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

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

extinct order of

eutherian Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...

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

Euarchontoglires Euarchontoglires (synonymous with Supraprimates) is a clade and a superorder of mammals, the living members of which belong to one of the five following groups: rodents, lagomorphs, treeshrews, colugos, and primates. Evolutionary affinities wi ...

(

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

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...

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 clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews (also k ...

. 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 distinguishe ...

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 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

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

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. Radiations may affect one clade or many, and be rapid ...

, originally bunched together in the order

Insectivora The 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 Eulipotyphla, wi ...

. The leptictids became extinct during the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

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

postcrania Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...

l anatomy has been studied from the well-preserved middle

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

'' Leptictidium'' 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 (from ar, جربوع ') are hopping desert rodents found throughout North Africa and Asia, and are members of the family Dipodidae. They tend to live in hot deserts. When chased, jerboas can run at up to . Some species are preyed on b ...

s, suggesting a jumping locomotion, the structure of the tarsal bones 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 monotypic 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 Le ...

***Genus ''

Gypsonictops ''Gypsonictops'' is an extinct genus of leptictidan mammals of the monotypic 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 Leptic ...

'' **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 ''Leptictis'' is an extinct genus of leptictid non-placental eutherian mammal known from the Late Eocene to Early Oligocene of North America. The type species, ''L. haydeni'', was named in 1868 by Joseph Leidy in honour of Ferdinand Vandeveer Hay ...

'' ****Genus '' Myrmecoboides'' ****Genus '' Ongghonia'' ****Genus '' Prodiacodon'' ****Genus '' Protictops'' **Family Pseudorhyncocyonidae ***Genus '' Diaphyodectes'' ***Genus '' Leptictidium'' ***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