Titanohyrax

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Titanohyrax
Titanohyrax molars

Titanohyrax molars

Temporal occurrence
Middle Eocene to Lower Oligocene
48 to 28 million years
Locations
Systematics
Higher mammals (Eutheria)
Afrotheria
Paenungulata
Schliefer (Hyracoidea)
Titanohyracidae
Titanohyrax
Scientific name
Titanohyrax
Matsumoto , 1921

Titanohyrax is an extinct genus from the order of the hyrax . Within the hyrax it belongs to an early line of development. The animals lived from the Middle Eocene to the Lower Oligocene , which covers the period from 48 to 28 million years ago. The find material consists largely of fragmented parts of the dentition and the skull and comes from various sites in northern Africa . The site of the Fayyum in Egypt is outstanding. This contained the most extensive and historically oldest material to date, it was also used to establish the genus in 1921. Titanohyrax includes several species. These are medium to very large representatives of the hyrax. The largest forms reached the size of small rhinos and represent the largest hyrax of their time. However, individual differences in the dimensions and anatomy within the species can be determined, which is possibly due to a sexual dimorphism .

features

Titanohyrax is a very large representative of the hyrax. The largest individuals weighed around a ton, making them one of the largest known hyrax forms. The size variation within the genus is however considerable. The found material on which the genus is based consists mainly of fragmented dentition and skull parts. Found postcranial remains have not yet been scientifically processed. According to the diagnosable skull features on the existing fragments, Titanohyrax had a short rostrum , which is consistent with other Titanohyraciden, but differs from the other early snouts with their rather long snouts. The symphysis combined as with all hyraxes, the two halves of the lower jaw firmly together. It was very strong and reached back to the second premolar . At the front, the lower edge was oriented steeply upwards. One mental foramen opened below the second premolar, another at the level of the last premolar or first molar . Some lower jaws had an air-filled chamber embedded in the bone below the posterior molar. The ascending branch rose almost vertically above the horizontal bony body. The characteristic is consistent with numerous other early sleepers, but differs from today's sleepers with an ascending branch sloping backwards. The crown and articular processes were close together.

The teeth are not fully known, only more extensive material is available for the posterior teeth. At least the two inner incisors were formed on the lower jaw . These were almost the same size and were of a spatula-like shape, which lacks the typical division into small, comb-like tips of other hyraxes. The diastema to the posterior segment of the teeth was very short in the upper row of teeth, possibly none in the lower row. The premolars were largely similar to the molars and can therefore be referred to as molarized. There were four main cusps on the upper molars, which gave the teeth a bilophodontic structure. The two outer cusps on the lip side (paraconus and metaconus) were connected by a W-shaped shear bar, the ectoloph; it gave the molars a selenodontic character. On the tongue side, the protoconus was inflated, unlike Rupestrohyrax , while the hypoconus had narrowed sides and appeared small. In contrast to this, Megalohyrax had two main humps of approximately the same size on the tongue side. The lower molars were also dominated by four main bumps (paraconid, metaconid, hypoconid, protoconid). In addition, there were individual minor humps such as the metastylid, which is missing in other representatives of the Titanohyracidae and in Megalohyrax , for example . The tooth crowns were relatively high ( hypsodont ), but the feature varied significantly between the individual types of titanohyrax .

Fossil finds

Titanohyrax first appeared in the transition from the Lower to the Middle Eocene about 48 million years ago. An upper jaw fragment and individual isolated upper and lower molars of T. tantulus are available from Chambi in Tunisia , which still refer to a rather small animal. The teeth had relatively low crowns. T. mongereaui can be regarded as almost simultaneous . The species is known from a poorly preserved middle upper molar from Gour Lazib in Algeria , which was, however, significantly larger than corresponding finds from Chambi. Remains of other representatives of Titanohyrax may still be present in Gour Lazib . Gour Lazib forms a complex of sites consisting of over a dozen individual sites. Most of the finds come from the Glib-Zegdou Formation , which is largely composed of fine-grain sedimentary rocks . This early appearance is followed by a long gap with no fossil record of the genus, which spans the entire Middle Eocene.

Only in the Upper Eocene and the following Lower Oligocene is Titanohyrax tangible again. The most extensive fossil material has so far been recovered from the important deposit of Fayyum in northern Egypt . The main discovery area is the Gebel-Qatrani Formation with its fine to coarse clastic sediments of limnic and fluvial origin. The remains of Titanohyrax were stored in various stratigraphic positions, the age of which, according to paleomagnetic investigations, is between 33 and 28.5 million years. They can be assigned to several species and thus give indications of a radiation of the genus during this time, the origins of which are so far unknown. A general characteristic of the species consists in the mostly higher crowns of the molars compared to the earlier forms. The oldest finds here, represented by various tooth remnants and numerous postcranial skeletal elements, refer to a medium-sized and probably rather graceful representative, but a formal description has not yet been given. They came to light at the site L-41 in the lower section of the Gebel-Qatrani Formation and thus still belong to the late Obereocene. The upper section of the rock unit with a Lower Oligocene time position also contained various remains. This includes, but T. angustidens from the branches R , V and I . This smaller to medium-sized form is occupied by several lower and upper jaws. As a special characteristic of the species, the molars were clearly narrow. T. andrewsi, in turn, is based on a relatively large amount of material, composed of lower jaws and individual upper jaw fragments. The largest representative is T. ultimus . So far, however, it has only a few, heavily chewed upper and lower teeth and a fragment of the upper jaw. The tooth crowns of the molars are slightly lower than those of the other later types. For both T. andrewsi and T. ultimus , only little information is available on the exact locations. The reason for this is the early discovery of the remains in terms of research history, for which there was mostly no location documentation. Two finds of T. ultimus were found in later excavations at site I in the uppermost section of the Gebel-Qatrani formation.

From the later radiation phase of Titanohyrax an upper and a lower jaw from the Guerran member of the Samlat Formation in southwestern Morocco , which belongs to the Upper Eocene, were reported. The finds show a mixture of original and modern features and could indicate the beginning of the radiation phase. They also provide information that the genus was not only present in Fayyum, but throughout North Africa during this time. A formal description of the species has not yet taken place.

Paleobiology

The representatives of the genus Titanohyrax show a strong variability in body size, which is expressed in the find material via the size of the teeth. The second upper molar was used as the basis for weight calculations. Early forms such as T. tantulus from the Middle Eocene of Chambi were sometimes very small, the second molar of which was just 1.1 cm in length. However, T. mongereaui from Gour Lazib , which was roughly the same age, had a significantly larger size with a 3.6 cm long central molar. Weight estimates range up to 626 kg. The Lower Oligocene T. angustidens from the Fayyum in Egypt weighed only around 180 kg, which was calculated using the approximately 2.3 cm long second molar. In contrast, the length of the middle molar of T. andrewsi from the same region was 3.3 cm, resulting in an estimated body weight of 430 kg. All of these forms were surpassed by T. ultimus also from the Fayyum. Its second molar was 4.1 cm long and the animals probably weighed 994 kg. Thus providing Titanohyrax the largest known hyrax of Paleogene in Africa. It is only in later times some members reached a different line of development Hyrax with about 1000 to 1300 kg again similar in size, such as Sogdohyrax and Postschizotherium from central and eastern Asia. Both date to the Pliocene . In comparison, today's species of hyrax weigh only 1.5 to 5.5 kg with a corresponding tooth size of the upper second molar of 0.7 to 0.8 cm for very large individuals. Titanohyrax can thus be regarded as a member of the megafauna in northern Africa of the Paleogene. It shared its habitat with other giant mammals of its time such as Arsinoitherium from the group of the Embrithopoda or Barytherium and Palaeomastodon from the group of the proboscis .

In addition to the general size differences between the different types of Titanohyrax , differences within the individual types can also be recognized. This concerns, among other things, T. andrewsi , whose lower jaws are of different masses. Some mandibles have a sturdy horizontal bone body with a height below the second molar of 8 cm, while in others it varies between 3.4 and 4.2 cm. There are also other deviations, such as a more strongly developed angular process on the larger mandibles. In general, larger and more massive lower jaws of a species are associated with male animals and smaller ones with female animals. For T. andrewsi this would mean that males weighed around 430 kg, while females weighed around 240 kg. This results in a size ratio of the sexes of 1.79: 1, which is much stronger than today's Schliefern. In these cases, there are also marked gender differences in various skull features, such as the robustness of the lower jaw and the shape of the upper incisors, but these do not result in any major deviations in overall body size. The ratio in today's snakes is therefore 1.1: 1 compared to males to females. The difference in T. andrewsi also exceeds the sexual dimorphism of numerous ungulates, but is within the range of variation of today's elephants .

Neither T. tantulus nor T. mongereaui or T. ultimus can currently show lower jaws. By T. angustidens some are known to date show little size variations. For this purpose, there is an internal, round, air-filled cavity below the two rear molars in the horizontal bone. Such cavities also occur in other early sleepers, for example in Thyrohyrax or Saghatherium, and in some species they occur exclusively in males, in others in both sexes with different characteristics. Their function is unknown, but some of them are associated with vocalization. Modern hyraxes do not have such a characteristic. There are too few lower jaws of T. angustidens to define this as a sex-differentiating criterion. In addition, they all represent not fully grown individuals, so that no statements can be made about the final form of the structure. It can be summarized, however, that within the early hyraxes there are various and largely independent forms of gender difference: on the one hand the development of internal air-filled chambers in the lower jaw, on the other hand through variations in the solidity of the lower jaw. A different mating behavior of the individual species is assumed to be the explanation for this phenomenon.

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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Titanohyrax is a genus from the extinct family of Titanohyracidae within the order of Hyraxes (Hyracoidea). The hyrax, together with the elephants and manatees, form a kinship group that is known as the Paenungulata and is part of the parentage of the Afrotheria . The Titanohyracidae, in turn, belong to the early forms of hyrax. They are first detectable in the Eocene in northern Africa . Together with the Namahyracidae , the Geniohyidae and the Saghatheriidae they belong to the first radiation phase of the hyrax , which took place in the Palaeogene and was limited to Africa. During this time the hyraxes formed a very diverse group with numerous representatives. These were adapted to the most varied of biotopes . The Titanohyracidae unite medium-sized to very large representatives, some forms such as Titanohyrax reached the dimensions of small rhinos and are among the largest known slivers. Characteristic features of the Titanohyracidae are the shortened snout part of the skull compared to other early sleepers, the typical selenodontic chewing surface pattern of the molars and the highly specialized lower incisors. In the postcranial skeleton, the Titanohyracidae were sometimes adapted to rapid locomotion. Sometimes the Titanohyracidae, together with the Geniohyidae and Namahyracidae, are referred to the subordination of the Pseudhippomorpha , which summarizes the primitive hyrax. As a sister group, it faces the more modern Procaviamorpha with the Saghatheriidae, the Pliohyracidae and the Procaviidae , the latter containing today's hyraxes.

Several species are recognized within the genus Titanohyrax :

The individual species show a drastic variability in body size. Other differences concern, among other things, the crown height of the molars, which is generally lower in early generic members than in later ones. In addition, a hump-like bulge appears on the upper molars of some early species on the cutting ridge between the proto- and paraconus, the so-called "paraconular swelling". Besides the mentioned species were T. palaeotherioides and schlosseri T. further introduced later but mostly with andrewsi T. united. A previously undescribed smaller species is suspected to be in the Upper Eocene of the Fayyum, as well as in the Samlat formation in southwestern Morocco, which is about the same age .

The lower jaw of Titanohyrax first published by Andrews, viewed by him as a possible fossil remnant of Megalohyrax ; A: front row of teeth; B: posterior row of teeth

The first finds of Titanohyrax came to light as early as the turn of the 19th to the 20th century in the Fayyum fossil area , but were not recognized as such. As early as 1904, Charles William Andrews introduced a new species of the genus Megalohyrax called Megalohyrax minor and assigned it a fragment of the upper jaw. He saw a partially preserved lower jaw as a likely fossil remnant of the species. Andrews presented the finds in his comprehensive catalog A descriptive catalog of the Tertiary Vertebrata of the Fayum, Egypt on the fauna of the Fayyum. In 1910 and 1911, Max Schlosser presented a processing of the Fayyum fossils of several German expeditions to the find area. In this he followed Andrews' view only to a limited extent. He divided the finds and kept the lower jaw in the genus Megalohyrax , for the upper jaw with what he believed to be a simpler tooth design, he created the new Mixohyrax shape . A decade later, while working on fossil hyraxes from American and British collections, Hikoshichiro Matsumoto revised the genus Megalohyrax . He came to the conclusion that Schlosser's allocation of the found material was correct, but his deduced assignments were incorrect. Accordingly corresponded Schlosser Mixohyrax the established Andrews Megalohyrax , Schlosser Megalohyrax represented an independent genus. Matsumoto created the name Titanohyrax for this and thus presented the first scientific description of the genus. The name alludes to the enormous size of the animals (after the titans of Greek mythology ). At the same time he recognized with T. andrewsi , T. palaeotherioides , T. schlosseri and T. ultimus in four ways. In 1978 synonymisierte then Grant E. Meyer T. palaeotherioides and T. schlosseri since there are no morphological and metric differences with T. andrewsi . He also transferred the type species from T. palaeotherioides to T. andrewsi , since the original material had been lost in addition to nomenclature problems. Other authors saw this as more problematic. Thus recognized D. Tab Rasmussen and Elwyn L. Simons 1988 T. palaeotherioides be quite different from T. andrewsi on. But they accepted Meyer's argumentation on the nomenclature and reintroduced the species under the new name T. angustidens . during the same period other species were described.

literature

  • Hikoshichiro Matsumoto: Megalohyrax Andrews and Titanohyrax ng - A revision of the genera of Hyracoids from the Fayûm, Egypt. Proceedings of the Zoological Society of London, 1921, pp. 839-850 ( [5] )
  • 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

Individual evidence

  1. ^ A b 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
  2. ↑ a b c d e D. Tab Rasmussen and Elwyn L. Simons: New Oligocene Hyracoids from Egypt. Journal of Vertebrate Paleontology 8 (1), 1988, pp. 67-83
  3. ↑ a b c d e f g h i 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
  4. ^ A b c d Nicholas Court and Jean-Louis Hartenberger: A new species of the hyracoid mammal Titanohyrax from the Eocene of Tunisia. Palaeontology 35 (2), 1992, pp. 309-317
  5. ↑ a b c d e f g h 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
  6. ^ A b c J. Sudre: Nouveaux mammifères éocènes du Sahara occidental. Palaeovertebrata 9, 1979, pp. 83-115
  7. ↑ Rodolphe Tabuce, Anne-Lise Charruault, Mohammed Adaci, Mustapha Bensalah, Mustapha Ben Haj Ali, El Mabrouk Essid, Laurent Marivaux, Monique Vianey Liaud and M'hammed Mahboubi: The early Eocene radiation of Hyracoidea (Mammalia, Afrotheria): New fieldwork evidence from northwestern Africa. In: Thomas Lehmann and Stephan FK 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, pp. 161–162
  8. ↑ a b c d R. Tabuce, S. Adnet, M. Benammi, L. Marivaux, O. Saddiqi, L. Baidder and M. Benammi: A New Titanohyrax species from the Priabonian of Dakhla, bridges a gap in the Morocco record of the 'Giant' Hyracoids (Mammalia). The First West African Craton and Margins International Workshop “WACMA1”, Dakhla, Morocco, 24th to 29th April 2017
  9. ↑ a b c d Hikoshichiro Matsumoto: Megalohyrax Andrews and Titanohyrax ng - A revision of the genera of Hyracoids from the Fayûm, Egypt. Proceedings of the Zoological Society of London, 1921, pp. 839-850 ( [1] )
  10. ↑ a b c Hikoshichiro Matsumoto: Contribution to the knowledge of the fossil Hyracoidea of ​​the Fayum, Egypt, with description of several new species. Bulletin of the American Museum of Natural History 56, 1926, pp. 253-350
  11. ^ A b Grant E. Meyer: Hyracoidea. In: Vincent J. Maglio and HBS Cooke (Eds.): Evolution of African Mammals. Harvard University Press, 1978, pp. 284-314
  12. ↑ Martin Pickford: Fossil hyraxes (Hyracoidea: Mammalia) from the Late Miocene and Plio-Pleistocene of Africa, and the phylogeny of the Procaviidae. Palaeontologia africana 41, 2005, pp. 141-161
  13. ↑ 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
  14. ↑ 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
  15. ↑ Martin Pickford: New Titanohyracidae (Hyracoidea: Afrotheria) from the Late Eocene of Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 200–214
  16. ^ 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
  17. ↑ Martin Pickford: Revision of the Early Miocene Hyracoidea (Mammalia) of East Africa. Comptes Rendus Palevol 3, 2004, pp. 675-690
  18. ^ Charles W. Andrews: Further notes on the mammals of the Eocene of Egypt. Part III. Geological Magazine 5 (1), 1904, pp. 211–215 ( [2] )
  19. ^ Charles W. Andrews: A descriptive catalog of the Tertiary Vertebrata of the Fayum, Egypt. London, 1906, pp. 1–324 (pp. 96–98 and plate 7)
  20. ↑ Max Schlosser: About some fossil mammals from the Oligocene of Egypt. Zoologischer Anzeiger 35, 1910, pp. 500–508 ( [3] )
  21. ^ Max Schlosser: Contributions to the knowledge of the Oligocene land mammals from the Fayum, Egypt. Contributions to the palaeontology and geology of Austria-Hungary and the Orient 24, 1911, pp. 51–167 ( [4] )