis

Several families of the Cimolodonta are listed as incertae sedis , which means that their systematic affiliation is disputed.

  • The Cimolomyidae (genera Buginbaatar , Cimolomys , Essonodon , Meniscoessus ) are known from the Upper Cretaceous North America and Asia. They were relatively large, outwardly probably rat-like animals that could reach a weight of 0.3 to 3 kilograms and were therefore among the largest mammals of the Cretaceous period.
  • The Boffiidae consist of only one genus, Boffius , which is known from Belgium from the lower Paleocene and which was also relatively large. Perhaps it was related to the Cimolomyidae.
  • The Kogaionidae (genera Barbatodon , Hainina and Kogaionon ) are known only from a few finds from Europe. They lived from the Upper Cretaceous to the Paleocene and were very small animals that were characterized by an elongated snout.
  • The Eucosmodontidae (genera Clemensodon , Eucosmodon , Stygimys ) lived mainly in North America from the Upper Cretaceous to the Paleocene. They are known only from relatively few jaw and tooth fossils and isolated skull bones. Possibly they were related to the Djadochtatherioidea.
  • The Microcosmodontidae (genera Acheronodon , Microcosmodon and Pentacosmodon ) were similar to the Eucosmodontidae, but were significantly smaller. Finds of this group are known from the Upper Cretaceous and the Paleocene of North America; there are also uncertain finds from Europe.

Ptilodontoidea

The Ptilodontoidea were a group of the Multituberculata that had their heyday in the Upper Cretaceous and the Paleocene and is known almost exclusively from North America. The eponymous genus Ptilodus had a prehensile tail and probably lived on trees, the extent to which this also applies to the other representatives is not known. The Ptilodontoidea can be divided into an isolated genus and three families:

  • Neoliotomus was relatively large with an estimated 2 kilograms, the genus lived in the Palaeocene and Eocene in North America.
  • The Neoplagiaulacidae are a group passed down through relatively sparse finds (mostly jaws and teeth). They were characterized by the narrow, forward-protruding lower incisor. The group originated in the Upper Cretaceous and lasted until the end of the Eocene (perhaps even until the early Oligocene), making it one of the youngest families of the Multituberculata. This family includes the genera Cernaysia , Ectypodus , Fractinus , Krauseia , Mesodma , Mesodmops , Mimetodon , Neoplagiaulax , Parectypodus , Xanclomys and Xironomys .
  • The Ptilodontidae are a group limited to North America that appeared in the Upper Cretaceous, had their heyday in the Paleocene and died out in the Lower Eocene. The most famous representative is Ptilodus , of whom the physique is also known. It was 30 to 50 centimeters long, the limbs were very flexible and reminiscent of those of the tree squirrel and the tail was designed as a prehensile tail. All of this speaks for a tree-dwelling way of life. Other, less fully preserved genera of this group are Baiotomeus , Kimbetohia and Prochetodon .
  • The Cimolodontidae (genera Anconodon , Cimolodon and Liotomus ) are primarily known for their teeth that were similar to those of the Ptilodontidae. Representatives of this group are known from the Upper Cretaceous and the Paleocene from North America and Europe.

Djadochtatherioidea

The Djadochtatherioidea are only known from the Upper Cretaceous Asia (mainly from Mongolia). Some of the best-preserved fossils of Multituberculata come from this group, which, unlike the tree-dwelling Ptilodontoidea, lived a terrestrial (ground-dwelling) way of life. This group is divided into three isolated genera and two families:

  • Bulganbaatar is completely preserved. Research on the skeleton suggests that the legs were placed under the body and the animal was presumably adapted to run fast on the ground.
  • Nemegtbaatar is also almost completely known and was relatively large. Its physique shows signs that the genus has moved in a jumping manner - possibly similar to the jerboa .
  • Chulsanbaatar is also preserved through complete skeletons. This genus was remarkably small compared to other Djadochtatherioidea.
  • The Sloanbaataridae (genera Kamptobaatar , Nessovbaatar and Sloanbaatar ) were relatively small representatives of the Djadochtatherioidea. They are named after the paleontologist Robert Evan Sloan.
  • The Djadochtatheriidae were also rather small animals that were widespread in the Upper Cretaceous Period. For Kryptobaatar , one of the best-studied multituberculata, a length of 13.5 centimeters and an estimate of 40 to 80 grams are given. Other genera of this family were Catopsbaatar , Djadochtatherium and Tombaatar .

Taeniolabioidea

The Taeniolabioidea comprise only one family, the Taeniolabidae. They were common in North America and Asia from the Upper Cretaceous to the end of the Paleocene. These animals are characterized by a blunt snout and a square skull. This group includes the largest Multituberculata, they reached the size of a beaver (head body length around 60 centimeters, estimated weight 25 to 30 kilograms). Genera of this group are Catopsalis , Kimbetopsalis , Lambdopsalis , Prionessus , Sphenopsalis , Taeniolabis and Valenopsalis . The genus Lambdopsalis is interesting for two reasons: on the one hand, traces of fur were found on its fossil, which is unusual for mammals of this age. On the other hand, the broad, stocky humerus may indicate a burrowing way of life similar to that of moles .

Note on naming

Many common names end in - baatar . This is the Mongolian word for "hero" and can also be found in the name of the city of Ulan Bator (Mongol. Ulaanbaatar). This name is originally derived from the fact that many complete skeletons were found in Mongolia ; In the meantime, however, this fashion is also applied to finds from other continents (such as Ameribaatar from America or Albionbaatar from Great Britain).

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literature

Individual evidence

  1. ^ Zofia Kielan-Jaworowska: Pelvic structure and nature of reproduction in Multituberculata . In: Nature 277, pp. 402-403 (1979).
  2. ↑ Kemp (2005), p. 155.
  3. ^ Zofia Kielan-Jaworowska, Richard L. Cifelli and Zhe-Xi Luo: Mammals from the Age of Dinosaurs: origins, evolution, and structure. Columbia University Press (2004); quoted from Kemp (2005), pp. 180-181
  4. ↑ Petr P. Gambaryan and Zofia Kielan-Jaworowska: Sprawling versus parasagittal stance in multituberculate mammals. In: Acta Palaeontologica Polonica, 41 (1997), pp. 13-44.
  5. ^ A b Thomas E. Williamson, Stephen L. Brusatte, Ross Secord, and Sarah Shelley: A new taeniolabidoid multituberculate (Mammalia) from the middle Puercan of the Nacimiento Formation, New Mexico, and a revision of taeniolabidoid systematics and phylogeny. Zoological Journal of the Linnean Society 2015 doi : 10.1111 / zoj.12336

Web links

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