Pappaceras

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Pappaceras
Skull of Pappaceras, holotype of P. meiomenus in different views

Skull of Pappaceras , holotype of P. meiomenus in different views

Temporal occurrence
Lower to Middle Eocene ( Ypresian to Lutetian )
52 to 37.7 million years
Locations
Systematics
Mammals (mammalia)
Higher mammals (Eutheria)
Laurasiatheria
Unpaired ungulate (Perissodactyla)
Indricotheriidae
Pappaceras
Scientific name
Pappaceras
Wood , 1963

Pappaceras is an extinct genus of the odd ungulate from the family of the Indricotheriidae . It represents the oldest representative of the Indricotheria so far. Most of the known fossil material came to light in Inner Mongolia . So far, mainly skull and dentition remains have been found. The fossil remains were stored in various rock formations whose ages range from the transition of the Lower to the Middle Eocene to the end of the Middle Eoceneextends. The absolute ages are therefore between around 50 and around 37 million years. The animals were relatively small for Indricotheria and probably fed on soft vegetable food that was chewed with mostly vertical chewing movements. The genus received its first scientific description in 1963 , but for a long time it was considered identical to Forstercooperia . Only further new discoveries led to recognition of Pappaceras as an independent genus in 2016 . Several species have been recorded.

features

Pappaceras is a small representative of the Indricotherien. It has so far been documented by several skulls and lower jaws. The skull had a length of around 39 cm and was elongated. At the rostrum , the ascending section of the midmaxillary bone was in contact with the nasal bone . This created a small nasal cavity, which in the rear area reached roughly to the position of the canine teeth . The horizontal section had an arch shape. The nasal bone occupied the entire section of the pre-eye region. It was thin, flat in cross-section, and pointed at the front. As with all indricotheria, there were no points of attachment for horn formation. The bone seam with the frontal bone was drawn in in an arc. The upper jaw was trapezoidal in side view and towered high. The infraorbital foramen was above the fourth premolar . The tearbone reached far into the face and was square here. The tear duct opened laterally in front of the orbit . The zygomatic arch was built gracefully and only protruded slightly. Its anterior attachment was about 40 mm behind the anterior orbital margin. Two weak ribs of bone were formed on the frontal bone, which pulled back and gradually thickened. They united at the parietal bone to form a crest . The occiput was broad and oriented almost vertically. It had only a few weak bones. The paroccipital process was slender and not completely fused with the posttympanic process, and it towered over the latter. The articular surfaces for contact with the cervical spine pointed downwards. At the base of the skull, on the scaled part of the temporal bone, there was the long-oval glenoid pit for articulation with the lower jaw.

Lower jaw of pappaceras with various marker points for the reconstruction of the muscles

The lower jaw was elongated and almost straight at the lower edge. Only the section of the symphysis had an upward orientation. The bit was the complete dentition of the early higher mammals with the following dental formula : . So there were a total of 44 teeth, but it is possible that the first premolar was reduced in some representatives and that they only had 40 teeth. The incisors reported with the exception of each inner pair at all about the same size. Generally they were small and conical in shape. Thus, the hypertrophied incisors typical of late Indricotheria were missing , which roughly corresponds to Forstercooperia , but in this one they varied more in size. Small diastemata were formed between the individual incisors , which were about 5 mm wide in the upper dentition, so that the front dentition did not form a closed row. The similarly shaped canine towered over the incisors. The anterior premolars did not resemble the molars , so they were not yet molarized; the three posterior premolars were significantly longer than the anterior. The molars were square to trapezoidal in shape. Their structure largely corresponded to those of the rhinos with a characteristic π-shaped enamel band pattern on the two anterior maxillary molars (composed of the ectoloph running along the outer edge of the tooth and the metaloph and protoloph standing at right angles). Individual distinctive topographical marks appeared on the last upper molar, such as the metaconus and the ectoloph, which Forstercooperia did not develop . The length of the upper and lower molars varied between 25 and 34 mm, the premolars were correspondingly shorter.

Fossil finds

Almost all of the fossil remains of Pappaceras have so far been found in Inner Mongolia in northern China . The eastern part of the Erlian Basin near the border with Mongolia is important here , the most important finding area is south of the city of Erlian . It is distributed over several localities in the vicinity of Iren Dabasu and Baron Sog. The oldest find was found here in the Arshanto Formation , which generally dates to the Lower Eocene . The location in the upper section of the rock unit speaks more for the transition period from the Lower to the Middle Eocene, which results in an age of around 50 million years (Upper Ypresium , locally stratigraphically Upper Arshantum ). This is also confirmed, among other things, by paleomagnetic investigations. Thus the find represents the oldest of a representative of the Indricotherien so far. It is an almost complete, very well preserved skull. The other fossil remains from the Erlian Basin are to be assigned to the Irdin Manha Formation from the Middle Eocene (Ypresium, locally stratigraphically Irdinmanhum ). There are individual partial skulls as well as numerous lower jaws and remains of teeth. Both the Arshanto and Irdin Manha Formations consist of sandy silt and fine-grain sandstones , which are partially interrupted by incorporated gravel channels . They represent the remains of former rivers. An almost complete lower jaw was also reported from the Shara Murun formation in the southeast of the find region. With an age in the late Middle Eocene (local stratigraphic Sharamurunian ), it can be regarded as the youngest find of the genus so far. An upper jaw from Lunan in the district-free city of Tangshan, east of Beijing, is classified as possibly one of the few bone remains from Pappaceras outside of Inner Mongolia . The piece probably has an Upper Oocene age.

Paleobiology

Live reconstruction of the head of Pappaceras

The low-crowned teeth with their simple structure allow for a diet based on a soft vegetable diet. This can also be assumed due to the generally narrow middle jawbone. The low ascending branch of the lower jaw and the pronounced masseteric fossa there point to a well-developed masseter muscle , which, however, was not quite as dominant as in the related Juxia due to the rather delicate zygomatic arch . The masseter muscle mainly causes vertical chewing movements. There is a groove on the alisphenoid (sphenoid wing bone), which indicates the anchor points for the pterygoideus medialis muscle . The muscle is well developed in today's horses and tapirs, but it does not play a role in rhinos. It acts as an opponent of the masseter muscle and allows rotating chewing movements. However, these were probably only of minor importance for Pappaceras , as the flat palate , for example, left little space for the tongue to move sideways. The pointed lower and upper incisors interlocked when the teeth were closed and show conspicuous facets of wear. Pappaceras could possibly also use harder parts of plants by piercing them with the front teeth. The incisors, however, were not suitable for cutting up food like those of horses with their straight edges.

Systematics

Pappaceras is a genus from the extinct family of the Indricotheriidae , which in turn belongs to the superfamily of the Rhinocerotoidea and thus belongs to the close relationship of today's rhinos . The Indricotheria produced large to extremely large forms, including Paraceratherium, one of the largest known land mammals. In general, unlike the rhinos, the representatives of the family had no horn formation on their noses. Furthermore, the Indricotheriidae can be distinguished from the rhinoceros on the basis of the front teeth. The former had short, conical incisors, from which later relatives developed a dagger-like pair in the upper and lower jaw. The rhinos, on the other hand, only have a dagger-like pair in the lower jaw, while a chisel-like pair of incisors appears in the upper jaw. Within the Indricotheria, Pappaceras is a very early form. Together with Forstercooperia it is partly placed in the subfamily of the Forstercooperiinae.

Internal systematics of the family of the Indricotheriidae according to Wang et al. 2016
 Indricotheriidae  


 Pappaceras


   

 Forstercooperia



   

 Juxia


   

 Urtinotherium


   

 Paraceratherium





Template: Klade / Maintenance / Style

The genus contains several species:

Of the three species, P. minuta is the smallest with a length of the upper molar row of 74.5 to 77.6 mm, P. confluens is the largest with a corresponding length of 87.1 to 90.5 mm. P. meiomenus lies between 77.6 and 80.9 mm. In the latter, the anterior premolars are also reduced. It is also with an age in the late Lower Eocene significantly older than the other two, which date to the Middle Eocene.

The first scientific description of Pappaceras was in 1963 by Horace Elmer Wood . It was based on an incomplete skull (copy number AMNH 26660) plus a lower jaw, both finds were found in mid-September 1930 during the Sixth American Museum Central Asiatic Expedition in the Irdin Manha Formation in Mongolia . The generic name Pappaceras is made up of the Greek words παππος ( pappos for "grandfather"), α ( a or alpha for "primitive" or "without") and κέρας ( kéras for "horn"). Only a few years after the first description, Leonard B. Radinsky saw the independent position of Pappaceras as problematic and synonymized the genus with Forstercooperia . Wood had already introduced this in 1938 on the basis of a partial skull, also from the Irdin Manha formation, initially renamed as Cooperia and later renamed Forstercooperia . The equation of the two genres was largely approved by experts. The discovery of further finds in the Arshanto Formation , Inner Mongolia, led to the recognition of Pappaceras again in 2016 . This was justified by the fact that Pappaceras and Forstercooperia differ in individual features of the teeth. In addition, in the species P. meiomenus, which was also newly established in 2016, the foremost premolar in the upper jaw had already disappeared, which means that the first signs of reducing the number of teeth in the dentition can be seen. In 1981, Spencer George Lucas and research colleagues named the new species Forstercooperia minuta . Not only did they provide numerous skull material from the Irdin Manha Formation to the species, but also a left lower jaw from the Galisteo Formation in Santa Fe County in the US state of New Mexico . When Pappaceras were recognized again in 2016, the authors of the study transferred the species F. minuta to the genus, but the material from North America was later separated from the Indricotheria. This means that Pappaceras remains limited to the Asian continent. There was a similar development at Forstercooperia , for which a North American distribution was initially assumed. A later assessment of the finds there resulted in the exclusion from the Indricotheria and in the description of Uintaceras as possibly very early representatives of the rhinos.

literature

  • Haibing Wang, Bin Bai, Jin Meng and Yuanqing Wang: Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids. Scientific Reports 6, 2016, p. 39607 doi: 10.1038 / srep39607
  • Horace Elmer Wood: A primitive rhinoceros from the late eocene of Mongolia. American Museum Novitates 2146, 1963, pp. 1-12

Individual evidence

  1. ↑ a b c d e f g h Haibing Wang, Bin Bai, Jin Meng and Yuanqing Wang: Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids. Scientific Reports 6, 2016, p. 39607 doi: 10.1038 / srep39607
  2. ↑ a b c d Horace Elmer Wood: A primitive rhinoceros from the late eocene of Mongolia. American Museum Novitates 2146, 1963, pp. 1-12
  3. ↑ a b c Hai-Bing Wang, Bin Bai, Jin Meng and Yuan-Qing Wang: A New Species of Forstercooperia (Perissodactyla: Paraceratheriidae) from Northern China with a Systematic Revision of Forstercooperiines. American Museum Novitates 3897, 2018, pp. 1–41
  4. ↑ a b c d e Spencer G. Lucas, Robert M. Schoch and Earl Manning: The Systematics of Forstercooperia, a Middle to Late Eocene Hyracodontid (Perissodactyla: Rhinocerotoidea) from Asia and Western North America. Journal of Paleontology 55 (4), 1981, pp. 826-841
  5. ↑ Jin Meng, Yuanqing Wang, Xijun Ni, Christopher Beard, Qian Li, Xun Jin and Bin Bai: New Stratigraphic Data from the Erlian Basin: Implications for the Division, Correlation, and Definition of Paleogene Lithological Units in Nei Mongol (Inner Mongolia) . American Museum Novitates 3570, 2007, pp. 1-31
  6. ↑ Yuanqing Wang, Jin Meng, Christopher K. Beard, Qian Li, Xijun Ni, Daniel L. Gebo, Bin Bai, Xun Jin and Ping Li: Early Paleogene stratigraphic sequences, mammalian evolution and its response to environmental changes in Erlian Basin, Inner Mongolia, China. Science China, Earth Sciences 53 (.12), 2010, pp. 1918-1926
  7. ↑ Chow Minchen, Chang Yuping and Ting Suyin: Some early Tertiary Perissodactyla from Lunan Basin, E. Yunnan. Vertebrata Palasiatica 12 (4), 1974, pp. 262-273
  8. ↑ Hai-Bing Wang, Bin Bai, Yan-Xin Gong, Jin Meng and Yuan-Qing Wang: Reconstruction of the cranial musculature of the paraceratheriid rhinocerotoid Pappa ceras meiomenus and inferences of its feeding and chewing habits. Acta Palaeontologica Polonica 62 (2), 2017, pp. 259-271
  9. ^ Leonard B. Radinsky: The families of the Rhinocerotoidea (Mammalia, Perissodactyla). Journal of Mammalogy 47 (4), 1966, pp. 631-639
  10. ^ Leonard B. Radinsky: A review of the Rhinocerotoid Family Hyracodontidae (Perissodactyla). Bulletin of the American Museum of Natural History 136 (1), 1967, pp. 1-47
  11. ↑ Horace Elmer Wood: Cooperia totadentata, a remarkable rhinoceros from the eocene of Mongolia. American Museum Novitates 1012, 1938, pp. 1-22
  12. ^ Spencer George Lucas and Jay C. Sobus: The systematics of Indricotheres. In: Donald R. Prothero and R. Schoch (Eds.): The evolution of Perissodactyls. New York, Oxford University Press, 1989, pp. 358-378
  13. ^ Luke T. Holbrook and Spencer George Lucas: A new genus of rhinocerotoid from the Eocene of Utah and the status of North American "Forstercooperia". Journal of Vertebrate Paleontology 17 (2), 1997, pp. 384-396

Web links

Commons : Pappaceras  - Collection of images, videos and audio files