Saghatherium

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Saghatherium
Lower jaw fragment from Saghatherium

Lower jaw fragment from Saghatherium

Temporal occurrence
Upper Eocene to Lower Oligocene
34 to 30 million years
Locations
Systematics
Higher mammals (Eutheria)
Afrotheria
Paenungulata
Schliefer (Hyracoidea)
Saghatheriidae
Saghatherium
Scientific name
Saghatherium
Andrews & Beadnell , 1902

Saghatherium is an extinct genus of hyrax thatlived in northern Africa and the Arabian Peninsula in the late Upper Eocene and Lower Oligocene 34 to 30 million years ago. The oldest finds in terms of research history are known from the important fossil deposit of Fayyum in Egypt , where the genus is relatively common. Outstanding remains in the form of complete skeletons come from Libya . The animals resembled today's snakes, but were on average slightly larger. It is noteworthy that claws instead of hooves were formed on the front and rear feet. The entire musculoskeletal system can beassumed toadapt to rapid locomotion in the toe , which differs significantly from today's Schläfer. With the discovery of complete skeletons of palaeogenic representatives of the hyrax, some features in the body skeleton that were previously considered relatively modern can be traced back to a more original blueprint. The genus was first described in 1902 using fossils from the Fayyum.

features

Saghatherium was a small form of hyrax, roughly comparable to a modern representative. A head-torso length of 45 to 50 cm is reconstructed on the basis of a not completely complete skeleton of an adult animal from Jebel al Hasawnah in Libya , for a young animal the corresponding value is around 46 cm. The body weight was estimated at 6.5 to 12 kg, which is slightly above the average of today's hyrax. In the entire body structure, Saghatherium largely corresponds to the recent slivers. The skull ranged in length from 9.6 to 11.5 cm. In general, the skull was elongated and narrow. He had a pulled out rostrum , accordingly the nasal bone was relatively long, sometimes it protruded beyond the front teeth. There was a broad contact between the upper jaw and the frontal bone , which is to be regarded as an original feature of the sleepers and possibly resulted from the position of the orbit , which was set far back . In Saghatherium, this was located above the second molar ; in today's snakes, the eye window is above the premolars . The orbit had a diameter of around 20 mm; the postorbital process on its posterior margin, unlike the more recent sacs, was formed only from the frontal bone. In comparison to the latter, the infraorbital foramen in Saghatherium was also relatively large. The zygomatic arch had a sturdy structure and was largely formed by the zygomatic bone . The ear opening pointed downward, there was no bony external auditory canal . The scaled part of the temporal bone above was clearly swollen. A crest rose on the back of the skull .

Lower jaw fragment from Saghatherium

The lower jaw was relatively sturdy and 7.7 to 9.7 cm long. The horizontal bone body was 1.6 to 1.8 cm high in the area of ​​the first molar . The symphysis was closed and relatively short, it reached about as far as the canine . The ascending branch inclined slightly backwards, the crown process was relatively small and lay slightly above the articular process, significantly higher than in today's Klippschliefern . The angular process had a rounded shape. In contrast to numerous other palaeogeneic hives, Saghatherium largely lacked an air-filled chamber in the lower jaw, the opening of which was mostly on the tongue side of the horizontal bone. The teeth had the original tooth number of higher mammals , and thus consisted of 44 teeth, the dental formula was: . In the upper dentition, the incisors and the canines were separated from each other by short diastemata . The inner incisor of the upper row of teeth was reminiscent of a tusks, in large individuals it reached a length of 12.7 mm. In the lower jaw, the second incisor was enlarged, and in some forms the first also. The appearance of the small canine corresponded to the subsequent anterior premolars and was therefore premolariform . The premolars increased in complexity from anterior to posterior; the posterior ones largely resembled the molars. The molars had low ( brachyodonte ) crowns and a bunoselenodontes chewing surface pattern, that is, there were small, flat humps between which crescent-shaped ridges were formed along the cheek side of the tooth. On the tongue side there were sometimes small folds, but the feature is not quite as pronounced as in the related selenohyrax . The length of the upper and lower row of teeth from the first incisor to the last molar was 6.9 cm each, of which the molars each took up about a third. the largest tooth in the rear dentition was the last molar with a length of 1.4 (above) and 1.6 cm (below).

The postcranial skeletal structure of Saghatherium is almost completely known. The spine was characterized by the higher number of thoracic and lumbar vertebrae typical of Afrotheria . However, this was lower than with today's hyrax, since Saghatherium had only 17 thoracic and 8 lumbar vertebrae, the recent species have 19 to 22 or 7 to 9. The number of caudal vertebrae is unknown, today's hyrax are short-tailed with 5 to 7 caudal vertebrae. The musculoskeletal system was characterized by longer limbs compared to today's sleepers. The humerus was up to 9.2 cm long, the higher position of the great rolling hill compared to the joint head, a reduced deltopectoral ridge as a muscle attachment point on the shaft, which expanded further down (distal), and a comparatively narrow one were striking developed elbow joint. However, the outer (lateral) joint role was shown to be relatively strong. As in today's snakes, the ulna and radius were not fused together, but in the latter they are very close together. Compared to Saghatherium, these have a significantly longer olecranon , the upper articular process of the ulna. The entire ulna reached a length of 9 cm in the fossil hyrax, the proportion of the functional section was around 80%, with today's species it is an average of 75%. The thigh bone has so far only been handed down in fragments in Saghatherium . The tibia and fibula , on the other hand, are completely present. They were not grown together, the former was 8.3 cm long in a young animal. Both bones hardly differed from those of today's hyrax. The ankle was also similar to that of the recent species, the furrows on the underside of the shin to the joint with the ankle were flat. However, individual differences had also developed, such as the position of the inner malleolus at the lower end of the tibia, which in Saghatherium was pointing downwards, but is pointing forward in today's snakes. The hand had five rays at Saghatherium , the inner finger (thumb) was not reduced, unlike today's shape. In contrast, the foot had three toes, and the inner and outer rays were receded, which is in accordance with the current species. A striking characteristic of the hyrax is the serial ( taxeopode ) arrangement of the carpal and tarsal bones , that is, the individual bones lay in rows and only minimally linked to neighboring root bones. The distal root bones were only connected to one or two of the subsequent metapodia. The same structure existed with Saghatherium . The main axis of the hand and foot also ran through the central ray (III), so that both had a mesaxonic structure, a feature that the hyrax share with the odd-toed ungulates , also in accordance with the more recent hawks . The metacarpal and metatarsal bones were elongated in a columnar fashion, with lengths of 3.3 and 3.8 cm at the powerful central ray, respectively. The laterally arranged metapodia became correspondingly shorter. The individual hand and finger joints also had an elongated shape. The last phalanx in each case was noticeable, on the one hand it was significantly larger in relation to the penultimate in Saghatherium , on the other hand, unlike today's Schliefern, it had a deep, V-shaped notch at the end. The notch indicates that claws were formed on the hands and feet. In contrast to this, the terminal phalanges in the recent species are significantly shorter, wider and transformed into hooves, the only exception being the second hind foot toe, which is equipped with a claw.

Fossil finds

Saghatherium is known from paleogenic deposits in northern Africa and the Arabian Peninsula . The most extensive fossil material so far was discovered in the Fayyum in northern Egypt , one of the most important fossil sites in Africa. In the 12,000 square kilometer area west of the Nile valley , around 80 kilometers south of Cairo several fossil-bearing rock units are open, the bottom-up Birket-Qarun formation which, Qasr el Sagha Formation and the Gebel-Qatrani lineup include . The three formations form a several hundred meters thick sequence of alluvial formed of sand and clay / silt , mainly still at the bottom of a certain marine show influence. The series is overlaid by the Widan el Faras basalt . With the help of radiometric dating methods, the basalt current could be determined to an age of 23.6 to 31.0 million years, which corresponds to the Oligocene . The lower limit is the Gehannam Formation , which is of purely marine origin and biostratigraphically belongs to the Middle Eocene around 38 to 39.5 million years ago. Accordingly, the entire sediment sequence of the Fayyum originated in the transition from the Upper Eocene to the Lower Oligocene. The more than 100 known outcrops and sites in the Fayyum produce an immensely extensive fossil community consisting of terrestrial and marine organisms, which include plants, remains of fish , reptiles , birds and mammals and which form a tropical to subtropical biotope on the edge of the former Tethys Reconstruct the ocean . The oldest Saghatherium finds came to light in an outcrop near the base of the Gebel-Qatrani Formation (locality L-41 ) and date to the end of the Upper Eocene with a magnetostratigraphically determined age of around 34 million years. In the following section of the lower part of the formation, the genus of hybrids is relatively common. In terms of research history, it is one of the first known finds of slates that were recovered at the turn of the 19th and 20th centuries. In the upper part of the Gebel-Qatrani formation it could only be detected in the 1990s. Finds here come from locality V , which dates a little younger than 32 million years. The entire finds from Saghatherium in the Fayyum are composed of numerous skull and lower jaw fragments as well as individual teeth and belong to three different species.

The finds from the Jebel al-Hasawnah site in Libya are outstanding . Jebel al-Hasawnah is one of the few fossil sites in Paleogene Africa from which articulated skeletons of land-dwelling mammals have come down to us. The remains of Titanohyrax , a gigantic form of hyrax, and also of frogs and fish were briefly mentioned for the first time in 1978 . In the 1990s, an amateur seeker discovered a total of four Saghatherium skeletons , which for the first time offer a glimpse into the postcranial skeletal structure of a fossil sleeper - previously only individual elements of the body skeleton were known. The preservation of the fossil material is so good that even the cartilaginous ends of the ribs are preserved. With the skeleton finds it was also possible to show that the early hyrax, like today's forms, had a taxeopod foot structure, and they also showed that the reduction of the lateral inner and outer rays and thus the formation of a mesaxonic foot very early in evolution the hyrax began. The material was stored in limestones of the Tarab Formation , which can be seen as relics of a former lake. Based on comparisons with the fauna of the Fayyum, an age can be assumed to be in the Lower Oligocene. Individual teeth that can be assigned to Saghatherium have been reported from the Arabian Peninsula, which was connected to the African mainland in the Paleogene . These include two molars from the Ashawq formation near Thaytiniti in the Dhofar governorate on the southwest coast of the Sultanate of Oman . The age of the finds correlates roughly with that of the Fayyum and should therefore also correspond to the Lower Oligocene with absolute age values ​​between 34 and 30 million years.

Paleobiology

The body skeleton of Saghatherium is largely similar to that of today's hyrax. Differences exist in the average larger body dimensions, some special skull features such as a longer nasal bone and the absence of the external auditory canal as well as features of the hand and foot skeleton. The latter have relatively longer bone elements ( metapodia and phalanges ) than today's hyraxes, and the hand characteristically has a thumb , which the recent representatives lack. Hands and feet each end in pointed claws and not in broad hooves, as is the case with today's snakes . In the latter, only the inner toe (ray II) of the hind feet is equipped with a claw that serves as a cleaning claw . Above all, the structure of the foot, due to the length of the individual bones, speaks in favor of an adaptation to rapid locomotion ( cursorial ), which was more pronounced than in today's species. In addition, the animals walked in toe gait , which also differs from today's snakes with their secondary sole gait. The toe gait of Saghatherium is indicated by the relatively short length of the heel bone compared to the metatarsal bones , especially that of the third ray. At the forefoot, the metacarpal bone of the median ray corresponds to about 38% of the humerus length, which is significantly more than in some primeval ungulates such as Phenacodus and comes close to the value of some basal odd ungulates such as Homogalax or Hyracotherium . In addition, the metapodia are generally columnar and the phalanges are rather slender and not wide, which also supports a toe walk. However, differences to other fast-moving mammals can be found in the structure of the ankle bone , since in the latter the joint surfaces of the talus are about the same size and the indentation in the middle between them is more pronounced, which promotes the longitudinal movement and prevents the foot from slipping sideways. The adaptations to rapid locomotion in Saghatherium are not as extreme as in Antilohyrax , another palaeogenic representative of the hyrax, in which parts of the posterior musculoskeletal system have been handed down. Antilohyrax also has an overgrown tibia and fibula as well as an approximately saddle-shaped connection of the ankle bone to the scaphoid bone , which is similar to today's antelopes with strong jumping ability such as springboks .

The bunoselenodonte chewing surface pattern of the rear molars distinguishes Saghatherium as a specialized herbivore. What is striking are the very large molars compared to the premolars, which also have strong ridges between the individual cusps and have distinctive grooves. Saghatherium was probably adapted to food that had to be crushed and ground, such as seeds , nuts or pods .

A striking gender dimorphism is remarkable . In two of the three known species, S. antiquum and S. bowni , there are variations in size, which are most clearly recognizable in the size of the molars and the solidity of the lower jaw and which obviously separate the two sexes. In S. antiquum, the horizontal bone body of males below the second molar can be almost twice as high as that of females. With many other fossil slivers from the Fayyum, on the other hand, no such differences in size can be measured, so that both sexes probably had similar body dimensions. Here the sexual dimorphism is expressed in the variable formation of an opening in the lower jaw, which is located on the inside of the horizontal bone below the third molar and leads into a large, air-filled chamber. This opening does not occur in today's Schliefern as well as in S. antiquum and S. bowni . The function of the lower jaw window is unknown, but it is assumed that the opening and the cavity acted as a resonance chamber during the vocalization. In most of the cases examined, the formation of a lower jaw window and the adjoining chamber are connected with enlarged external incisors, the latter being a characteristic of male animals in today's snakes. It should be emphasized that in the third species of Saghatherium , S. humarum , there is also a cavity in the lower jaw, but investigations into sexual dimorphism are not yet available. It is possible that the different forms of sexual dimorphism in the sleepers can be traced back to different patterns in mating behavior.

Systematics

Internal classification of the early hyrax according to Pickford 2015
  Hyracoidea  


 Seggeurius


   

 Namahyrax


   

 Dimaitherium




   

 Microhyrax


   


 Bunohyrax


   

 Pachyhyrax


   

 Thyrohyrax


   



 Selenohyrax


   

 Saghatherium



   


 Rupestrohyrax


   

 Titanohyrax



   

 Antilohyrax




   

 Megalohyrax






   

 Geniohyus





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Saghatherium is a genus from the extinct family of Saghatheriidae within the order of Hyraxes (Hyracoidea). In general, the hyraxes are related to the elephants and manatees , all three groups together form the Paenungulata within the parentage of the Afrotheria . The Saghatheriidae are early forms of hyrax that first appeared in northern Africa in the Eocene . Together with the Geniohyidae and the Titanohyracidae , they belong to the first radiation phase of the order, which took place entirely in Africa and lasted largely up to the Oligocene . It produced representatives rich in forms and variants with numerous adaptations to different biotopes . In the fossil record of these epochs, the individual genera and species of the Saghatheriidae are among the most frequently found members of the hyrax. The family includes small to medium-sized animals, which are characterized by low-crowned molars with a bunoselenodont chewing surface pattern. In contrast to the Titanohyracidae, the ridges between the cusps on the molars were not so clearly developed, while the more primitive Geniohyidae had a purely bunodontic (humped or humped) chewing surface pattern. In some cases, the Saghatheriidae are closely related to today's snakes because, in contrast to the other early forms of hyrax, they already had a significantly shortened skull and a similarly constructed ankle bone . For this reason, according to some scientists, together with the recent family of the Procaviidae (and the extinct Pliohyracidae ) they form the suborder of the Procaviamorpha , while all other families belong to the Pseudhippomorpha . Within the Saghatheriidae, among other things, Selenohyrax can be counted among the closest relatives of Saghatherium , a little further outside there is possibly Thyrohyrax .

A total of three types are recognized today:

In the first 30 years of the 20th century in particular, numerous other species from the Fayyum were described, such as S. annectens , S. euryodon , S. macrodon , S. magnus , S. majus , S. minus and S. sobrina . Today these are usually taken as synonyms of S. antiquum .

The first scientific description of Saghatherium was in 1902 by Charles William Andrews and Hugh John Llewellyn Beadnell . For this they used a damaged skull with a well-preserved row of teeth from the lower sections of the Gebel-Qatrani formation of the Fayyum , which is considered a holotype (copy number CGM 8635). The generic name refers to the ancient Egyptian ruin Qasr el Sagha ("Temple of the Goldsmith"), which is in the immediate vicinity of the site, and to the Greek word θηρίον ( thērion ) for "animal".

The discovery of the skeletons of Saghatherium at the Jebel al-Hasawnah site is of great importance for research into the tribal history of the hyrax, as this gives an insight into the complete skeleton structure of a palaeogenic representative of the hyrax for the first time. Both hand and foot show the typical taxeopode or serial arrangement of the root bones, which is a common feature of all Paenungulata and also occurs in today's elephants. This arrangement of bones, which enables the hand and foot to rotate in the area of ​​the metapodia and which enables today's hyrax to climb despite the lack of claws, was originally only suspected for extinct hybrids. According to the findings of Jebel al-Hasawnah, however, it belongs to a characteristic developed very early in the order. In addition, the skeletons showed that the reduction of the outer and inner toes on the feet and the formation of a mesaxonic toe position is also a relatively early development within the hyrax. The mesaxonische Fußbau misled some scholars in the past to the Hyrax near the Unpaarhufer classify. Accordingly, the serial arrangement of the carpal and tarsal bones was sometimes also seen as a derived feature of the recent hyrax , which had formed secondarily from the diplarthral or alternating arrangement of the bones in the odd- toed ungulates as a special adaptation to a climbing lifestyle. Finally, the proven adaptation of Saghatherium to a toe gait and the formation of claws instead of hooves could also represent an original feature. As a result, the hooves of today's hyrax developed later, while the cleaning claw on the hind foot is a relic. Experts had previously assumed the opposite development.

literature

  • Emmanuel Gheerbrant, Stéphane Peigné and Herbert Thomas: Première description du squelette d'un hyracoide paléogène: Saghatherium antiquum de l'Oligocène inférieur de Jebel al Hasawnah, Libye. Palaeontographica A 279 (4-6), 2007, pp. 93-145
  • D. Tab Rasmussen and Mercedes Gutiérrez: Hyracoidea. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 123-145

Individual evidence

  1. ↑ a b c d e f g Emmanuel Gheerbrant, Stéphane Peigné and Herbert Thomas: Première description du squelette d'un hyracoide paléogène: Saghatherium antiquum de l'Oligocène inférieur de Jebel al Hasawnah, Libye. Palaeontographica A 279 (4-6), 2007, pp. 93-145
  2. ^ Gary T. Schwartz, D. Tab Rasmussen and Richard J. Smith: Body-size diversity and community structure of fossil hyracoids. Journal of Mammalogy 76 (4), 1995, pp. 1088-1099
  3. ↑ a b c d e f D. Tab Rasmussen and EL Simons: The oldest hyracoids (Mammalia: Pliohyracidae): new species of Saghatherium and Thyrohyrax from the Fayum. New Yearbook for Geology and Paleontology Abhandlungen 182, 1991, pp. 187-209
  4. ↑ a b c d e f Herbert Thomas, Emmanuel Gheerbrant and Jean-Michel Pacaud: Découverte de squelettes subcomplets de mammifères (Hyracoidea) dans le Paléogène d'Afrique (Libye). Comptes Rendus Palevol 3, 2004, pp. 209-217
  5. ↑ John Kappelman, Elwyn L. Simons and Carl C. Swisher III: New Age Determinations for the Eocene-Oligocene Boundary Sediments in the Fayum Depression, Northern Egypt. Journal of Geology 100 (6), 1992, pp. 647-667
  6. ↑ a b c Erik R. Seiffert: Revised age estimates for the later Paleogene mammal faunas of Egypt and Oman. PNAS 103, 2006, pp. 5000-5005
  7. ^ A b Erik R. Seiffert, Thomas M. Bown, William C. Clyde and Elwyn Simons: Geology, Paleoenvironment, and Age of Birket Qarun Locality 2 (BQ-2), Fayum Depression, Egypt. In: JG Fleagle and CC Gilbert (Eds.): Elwyn L Simons: a search for origins. New York, 2008, pp. 71-86
  8. ↑ Thomas M. Bown, Mary J. Kraus, Scott L. Wing, John G. Fleagle, Bruce H. Tiffney, Elwyn L. Simons, and Carl F. Vondra: The Faywn Primate Forest Revisited. US Geological Survey Professional Paper 1452, 1988, pp. 1-60
  9. ↑ a b Thomas M. Bown and Mary J. Kraus: Geology and Paleoenvironment of the Oligocene Jebel Qatrani Formation and Adjacent Rocks, Fayum Depression, Egypt. Journal of Human Evolution 11, 1982, pp. 603-632
  10. ^ A b Charles William Andrews and Hugh John Llewellyn Beadnell: A preliminary note on some new mammals from the Upper Eocene of Egypt. Survey Department, Public Works Ministry, Cairo, 1902, pp. 1-9
  11. ^ Charles W. Andrews: A descriptive catalog of the Tertiary Vertebrata of the Fayum, Egypt. London, 1907, pp. 1–324 (pp. 84–91)
  12. ^ A b D. Tab Rasmussen and EL Simons: New Oligocene hyracoids from Egypt. Journal of Vertebrate Paleontology 8, 1988, pp. 67-83
  13. ↑ a b c d D. Tab Rasmussen and Mercedes Gutiérrez: Hyracoidea. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 123-145
  14. ↑ Martin Pickford, Herbert Thomas, Sevket Sen, Jack Roger, Emmanuel Gheerbrant and Zaher Al-Sulaimani: Early Oligocene Hyracoidea (Mammalia) from Thaytiniti and Taqah, Dhofar Province, Sultanate of Oman. Comptes Rendus de l'Académie des Sciences Series II 318, 1994. pp. 1395-1400
  15. ↑ D. Tab Rasmussen: The evolution of the Hyracoidea: A review of the fossil evidence. In: Donald R. Prothero and R. Schoch (Eds.): The evolution of Perissodactyls. New York, Oxford University Press, 1989, pp. 57-78
  16. ↑ Rodolphe Tabuce: A mandible of the hyracoid mammal Titanohyrax andrewsi in the collections of the Muséum National d'Histoire Naturelle, Paris (France) with a reassessment of the species. Palaeovertebrata 40 (1), 2016, p. E4 doi: 10.18563 / pv.40.1.e4
  17. ↑ Donald D. de Blieux, Michael R. Baumrind, Elwyn L. Simons, Prithijit S. Chathrath, Grant E. Meyer and Yousry S. Attia: Sexual dimorphism of the internal mandibular chamber in Fayum Pliohyracidae (Mammalia). Journal of Vertebrate Paleontology 26 (1), 2006, pp. 160-169
  18. ↑ Martin Pickford: New Titanohyracidae (Hyracoidea: Afrotheria) from the Late Eocene of Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 200–214
  19. ^ Martin Pickford, Salvador Moyà Solà and Pierre Mein: A revised phylogeny of the Hyracoidea (Mammalia) based on new specimens of Pliohyracidae from Africa and Europe. New Yearbook for Geology and Paleontology, Treatises 205 (2), 1997, pp. 265–288
  20. ↑ Martin Pickford: Revision of the Early Miocene Hyracoidea (Mammalia) of East Africa. Comptes Rendus Palevol 3, 2004, pp. 675-690
  21. ↑ D. Tab Rasmussen, Mario Gagnon and Elwyn S. Simons: Taxeopody in the carpus and tarsus of Oligocene Pliohyracidae (Mammalia: Hyracoidea) and the phyletic position of Hyraxes. PNAS 87, 1990, pp. 4688-4691
  22. ↑ Martin S. Fischer: Hyracoids, the sister group of perissodactyls. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of perissodactyls. New York and London 1989, pp. 37-56