Buxolestes

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Buxolestes
Temporal occurrence
Middle Eocene
47.8 to 38 million years
Locations
Systematics
Synapsids (Synapsida)
Mammals (mammalia)
Higher mammals (Eutheria)
Pantolesta
Pantolestidae
Buxolestes
Scientific name
Buxolestes
Jaeger , 1970

Buxolestes is a now extinct genus of insectivore-like animals from the Pantolestidae group . The representatives of the genus lived mainly in the Middle Eocene 48 to 41 million years ago and are known from several, mostly complete skeletons from the Messel Pit , but also from finds from the Geiseltal and Bouxwiller in France . The skeletal structure of Buxolestes is rather original, so that the animals are characterized by a curved back and a very long tail. But it shows special adaptations to a partly aquatic (semi-aquatic), partly underground (fossorial) way of life. Ecologically, the representatives of Buxolestes took the niche of today's otters . On the basis of fossil stomach remains, fish and small vertebrates , but also plant material, could be detected as food residues, so that Buxolestes , analogous to today's martens and foxes, maintained an omnivorous diet. The first description of buxolestes carried 1970th

description

Buxolestes was a small to medium-sized, insectivore-like animal and had a head-to-trunk length of 36 to 46 cm. The extremely long tail, characteristic of early higher mammals , measured between 24 and 36 cm and was thus about as long as the trunk. The body weight should have been around 2 kg. Another typical feature was the bulging trunk spine. The skull had lengths of 7.1 to 9.3 cm. It was built compactly, which made it look tall rather than long. The same applies to the rostrum , which was also characterized by a large nasal space between the nasal bone and the middle jawbone . The nasal bone itself was slender and clearly extended backwards so that it reached the level of the orbit . The eye socket was wide open backwards. The pair of frontal bones had a small crest , while the zygomatic arch was either curved upwards or relatively straight. The occiput , which protruded far back , had a very strong bulge as an attachment point for the neck muscles and strong joint ends (condyles) for the cervical spine.

The lower jaw was massive and between 4.9 and 6.9 cm long. The strong bone body reached about 1.1 cm in height in the area of ​​the first molar . The bit was the complete tooth number of early higher mammals that bite formula was thus: . The incisors were characterized by unequal sizes. The second in the lower dentition, the first and third in the upper one, was enlarged, the latter looking more like a canine ( canin- shaped ) due to its conical shape . The canines were clearly developed and conical, also pointed. The lower one had a distinctive groove on the inside, but it was not as strongly developed as in related genera. Both the incisors and the rear teeth had a smaller diastema , so that the canine was free. The rear teeth formed a closed row of teeth. The premolars showed up on the rear significant deviations from the molars and had therefore little or no molarisiert. However, they each had several pointed enamel cusps on the chewing surface . There were five on the lower molars, with the three higher ones forming a group that were separated from the two lower ones by a groove ( tribosphenic tooth structure). The upper molars also had several pointed cusps, two of which were grouped on the outside and a third a little further inwards, the inside of the teeth was surrounded by a wide enamel belt ( cingulum ). The length of the molars varied around 4.8 mm, the width was slightly larger at around 6 mm. The rearmost molar showed some stretching in places. The entire row of teeth from the canine to the last molar was up to 4 cm in large species.

The body skeleton is well known through several fossil finds. The spine consisted of 7 cervical, 13 thoracic, 5 to 6 lumbar and 22 to 28 caudal vertebrae; the number of sacral vertebrae is unknown, but was 3 in closely related genera such as Pantolestes, mainly on the 6 anterior caudal vertebrae noticeably broad transverse processes. In addition, they were each large with a length of 1.5 cm. The vertebrae behind it became increasingly smaller and only had rudimentary appendages. The front and rear extremities had a balanced length ratio and were relatively short overall, but the rear extremities were more massive. The humerus measured up to 5.4 cm and was slightly curved along the shaft. The bones of the forearm were not connected, the ulna reached over 6 cm in length and showed a large upper joint ( olecranon ). The sturdy femur with the strong joint head had a well-developed third trochanter and was 7 cm long, the shin a little longer. This thus represented the longest tubular bone in the skeleton. The tibia and fibula were firmly fused. Front and rear legs each ended in five-pointed feet. The middle three rays (II to IV) had the longest expression and here again the third. Overall, the fore and hind feet did not show any strong specializations, such as significant lengthening or shortening of the metapodia or phalanges . However, the end links of the toes tapered to a point, indicating the existence of long claws, and there were also slight indentations on the surface.

Fossil finds

Finds from Buxolestes come mainly from the Middle Eocene around 48 to 43 million years ago and are largely only known from Europe . It is worth highlighting four almost complete skeletons from the Messel mine near Darmstadt, which have been handed down in a lateral position. A fourth skeleton from the same location was damaged during the rescue and is therefore less well preserved. All finds from Messel can be assigned to the lower section of the Middle Eocene. There were also reports of a crushed skull from the Geiseltal near Halle . It comes from the Upper Middle Coal there, which represents the upper section of the Middle Eocene. Further finds come from Bouxwiller in Alsace in France . In addition to a few isolated teeth and longer rows of teeth, these also include several complete lower jaw branches. Their age is somewhere between the fossils of the Geiseltal and those of the Messel pit.

Paleobiology

Live reconstruction of Buxolestes

In general physique, especially the limbs, which are short compared to the trunk, the long tail and the structure of the teeth, which suggests meat, Buxolestes corresponds to a modern otter ( Lutra lutra ) from the marten family . A semi-aquatic way of life comparable to the otter can be recognized from the skeletal morphology. The occiput protruding backwards , the strong attachments of the cervical spine and the small crest point to a well-developed, short neck muscles, which speaks for a very mobile head. This high mobility was necessary to keep the head afloat when swimming. On the other hand, the strong appendages on the atlas , the first cervical vertebra, show that the musculus obliquus was particularly well developed and ensured increased lateral mobility of the head. This is particularly advantageous when hunting, when the prey swings sideways. Clear foramina, openings in the bone, such as the mental or infraorbital foramen , are formed on the upper and lower jaw . As a result, a very sensitive snout region can be assumed and the presence of whiskers around the mouth is likely. However, the infraorbital foramen does not reach the same size as in the otter, so that the vibrissae in Buxolestes were not as pronounced. Possibly the representatives of Buxolestes were diurnal or hunted in mostly clear water.

Certain adaptations to a partially swimming way of life can also be seen on the tail. The six large vertebrae of the tail base with their broad transverse processes, which take up a third of the entire tail length, are found again in the otter, which uses the tail as a drive organ. The muscles attached there enable powerful gliding up and down as well as sideways winding of the tail. Remnants of the soft tissue from the Messel pit have also been traced by bacteria (bacteriography) and have therefore been handed down. They show a rounded, not flattened tail, as the otter also shows today. The limbs, on the other hand, show only a few special adaptations to swimming. The thigh bone is not shortened, which would be considered a special adaptation to swimming, as the resulting shortened lever function on the foot would make paddling easier. An elongation of the toe phalanx as in the sea ​​otter cannot be determined. The hind foot was restricted in its lateral movements due to the adhesion of the fibula with the shin . The shape of the heel bone , especially the heel cusp, enabled a powerful backward movement of the foot. The unconnected bones of the forearm indicate a freely movable forefoot. The strongly developed upper joint of the ulna also allows the foreleg to be stretched significantly. This is typical of animals with a burrowing way of life, which means that Buxolestes was also able to search for food or dig shelters underground. The long middle finger, which is typical for fossilized armadillos , as well as the already mentioned good return movement of the foot to push away the excavation could further indicate a digging activity .

Often Buxolestes is seen as a predatory animal specializing in fish food. In addition to the general structure of the teeth, the molars with their very pointed cusps provide indications for this. However, there is no pair of pruning scissors in the rear teeth , which are typical for predators and the extinct " Creodonts " ( Hyaenodonta and Oxyaenodonta ). A first, almost complete, but somewhat damaged skeleton find from the Messel Pit also contained remains from the gastrointestinal area. These included innumerable, splintered long bones and vertebral remains of small vertebrates , but also thin bone platelets that can be regarded as fish scales, but were mostly not meaningful enough. A jaw fragment only 2.2 mm long with remnants of the dentition turned out to be a remnant of Atractosteus , a fish form often found in Messel. Another skeleton find at the same location so far only contained undetermined bone material. From the stomach contents of two other Messel individuals, however, only plant residues, such as seeds and fruits, could be determined. These findings from the digestive tract therefore seem to contradict one another. But since today's predators , especially from the group of dogs and martens, sometimes eat more plant-based food, the traditional remains of the stomach of Buxolestes may indicate a diet that may vary depending on the season. All in all, based on these findings, Buxolestes has a similar way of life as that of today's otter, which means that it occupied its ecological niche in the Middle Eocene . Buxolestes , as Wighart von Koenigswald emphasized in 1980, “ need neither the same elegance in swimming nor the extent of the sensory performance as with Lutra ”.

Systematics

Buxolestes is a genus of the family of Pantolestidae . These include primeval insectivore-like animals that have been recorded from the Middle to Upper Paleocene to the Lower Oligocene in North America and Eurasia and also temporarily appeared in northern Africa in the transition from the Paleocene to the Eocene . Both the internal and the other relationships of the Pantolestidae are only insufficiently clarified. They are often considered to be members of the subordination of the Pantolesta . These in turn are referred by some authors to the superordinate group of the Cimolesta , which represent early insectivore-like mammals, which may have a closer connection to the ferae . Other authors, however, assign the Pantolesta to the Proteutheria and see them in the close relationship of the insectivores. In general, the pantolesta can be classified as more basal within the higher mammals . A 2013 study suggests a closer relationship with the Leptictida and the Palaeanodonta . Within the Pantolestidae, Buxolestes can be incorporated into the subfamily of the Pantolestinae . In contrast to those of the Pentacodontinae, their representatives show clear adaptations to a semi-aquatic way of life. In the closer relationship of buxolestes can palaeosinopa and Pantolestes from the Lower and Middle Eocene of North America and Pagonomus be made from the Paleocene of Europe. The latter is also handed down from Walbeck in Saxony-Anhalt. The origin of the Pantolesta is partly seen with the Leptictida, which are already known from the Upper Cretaceous .

Today three types are known:

Two of the three species ( B. minor and B. piscator ) were found in the Messel pit . Possibly it concerns with minor as a not yet full-grown form of B. piscator , though broken in the last molar, was not yet engaged. The former also lacks the clearly protruding occiput and the transverse processes on the caudal vertebrae.

The first description of buxolestes was carried out by Jean-Jacques Jaeger in 1970. The basis for this were several tooth finds from Bouxwiller. The holotype (copy number: Bchs 100) comprises a left branch of the lower jaw with dentition from the canine to the last molar, whereby the anterior premolar is incomplete. It is located in the Natural History Museum of Basel . The name Buxolestes refers on the one hand to the locality Bouxwiller, on the other hand to the similarity and close relationship to the North American Pantolestes .

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 j Wighart von Koenigswald: The skeleton of a Pantolestiden (Proteutheria, Mammalia) from the middle Eocene from Messel near Darmstadt. Paläontologische Zeitschrift 54 ​​(3/4), 1980, pp. 267-287
  2. ↑ a b c d Wighart von Koenigswald: The second skeleton of a Pantolestidae (Pantolestidae, Proteutheria, Mammalia) from the Middle Eocene from Messel near Darmstadt. Carolines 45, 1987, pp. 36-42
  3. ↑ a b c d e f g Hans-Ulrich Pfretzschner: Buxolestes minor n. Sp. - a new Pantolestide (Mammalia, Proteutheria) from the Eocene Messel formation. Courier Forschungsinstitut Senckenberg 216, 1999, pp. 19-29
  4. ↑ 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
  5. ↑ a b c d Jean-Jaques Jaeger: Pantolestidae nouveaux (Mammalia, Insectivora) de L'Éocène Moyen de Bouxwiller (Alsace). Palaeovertebrata 3, 1970, pp. 63-82
  6. ↑ Kenneth D. Rose: The importance of Messel for interpreting Eocene Holarctic mammalian faunas. Palaeobiology and Palaeoenvironments 92, 2012, pp. 631-647
  7. ↑ a b c d e Hans-Ulrich Pfretzschner: Muscle reconstruction and aquatic locomotion in the Middle Eocene Buxolestes piscator from Messel near Darmstadt. Kaupia 3, 1993, pp. 75-87
  8. ^ Wighart von Koenigswald: The first Pantolestide (Proteutheria, Mammalia) from the Eocene of the Geiseltal near Halle. Journal of Geological Sciences 11, 1983, pp. 781-787
  9. ↑ Gotthard Richter: Studies on the nutrition of Eocene mammals from the Messel fossil site near Darmstadt. Courier Forschungsinstitut Senckenberg 91, 1987, pp. 1-33
  10. ^ Wighart von Koenigswald: The skeleton of a Pantolestiden (Proteutheria, Mammalia) from the middle Eocene from Messel near Darmstadt. Palaeontological Journal 54 (3/4), 1980, pp. 267–287 (p. 286)
  11. ↑ 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
  12. ↑ 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)
  13. ↑ Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1–431 (pp. 94–118)
  14. ↑ Leigh van Valen: New Paleocene insectivores and insectivore classification. Bulletin of the American Museum of Natural History 135, 1967, pp. 217-284 (pp. 222-230)
  15. ^ A b 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
  16. ↑ Jerry J. Hooker: Origin and evolution of the Pseudorhyncocyonidae, a European Paleogene famaly of insectivorous placental mammals. Palaeontology 56 (4), 2013, pp. 807-835
  17. ↑ Kenneth D. Rose and Wighart von Koenigswald: An exceptionally complete skeleton of Palaeosinopa (Mammalia, Cimolesta, Pantolestidae) from the Green River Formation, and other postcranial elements of the Pantolestidae from the Eocene of Wyoming (USA). Palaeontographica A 273, 2005 (3-6), pp. 55-96
  18. ↑ 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

Web links

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