Leptictida (''leptos iktis'' "small/slender weasel") is a possibly

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

extinct order of

eutherian Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distingu ...

mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to

Euarchontoglires Euarchontoglires (from: '' Euarchonta'' ("true rulers") + '' Glires'' ("dormice")), synonymous with Supraprimates, is a clade and a superorder of placental mammals, the living members of which belong to one of the five following groups: rodents ...

(

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s and their relatives), although they are more recently regarded as the first branch to split from basal eutherians. One recent large-scale cladistic analysis of eutherian mammals favored lepictidans as close to the placental crown-clade; and several other recent analyses that included data from Cretaceous non-eutherian mammals found ''Leptictis'' to belong to the superorder

Afrotheria Afrotheria ( from Latin ''Afro-'' "of Africa" + ''theria'' "wild beast") is a superorder of placental mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephan ...

. The most recent phylogenetic studies recover it as actually a

assemblage leading to

Placentalia Placental mammals ( infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distingui ...

Description

The leptictids are a characteristic example of the non-specialized placental mammals that took part in the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. A significantly large and diverse radiation within ...

, originally bunched together in the order

Insectivora The Order (biology), order Insectivora (from Latin ''insectum'' "insect" and ''vorare'' "to eat") is a now-abandoned biological grouping within the class of mammals. Some species have now been moved out, leaving the remaining ones in the order ...

. The leptictids became extinct during the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

. Their archaic cranium and dentition make it difficult to determine their relationship to other groups. Leptictid

postcrania The postcranium ("behind the cranium"; plural: postcrania) or postcranial skeleton in zoology and vertebrate paleontology is the skeleton apart from the skull. The postcranium encompasses the axial skeleton, which includes the entirety of the verte ...

l anatomy has been studied from the well-preserved middle

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

Leptictidium ''Leptictidium'' is an extinct genus of small mammals that were likely bipedal. Comprising eight species, they resembled today's bilbies, bandicoots, and elephant shrews, and occupied a similar niche. They are especially interesting for their c ...

'' specimens found at

Messel Messel is a municipality in the district of Darmstadt-Dieburg in Hesse near Frankfurt am Main in Germany. The village is first mentioned, as ''Masilla'', in the Lorsch codex. Messel was the property of the lords of Groschlag from ca. 1400 to 1799 ...

, Germany.Augustí and Antón, 2002, p. 5 Judging from these specimens, lepticids were small placentals with a body length ranging from . The head had a long and slender snout, probably featuring a short trunk, which may have been used for scratching the undergrowth in search of insects and worms. The mouth's archaic dentition included two or three incisors, a canine, and V-shaped cheek-teeth - four premolars and three molars. Their forelegs were shortened, but their hind legs were elongated. While this anatomy is reminiscent of small kangaroos and

jerboa Jerboas () are the members of the family Dipodidae. They are hopping desert rodents found throughout North Africa and Asia. They tend to live in hot deserts. When chased, jerboas can run at up to . Some species are preyed on by little owls (''A ...

s, suggesting a jumping locomotion, the structure of the

tarsal bones In the human body, the tarsus (: tarsi) is a cluster of seven articulating bones in each foot situated between the lower end of the tibia and the fibula of the lower leg and the metatarsus. It is made up of the midfoot (cuboid, medial, intermedi ...

hints at a specialization for terrestrial running. Perhaps these animals were capable of both modes of locomotion; running slowly in search for food, and jumping quickly to avoid threats. Additionally, the Messel specimens feature a surprisingly long tail, unique among modern placental mammals, formed by 40 vertebrae and probably used for balance.

Classification

*Order Leptictida **Family

Gypsonictopidae ''Gypsonictops'' is an extinct genus of leptictidan mammals of the family Gypsonictopidae, which was described in 1927 by George Gaylord Simpson. Species in this genus were small mammals and the first representatives of the order Leptictida, tha ...

***Genus ''

Gypsonictops ''Gypsonictops'' is an extinct genus of leptictidan mammals of the family Gypsonictopidae, which was described in 1927 by George Gaylord Simpson. Species in this genus were small mammals and the first representatives of the order Leptictida, tha ...

'' ***Genus ''

Sikuomys ''Sikuomys'' is a genus of early eutherian mammals from the Late Cretaceous of Alaska. It is known from a few teeth and part of a jawbone in deposits of Campanian age and, , is the only known Mesozoic The Mesozoic Era is the Era (geology), er ...

'' **Family Leptictidae ***Genus '' Amphigyion'' ***Genus '' Gallolestes'' ***Genus '' Labes'' ***Genus '' Lainodon'' ***Genus '' Leptonysson'' ***Genus '' Palaeictops'' ***Genus '' Praolestes'' ***Genus ''Wania'' ***Subfamily Leptictinae ****Genus '' Blacktops'' ****Genus '' Ictopidium'' ****Genus '' Leptictis'' ****Genus '' Myrmecoboides'' ****Genus '' Ongghonia'' ****Genus '' Prodiacodon'' ****Genus '' Protictops'' **Family Pseudorhyncocyonidae ***Genus '' Diaphyodectes'' ***Genus ''

'' ***Genus '' Phakodon'' ***Genus '' Pseudorhyncocyon''

Notes

References

External links

Insectivore-like mammals: Tiny teeth and their enigmatic owners
Prehistoric eutherians * Paleocene mammals Eocene mammals Late Cretaceous first appearances Oligocene extinctions {{paleo-mammal-stub

Description

Classification

Notes

References

Further reading

External links