Propalaeotherium

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Propalaeotherium
Propalaeotherium

Propalaeotherium

Temporal occurrence
Middle Eocene to Lower Oligocene
50.7 to 41.1 million years
Locations
Systematics
Higher mammals (Eutheria)
Laurasiatheria
Unpaired ungulate (Perissodactyla)
Hippomorpha
Palaeotheriidae
Propalaeotherium
Scientific name
Propalaeotherium
Gervais , 1849

Propalaeotherium is an extinct genus of mammals , which is classified in thefamily of the Palaeotheriidae, which isrelatedto the horses , but which is not the immediate ancestor of the horses, but formed a side branch that died out again relatively early. The genus is proven by numerous finds, mostof which comefrom Europe and of which the partly complete skeletons of the Geiseltal and the Messel Pit are among the best known. The fossil remains date from the Middle Eocene to the Upper Oligocene 50 to 41 million years ago. The representatives of Propalaeotherium lived mainly in forests and fed on soft vegetable diet. Individual finds indicate that the animals were already pursuing a reproductive strategy similar to that of today's horses. The genus was scientifically introduced in 1849.

features

Skeletal reconstruction of Propalaeotherium based on finds from the Geiseltal

Propalaeotherium was similar in physique to the well-known Hyracotherium . Several species of this genus are known, of which the larger had a total length of around 90 cm, but of which around 26 cm was attributable to the tail. The height at the withers was 43 cm, due to the strong curvature of the spine, the highest point of the trunk was approximately in the area of ​​the lumbar vertebrae and reached a height of about 53 cm. Body weight reconstructions resulted in around 30 to 35 kg for individual finds from Messel. A variation between 10 and 53 kg could be determined for the numerous documents from the Geiseltal. A significant decrease in weight can be seen here in the course of the phylogenetic development. The decline from an initial average of 39 kg to an average of 26 kg later took place in the Geiseltal over a period of almost 3 million years. The short neck was characteristic of the genus. The skull measured up to 22 cm and was elongated and shaped like a wedge when viewed from the side. The occiput was rather short and rectangular in shape, but partly clearly concave when viewed from the side. The nasal bone took up almost half the length of the skull, sometimes over 10 cm. It is noteworthy, however, that the nasal incision for the formation of the nasal cavity only protruded about 3 cm and was therefore comparatively short in contrast to Palaeotherium . The forehead line was relatively straight and was not as strongly curved as in Hyracotherium or Palaeotherium , so that this feature was clearly reminiscent of modern horses.

Lower jaw with the posterior molars of Propalaeotherium
Lower jaw of Propalaeotherium hassiacum from the Geiseltal

The lower jaw reached a length of around 20 cm and had a weak symphysis , the branches of the lower jaw were relatively low. In both the upper and lower jaws the full Säugetierbezahnung was using the following formula for the permanent dentition: . The front teeth were relatively small and pointed. There was a small diastema for each of the following canines . The canine itself was significantly larger than the incisors and was conically pointed. Another, this time larger, diastema was to the posterior teeth. These had only low tooth crowns ( brachyodont ), while the chewing surface of the molars was formed from two tooth enamel ridges that were transverse and had bumpy elevations at the ends ( bunodont ). In contrast, the premolars , especially the anterior ones, were only slightly molarized and had only individual cusps.

The postcranial skeleton is well known due to the numerous finds. The spine consisted of seven cervical, eighteen thoracic, five lumbar and five sacral vertebrae. The caudal vertebrae reached a total of nineteen. The spine is characterized by a high curve-like course. In larger species, the femur reached an average length of 18 cm, the shin one of 15 cm. The fibula was still preserved as a separate narrow bone and not reduced as in today's horses, such a reduction only began later in the Miocene . The length of the humerus averaged 14 cm. The ulna and radius were fused, the spoke reached 13 cm in length. The hind limbs each ended in three toes, with the middle frog being the strongest. As with many early odd-toed ungulates, the front legs also had an additional, smaller fourth toe.

References

Propalaeotherium skeleton from the Geiseltal
Propalaeotherium skeleton from the Messel Pit

Propalaeotherium lived in the Middle and Upper Eocene and is known from several localities in Europe . One of the most important is the Geiseltal near Halle in Saxony-Anhalt . More than 300 remains of this prehistoric horse, including numerous bones, teeth and articulated skeletal elements, but also an almost complete skeleton, which was recovered in 1933, come from the find areas of the lower, middle and upper lignite seams . Other outstanding finds came to light in the Messel mine near Darmstadt ( Hesse ). The site revealed more than a dozen complete skeletons embedded in oil shale . The third site in Germany with high-quality fossils is the Eckfelder Maar in Rhineland-Palatinate . Here, too, several related skeletons have survived, including one of a pregnant mare.

In addition to these three important sites, there are others in England , France , Spain and Switzerland , but most of them only yielded fragmented material. The karst fissure near Egerkingen (canton Solothurn ) in Switzerland, from which some of the most recent finds of Propalaeotherium come, is remarkable . In France, numerous finds are known from the Paris Basin , as well as from the south of the country, for example from Aumelas , from where more than two dozen skull and dentition remains as well as isolated teeth are present.

Paleobiology

Live reconstruction of Propalaeotherium

Male and female animals of Propalaeotherium can be differentiated by the shape of the pelvis, in addition to the different sizes of the canines, which are much longer in stallions. In mares the opening of the iliac bone is much wider due to the birth canal, while in stallions it is not only narrower, but is also narrowed even further by the protrusions on the iliac bone. The overall habit of the genus is characterized by the short neck and the high curved back line. Similar body shapes are rare in hoofed animals today , but occur in the duckers , especially the zebra sugar in West Africa , which, however, belong to the bovids and thus to the articulated ungulates . Nevertheless, this special body shape should be a special adaptation to the tropical rainforest with dense undergrowth vegetation and dry terrain. The four-rayed forefeet of Propalaeotherium also enabled good locomotion in damp to swampy terrain. Rainforests with several layers of vegetation and interspersed with moist biotopes are being reconstructed for the Geiseltal and Messel.

With regard to the preservation of the soft tissue , the findings of Messel are outstanding, whereby the soft tissues are not traced themselves but by bacterial processes (bacteriography). In a fossil of Propalaeotherium , the rest of the tail hair is shown as a shadow. In contrast to the tail of today's horses, the hair is bushy and protruding. For the related genus Eurohippus , the shape of the ears has also been passed down, which hardly differs from that of today's wild horse , but was not as bag-shaped as that of the zebras . Internal organs could also be detected in a fossil of the also closely related genus Hallensia . This shows that the primitive horses already had a greatly enlarged intestinal tract and were probably rectum fermenters even then, which means that digestion in these animals took place largely in the intestines. Such early evidence of such a digestive process could mean that the development of this special gastrointestinal tract was already developed in the oldest odd-toed ungulates and did not develop independently.

The low-crowned teeth and their bunodontic structure generally speak in favor of specializing in soft vegetable foods such as leaves or fruits . The well-preserved skeletal finds with partially intact gastrointestinal contents confirm this assumption. As early as the 1970s, some fossils from Messel, which today belong to the closely related genus Eurohippus , were found to have leftover leaves from twelve different types of laurel family, along with five other plant families, such as the hickory nut tree , fig , myrtle and dog poison plants . In further investigations in Messel, countless seeds of grapevine plants were detected, which confirm that fruits also made up a considerable proportion of the food spectrum. A complete skeleton of a female individual from the Eckfelder Maar showed numerous remains of leaves in the gastrointestinal area as indications of food. In the early 2000s, the digestive tract of the Propalaeotherium skeleton, which was recovered in Geiseltal in 1933, was also successful . Numerous remains of heather and belt flowers came to light here, but also fruits and flowers , as the existing seeds and pollen show, were obviously not spurned. Furthermore, grains of sand and quartz were frequently observed, which indicate that Propalaeotherium ate its food largely by grazing in plant waste lying on the ground, without making any special pre-selection.

The complete skeleton of the mare from the Eckfelder Maar also contained the remains of a fetus in the lumbar area, which was additionally covered by the placenta through bacterial traces . This is the first evidence in an early horse relative. This finding gives an important insight into paleobiology. The presence of a single fetus indicates the characteristic reproductive strategy of today's ungulates, which usually only give birth to one young, but which is intensively cared for (" k-strategy "). Even with the closely related genus Eurohippus , at least half a dozen mares with one fetus each are known from Messel, which means that this method of reproduction is to be regarded as typical for the primitive horses. This also indicates that the early horse representatives like the present day lived in herds or at least in small group associations and thus took care of the protection of the descendants. However, whether the stallions already assumed a dominant position at that time is rather questionable, since the “harem structures” known today in wild horses are a result of adapting to open landscapes.

Despite numerous excellent fossil finds, few pathological findings have so far been proven. One of the few is a different position of a premolar in a lower jaw from the Geiseltal. The tooth was rotated 180 °, which initially meant that the animal could not close its jaw completely. However, the abrasion of the teeth shows that this did not affect the animal much.

Systematics

Internal systematics of the Equoidea according to Remy et al. 2019
 Equoidea  


 Cardiolophus


   

 Hallensia



   

 Pliolophus


   

 Hyracotherium


   

 Orolophus


  Palaeotheriidae  

 Pachynolophus


   


 Lophiatherium


   

 Eurohippus



   

 Propalaeotherium


   

 Leptolophus


   

 Plagiolophus


   

 Palaeotherium









Template: Klade / Maintenance / 3

Template: Klade / Maintenance / Style

There are different views on the taxonomic position of Propalaeotherium . It is widely believed that the genus belongs to the family of Palaeotheriidae , the sister taxon of the family of horses (Equidae) within the superfamily of the Equoidea (equine species) . Within the group of Palaeotheriidae, Propalaeotherium represents the ancestor of Palaeotherium , which is also indicated by the scientific name. Other researchers, mostly from Central Europe, are of the opinion that Propalaeotherium is a representative of the Equidae and there belongs to the subfamily of Hyracotheriinae. Reasons for this include the much larger nasal cavity in the Palaeotheriids, which is significantly smaller in Propalaeotherium and equidae, and the molars in Palaeotherium are noticeably higher crowned. Another difference lies in the shape of the hand and foot bones, with the Palaeotheriids the former being significantly longer than the latter, which is exactly the opposite in the Equidae and Propalaeotherium . Because of this, Propalaeotherium possibly occupies a kind of intermediate position between the two families. Reasons for the different assessment of the position of Propalaeotherium and other early equoids within Central European research can, according to some experts, be found partly in the Frankfurt theory of evolution . A phylogenetic study from 2019 anchors Propalaeotherium in a clade together with Palaeotherium and Plagiolophus . This, in turn, faces a community of Eurohippus and Lophiotherium , while more primitive Palaeotheria such as Pachynolophus are positioned further out.

Paul Gervais

The first scientific description of Propalaeotherium was made in 1849 by Paul Gervais (1816–1879) using fossils from Issel, which were considered to belong to the species Pachynolophus isselanus by Georges Cuvier as early as 1824 . P. isselanum therefore forms the type species of the genus. In addition, five other species are often listed, so that a total of six species are widely recognized:

Four of the six species mentioned were assumed for the Geiseltal ( P. argentonicum , P. hassiacum , P. isselanum and P. voigti ). The most common of these is the large P. hassiacum , which makes up around half of the total finds. The form is largely limited to the lower coal and is represented quite numerous at the site XIV . P. isselanum and P. voigti are detected approximately equally. The former was similar in size to P. hassiacum , but could largely only be documented from the middle coal; the famous skeleton of the site also belongs to the species. The significantly smaller P. voigti occurs in both the lower and middle coal. The largest known species from the Geiseltal, P. argentonicum , is only known from individual finds from the lower coal . A study conducted in 2020, however, combines P. hassiacum and P. voigti due to less divisive or inaccurately defined features with P. isselanum . Around half a dozen other species were also listed. This also includes P. messelense from the Messel pit , which Oskar Haupt managed as an independent species in 1925 . This was equated in 1986 with P. parvulum , which Charles Léopold Laurillard had already introduced in 1849 (but as Lophiodon parvulum ). In 2006 Jens Lorenz Franzen assigned P. parvulum to the new genus Eurohippus , which is closely related to Propalaeotherium , but is significantly smaller and also differs in individual tooth features. A large part of the Messel primeval horse skeletons, more than 40, belong to Eurohippus . The independence of the genus, however, was questioned in the study from 2020. The skull fragments from China, described on the one hand by Otto Zdansky as P. sinense in 1930 and on the other by Chung-Chien Young as P. hengyangensis in 1944 , are more recently assigned to the basal chalicotheria .

Propalaeotherium first appeared at the beginning of the Middle Eocene . It is largely only proven in Europe. The important finds from the Geiseltal, the Messel pit and the Eckfelder Maar are each to be classified in a later phase of the spread of the primitive horse species. Propalaeotherium disappeared again in the Upper Eocene . The latest finds include those from Egerkingen in Switzerland.

literature

  • Jens Lorenz Franzen: The primeval horses of the dawn. Elsevier, Spektrum Akademischer Verlag, Munich 2007, ISBN 3-8274-1680-9
  • Jens Lorenz Franzen: Unpaired ungulates - primitive horses and tapirs. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messelein fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 293-301

Individual evidence

  1. ^ Holger Preuschoft and Jens Lorenz Franzen: Locomotion and biomechanics in Eocene mammals from Messel. Palaeobiology Palaeoenvironment 92, 2012, pp. 459-476
  2. ↑ a b c Simon J. Ring, Hervé Bocherens, Oliver Wings and Márton Rab: Divergent mammalian body size in a stable Eocene greenhouse climate. Scientific Reports 10, 2020, p. 3987, doi: 10.1038 / s41598-020-60379-7
  3. ↑ a b c d e Meinolf Hellmund: Skeleton reconstruction of Propalaeotherium hassiacum (Equidae, Perissodactyla, Mammalia) based on the finds from the Eocene Geiseltal (Saxony-Anhalt, Germany). Hallesches Jahrbuch für Geoswissenschaften, Series B, Supplement 12, 2000, pp. 1–55
  4. ↑ a b c d e f g Jens Lorenz Franzen: The primeval horses of the dawn. Munich, 2007, pp. 45-73
  5. ↑ a b c d e f Jean A. Remy: Sur le crâne de Propalaeotherium isselanum (Mammalia, Perissodactyla, Palaeotheriidae) de Pépieux (Minervois, Sud de la France). Geodiversitas 23 (1), 2001, pp. 105-127
  6. ↑ a b c d e Jens Lorenz Franzen: The Equoidea of ​​the European Middle Eocene (Geiseltalium). Hallesches Jahrbuch für Geoswissenschaften B17, 1995, pp. 31–45
  7. ↑ a b Jens Lorenz Franzen and Hartmut Haubold: Revision of the Equoidea from the Eocene brown coal of the Geiseltal near Halle (GDR). Palaeovertebrata 16 (1), 1986, pp. 1-34
  8. ↑ Meinolf Hellmund: Excursion: Former Geiseltalrevier, southwest of Halle (Saale). From the Vita of the Eocene Geiseltal. In: Jörg Erfurt and Lutz Christian Maul (eds.): 34th meeting of the working group for vertebrate palaeontology of the paleontological society March 16 to March 18, 2007 in Freyburg / Unstrut. Hallesches Jahrbuch für Geoswissenschaften, Series B, Supplement 23, 2007, pp. 1–16
  9. ↑ a b Jens Lorenz Franzen: A pregnant mare with preserved placenta from the Middle Eocene maar of Eckfeld, Germany. Palaeontographica Department A 278, 2007, pp. 27-35
  10. ^ A b Jean Albert Remy, Gabriel Krasovec and Bernard Marandat: A new species of Propalaeotherium (Palaeotheriidae, Perissodactyla, Mammalia) from the Middle Eocene locality of Aumelas (Hérault, France). Palaeovertebrata 40 (2), 2016, doi: 10.18563 / pv.40.2.e1
  11. ^ A b c Jean A. Remy, Gabriel Krasovec, Éric Lopez, Bernard Marandat and Fabrice Lihoreau: The Palaeotheriidae (Equoidea, Perissodactyla, Mammalia) from the Eocene fauna of Aumelas (Hérault department, France). Geobios 41 (13), 2019, pp. 525-585, doi: 10.5252 / geodiversitas2019v41a13
  12. ↑ Jörg Erfurt and Hans Altner: Habitus reconstruction of Anthracobunodon weigelti (Artiodactyla, Mammalia) from the Eocene of the Geiseltal. In: Jan Michal Burdukiewicz, Lutz Fiedler, Wolf-Dieter Heinrich, Antje Justus and Enrico Brühl (eds.): Knowledge hunters . Festschrift for Dietrich Mania. Publications of the State Museum for Prehistory in Halle 57. Halle / Saale 2003, pp. 153–176
  13. ↑ a b c d Jens Lorenz Franzen: Unpaarhufer - primitive horses and tapirs. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messelein fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 293-301
  14. ↑ Wighart von Koenigswald and Friedemann Schaarschmidt: A primeval horse from Messel that ate grapevines. Natur und Museum 113 (3), 1983, pp. 79-84
  15. ↑ Herbert Frankenhäuser, Werner Löhnertz, Jens L. Franzen, Uwe Kaufluss, Martin Koziol Herbert Lutz, Dieter F. Mertz, Jens Mingram, Torsten Wappler, Volker Wilde: The Eckfelder Maar in the Vulkaneifel - a window into a habitat off the coast 44 million years ago . Mainz Natural Science Archive 47, 2009, pp. 263–324
  16. ↑ Volker Wilde and Meinolf Hellmund: First record of gut contents from a middle Eocene equid from the Geiseltal near Halle (Saale), Saxony-Anhalt, Central Germany. Palaeobiodiversity and Palaeoenvironments 90, 2010, pp. 153-162i
  17. ^ Jens Lorenz Franzen: Report on the Discovery of Fossil Mares with Preserved Uteroplacenta from the Eocene of Germany. Fossil Imprint, 73 (1-2), 2017, pp. 67-75
  18. ↑ Meinolf Hellmund: Aberrant tooth position (position anomaly) in a mandible from Propalaeotherium hassiacum HAUPT 1925 (Equidae, Perissodactyla, Mammalia) from the Geiseltal near Halle (Saale). Hallesches Jahrbuch für Geoswissenschaften B22, 2000, pp. 99-104
  19. ↑ Meinolf Hellmund: Odontological and osteological investigations on propalaeotheriids (Mammalia, Equidae) from the Eocene Geiseltal Fossillagerstätte (Central Germany) - a full range of extraordinary phenomena. New Yearbook for Geology and Palaontology Abhandlungen 267/2, 2013, pp. 127–154
  20. ^ Donald R. Prothero and Robert M. Schoch: Classification of the Perissodactyla. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of the Perissodactyls. New-York, 1989, pp. 530-537
  21. ↑ David J. Froehlich: Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zoological Journal of the Linnean Society, 134, 2002, pp. 141-256
  22. ^ Luke Holbrook: Book Review: The Rise of the horses, by Jens Lorenz Franzen. Journal of Vertebrate Palaeontology 31 (4), 2011, pp. 934-935
  23. ^ Jens Lorenz Franzen: Eurohippus ng, a new genus of horses from the Middle to Late Eocene of Europe. Senckenbergiana lethaea 86 (1), 2006, pp. 97-102
  24. ↑ Chung-Chien Young: Note on the first Eocene mammal from South China. American Museum Novitates 1268, 1944, pp. 1-3
  25. ↑ Suyin Ting, Gabriel J. Bowen, Paul L. Koch, William C. Clyde, Yuanqing Wang, Yuan Wang and Malcolm C. McKenna: Biostratigraphic, chemostratigraphic, and magnetostratigraphic study across The Palaeocene-Eocene boundary in the Hengyang basin, Hunan, China. Geological Society of America Special Paper 369, 2003, pp. 521-535
  26. ↑ Bin Bai, Yuan-Qing Wang and Jin Meng: The divergence and dispersal of early perissodactyls as evidenced by early Eocene equids from Asia. Communications Biology 1, 2018, p. 115, doi: 10.1038 / s42003-018-0116-5

Web links

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