Leptictida
Encyclopedia
Leptictida is an extinct order of placental mammals
. According to cladistic studies, they may be (distantly) related to Euarchontoglires
(rodent
s and primate
s and their relatives), although they are more often regarded as the first branch to split from basal eutherians.
-Paleocene
evolutionary radiation
, originally bunched together in the order Insectivora
. The leptictids went extinct during the Oligocene
, and their archaic cranium and dentition makes it difficult to determine their relationship to other groups. What is known of leptictid postcrania
l anatomy and lifestyle has been inferred from preserved middle Eocene
Leptictidium
specimens found at Messel
, Germany.
Judging from these specimens, lepticids were small placentals with a body length ranging between 60-90 cm. The head had a long and slender snout, probably featuring a short trunk which was probably used for scratching the undergrowth in search of insects and worms. The mouth's archaic dentition included two to three incisors, a canine, and V-shaped cheek-teeth - four premolars and three molars.
Their forelegs were shortened but their hind legs elongated. While this anatomy is reminiscent of small kangaroos and jerboa
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 forty vertebrae and probably used for balance.
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
. According to cladistic studies, they may be (distantly) related to Euarchontoglires
Euarchontoglires
Euarchontoglires is a clade of mammals, the living members of which are rodents, lagomorphs, treeshrews, colugos and primates .-Evolutionary relationships:...
(rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s and primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s and their relatives), although they are more often regarded as the first branch to split from basal eutherians.
Description
The leptictids are a characteristic example of the non-specialized placental mammals that took part in the late CretaceousCretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
-Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
evolutionary radiation
Evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...
, originally bunched together in the order Insectivora
Insectivora
The order Insectivora is a now-abandoned biological grouping within the class of mammals...
. The leptictids went extinct during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, and their archaic cranium and dentition makes it difficult to determine their relationship to other groups. What is known of leptictid postcrania
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
l anatomy and lifestyle has been inferred from preserved middle Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
Leptictidium
Leptictidium
Leptictidium is an extinct genus of small mammals; together with macropods and humans, they are the only known completely bipedal mammals. Comprising five species, they resembled today's elephant shrews...
specimens found at Messel
Messel pit
The Messel Pit is a disused quarry near the village of Messel, about southeast of Frankfurt am Main, Germany. Bituminous shale was mined there. Because of its abundance of fossils, it has significant geological and scientific importance...
, Germany.
Judging from these specimens, lepticids were small placentals with a body length ranging between 60-90 cm. The head had a long and slender snout, probably featuring a short trunk which was probably used for scratching the undergrowth in search of insects and worms. The mouth's archaic dentition included two to three incisors, a canine, and V-shaped cheek-teeth - four premolars and three molars.
Their forelegs were shortened but their hind legs elongated. While this anatomy is reminiscent of small kangaroos and jerboa
Jerboa
The jerboa form the bulk of the membership of the family Dipodidae. Jerboas are hopping desert rodents found throughout Asia and Northern Africa. They tend to be found in hot deserts....
s, suggesting a jumping locomotion, the structure of the tarsal bones
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
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 forty vertebrae and probably used for balance.
Classification
- Order Leptictida
- Family Didymoconidae
- Family Gypsonictopidae
- Family Kulbeckiidae
- Family Leptictidae
- Genus LeptictisLeptictisLeptictis is an extinct genus of mammal. It was related to the better-known Leptictidium.-References:*McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8...
- Genus Leptictis
- Family Pseudorhyncocyonidae
- Genus LeptictidiumLeptictidiumLeptictidium is an extinct genus of small mammals; together with macropods and humans, they are the only known completely bipedal mammals. Comprising five species, they resembled today's elephant shrews...
- Genus Leptictidium