Eurohippus

from Wikipedia, the free encyclopedia
Eurohippus
Skeleton of Eurohippus with fetus (in oval), black line = 10 cm

Skeleton of Eurohippus with fetus (in oval),
black line = 10 cm

Temporal occurrence
Middle Eocene to Upper Eocene
47.4 to 37.7 million years
Locations
Systematics
Higher mammals (Eutheria)
Laurasiatheria
Unpaired ungulate (Perissodactyla)
Equoidea
Palaeotheriidae
Eurohippus
Scientific name
Eurohippus
Franzen , 2006

Eurohippus is an extinct genus of the odd ungulate and an early relative of today's horses , which lived in the Middle and Upper Eocene in central and western Europe . Significant and extensive finds come from the Messel Pit , where numerous, partly complete skeletons have come down to us. The small animals lived in the tropical rainforest and mainly fed on leaf-eating. The excellent preservation conditions in Messel also made it possible to reconstruct various internal organs. Single female individuals were pregnant at the time of their deathand each carried a fetus . Originally, the representatives of Eurohippus were placed in the closely related genus Propalaeotherium . Individual differences in the skeletal structure led to the creation of the new genus Eurohippus in 2006. With E. parvulus and E. messelensis two types are distinguished.

features

Living reconstruction of Eurohippus in the Natural History Museum Berlin

In habit, Eurohippus was similar to the other known genera of the Palaeotheriidae and had a slender body with a clearly curved back. It was smaller and slimmer than Propalaeotherium but larger than Lophiotherium . The shoulder height was around 30 to 35 cm, the assumed body weight was 5 to 6.5 kg. The skull was 13.4 to 16.4 cm long and was clearly more wedge-shaped in side view than that of Propalaeotherium . The interior of the nose reached just behind the canine and was 1.2 cm long. It was framed by the nasal bone at the top and the middle jawbone at the bottom , so the upper jaw was excluded. Both the nasal bone and the central jawbone protruded about the same distance in front, the nasal bone ended at the rear at the level of the last premolar and the first molar . The infraorbital foramen was relatively large and sat above the penultimate premolar, while the anterior edge of the orbit was above the second molar. Since its rear end is roughly indicated by the suture of the cheekbone and temporal bone , the eye window was thus roughly in the middle of the skull. The posterior part of the parietal bone protruded slightly from the occiput . The articular surfaces of the occiput sat at the lower end of the skull and were rounded in shape. At the base of the skull, the rather wide glenoid pit (which connects the skull with the lower jaw) was bordered at the back by the button-like postglenoidal process . Behind this, the outer ear canal opened .

Lower jaw of Eurohippus from the Geiseltal

The lower jaw was elongated with dimensions between 11 and 13 cm. The horizontal bone body was low and tapered continuously towards the front; it was 1.9 cm deep below the last molar and 1.5 cm deep below the last premolar. The symphysis at the anterior end, connecting the two halves of the lower jaw, began between the third and second premolars. Here the lower jaw bulged slightly downwards. A large mental foramen was located below and just before the first, a second smaller one below the fourth premolar. The crown process of the ascending branch ended in a hook shape, it protruded and 2.5 cm above the chewing plane of the molars. A deep indentation separated it from the articular process, which rose a good 1.3 cm above the occlusal plane and was therefore lower. At the rear end of the lower jaw a rounded angular process was evident. The dentition of the dentition consisted of the complete unreduced tooth number of higher mammals and therefore had the following dental formula: . The front teeth were small and rounded in shape when viewed from the side. They formed a clear arch in the lower jaw. The canine looked like a dagger. It stood free at the top and bottom, as an extensive diastema separated it from the preceding and following tooth. Another, significantly shorter tooth gap opened up between the first and second premolars. The molars were characterized by clearly low crowns ( brachyodont ), the premolars were different from the molars, i.e. not or only slightly molarized. However, the paraconus and metaconus were already differentiating from the ectoloph (a cutting ridge) on the lip side of the last two upper anterior teeth. The lower premolars had a main cusp, the protoconid. However, the molars already had two transverse enamel ridges ( bilophodont ) on the chewing surfaces and were no longer designed as bumpy ( bunodont ) as in older genera, such as Hyracotherium . A third ridge appeared here due to the development of a stronger hypoconulid on the lower posterior molar. Cingula, i.e. small protruding enamel bulges, were generally weak on the outside of the molars and only longer on the rearmost molar. The entire rear upper row of teeth from the first premolar to the last molar measured between 5.1 and 6 cm, the molars extended over 2.6 to 3.2 cm in length.

The musculoskeletal system has largely been handed down in full. The humerus was between 9 and 10.6 cm in length. Its joint head was hemispherical, the articulation surface expanded between the large and small protrusions (greater and lesser tuberosities). A medium lead, as is typical for today's horses, did not occur. There were individual noticeable bone ridges at the lower end of the joint. The comparatively extensive upper articular process ( olecranon ) was characteristic of the ulna . With a length of 9.8 to 11.4 cm, the ulna exceeded the humerus in its dimensions. The femur was between 11.8 and 13.8 cm long and had a hemispherical joint head. This was surmounted by more than a centimeter from the great roll mound (greater trochanter). On the side of the Great Rolling Hill there was a prominent bone rib. A third roll mound (trochanter tertius) existed about halfway up the shaft on the outside. The lower section of the hind leg was shorter than the upper, which differs from the proportions on the front leg. The tibia reached a length of 10.5 to 12.5 cm, the fibula from 9.6 to 11.3 cm. As in all early Eocene equine relatives, the limbs ended in four toes on the forefoot (ray II to V) and three toes at the hind foot (ray II to IV). However, a rudimentary remnant of the inner ray (I) appeared on the forefoot during there was such a thing for the outer ray (V) at the hind foot. A similar observation was made with the early horse representative Sifrhippus . The central ray (III) in each case had the largest dimensions, typically for odd-toed ungulates. At the forefoot it clearly exceeded the second, which was again larger than the fourth. The situation was similar at the hind foot. In accordance with other equine shapes, a sagittal spine was formed at the lower joint end of the metapodia . The terminal phalanges of both fore and hind feet had split tips. In general, the hind feet showed larger dimensions than the front feet.

Fossil finds

Skeleton of Eurohippus from the Messel Pit

Finds of Eurohippus have been found in Central and Western Europe and date to the Middle to Upper Eocene . The earliest fossils were discovered at Argenton-sur-Creuse in France in the early 19th century . The most important find, however, is the Messel mine near Darmstadt , which is assigned to the Geiseltalium and where at least 43 skeletons, some of them almost complete, have survived due to the storage in oil shale. This makes Eurohippus the most common representative of the equine species there, with evidence of individuals of both sexes and different ages. Finds by Eurohippus from the Geiseltal south-west of Halle are documented quite numerous . The finds are distributed over the entire stratigraphic sequence with individual finds from the lower coal and a greater dominance in the middle and upper coal. The chronological order of the lower coal corresponds roughly to that of the Messel pit, the middle and upper coal are somewhat younger. Mainly remains of skulls and teeth were found here, the total number is about three dozen objects. Other finds with teeth and upper jaw fragments come from the Prince of Hesse pit , also near Darmstadt. The latest and northernmost finds in Europe include those from Fürstenau in Lower Saxony and Ghent in Belgium , although they only contain isolated teeth.

Paleobiology

Eurohippus lived in the tropical forests, which is shown above all by the finds from the Messel pit, where the species' habitat can be reconstructed using the excellently preserved flora. Here the animals lived as bush hats, as their body shape suggests. They mainly nourished themselves on soft vegetable food ( browsing ), which is proven by the low-crowned molars with their partly bumpy surface structure. Investigations of the stomach contents from Messel, which have also been excellently handed down, revealed leaf remains of at least twelve different species of laurel family , and five other plant families such as hickory nut tree , figs , myrtle and dog poison plants could be identified. Further investigations also revealed innumerable grains of grapevine plants . This shows that fruits also still had a considerable share in the food spectrum. The food ingested may have been digested in the rectum , as in today's horses, with the participation of numerous microorganisms . This is suggested by the findings of an animal from the Messel pit, which, through bacteriography of the internal organs, shows a large appendix in the area of ​​the lumbar spine, in which plant material is still preserved. Something similar could also be proven in the closely related genus Hallensia .

The uterus of Eurohippus , recognizable in the photo as a black shadow; the arrows point to the folded structures of the former surface
pregnant mare by Eurohippus with fetus in the X-ray

In addition, traces of other organs could also be identified. This includes the uterus, also in the lumbar region, which is similar in structure to today's horses and had a multilayered wall. Occasionally wrinkled structures can be seen in the wall, which refer to analogous formations in recent highly pregnant horse mares. The uterus itself is connected to the loin and pelvis by the broad ligament of the mother , like today's horses. In at least half a dozen of Eurohippus mares from the Messel pit , there were still indications of a fetus in the area of ​​the uterus . The number and arrangement of the bones speak for singular fetuses, so that the females of Eurohippus, like today's horses, only gave birth to one foal per birth. This is typical for a close mother-young social association during the rearing period and is referred to as the k-strategy in reproduction, in which the parent animal invests a lot of time and energy in rearing the offspring. A comparable finding is available from an animal of the genus Propalaeotherium from the Eckfelder Maar , so that this can be regarded as typical for the earliest representatives of the equine relationship. Furthermore, due to the bacterial tracing of the former soft tissues, it is known that Eurohippus had tassel-shaped tail hair and that the ears were rather short as in wild horses and not as long and bag-shaped as in today's donkeys and zebras .

An approximately equal number of female and male individuals has been recorded for the Messel Pit. A balanced gender ratio can be traced back to a social structure in which stallions have not yet played such a dominant role as is the case with today's wild horses. Accordingly, there was probably no “harem structure” that only emerged with the emergence of more open landscapes and the greater threat from predators that this entailed . This is also supported by individual anatomical features in Eurohippus, such as the relatively similar body sizes in stallions and mares and the canines, which differ only slightly in their dimensions. A distinctive gender dimorphism , however, exists in the structure of the pelvis. The pelvic canal in mares is wider than in stallions, in which the opening is narrowed by protrusions of the iliac bone .

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

Eurohippus is a genus from the superfamily of the Equoidea (equine species) and the subordination of the Hippomorpha within the order of the odd ungulate (Perissodactyla). There are different views on the taxonomic position of the genus within the Equoidea. In his first description of Eurohippus in 2006, Jens Lorenz Franzen favored an assignment to the family of Equidae and thus to the early relationship of today's horses ( Equus ). He placed Eurohippus in the subfamily of Hyracotheriinae with a closer relationship to Hyracotherium , Propalaeotherium and Lophiotherium . However, the position of this subfamily and the forms it contains within the Equidae is controversial and is mainly advocated by Central European researchers, who see them as the base group in the development of horses. Other, often Anglo-American researchers, on the other hand, prefer an assignment of the hyracotheriine horse forms within the family of Palaeotheriidae , which are largely only known from Eurasia and form the sister group of the Equidae. More recently, however, there have also been votes for an assignment of the Hyracotheriinae to the horses. The difference between the Palaeotheriidae and the early representatives of the horses lies in the partly higher crowns on the molars, a larger nasal cavity, longer vertebral bodies and, compared to the metatarsals, longer metacarpal bones . The internal structure of the Palaeotheriidae (and the early equine relationship in general) is complex and not yet fully understood. Several phylogenetic analyzes see Eurohippus, together with Lophiotherium, facing a clade composed of Propalaeotherium , Palaeotherium and Plagiolophus . Both of the latter representatives form the subfamily of the Palaeotheriinae and together with the two genera mentioned first form the crown group of the Palaeotheriidae. Other, more primitive members such as Pachynolophus are positioned further out (and belong to the subfamily of the Pachynolophinae). In contrast, Franzen derived Eurohippus in 2006 from Pachynolophus and Propalaeotherium from Propachynolophus .

A distinction is made between two types,

The genus Eurohippus was first scientifically described in 2006 by Jens Lorenz Franzen. The name is derived from the continent of Europe and the Latin name hippus for "horse". The first fossil discoveries in terms of research history came to light as early as 1849 in Les Prunes near Argenton-sur-Creuse , (France) and were described by Charles Léopold Laurillard as Lophiodon parvulum . Ludwig Rütimeyer equated this with Propalaeotherium in 1891 and called it P. parvulum . The holotype represents a single first upper molar. In 1925 Oskar Haupt introduced the species Lophiotherium messelense , which was renamed Propalaeotherium messelense in 1965 and synonymized with P. parvulum in 1981 . The lectotype is a largely headless skeleton (copy number HLMD-Me 58, originally 4358) from the Messel mine, which was only determined by Franzen in 2006, but is shown in Haupt's first publication; Some upper and lower jaw fragments are assigned to this skeleton. The genus Eurohippus was split off from Propalaeotherium due to different anatomical features in the skull and skeleton structure as well as in the dentition. Initially, Franzen only listed the two now recognized representatives as subspecies of E. parvulus , but later he established an independent species with E. messelensis . A study from 2020, on the other hand, doubts the independence of Eurohippus compared to Propalaeotherium and cites a lack of statistical reliability as the reason of the separating characteristics.

literature

  • 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 ( [2] )
  • Jens Lorenz Franzen and Jörg Habersetzer: Complete skeleton of Eurohippus messelensis (Mammalia, Perissodactyla, Equoidea) from the early middle Eocene of Grube Messel (Germany). Palaeobiodiversity and Palaeoenvironments 97 (1), 2017, pp. 1–26
  • 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 d e Jens Lorenz Franzen and Jörg Habersetzer: Complete skeleton of Eurohippus messelensis (Mammalia, Perissodactyla, Equoidea) from the early middle Eocene of Grube Messel (Germany). Palaeobiodiversity and Palaeoenvironments 97 (1), 2017, pp. 1–26
  3. ↑ a b c 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 ( [1] )
  4. ↑ a b c d e f Jens Lorenz Franzen: The primeval horses of the dawn. Munich, 2007, pp. 45-73
  5. ↑ a b 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
  6. ↑ 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
  7. ↑ Jens Lorenz Franzen: Eurohippus parvulus parvulus (Mammalia, Equidae) from the Prince of Hesse pit near Darmstadt (southern Hesse Germany). Senckenbergiana lethaea 86 (2), 2006, pp. 265-269
  8. ↑ Jens Lorenz Franzen and Thomas Mörs: The northernmost occurrence of palaeogenic mammals in Europe. Paläontologische Zeitschrift 81 (4), 2007, pp. 447–456
  9. ↑ Wighart von Koenigswald and Friedemann Schaarschmidt: A primeval horse from Messel that ate grapevines. Natur und Museum 113 (3), 1983, pp. 79-84
  10. ↑ a b c d 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
  11. ↑ 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
  12. ↑ Jens Lorenz Franzen, Christine Aurich and Jörg Habersetzer: Description of a Well Preserved Fetus of the European Eocene Equoid Eurohippus messelensis. PLoS ONE 10 (10), 2015, p. E0137985 doi: 10.1371 / journal.pone.0137985
  13. ↑ a b c d e 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. ^ A b 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
  15. ^ Robert L. Evander: Phylogeny of family Equidae. In: Donald R. Prothero and RM Schoch (Eds.): The evolution of the Perissodactyls. New-York 1989, pp. 109-126
  16. ↑ 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
  17. ^ Matthew C. Mihlbachler, Florent Rivals, Nikos Solounias and Gina M. Semperbon: Dietary Change and Evolution of Horses in North America. Science 331, 2011, pp. 1178-1181
  18. ^ Jens Lorenz Franzen: Origin and systematic position of the Palaeotheriidae. In: Donald R. Prothero and RM Schoch (Eds.): The evolution of the Perissodactyls. New-York 1989, pp. 102-108
  19. ↑ Jens Lorenz Franzen: The Equoidea of ​​the European Middle Eocene (Geiseltalium). Hallesches Jahrbuch für Geoswissenschaften B17, 1995, pp. 31–45
  20. ↑ Laure Danilo, Jean A. Remy, Monique Vianey-Liaud, Bernard Marandat, Jean Sudre and Fabrice Lihoreau: A New Eocene Locality in Southern France Sheds Light on the Basal Radiation of Palaeotheriidae (Mammalia, Perissodactyla, Equoidea) Journal of Vertebrate Paleontology 33 (1), 2013, pp. 195-215
  21. ↑ 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

Web links

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