Leptictidium

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Leptictidium
Skeleton of Leptictidium

Skeleton of Leptictidium

Temporal occurrence
Eocene
56 to 33.9 million years
Locations
Systematics
Synapsids (Synapsida)
Mammals (mammalia)
Higher mammals (Eutheria)
Leptictida
Pseudorhyncocyonidae
Leptictidium
Scientific name
Leptictidium
Tobien , 1962

Leptictidium is an extinct species of mammals from the fossil order of leptictida . The representatives of the genus livedin Europe in the Eocene 55 to 35 million years ago. Fossils were found in the Messel pit near Darmstadt and in the south of France , among other places. The medium-sized animals had long and slender hind legs and very short front legs and a characteristically long tail. According to reconstructions, they were hunters with great speed whowent looking for foodin the dense undergrowth of the then subtropical forests. The food consisted mainly of insects , lizards and small mammals, which could be determined from stomachremains. Here, moving Leptictidium -individuals with their muscular hind legs, their feet were also significantly extended, jumping on, due to which they are considered to be highly specialized hunters. In terms of tribal history, there is a presumed closer relationship to today's insectivores .

description

Skeleton of Leptictidium from the Geiseltal

Members of the genus Leptictidium were relatively large representatives of early, insectivore-like mammals, which have been proven through numerous fossil remains. On the basis of complete skeletal remains, a head-trunk length of 21.5 to 37.5 cm could be determined, the estimated body weight is 466 and 627 g. The strikingly long tail could reach around 60% of the total length and measured between 37.5 and 50 cm. Further distinctive features were found in the clearly short front and very long rear limbs. In addition, the course of the back showed a strong upward curvature. As a result, the body's center of gravity was roughly level with the rear extremities. The skull measured between 6.7 in smaller and 10.1 cm in larger forms. A noticeable feature was the long, clearly tapering rostrum , which reached up to 58% of the total length of the skull. As a result, the skull was relatively short, which is generally considered to be primeval. The orbit was above the third molar and was therefore a little further back than in North American Leptictida representatives. In contrast to this, the skull roof was clearly rounded and did not have a crest . The lower jaw was long and slender and reached a maximum height of 2.9 cm at the jawbone, although this was just under 1 cm below the second molar.

The bit was the complete number of teeth of the early higher mammals , and thus had the following dental formula of: . The teeth as a whole were rather small compared to the size of the animals. The incisors had a spatula shape and were not in a closed row in the upper jaw. After each one longer diastema followed canine , the maxillary conical -spitz ( caniniform ) was in the lower jaw, however the incisors possible. A large gap between the teeth also separated the first premolars from the canines, which were canine-shaped in the lower dentition . The upper one, on the other hand, had a pointed enamel cusp . The remaining premolars, which were a short distance from one another, each had two or more pointed cusps, but the last premolar approximated the shape of the posterior molars. Only the molars formed a gapless row of teeth in the rear dentition. The chewing surface was characterized by five pointed cusps. Typically, three humps formed a closed, triangular unit ( trigon ) and were separated from the remaining two by a deep groove ( talon ). This structure of the posterior molars, called tribosphenic , is to be regarded as very primitive and shows the descent Leptictidium s from Mesozoic early Eutheria . It is noteworthy that the cusps of the lower molars were significantly higher than those of the upper molars. The size of the molars varied from 3.1 to 4.9 mm.

The postcranial skeleton is known from several skeletal finds. The back was clearly arched, the rear section of the trunk spine comprised 6 to 7 lumbar and 1 sacral vertebrae; the latter is unusual for mammals. The lumbar vertebrae were characterized by their long spinous processes for strong back muscles. The caudal spine is remarkable, sometimes more than twice as long as the rest of the spine and consisting of 43 to 44 individual vertebrae. This is atypical for a large part of the mammals living today, whose number of tail vertebrae rarely exceeds 30 (exceptions are the long-tailed pangolin and the small long-tailed small tenrek ). However, the most noticeable features appeared on the limbs. The front legs were found to be extremely short and had a humerus up to 4.6 cm long , while the ulna reached a length of 5.1 cm. The hind legs, on the other hand, were markedly longer, their thigh bones measuring a maximum of 8.6 cm and the shin up to 9.2 cm. Thus, the length of the front legs was only a little more than half the length of the hind legs, which is much more pronounced than in the recent proboscis dog , which is morphologically similar to the Leptictidium representative without being closely related to it. Only today's kangaroos achieve lower values . As a result, the individual sections of the front legs (upper arm, forearm, hand) were between 13 and 21% of the length of the trunk spine, while those of the rear legs (thigh, lower leg, foot) were 34 to 52%. On the hind legs there was a very long and slender foot with a length of 10 cm, which had five rays, of which the middle three (II to IV) showed clearly elongated bones. The hand also had an analog structure, although it was significantly shorter. Both the hand and the foot each had long and pointed end phalanges.

Fossil finds

Skeleton of Leptictidium from the Messel Pit

Finds of the genus Leptictidium are restricted to today's Europe and date to the Eocene 55 to 35 million years ago. Significant fossil remains come from the Messel pit near Darmstadt in Hesse , where there are almost 20 complete skeletons, all of which are fossilized in a lateral position. In addition, partial skeletons and individual bone fragments and teeth are also known. A total of three species can be distinguished here, all of which lived at the beginning of the Middle Eocene around 47 million years ago. The finds of a partial skeleton and a lower jaw from the lower middle coal of the Geiseltal near Halle in Saxony-Anhalt are about the same age . Recent finds include tooth remains from Baby in the Dordogne and the phosphorite banks of Quercy , both France , which are around 35 million years old. Isolated teeth from the Blackheath Formation in the eastern part of London are also significantly older, at almost 55 million years .

Paleobiology

Live reconstruction of Leptictidium

The genus Leptictidium is characterized by a slender lower jaw, the teeth are extremely small compared to the overall size of the animals. The chewing surfaces of the molars with the pointed enamel cusps , which indicate a specialization in animal food that was rather crushed than chewed, also appear striking . The position of the caniniform first lower premolar behind the upper canine (when the dentition is closed) also indicates that the Leptictidium species did not have a real predatory dentition (in these, the lower canine is in front of the upper). Since the facial skull shows only a few distinct muscle attachment points, the masticatory muscles are likely to have been only slightly developed, which limited the size of the prey. Overall, this gives the impression of a living being that specializes in animal prey and that is basically similar to today's insectivores . In the Messel Pit , food residues were found in the gastrointestinal region of some individuals. These include numerous splintered tubular bones and vertebrae, which indicate smaller reptiles such as lizards , but also mice or insectivores. Furthermore, chitin residues have also been proven to be leftovers from insect food. It is assumed that the size of the prey did not exceed 10 to 15 cm. As the prey animals identified were mostly nimble animals, a quick sprint hunt can be assumed. Due to the structure of the small forelegs, it is unlikely that the prey will be excavated from their burrows. Whether Leptictidium individuals hunted during the day or at night is unknown, but the sense of sight most likely played an important role due to the size of the orbit . The trunk-like nose probably served as a tactile organ. In addition to animal remains, plant material continued to appear in the stomach contents, as well as sand , which was probably actively or passively swallowed when the food was taken from the ground.

The distinctive physique with the very short front and long hind limbs made people think about the locomotion of Leptictidium early on . Above all, the lower sections of the legs, which are significantly longer than the upper ones, can be seen particularly clearly on the rear limbs, indicate an ancestry from fast-moving ( cursorial ) animals. Initially, a fast, two-legged ( bipede ) and continuous movement was assumed. However, recent studies have shown a different picture. Above all, the slender formation of the foot with the three strongly elongated middle toes that could not be splayed off shows similarities to today's kangaroos . The high mobility of the lumbar spine, the short sacrum and the rod-like shape of the pelvis also point to a hopping locomotion similar to that of a kangaroo, whereby the low position of the joints for the cervical spine on the back of the skull encourages a more semi-upright posture. In connection with the massive thigh bone, it can be concluded that there are strong leg muscles. As a result, the representatives of Lepticidium appear as fast and agile, but not very persistent hops. The long tail, which became very narrow towards the end and was therefore not designed as a grasping organ, ensured balance on the one hand, and on the other hand was able to control the direction of travel through individual movements. However, since the pelvis is suspended from just one vertebra and the lower leg bones, which are not firmly attached, but which were closely connected by ligaments, are untypical for saltatory mammals, simple running locomotion cannot be ruled out. It is therefore believed that Leptictidium individuals walked on all fours at slower speeds. In addition to the anatomy of the limbs, the agility of Leptictidium can also be inferred from the formation of the semicircular canals in the inner ear . Accordingly, the semicircular canals are designed very wide, which usually goes hand in hand with nimble locomotion, and reach dimensions comparable to those of the elephants and some representatives of the jerboa . Leptictidium can therefore be regarded as highly specialized in its locomotion. In comparison, some related forms from North America such as Leptictis or Palaeoictops had less expansive semicircular canals and were therefore possibly more movement generalists . The predominant habitat of Leptictidium was the soil of the tropical to subtropical forests of that time.

Systematics

Internal systematics of Leptictida according to Hooker 2013
  Leptictida  
  Pseudorhyncocyonidae  


 Phacodon


   

 Fordonia


   

 Pseudorhyncocyon




   

 Diaphyodectes


   

 Leptictidium




   

 Leptictidae


   

 Pantolesta


   

 Palaeanodonta





Template: Klade / Maintenance / Style

Leptictidium is a now extinct genus from the also extinct family of the Pseudorhyncocyonidae , which belongs to the order of the Leptictida . These are characterized by relatively primeval features and are closely related to today's insectivores (Eulipotyphla). The closest relatives of the Pseudorhyncocyonidae are the Leptictidae , which have been found in North America and are represented there by genera such as Leptictis and Megaleptictis . The Leptictidae differ from the Pseudorhyncocyonidae in that they are relatively longer forelegs and fused lower leg bones; in addition, they are consistently smaller than the European representatives. The family of the Pseudorhyncocyonidae is divided into two clades based on the morphological details of the posterior molars . It is Leptictidium closer with Diaphyodectes related. This represents the phylogenetic ancestor of the genus Leptictidium and has been proven from the Middle Paleocene around 60 million years ago, including more than a dozen remains of teeth from Walbeck in Saxony-Anhalt.

Eight species have been validly described within the genus Leptictidium :

It turns L. prouti the oldest type from the Lower Eocene, L. Storchi , L. sigei and L. ginsburgi is the latest starting from the Upper Eocene. The other types are widely spread in the Middle Eocene. The validity of the three species found in the Messel pit ( L. auderiense , L. nasutum and L. tobieni ) is partly questioned and viewed as a form ( L. auderiense ), but according to other researchers, they can be based on their dimensions and clearly separate the tooth structure from each other.

The first description of Leptictidium was made in 1962 by Heinz Tobien based on findings from the Messel Pit . The basis for this was formed by some older remains of the lower jaw and a poorly preserved skeleton from 1961. The holotype (copy number HLMD Me 4420) comprises a skull with the two preserved lower jaw branches and largely complete dentition. The finds are now in the Hessian State Museum in Darmstadt . The generic name Leptictidium refers to the similar tooth morphology to the North American Leptictid as the closest related group.

literature

  • Wighart von Koenigswald, Gregg F. Gunnell, Thomas Lehmann, Kenneth D. Rose and Irina Ruf: Four original, but highly specialized mammals. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messel - a fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 223-233
  • Wolfgang Maier, Gotthard Richter and Gerhard Storch: Leptictidium nasutum - an archaic mammal from Messel with extraordinary biological adaptations. Natur und Museum 116 (1), 1986, pp. 1-19
  • Heinz Tobien: Insectivores (Mammalia) from the Middle Eocene (Lutetium) from Messel near Darmstadt. Notes from the Hessian State Office for Soil Research 90, 1962, pp. 7–47

Individual evidence

  1. ↑ a b Irina Ruf, Virginie Volpato, Kenneth D. Rose, Guillaume Billet, Christian de Muizon and Thomas Lehmann: Digital reconstruction of the inner ear of Leptictidium auderiense (Leptictida, Mammalia) and North American leptictids reveals new insight into leptictidan locomotor agility. Paläontologische Zeitschrift 90 (1), 2016, pp. 153–171 doi: 10.1007 / s12542-015-0276-2
  2. ↑ a b c d e Gerhard Storch and Adrian M. Lister: Leptictidium nasutum n sp., A Pseudorhyncocyonide from the Eocene of the "Messel Pit" near Darmstadt (Mammalia, Proteutheria). Senckenbergiana Lethaea 66, 1985, pp. 1-37
  3. ↑ a b c d e Wighart von Koenigswald and Gerhard Storch: Leptictidium tobieni n sp., A third Pseudorhyncocyonide (Proteutheria, Mammalia) from the Eocene of Messel. Courier Forschungsinstitut Senckenberg 91, 1987, pp. 107-116
  4. ↑ a b c d Wolfgang Maier, Gotthard Richter and Gerhard Storch: Leptictidium nasutum - an archaic mammal from Messel with extraordinary biological adaptations. Natur und Museum 116 (1), 1986, pp. 1-19
  5. ↑ a b c Heinz Tobien: Insectivoren (Mammalia) from the Middle Eocene (Lutetium) from Messel near Darmstadt. Notes from the Hessian State Office for Soil Research 90, 1962, pp. 7–47
  6. ↑ a b c d e f g Jerry J. Hooker: Origin and evolution of the Pseudorhyncocyonidae, a European Paleogene famaly of insectivorous placental mammals. Palaeontology 56 (4), 2013, pp. 807-835
  7. ↑ a b c Wighart von Koenigswald, Gregg F. Gunnell, Thomas Lehmann, Kenneth D. Rose and Irina Ruf: Four original, but highly specialized mammals. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messel - a fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 223-233
  8. ↑ a b Wighart von Koenigswald and Michael Wuttke: On the taphonomy of an incomplete skeleton of Leptictidium nasutum from the oil shale of Messel. Geologisches Jahrbuch Hessen 115, 1987, pp. 65-79
  9. ↑ Gerhard Storch: Small mammals from the Geiseltal and Messel in the context of ancient tertiary fauna developments. Hallesches Jahrbuch für Geoswissenschaften B 17, 1995, pp. 59–64
  10. ^ A b Christian Mathis: Quelques insectivores primitifs nouveaux de l'Eocène supérieur du sud de la France. Bulletin du Muséum national d'histoire naturelle C 11, 1989, pp. 33-64
  11. ↑ Gotthard Richter: Studies on the nutrition of Eocene mammals from the Messel fossil site near Darmstadt. Courier Forschungsinstitut Senckenberg 91, 1987, pp. 1-33
  12. ^ Eberhard Frey, Bernd Herkner, Friedemann Schrenk and Christina Seiffert: Reconstruction organismic constructions and the problem of Leptictidium's locomotion. Kaupia 3, 1993, pp. 89-95
  13. ^ Andreas Christian: On the biomechanics of the locomotion of Leptictidium (Mammalia, Proteutheria). Courier Forschungsinstitut Senckenberg 216, 1999, pp. 1-18
  14. ^ Holger Preuschoft and Jens Lorenz Franzen: Locomotion and biomechanics in Eocene mammals from Messel. Palaeobiology and Palaeoenvironments 92, 2012, pp. 459-476
  15. ↑ Kenneth D. Rose: The postcranial skeleton of early Oligocene Leptictis (Mammalia, Leptictida) with a preliminary comparison to Leptictidium from the middle Eocene of Messel. Palaeontographica A 278, 2006, pp. 37-56
  16. ^ TJ Meehan and Larry D. Martin: New large leptictid insectivore from the Late Paleogene of South Dakota, USA. Acta Palaeontologica Polonica 57 (3), 2012, pp. 509-518
  17. ↑ Kenneth D. Rose, Gerhard Storch and Katrin Krohmann: Small-mammal postcrania from the middle Paleocene of Walbeck, Germany. Paläontologische Zeitschrift 89 (1), 2015, pp. 95–124

Web links

Commons : Leptictidium  - collection of images, videos and audio files