Kopidodon

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Kopidodon
Skeleton of Kopidodon

Skeleton of Kopidodon

Temporal occurrence
Middle Eocene ( Lutetium )
47.4 to 46.3 million years
Locations
Systematics
Synapsids (Synapsida)
Mammals (mammalia)
Higher mammals (Eutheria)
Pantolesta
Paroxyclaenidae
Kopidodon
Scientific name
Kopidodon
Weitzel , 1933

Kopidodon is a now extinct genus of the Paroxyclaenidae family, which belongs to the Pantolersta , a group of early, insectivore-like representatives of the higher mammals . It lived in the Middle Eocene around 47 million years ago and is so far only known from the Messel mine near Darmstadt . Several complete skeletons have survived from there, representing a medium-sized animal with a long tail. Due to the skeletal structure, a partially tree-climbing lifestyle can be inferred, the structure of the teeth and additionally found stomach remains speak for a plant-based diet. The first description of Kopidodon took place in 1933, the taxonomic position was discussed controversially for a long time.

description

Skull of Kopidodon

Kopidodon was a medium - sized insectivore - like animal with a head-to-trunk length of 55 to 60 cm. In addition, there was an extraordinarily long tail measuring 47 to 55 cm. The body weight is calculated to be about 3 to 6 kg, making the Kopidodon about the size of today's smaller badger . The skull measured 13.3 to 14 cm, the width of the protruding zygomatic arches was up to 7.7 cm. In the side view, the skull had a clearly rounded profile, which is also evident in the course of the frontal and nasal bones . The rostrum was not elongated, but rather short and narrow. The occiput pulled out clearly to the rear. At the contact surfaces of the parietal bones , an occasionally strong crest was formed. The eye window was above the first molar , the infraorbital foramen in front of it above the last premolar .

The lower jaw reached lengths of 10 to 11 cm. The two branches were not attached to the symphysis and were only connected by ligaments. Below the third premolar the bone body reached a height of 1.6 cm, and the underside of the branches was clearly curved downwards. The bit consisted of three incisors , one canine , four premolars and molars 3 per pine bough and was therefore against the early higher mammals not reduced, the dental formula was thus: . The incisors had small tips and looked very small with an average of 3 to 4 mm crown height. The canine, on the other hand, was solid and had a teardrop-shaped cross-section, was flattened on the sides and curved slightly backwards. It was up to 2 cm long and had a distinctive, sharp, but not serrated edge at the back. There was only a diastema to the posterior teeth in the lower jaw. The premolars had a long, narrow shape and pointed enamel cusps . As with all representatives of the Paroxyclaernidae, there was a tendency towards enlargement of the posterior premolars. As a result, the last pre-grinding tooth with a length of 7 mm was the longest tooth in the dentition. The molars were characterized by a tribosphenic tooth structure, which is typical of early higher mammals. Three enamel cusps formed a tight group ( trigon ), which was separated from the other cusps ( talon ) by a deep groove. The foremost molar reached a length of up to 6 mm, the size of the teeth decreased significantly towards the rear, another characteristic of the family.

The body skeleton is well known due to numerous fossil finds. The spine was composed of 7 cervical, up to 13 thoracic, a maximum of 9 lumbar, 3 sacrum and 31 tail vertebrae. The number of thoracic vertebrae in the known skeletal individuals fluctuates between 10 and 13, that of the lumbar vertebrae between 7 and 9. In general, the number of vertebrae (thoracic and lumbar vertebrae) is therefore given as at least 19. The foremost caudal vertebrae had strong spinous and transverse processes and short vertebral bodies. These became continuously smaller towards the end. The limbs were well built. The humerus was around 10 cm long and had prominent muscle attachment points. In addition, the shaft was only slightly curved. The ulna and radius were short and not fused together. The ulna was slightly longer than the humerus and also had a massive upper joint ( olecranon ). At around 12 cm in length, the thigh bone was the longest tubular bone. It was also massive and had a poorly developed third trochanter on the shaft. The tibia and fibula were also not fused. The fore and hind feet each had five rays. These were slightly spread apart from one another, with the inner jet (I) also being somewhat offset. The central ray (III) dominated, but only slightly exceeded the adjacent rays. The hind feet were larger than the front feet, so the Metsatarsus III reached a length of up to 3.8 cm, the Metacarpus III, however, of 3 cm. The end links had a slightly curved and pointed shape and were extremely high and narrow. They carried the former claws, which were made relatively the same size on each beam due to the size of the end links.

Fossil finds

Skeleton find of the rear part of the body of Kopidodon with the tracing of a bushy tail

Finds of Kopidodon could only be brought to light from the Messel pit near Darmstadt in Hesse. The site dates to the Middle Eocene and is around 47 million years old. Remains of at least two dozen individuals have become known which, in addition to individual lower jaw and skull finds, also include several partial skeletons and at least five largely complete skeletons. As for most of the Messel mammal fossils, these lie on their sides, with both the right and the left occurring. Some of the complete and partially preserved skeletal finds also show a fine tracing of the former body contours.

Paleobiology

Live reconstruction of Kopidodon

Kopidodon was a medium-sized mammal with a long tail and short limbs. On the basis of some fossils, the soft tissue itself is not preserved, but traced by bacteria (bacteriography). This can be used to identify a very bushy tail. In addition, the ears are clearly rounded and relatively small.

The postcranial skeleton had only a few special adaptations. The hind legs are only slightly longer than the front legs. The fully articulated forearm, which is indicated by the ulna and radius that are not fused together , was not geared towards fast-moving ( cursorial ) movement; the same should be noted for the lower leg. However, the humerus has strong muscle attachment points, and the ulna also has an extensive upper joint, which is typical for digging or climbing animals. The structure of the front feet contradicts a digging way of life. The hands are large and broad, but the claws are of the same length; Burrowing animals such as armadillos , on the other hand, often have an elongated central ray. The clear separation of the individual finger and toe rays from each other suggests a high degree of mobility of the front and rear feet, with the slightly protruding inner ray indicating greater freedom of the thumb or big toe. In addition, the claws are higher than they are wide and therefore offer little contact surface when digging in the ground. Rather, they resemble today's tree squirrels and thus, together with their flexible fingers and toes, refer to a tree-climbing ( arboreral ) way of life. However, the shorter hind legs in comparison to the tree squirrels indicate a less developed agility in the Kopidodon . Thus Kopidodon could hardly have jumped from branch to branch, but rather climbed, with the sharp claws digging into the bark to hold on to. The long tail shows a continuous reduction in the size of the vertebral bodies, whereby the tail obviously did not serve as a grasping organ; in South American primates the prehensile tails show an abrupt change in the size of the vertebral bodies. As a result, the tail of the Kopidodon in connection with the strong tail muscles attached to the large anterior vertebral bodies could have served to support the trunk, but also to regulate balance. On the ground, Kopidodon moved plantigrad due to the structure of the front and rear feet .

The posterior molars have the tribosphenic tooth structure typical of early higher mammals with a characteristic arrangement of high cusps on the chewing surfaces. Originally, a carnivorous way of life was therefore considered for Kopidodon , which was geared towards the numerous primeval horses in Messel. However, the tribosphenic structure is somewhat modified and lacks the sharp cutting edges, so that the teeth are less suitable for crushing animal, but more suitable for crushing vegetable food. This is also supported by the traces of abrasion on the molars, which are located on the inside of the teeth and are reminiscent of those of specialized fruit-eaters. This assumption could also be proven with the help of a skeletal individual discovered in 1989, which contained food residues in the gastrointestinal area in the form of extensive plant material and which, in addition to a few leaves, was mainly composed of fruits and seeds. The large canine teeth therefore obviously did not serve to procure food, but could have been used in intra-species disputes. As a pathological deviation, an extra fourth molar was formed in one individual.

Systematics

Kopidodon is a genus of the family of Paroxyclaenidae . These represent primeval insectivore-like animals, which are mainly known from the Eocene of Europe and partly also from Asia . The Paroxyclaenidae are now considered members of the subordination of the Pantolesta , whose internal as well as further relationships have not been adequately clarified. Partly the Pantolesta are added to the order of the Cimolesta , which summarizes early insectivore-like mammals and is possibly more closely tied to the Ferae . Other authors place the Pantolesta in a higher-level group called Proteutheria with a closer relationship to the insectivores. In general, the Pantolesta can be classified as more basal within the higher mammals . A 2013 study puts them in the vicinity of the Leptictida and the Palaeanodonta . The Pantolestidae also belong to the Pantolestae and are thus closely related to the Paroxyclaenidae. The members of this group lived, however, semi-aquatic and fed on animal remains. However, Buxolestes is also known to be a representative in Messel. The origin of the Pantolesta is partly seen with the Leptictida, which already appeared in the Upper Cretaceous .

Within Paroxyclaenidae, Kopidodon belongs to the subfamily of Paroxyclaeninae . Its members are characterized by a molarized last lower premolar with a well-developed metaconid (one of the main cusps on the chewing surface). In contrast to the Paroxyclaeninae, the Merialinae have a simply designed last lower anterior molar . Because of this feature are as next of kin of kopidodon about Paroxyclaenus , Vulpavoides and Pugiodens to look at, from the latter two can be found among other documents in the Messel to about the same age find complex of Geiseltal . All representatives of the Paroxyclaenidae, of which skull material is known, have, like the Kopidodon, a corresponding blunt snout and a pronounced crest. This suggests a comparable specialization in diet. However, the Kopidodon is the only form with surviving postcranial skeletal material, and it is one of the largest members of the family. It cannot therefore be said whether the closest relatives of Kopidodon lived a similar tree-dwelling way of life.

With Kopidodon macrognathus only one species is known so far. This was originally described in 1902 by Ernst Wittich based on a lower jaw find as Cryptopithecus macrognathus , whereby the genus Cryptopithecus was then considered a member of the primates. A crushed skull prompted Karl Weitzel to first describe the genus Kopidodon in 1933 . Due to the dental structure, he recognized similarities to Paroxyclaenus , he continued to refer the entire Paroxyclaenidae family named by him to the " Creodonta ", a group of primeval, predatory mammals, which from today's point of view does not form a closed unit. He justified this among other things with the formation of the canines and the decrease in size of the rear molars. After a position of the family within the " Condylarthra ", primitive ungulates, was favored in the early 1960s , Heinz Tobien subjected the genus Kopidodon to a new description in 1969. In the meantime, however, it was also considered a possible member of the insect eater. Further investigations and comparisons with other palaeogenic mammals, such as Buxolestes among others, resulted in a closer relationship to the Pantolesta in the 1990s.

The holotype (copy number : HLMD Me 7226 and 7227) comprises a lower jaw, an upper canine and an upper part of a cubit which Wittich had used to describe the type species; However, since the originals are missing, these are only available as casts. As a neotype (copy number: HLMD Me 1388) is therefore the crushed skull from Weitzel's first description of the genus. The generic name Kopidodon comes from the Greek and is made up of the words χορις ( kopis "slaughter knife " or "saber") and ὀδούς ( odoús "tooth"), thus referring to the particularly large shape of the canine tooth.

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

Individual evidence

  1. ↑ a b c d e f g h i Wighart von Koenigswald: Skeleton finds of Kopidodon (Condylarthra, Mammalia) from the Middle Eocene oil shale from Messel near Darmstadt. New Yearbook for Geology and Paleontology Abhandlungen 167 (1), 1983, pp. 1–39
  2. ↑ a b c d e f g h William A. Clemens and Wighart von Koenigswald: A new skeleton of Kopidodon macrognathus from the Middle Eocene of Messel and the relationship of paroxyclaenids and pantolestids based on postcranial evidence. Kaupia 3, 1993, pp. 57-73
  3. ↑ a b c d Clara Stefen and Thomas Lehmann: On new material of Kopidodon macrognathus (Mammalia, Paroxyclaenidae) from Messel. In: T. Lehmann and SFK Schaal (eds.): The World at the Time of Messel: Puzzles in Palaeobiology, Palaeoenvironment and the History of Early Primates. 22nd International Senckenberg Conference Frankfurt am Main, 15th - 19th November 2011. Frankfurt am Main, 2011, pp. 157–158
  4. ↑ a b c d Karl Weitzel: Kopidodon macrognathus Wittich, a predator from the Middle Eocene from Messel. Notes of the Geography Association of the Hessian Geological State Institute Darmstadt 14, 1933, pp. 81–88
  5. ↑ a b c Heinz Tobien: Kopidodon (Condylarthra, Mammalia) from the Middle Eocene (Lutetium) from Messel near Darmstadt (Hesse). Notes from the Hessian State Institute for Soil Research 97, 1969, pp. 7–37
  6. ↑ 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
  7. ↑ Wighart von Koenigswald: Kopidodon, a relative of the primeval ungulates who lived on trees. In: S. Schaal and W. Ziegler (eds.): Messel - A shop window into the history of the earth and life. Frankfurt am Main, 1988, pp. 235-237
  8. ↑ Malcolm C. McKenna: Toward a phylogenetic classification of the Mammalia. In W. Patrick Luckett and Frederick S. Szalay (Eds.): Phylogeny of the primates: a multidisciplinary approach. New York, London, 1975, pp. 21-46
  9. ↑ Malcolm C. McKenna and Susan K. Bell: Classification of mammals above the species level. Columbia University Press, New York, 1997, pp. 1-631 (pp. 217-219)
  10. ↑ a b Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1-431 (pp. 99-103)
  11. ^ A b Leigh Van Valen: New Paleocene Insectivores and Insectivore classification. Bulletin of the American Museum of Natural History 135, 1967, pp. 217-284
  12. ^ Gregg F. Gunnell, Thomas M. Bown, Jonathan I. Bloch and Douglas M. Boyer: Proteutheria. In: Christine M. Janis, Gregg F. Gunnell and Mark D. Uhlen (eds.): Evolution of Tertiary Mammals of North America: Vol. 2, Small Mammals, Xenarthrans, and Marine Mammals. Cambridge University Press, 2008, pp. 63-81
  13. ↑ Jerry J. Hooker: Origin and evolution of the Pseudorhyncocyonidae, a European Paleogene famaly of insectivorous placental mammals. Palaeontology 56 (4), 2013, pp. 807-835
  14. ↑ Doug M. Boyer and Justin A. Georgi: Cranial Morphology of a Pantolestid Eutherian Mammal from the Eocene Bridger Formation, Wyoming, USA: Implications for Relationships and Habitat. Journal of Mammalian Evolution 14, 2007, pp. 239-280
  15. ^ A b Leigh Van Valen: Paroxyclaenidae, an Extinct Family of Eurasian Mammals. Journal of Mammalogy 46 (3), 1965, pp. 388-397
  16. ^ Donald E. Russell and Marc Godinot: The Paroxyclaenidae (Mammalia) and a new form from the early Eocene of Palette, France. Palaeontological Journal 62 (3/4), 1988, SS 319–331
  17. ↑ a b Floréal Solé, Olivia Plateau, Kévin Le Verger and Alain Phélizon: New paroxyclaenid mammals from the early Eocene of the Paris Basin (France) shed light on the origin and evolution of these endemic European cimolestans. Journal of Systematic Palaeontology, 2019 doi: 10.1080 / 14772019.2018.1551248

Web links

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