Sellamynodon
| Sellamynodon | ||||||||||||
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Sellamynodon skull and mandible (holotype) |
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| Temporal occurrence | ||||||||||||
| Upper Eocene to Lower Oligocene | ||||||||||||
| 38 to 28.1 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Sellamynodon | ||||||||||||
| Tissier , Becker , Codrea , Costeur , Fărcaş , Solomon , Venczel & Maridet , 2018 | ||||||||||||
Sellamynodon is a genus from the extinct family of Amynodontidae , whichbelongsto the immediate family of today's rhinos . So far, a single skull with a corresponding lower jaw has been found on the edge of the Transylvanian Basin in southeastern Europe . This makes the genus one of the few representatives of the family known from this continent. The finds date to the Upper Eocene and the Lower Oligocene . The animals were characterized by a deeply saddled forehead and a strong bulge on the occiput. Some features such as the lack of a crest are atypical for the Amynodontidae. The first scientific description of Sellamynodon took place in 2018. However, a single find was presented as early as the late 1980s, but referred to another form of the Amynodontidae.
features
Sellamynodon is a medium-sized representative of the Amynodontidae. It is estimated that the body weight was around 410 to 550 kg. So far, a partial skull with a lower jaw has been found. The skull lacks the anterior part of the rostrum in front of the last molar. In side view, the forehead line showed a deep saddle. This was caused by the massive and strongly drawn out bulge of the occiput , which is the most distinctive feature of Sellamynodon . It started roughly at the mastoid process and ran around the back of the skull in a semicircle. At the highest point it rose about 8 cm above the skull. The entire construction is unusual for amynodonts, as the skull is more reminiscent of that of the Brontotheriidae due to the deep saddle . The joint rollers of the occiput to connect with the cervical spine were prominent and were oriented diagonally downwards. In the top view, the clearly protruding zygomatic arches also stood out, which in their course formed an almost right angle. They protruded up to 31.7 cm apart and were extremely massive, up to 6 cm thick. The anterior attachment of the zygomatic arches was approximately level with the second molar . The entire brain skull pulled in strongly behind the eye sockets . The frontal bone was generally broad in shape with an extension of 19.6 cm between the side edges. The ratio of the zygomatic arch to the forehead width was around 1.6 in Sellamynodon , which is more than in Zaisanamynodon and Amynodon . On the parietal bone , only a slight bulge marked a crest . This also distinguishes Sellamynodon strikingly from other amynodonts, as well as the lack of parasagittal ripples, which gave the brain skull a smooth contour. The orbit itself was well formed and measured about 6 cm in diameter. At the posterior margin it was not completely closed by the postorbital process of the frontal bone. Its anterior margin has not been recorded and was well in front of the third molar , probably above the first. On the underside of the skull, the choans opened behind the third molar. The occipital opening was triangular in shape.
Almost all of the lower jaw has survived, the length that has been preserved is 30.9 cm. The horizontal bone body increased continuously in height towards the rear; behind the last tooth it reached almost 6.7 cm. The symphysis was relatively delicate and ended at the last premolar . A large mental foramen, 11.5 mm in diameter, lay below the anterior root of the third premolar, while a smaller one, 5.8 mm in diameter, was only half as large below the posterior root. The ascending branch towered about 16.4 cm, its front edge leaning forward. The crown process was drawn out long and thin, a broad indentation separated it from the articular process. The angular extension, in turn, had a massive, rounded structure. On the outer surface of the ascending branch, the deep pits of the masseteric fossa emerged .
Nothing is known about the anterior dentition of Sellamynodon . The skull bears only the last molar of the upper posterior set of teeth. In the lower jaw, the rear dentition consisted of the last two premolars and the three molars. The absence of the two anterior premolars refers Sellamynodon to the developed amynodonts. The molars were typically long and rectangular in shape. The chewing surface of the upper molar teeth was characterized by a clearly π-shaped enamel pattern , which is to be understood as a characteristic of the rhino relationship. The ectoloph ran parallel to the longitudinal edge of the tooth, the meta- and protoloph were more or less at right angles to it. A similar pattern occurred on the lower molars, but here the metalophid and hypolophid formed an angle of 35 ° to 36 ° to the ectolophid. The premolars were only partially molarized. The entire back row of teeth in the lower jaw extended over 16.0 cm in length, the molars took up 11.4 cm. The largest tooth here was the last molar with a length of 4.76 cm and a width of 2.16 cm.
Fossil finds
From Sellamynodon only a partial skull with associated lower jaw is available. Both remains come from Dobârca in Sibiu County in Transylvania in Romania . The exact location is unknown, as the fossils came to the University of Cluj-Napoca via a private collector . Dobârca lies on the border of the Transylvanian Basin in the transition to the southern Carpathians . In the Dobârca valley, red-colored fluvial deposits are exposed, followed by sandstones in the hanging wall . The age of the sediment sequence is unknown. A similar deposition sequence can be found at Apoldu de Sus , also in Sibiu County. It dates from the Upper Eocene to the Lower Oligocene .
Paleobiology
The absence of the crest in Sellamynodon is unusual for a member of the Amynodontidae. The fact that the present skull is that of a young animal can be excluded due to the presence of the molars and their degree of chewing. There may be a sexual dimorphism and the skull represents a female animal, which could also explain the absence of parasagittal ripples. At the moment there is too little found material to be able to provide more detailed information.
Systematics
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Internal systematics of the Amynodontidae according to Tissier et al. 2018
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Sellamynodon is a genus of the extinct family of Amynodontidae . The Amynodontidae belong to the immediate family of the rhinoceros (Rhinocerotidae) and are grouped together with these and with other extinct groups such as the Hyracodontidae and the Indricotheriidae (= Paraceratheriidae) in the superfamily of the Rhinocerotoidea. This in turn forms with the close relationship of the tapirs (Tapiridae) the superordinate group of the Tapiromorpha , one of the main lines within the order of the odd ungulate (Perissodactyla). The Amynodontidae differ from the rhinos in their anterior dentition, which is less specialized than the former and consists of a large, triangular canine and small incisors . In general, the representatives of the Amynodontidae were comparatively large, had strong crests and had no horn formations. According to phylogenetic analyzes, Sellamynodon is more closely related to Metamynodon . This makes a position within the subfamily of the Amynodontinae and the tribe of the Metamynodontini likely. The animals in this group were characterized by massive bodies and skulls with wide zygomatic arches. Their high position of the orbit and the shortened metapodia lead to the assumption that they lived semi-aquatic. The metamynodontini are opposed to the Cadurcodontini , in which the clearly reduced nasal bone indicates a pronounced trunk formation . The Amynodontidae lived in the Eocene and Oligocene in Eurasia and North America .
The first scientific description of the genus Sellamynodon was made in 2018 by a research team led by Jérémy Tissier . The skull and the lower jaw from Dobârca were determined as holotype (specimen number UBB MPS15795). The name Sellamynodon is derived from the Latin word sella for "saddle" and refers to the unusual shape of the skull with the indented forehead line. The second part of the name refers to Amynodon , the type form of the Amynodontidae. Vlad Codrea had already published the lower jaw in 1989 and assigned it to the newly named species Cadurcodon zimborensis . The species name is a reference to the Zimbor layers in the northwest of the Transylvanian Basin . At that time Codrea assumed that the lower jaw originated from this deposition sequence in Sălaj County . In 2000, however, he corrected the find region with Dobârca in Sibiu County . The corresponding skull was later found in the holdings of the University of Cluj-Napoca , it was also identified with the Dobârca region. In their first description, Tissier and colleagues transferred C. zimborensis to Sellamynodon as the only recognized species.
The discovery and description of Sellanymnodon increases the diversity of the European representatives of the Amynodontidae. During the Eocene, Europe existed largely as a separate island isolated from other large land masses. It was not until the Oligocene that the Turgai Strait was closed to establish a connection with Asia . The result was an exchange of fauna and an extinction event known as the Grande Coupure . Amynodonts are generally very sparsely documented in Europe. Remains of Amynodon and Cadurcodon are found from the Middle Eocene, and those of Amynodontopsis and Cadurcotherium from the Upper Eocene and Lower Oligocene . With the exception of Amynodon , the other three representatives belong to the Cadurcodontini. Sellamynodon would thus be the first member of the Metamynodontini from Europe, which are otherwise only found in Asia and North America.
literature
- Vlad Codrea and N. Şuraru: About an amynodontid: "Cadurcodon" zimborensis n. Sp. in the Zimbor strata of Zimbor, Salaj district in the north-west of the Transylvanian Basin. In: The Oligocene from the Transylvanian basin. Cluj Napoca, 1989, pp. 319-338
- Jérémy Tissier, Damien Becker, Vlad Codrea, Loïc Costeur, Cristina Fărcaş, Alexandru Solomon, Marton Venczel and Olivier Maridet: New data on Amynodontidae (Mammalia, Perissodactyla) from Eastern Europe: Phylogenetic and palaeobiogeographic implications around the transitionocene-Oligocene. PLoS ONE 13 (4), 2018, p. E0193774 doi: 10.1371 / journal.pone.0193774
Individual evidence
- ↑ a b c d e f g h i Jérémy Tissier, Damien Becker, Vlad Codrea, Loïc Costeur, Cristina Fărcaş, Alexandru Solomon, Marton Venczel and Olivier Maridet: New data on Amynodontidae (Mammalia, Perissodactyla) from Eastern Europe: Phylogenetic and palaeobiogeographic implications around the Eocene-Oligocene transition. PLoS ONE 13 (4), 2018, p. E0193774 doi: 10.1371 / journal.pone.0193774
- ↑ a b c d Vlad Codrea and N. Şuraru: About an Amynodontid: "Cadurcodon" zimborensis n. Sp. in the Zimbor strata of Zimbor, Salaj district in the north-west of the Transylvanian Basin. In: The Oligocene from the Transylvanian basin. Cluj Napoca, 1989, pp. 319-338
- ↑ a b Vlad Codrea: Rinoceri și tapiri terțiari din România. Cluj-Napoca, Presa Universitară Clujeană, 2000, pp. 1–174 (pp. 19–23)
- ^ Leonard B. Radinsky: The families of the Rhinocerotoidea (Mammalia, Perissodactyla). Journal of Mammalogy 47 (4), 1966, 631-639
- ^ A b Donald R. Prothero, Earl Manning and C. Bruce Hanson: The phylogeny of the rhinocerotoidea (Mammalia, Perissodactyla). Zoological Journal of the Linnean Society 87, 1986, pp. 341-366
- ^ Luke T. Holbrook: Comparative osteology of early Tertiary tapiromorphs (Mammalia, Perissodactyla). Zoological Journal of the Linnean Societ 132, 2001, pp. 1-54
- ↑ William P. Wall: Cranial evidence for proboscis in Cadurcodon and a review of the snout structure in the family Amynodontidae (Perissodactyla, Rhinocerotoidea). Journal of Paleontology 54 (5), 1980, pp. 968-977
- ^ William P. Wall: The phylogenetic history and adaptive radiation of the Amynodontidae. In: Donald R. Prothero and RM Schoch (eds.): The evolution of Perissodactyls. New York, 1989, pp. 341-354
- ↑ 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
- ↑ Alexander Averianov, Igor Danilov, Jianhua Jin and Yingyong Wang: A new amynodontid from the Eocene of South China and phylogeny of Amynodontidae (Perissodactyla: Rhinocerotoidea). Journal of Systematic Palaeontology 15 (11), 2017, pp. 927-945 doi: 10.1080 / 14772019.2016.1256914
