Juramaia
- Tiaojishan, Central Asia
Juramaia sinensis is an extinct species of mammals. It is the only known member of the genus Juramaia and lived around 160 million years ago in the early Jurassic of Central Asia. Juramaia sinensis shows the construction of the skeleton and teeth in common with modern placental animals, which is why it is the earliest representatives of this group. The structure of the forelegs indicates that approximately shrew large Juramaia sinensis was a tree dweller.
This serves as the holotype fossil of Juramaia sinensis comes from the Tiaojishan formation in the Chinese province of Liaoning and was first described by Zhe - Xi Luo, Chong- Xi Yuan, Qing -Jin Meng and Qiang Ji, 2011.
Features
Juramaia sinensis had an elongated, pointed head with a narrow jaw and was befellt. The skull measured about 22 mm in length and 10 mm in width, the jaw measured about 17 mm. The front feet were about 10 mm long. The weight of the animal was 13-15 g The dental formula is I 5 /4 - C 1/ 1 - P 5/5 - M 3 /3 System. This dental formula is that of the Cretaceous Eomaia scan soria - also an early placenta animal - identical. The five premolars and three molars are also typical of later Cretaceous placental mammals. The mandibular foramen is not at the level of the first molar as in marsupials, but as with most placental animals between the fourth and fifth premolar.
Among the toe bones of the front feet, the I and the II phalanx are relatively long. The third phalanx they are composed 1.21 times as long as the corresponding metacarpal bone, representing a Phalangenindex 121. The proximal Phalangenindex, so hundredfold ratio of I to II phalanx, is 65; the middle toe bones are therefore also relatively long.
Way of life
Because of its tooth structure Juramaia sinensis fed very likely by insects. The long toe bones suggest that Juramaia sinensis had the ability to climb trees. Almost all extant mammals, especially rodents with similar Phalangenindizes are tree dwellers. While most known mammals of the Jurassic were bottom dwellers, Juramaia sinensis occupied so obviously a new ecological niche.
Taxonomy and systematics
The first description of the species by Zhe - Xi Luo, Chong- Xi Yuan, Qing -Jin Meng and Qiang Ji was released in August 2011 in the journal Nature. The genus name Juramaia means " Jurassic Mother" ( with reference to the ancestors of the shank type ), the epithet sinensis " from China". The holotype ( BMNH PM1343 ) comes from the archaeological site of Daxigou Tiaojishan formation in the Chinese province of Liaoning. It consists of a partially preserved fossil, with parts of the skull and abdomen missing, the upper body and teeth but completely and traces of the Fells are partly preserved.
Juramaia sinensis is classified due to the unique tooth structure in the higher mammals and placental mammals ( Eutheria ) and provides the earliest known representatives Represents the earliest to the description of the type known placenta animal was about 125 million years old Eomaia scan soria from the Lower Cretaceous. The oldest members found the marsupials ( Metatheria ) Sinodelphys szalayi, has approximately the same age. The splitting of the Theria in placental and marsupial must be brought forward 35 million years due to the discovery of Juramaia sinensis. Thus models for DNA analysis of the two groups can be better calibrated. In addition, it can be concluded that, in the Middle Jurassic bag and mammals must have existed from the existence of a placental animal already in the Upper Jurassic. That possessed both the earliest representatives of the placental mammals and marsupials have the ability to climb, indicates a key role of this property in the removal of the two groups of the early mammals.
The position of Juramaia sinensis within the placental mammals is unclear. While there is a basal representative, the relationship to other basal placental animals is unknown.
Phylogenetic relationships of Juramaia sinensis by Luo et al. 2011 are presented in the following cladogram:
Sinodelphys szalayi
Cenozoic marsupial
Juramaia sinensis
Montanalestes keeblerorum
Murtoilestes Abramovi
Eomaia scan soria
Prokennalestes trofimovi
Cenozoic placental mammals