Leptictidium
Skeleton of Leptictidium
Leptictidium is an extinct genus of mammals from the fossil order of Leptictida. The representatives of the genus lived in the Eocene, 55-35 million years ago in Europe. Fossils have been found, among other things, in the Messel near Darmstadt and in the south of France. The medium sized animals had long and slender rear and very short front legs and a characteristic long tail. There were, according to reconstructions past fast hunters who went in the dense undergrowth of the former subtropical forests in search of food. The food consisted mainly of insects, lizards and small mammals, which could be determined on the basis of gastric residues. Here, Leptictidium individuals moving with their muscular hind legs, whose feet were also significantly extended, by jumping, due to which they considered to be highly specialized hunters. Tribal History is a suspected closer affinity to the modern insectivores.
Description
Members of the genus Leptictidium were relatively large representative earlier, insectivore -like mammals that have been proven over many fossil remains. They came to a head -body length from 21.5 to 37.5 cm, and had an estimated body weight of 0.5 to 1 kg. The strikingly long tail could reach around 60 % of the total length, and measured 37.5 to 50 cm. Other distinguishing features were found in the clear front short and very long hind limbs. In addition, the ridge path had a strong upward curvature. Thus, the center of gravity was located approximately at the level of the hind limbs.
The skull measured between 6.7 and 10.1 cm at smaller for larger forms. A striking feature of the presented long to constitute forward significantly tapered rostrum, which reached up to 58 % of the total skull length. Thus, the brain skull was relatively short, which is generally regarded as primordial. The orbit was above the third molar, and therefore was a bit further back than in North American Leptictida representatives. The skullcap was in contrast to these clearly rounded and did not have a head crest. The lower jaw had a long and slender figure and reached the jawbone maximum height of 2.9 cm, which was only about 1 cm below the second molar.
The teeth included the full number of teeth of the early higher mammals, and thus had the following dental formula:. The teeth in total were rather small compared to the size of the animals. The incisors had a blade shape and were in the upper jaw is not in a closed series. After each one longer diastema the incisors followed the canine, the maxillary conical- pointed ( caniniform ) was in the lower jaw, however, possible. Also a large tooth gap separated the respective first premolars of the canines, which was formed in the lower dentition caniniform. In contrast, the upper wore a pointed tooth enamel cusps. The remaining premolars, which were at a small distance from each other, each had two or more pointed cusps, but the last premolar of the shape of the posterior molars approached. Only the molars formed an unbroken row of teeth in the posterior dentition. The Kauoberfläche was characterized by five pointed cusps. Typically formed three humps a closed triangular unit ( trine ) and were separated by a deep furrow ( Talon ) from the remaining two. This, tribosphenisch mentioned structure of the molars is to be regarded as a very earthy and shows the origin of Mesozoic Leptictidiums early Eutheria on. Remarkably, the cusps of the mandibular molars were significantly higher than those of the molars of the upper jaw. The size of the molars varied from 3.1 to 4.9 mm.
The postcranial skeleton is known by several skeletal remains. The back was significantly bulged, the rear portion of the fuselage spine comprised 6-7 lumbar and 1st sacral vertebrae; the latter is unusual for mammals. The lumbar vertebrae were characterized by quite a long spinous processes from a strong back muscles. Noteworthy is the tail spine, which was partly more than twice as long as the rest of the spine, and consisted of 43-44 individual vertebrae. This is not typical of all extant mammals, the number of which exceeds in caudal vertebrae rarely 30. However, the most striking features occurred on the limbs. Thus, the front legs, and had been shown to be extremely short, one of up to 4.6 cm long humerus, the ulna during reached a length of 5.1 cm. Striking longer, however, the hind legs were formed, the maximum femur 8.6, tibia measured up to 9.2 cm. Thus, the length of the front legs was only slightly more than half of the hind legs, which is more pronounced than in the recent elephant shrew, similar to the Leptictidium representative morphologically, but are not closely related to him. Lower values only reach today's kangaroos. Wherein the front legs showed about 16 % of the length of the hull spine, on the other hand, the rear legs 47 to 52 %. On the hind legs with a 10 cm very long and slender foot was formed, which had five rays, of which the middle three ( II-IV ) significantly prolonged bone revealed. A similar structure also had the hand, which was significantly shorter. Both the hand and the foot each had long and pointed ending terminal phalanges.
Fossil finds
Finds from the genus Leptictidium limited to the Europe of today and dated to the Eocene, 55-35 million years ago. Significant fossil remains are from the Messel Pit near Darmstadt in Hesse, where several complete skeletons occur, all of which are fossilized in the lateral position. However, one also partial skeletons additional individual bone fragments and teeth are known. Overall, three types can be distinguished, all of whom lived at the beginning of the Middle Eocene, around 47 million years. Around the same age are the findings of a partial skeleton and a lower jaw from the lower middle of the coal Geiseltal at Halle in Saxony -Anhalt. Among the most recent discoveries include dental remains from baby in the Dordogne and the Phosphoritbänken of Quercy, both from France, which are around 35 million years old. Significantly older with almost 55 million years ago are also isolated teeth from the Blackheath Formation in the eastern city of London.
Paleobiology
The genus Leptictidium is characterized by a slender lower jaw, the teeth are compared to the overall size of the animals extremely small. Striking also appear the Kauoberflächen the molars with sharp distinct tooth enamel cusps, indicating a specialization in animal food, which was more crushed than chewed. The location of the caniniformen first lower premolar behind the upper canine (with closed teeth ) indicates further that at Leptictidium species no real predator's teeth had been trained ( in these is the lower canine tooth before the top ). Since the facial skeleton shows little significant muscle attachment points, the chewing muscles may have been developed only small, which limited the size of the prey. Overall, this gives the impression of a dedicated animal prey organism that is similar to the basic features of today's insectivores. In the Messel food residues were found in the gastrointestinal area in some individuals. These include many splintered bones and vertebrae, which indicate small reptiles such as lizards, but also mice and insectivores. Furthermore, Chitinreste are detected as remnants of insects. It is assumed that the size of the prey did not exceed 10 to 15 cm. As the determined prey nimble animals were usually can take a quick sprint hunting. Due to the structure of the small forelimbs a digging out the spoils of their caves must be regarded as unlikely. Whether Leptictidium individuals hunted day or night, is unknown, but the sense of sight played most likely due to the size of the orbit a significant role. The trunk-like nose was used here probably as a tactile organ. In addition to animal remains also vegetable matter still came in the stomach contents to the fore, as well as sand, which was probably swallowed active or passive in receiving the food from the ground with.
The striking physique with the very short front and long hind limbs was thinking early about the locomotion of Leptictidium. Especially the over the top much longer lower portions of the legs, particularly clearly in the rear limbs, indicate a descent from schnellläufigen ( cursorialen ) animals. Initially this a fast, two-legged ( bipedal ) and ongoing locomotion was adopted. However, recent studies revealed a different picture. This shows especially the slim design of the foot with the three highly elongated middle toes, which were not spreadable, similarities to that of today's kangaroos. The high mobility of the lumbar spine, the sacrum and the short rod-like shaped basins refer to a, the corresponding kangaroos, hopping locomotion, the low position of the joint approaches to the cervical spine at the posterior cranial advocates a rather half- upright posture. In conjunction with the powerful thigh bone can be closed on a strong leg muscles. Thus, the representatives of Lepticidium appear as fast and manoeuvrable, but not very persistent hop. The long tail, which was very narrow towards the end and was therefore not designed as a prehensile organ, caused on the one hand for balance, on the other hand he could by individual movements to control the running direction. However, since the suspension of the basin at only one vortex and the non-fixed overgrown lower leg bones, but they were closely connected by ligaments, are not typical of saltatory mammals, also an easy -going locomotion can not be excluded. Suppose therefore that Leptictidium individuals were run at lower speeds on all fours. Your predominant habitat was the bottom of that tropical to subtropical forests.
System
Phakodon
Fordonia
Pseudorhyncocyon
Diaphyodectes
Leptictidium
Leptictidae
Pantolestida
Palaeanodontida
Leptictidium is a now extinct genus of the extinct family of Pseudorhyncocyonidae also which belongs to the order Leptictida. These are characterized by relatively primitive features and are in a closer relationship with today insectivores ( Eulipotyphla ). The closest relatives of Pseudorhyncocyonidae represent the Leptictidae which are detected eg from North America and represented there by genres such as Leptictis and Megaleptictis. The Leptictidae differ from the Pseudorhyncocyonidae by relatively slightly longer front legs and deformed bones of the leg; Moreover, they are consistently smaller than the European representatives. The Pseudorhyncocyonidae family is divided into two clades due zahnmorphologischer details of the posterior molars. This Leptictidium is more closely related Diaphyodectes. This represents the phylogenetic ancestors of the genus Leptictidium and has already been demonstrated from the Middle Paleocene to around 60 million years ago.
Have been described in the genus valid Leptictidium eight types:
- L. audriense Tobien, 1962
- Ginsburgi L. Mathis, 1989
- L. Lister Hooker, 2013
- Nasutum L. Storch & Lister, 1985
- Prouti L. Hooker, 2013
- Sigei L. Mathis, 1989
- L. Storchi Hooker, 2013
It turns L. prouti the oldest type from the Lower Eocene, L. Storchi, L. and L. Sigei ginsburgi the latest from the early Upper Eocene represents the other species are widely distributed in the Middle Eocene.
The first description of Leptictidium occurred in 1962 by Heinz Tobien based on findings from the Messel Pit. The basis for this were some older mandibular remains and a poorly preserved skeleton from the year 1961. The holotype ( specimen number HLMD Me 4420 ) includes a skull with the two remaining mandibular branches and largely complete dentition. The finds are now in the Hessian State Museum in Darmstadt. The genus name refers to the Leptictidium similar tooth morphology to the North American Leptictiden as the closest related group.