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Pliohyrax graecus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Hyracoidea
Family:	†Pliohyracidae
Subfamily:	†Pliohyracinae
Genus:	†Pliohyrax Osborn, 1899
Type species
Leptodon graecus Gaudry, 1862
Species
P. graecus (Gaudry, 1862) P. occidentalis (Viret & Thenius, 1952) P. orientalis (Tong & Huang, 1952) P. rossignoli (Viret, 1947)
Synonyms
Genus synonymy Neoschizotherium Viret, 1947 Sogdohyrax Dubrovo, 1978 Species synonymy Pliohyrax kruppi Osborn, 1899

Pliohyrax, is a genus of hyracoids (the cavy-like group of animals most closely related to elephants and manatees). It grew to sizes greatly exceeding those of any living hyrax, though it was by no means the largest member of this family.

Life restoration

Fossils of this Miocene-Pliocene, scansorial herbivore have been found in Afghanistan, France, and Turkey. In Spain, Pliohyrax graecus is among the large mammals species found in the Almenara site, deposited during the Messinian salinity crisis, together with Macaca sp., Bovidae indet., cf. Nyctereutes sp., and Felidae indet.

History

In 1853, following a field trip in Cyprus, French palaeontologist and geologist Albert Gaudry stopped in Greece on his way back to France, and, on the invitation of the ambassador of France to Greece Alexandre de Forth-Rouen, visited a local fossil site at Pikermi, in the Attica peninsula, near Athens, first visited by German scientists. Gaudry immediatly recognized the importance of the deposits and led, in 1855 and in 1860, two excavation campaigns in Attica under the commission of the French Academy of Science. In Pikermi, Gaudry excavated the fossils of a diverse fauna whose preservation was almost unprecedented in the Neogene of Europe. Among those discoveries figured two large but isolated mandibles belonging to the same adult individual of a yet unknown large species of mammal. In a seminal book published in 1862, Gaudry described these incomplete remains under the name Leptodon graecus, after the slender shape of its molars. At the time of Gaudry, Hyracoids, Proboscideans, Perissodactyls and Artiodactyls were classified together within the order Pachydermata. Gaudry speculated that Leptodon was an extinct member of a clade including the modern rhinoceros and hyraxes.

The relationship between the Pikermi fossils and modern rhinoceros were however eventually contested, as more fossil localities were explored in Greece, particularly in the island of Samos in the Aegean Sea, and more material whose traits ressembled those of Leptodon were unearthed by German-led expeditions. In 1899, Max Schlosser and Karl von Zittel, from Munich, noted that a specimen found in Samos and storaged in the Stuttgart Natural History Cabinet, temporarily named "Hyrax kruppii" in honour of Friedrich Krupp, who had donated the specimen, to be described in the near future as a new genus of giant hyrax, shared several similarities with Leptodon graecus and with an undescribed specimen from Samos possessed by the Munich Palaeontological Museum. Schlosser and Von Zittel found that those remains, probably too similar to each other to belong to different species, belonged to a yet-unknown fossil group of large hyracoids, more closely related to modern hyraxes than to anything else. The same year, Henry Fairfield Osborn described formally the Stuttgart specimen, a very large fragmentary skull reaching twice the size of that of the largest modern hyrax, as Pliohyrax kruppii, a new type of hyracoid warranting the creation of the eponymous family Pliohyracidae, and the first fossil hyracoid known to science.

Finally, in the United Kingdom, Charles Forsyth Major published two papers regarding the genus ; the first, published in November, synonymyzed Leptodon graecus with Pliohyrax kruppi. Leptodon being already in use for a genus of kite, Pliohyrax was to be kept as the genus name, while at the species level the name graecus, given first, had priority over kruppi. The second article covered the anatomy of a new specimen from Samos, acquired in 1894 by the British Museum, firstly attributed by Johann Andreas Wagner to a newly described species of rhinoceros, Rhinoceros pachygnathus, being reassigned as belonging to Leptodon, now Pliohyrax. The specimen had been artificially altered to make it look more complete, but was nonetheless still complete enough to warrant a complete description, definitely prouving that the four then known specimens belonged to the same genus and possibly the same species, owing their differences to individual rather than interspecific variations.

The early 20th century

During the two first decades of the 20th century, the genus was recovered as part of a Saghatheriidae family that included most extinct genera of hyraxes by Charles William Andrews in 1906 and Schlosser in 1911. In 1926, Matsumoto Hikoshichirō proposed the new monotypic family Pliohyracidae, in which he included Pliohyrax, Saghatherium and Pachyhyrax. The inclusion of the latter genus was only tentative, due to its fragmentary nature.

In 1916, Greek paleontologist Theodoros Skoupos led an expedition to Halmyropotamos, near Zarakes, in the Greek island of Euboea, to explore Miocene-aged fossiliferous outcrops. The abundant fossil remains found there, less complete than those of Pikermi and rarely found associated, were then storaged in the cellars of the Athens University Museum. In 1933, Camille Arambourg described formally a new species of Pliohyrax, as P. championi, that he had collected the year prior at Mount Losodok near Turkana Lake in Kenya. While seemingly more closely related to P. graecus from Pikermi, the new species had distinctly more primitive trait, more reminding of Saghatherium.

The 1940s and 1950s

In the aftermath of the Second World War, high demands in coal to reconstruct France led to the reopening of lignite exploitation near Saint-Martin-du-Mont, Ain, in the Soblay locality. There, paleontologists and biologists monitoring the exploitation collected several isolated dental remains, a molar and three premolars, of a new type of animal. In 1947, Jean Viret described several teeth collected by Robert Barone in the locality. Viret constated that the specimens shared several similarities with Postschizotherium, from the Pleistocene of Nihewan, in China, that was, at the time, thought to be a chalicothere. Hence, Viret described the remains as Neoschizotherium, without providing a species name, and thinking that it represented an ancestral form of Postschizotherium. A couple of years later, in 1949, Viret described a second molar discovered among the last fossils extracted in Soblay, superficially ressembling that of Palaeotherium. Viret noted that the teeth anatomy of Postschizotherium and Neoschizotherium went against the evolutionary trends of the chalicotheres and more closely ressembled that of hyracoids. Therefore, he stated that Neoschizotherium was sufficiently similar in shape to Pliohyrax to be included within the genus as its own species, P. rossignoli. During a visit at the University of Lyon, Austrian paleontologist Erich Thenius noticed among indeterminate fossils found in the Pliocene-aged Sables de Montpellier near the eponymous city a single upper molar, that had been tentatively labelled as belonging to Palaeotherium by Maurice Gennevaux, and identified it as belonging to a fossil hyracoïd. In 1952, Thenius and Viret formally described this molar as the holotype specimen of the new species Pliohyrax occidentalis, noting that its shape was intermediate between the molars of the Miocene species of Pliohyrax and those of its Late Pliocene-Early Pleistocene relative Postschizotherium.

The assignation of P. championi to Pliohyrax was challenged in 1954 by Thomas Whitworth, who referred the species to Megalohyrax, as M. championi, due to an abundance of new and better preserved fossil remains belonging to the species being discovered in Rusinga Island and adjacent localities. Whitworth additionaly speculated that the apparition of Pliohyrax in the Hipparion fauna of Europe was only the result of a single island hoping colonisation event and that Eurasian hyraxes were limited to Greece, without taking into account however neither P. rossignoli nor Postschizotherium. He noted the great resemblance of Pliohyrax with the modern genus Procavia, that he attributed to the remoteness of the genus relatively to the .

The 1960s and 1970s

In 1966 and 1970, Johann K. Melentis, formally describing the fossil remains uncovered by Skoupos in Halmyropotamos, assigned several additional hyracoid mandibles from the locality to P. graecus. In 1972, during a scientific expedition in Shanxi, two hyracoid teeth presumably coming from the Baode locality were bought from a particular in Linfen. These two teeths were attributed to the genus Pliohyrax in 1974 by Tong Yongsheng and Huang Wanbo, as the new species P. orientalis. Tong and Huang additionally proposed that the French species P. rossignoli and P. occidentalis were distinct from Pliohyrax, and reerected the genus Neoschizotherium created by Viret for the species, as N. orientalis and N. rossignoli.

Megalohyrax

In 1932, during an expedition in East Africa, French paleontologist Camille Arambourg had the opportunity to explore fossil bearing deposits in Mount Losodok, near Lake Turkana, in Kenya. The fossils discovered were shipped to the National Museum of Natural History in Paris, in which they were studied under the supervision of Marcellin Boule. In 1933, Arambourg, back from Africa, published the description of the fauna uncovered. Among the remains was a single fragmentary left mandible bearing two molars, presenting important similarities with several fossil hyraxes, and seemingly more closely related to the Pliohyrax graecus from Pikermi. The first remains of Pliohyrax discovered in Africa, it was still substantially different from the European species, seemingly retaining primitive traits more typical of Oligocene hyraxes such as Saghatherium. Arambourg named the new species P. championi, to honour the colonial Provincial Commissionner of Turkana County, M. Champion.

Meroehyrax

Larrayal/sandbox Temporal range:
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Hyracoidea
Family:	†Pliohyracidae
Subfamily:	†Pliohyracinae
Genus:	†Meroehyrax Whitworth, 1954
Type species
Meroehyrax batae Whitworth, 1954

History of research

In 1954, Thomas Whitworth described several new genera and species of hyracoids found in Early Miocene deposits in Rusinga Island and adjacent localities, in Kenya. Among these taxa, Whitworth described a new type of Sagatheriinae, Meroehyrax batae (then orthographied Meroëhyrax), based on a single, holotype fragmentary right mandible bearing molars and premolar, mostly distinguished from the genus Saghatherium by the presence of a distinct fossa on the mandible, resembling that of Geniohyus. Two additional cheek teeth from Rusinga, and another from an unknown Kenyan locality, were also proposed to belong to the genus.

The species name, bateae, honours Welsh palaeontologist Dorothea Bate.

Postschizotherium

Larrayal/sandbox Temporal range:
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Hyracoidea
Family:	†Pliohyracidae
Subfamily:	†Pliohyracinae
Genus:	†Postschizotherium Von Koenigswald, 1932
Type species
Postchizotherium chardini Von Koenigswald, 1932
Species
P. chardini (Von Koenigswald, 1932) P. intermedium (Von Koenigswald, 1966) P. licenti (Von Koenigswald, 1966)

History of research

Between 1924 and 1926, Emile Licent, founder and director of the Musée Hoangho Paiho of Tianjin, and his fellow Jesuit Pierre Teilhard de Chardin led extensive field work in the Nihewan Basin, collecting a vast diversity of fossils belonging to a then unknown Pleistocene fauna. Those fossils were then formally described by Teilhard de Chardin and Jean Piveteau in 1930, forming the basis of what is today known as the Nihewan Fauna. Among the remains found by Licent in Nihewan figured a first upper left molar and an associated third premolar. Teilhard de Chardin and Piveteau noted that, by their general shape, those teeth shared considerable similarities with those of the chalicotheres, a group of large, clawed perissodactyls also present in Nihewan. However, the differences with known chalicotheres being substantial, Teilhard de Chardin and Piveteau concluded that those remains represented a new genus of chalicothere.

In 1932, following this identification, Gustav von Koenigswald redescribed those remains as the new genus and species Postschizotherium chardini. In 1933, Teilhard de Chardin and Pei Wenzhong tentatively refered a lower molar discovered in the Locality 12 of Zhoukoudian, near Beijing, to the genus. In 1936, Teilhard de Chardin and Licent described additional material referable to Postschizotherium sp., the anterior parts of a mandible and a maxilla belonging to the same individual, discovered in the Yushe Basin in Shanxi ; they noted that Postschizotherium represented an abherrant type of chalicothere. In 1939, Teilhard de Chardin described two additional anterior parts of the mandible discovered by Licent and Trassaert in the same Pliocene-aged deposits in Shanxi that had yielded the first mandible. He considered that all three specimens represented different species, firstly differentiated by their size, one much larger, the other much smaller than the jaw described in 1936. The exact zoological affinities still puzzled Teilhard de Chardin ; the discovery of postcranial chalicothere material in Nihewan seemed to support his previous assumption, while George Gaylord Simpson noted that the teeth shared similarities with those of hyracoids, and Edwin H. Colbert proposed an affinity with the palaeotheres, based on the shape of the molars. Between 1937 and 1939, an additional tooth of enigmatic affinities was uncovered in the Middle Pliocene "Cap" Formation in Zhoukoudian by Pei Wenzhong, which tentatively attributed it to Postschizotherium.

During the late 1940s, teeth remains discovered in the Soblay lignites in southern France were identified as belonging to a close relative of Postschizotherium, that Jean Viret named Neoschizotherium rossignoli. In 1949, with the discovery of additional material from the same locality, Viret constated that the Soblay specimens likely belonged to the widespread hyracoid genus Pliohyrax, as P. rossignoli. Therefore, on the basis of the ressemblance with the dentition of Pliohyrax, and as Gaylord Simpson had predicted, Viret repositionned Postschizotherium as an hyracoid closely related to Pliohyrax. He inferred that, originating in Africa, the hyracoid lineage had expanded northward, briefly entering Europe up to the Atlantic, and surviving up to the Quaternary in East Asia.

In 1966, Von Koenigswald distinguished three distinct species of Postschizotherium in China, representing three different stages, P. chardini being the younger. He therefore established two new species : P. licenti, based on a single tooth he bought in Hong Kong, of unknown provenance , and to which he referred an additional fragmentary mandible from the Yushe Basin ; and P. intermedium, based on a mandible from Yushe and the tentatively assigned fossilized teeth from Zhoukoudian discovered by Pei in 1939. In a 1974 article which reestablished Neoschizotherium for the two French species of Pliohyrax, Tong Yongsheng and Huang Wanbo criticized this split as premature due to a lack of overlapping material and difficulties to ensure precise datations. They also signaled the discovery of additional remains tentatively assigned to the genus in Zhoukoudian, and removed the mandible fragment from P. licenti, as the absence of overlapping material limited its exact identification.

Thyrohyrax

Larrayal/sandbox Temporal range:
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Hyracoidea
Family:	†Pliohyracidae
Genus:	†Thyrohyrax Meyer, 1973
Type species
Thyrohyrax domorictus Meyer, 1973

From 1961 to 1967, expeditions organized by Yale University to the Fayoum uncovered a rich diversity of fossil taxa from the Jebel el Qatrani Formation. Among the remains were a vast array of fragmentary dentaries and associated postcranial remains belonging to a new type of hyracoid, collected between 1962 and 1967 in the quarries G, M and I. In 1973, Grant E. Meyer, who had participated in the expeditions, described formally the remains as the new genus and species that he named Thyrohyrax domorictus, based on the only fragmentary right mandible collected in Quarry M during the last year of the expeditions by Meyer himself. Meyer noted the great resemblance between Thyrohyrax and Meroehyrax, then placed among the Pliohyracinae, and proposed that T. domorictus, while a Sagatheriinae, was closely related to the last common ancestor of the more derived pliohyracins.

The genus name, Thyrohyrax, is formed from the Greek prefix "thyra-", meaning "window", and the suffix "-hyrax", referring to the internal fenestra in the mandible of the presumed females. The type species name is formed from the Greek "domos-", meaning "house" and the Latin -ramus, meaning "jaws", referring to the chambered jaws of the type species.

References

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Most important fossiliferous localities

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Most important fossiliferous localities

Paleontology

Invertebrates

Genus	Species	Order	Family	Notes	Images
Aspidoceras	A. cf. catalaunicum	Aspidoceratidae	Ammonitida
Oppeliidae indet.		Oppeliidae	Ammonitida
Perisphinctidae indet.		Perisphinctidae	Ammonitida
Hibolites		Belemnopseidae	Belemnitidae	Very small members of the genus.
Terebratulida indet.			Terebratulida
Rhynchonellida indet.			Rhynchonellida
Solanocrinites	S. thiollieri		Comalutida
Pentasteria	P. (Archastropecten) lithographica	Astropectinidae	Paxillosida
Comptoniaster	C. chantrei	Goniasteridae	Asteroidea