Tonnicinctus
| Tonnicinctus | ||||||||||||
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Tonnicinctus ( holotype , representation of the temporal bone (above; side view and view from below) and of two thoracic vertebrae (middle and below; each front and rear view); scale 50 mm) |
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| Temporal occurrence | ||||||||||||
| Lower Pleistocene to Lower Holocene | ||||||||||||
| 1.8 million years to 8,000 years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Tonnicinctus | ||||||||||||
| Góis , González Ruiz , Scillato-Yané & Soibelzon , 2015 | ||||||||||||
Tonnicinctus is an extinct genus from the Pampatheriidae family, close relatives of today's armadillos . So far it is known from individual parts of the skeleton and the remains of the body armor. The fossils come from only two sites in central and northern Argentina and date from the Lower Pleistocene to the Lower Holocene about 1.8 million years ago to 8,500 years ago. The first scientific description took place in 2015. In addition to the well-known genera Pampatherium and Holmesina, a third representative of the Pampatheria from the later phase of their occurrence could be presented. It differs characteristically in the structure of the individual bone plates of the back armor from the other members of the family.
features
Tonnicinctus was a medium-sized representative of the Pampatheria, whose body dimensions mediated between the smaller Plaina and the very large Pampatherium and Holmesina . The genus is known through individual skeletal elements and some remains of the body armor. Only the temporal bone of the skull has survived. This had fewer foramina and smaller blood tubules than in comparison to most other pampatherias, but corresponding to Holmesina . The point of attachment of the zygomatic arch ran roughly parallel to the side edge of the skull bone. In the view from below, the glenoid pit, into which the mandibular joint engages, was at the base of the zygomatic arch. Two posterior thoracic vertebrae were recovered from the spine. These had - typical for secondary articulated animals - two additional joints on the vertebral arch, the so-called xenarthric joints (secondary joints or xenarthrals). The spinous process was relatively shorter than that of Holmesina . The thigh bone is almost completely preserved and reached a length of around 29 cm. The large rolling mound, consistent with Kraglievicha and Pampatherium, but unlike Holmesina , protruded clearly above the femoral head. The head itself had a round shape and a pronounced femoral head pit to accommodate the joint ligaments. In contrast to Kraglievicha, the neck was poorly defined. A third trochanter (rolling hillock) appeared on the shaft, also typical of secondary articulated animals. As with most pampatherias, it was in the middle of the shaft, but was remarkably robust and had a distinctive profile line that stood out more clearly than other representatives of the family. Also in contrast to other pampatherias, the lower joint end was more asymmetrically shaped with a smaller inner joint roller. The depression between the two joint rollers protruded deeper than in Kraglievicha and Holmesina , but not quite as deep as in Pampatherium . In addition, a kneecap is also available for the first time for pasmpatheria . It was triangular in shape with rounded corners with the tip pointing down. The outer surface of the kneecap was curved.
With armored articulated animals, the characteristics of the armor are often used to determine the species and genus. The armor of the back consisted of all Pampatheria with completely known armor in accordance with the armadillos of a fixed shoulder and pelvis, between which there were movable ligaments. While the armadillos have a varying number of movable ligaments, depending on the species, only three were formed in the pampatheria. The fixed and movable armor parts consisted of small bone platelets ( osteoderms ) arranged in a row . From Tonnicinctus such bone platelets are preserved from all areas of the back armor. Those of the shoulder and pelvic part had a hexagonal or square outline. Their dimensions in the front armor area were 4.0 cm in length and 3.1 cm in width, in the rear they were 4.9 cm long and 3.4 cm wide. On the moving belts, their length was 7.6 cm and their width 3.3 cm. So they were significantly longer here, with part of them functioning as a joint surface to the corresponding osteoderm of the adjacent ligament. The surface of each individual bone plate showed a typical ornamentation, which in the Pampatherien included a longitudinal central elevation. In Tonnicinctus this elevation was very wide at the rear end, but became narrower towards the front. It merged into the marginal bulges of the osteoderm, as a result of which the depressions running along the side of the central longitudinal bulge appeared rather shallow. As a special feature of Tonnicinctus , irregularly shaped fringes appeared on the side of the central elevation. These are not known in other pampatheria; the central elevation of the bone platelets was either sharp or fuzzy.
Fossil finds
The genus is only known from two sites in Argentina . The older of the two is in Ensenada , a suburb of La Plata in the province of Buenos Aires . The fossil material from the site includes the known skeletal material and a total of 27 bone platelets. The remains were found in a road outcrop at a depth of 17 m. Due to the addition of Mesotherium , a member of the South American ungulates , the entire ensemble of finds is placed in the Lower and Middle Pleistocene (local stratigraphic Ensenadum ; 1.8 million to 400,000 years ago). The second site is on the Río Salado in the province of Santa Fe . So far, however, only a bone plate has come to light that was collected during the construction of a railway bridge. Due to the uncovered remains of an extinct horse of the Amerhippus subgenus , the bone platelet dates to the late Pleistocene and early Holocene (locally stratigraphically Lujanian ; from 126,000 to 8,500 years ago). A cool climate with open landscapes is being reconstructed for both sites at the time of the deposition.
Systematics
Tonnicinctus is a genus of the extinct family of the Pampatheriidae . The family belongs to the order of armored articulated animals , the only members of which are armadillos (Dasypoda) today. Within the order the Pampatherien are closely related to the gigantic Glyptodontidae . Common features of the two groups can be found in the structure of the ear canal and in the construction of the chewing apparatus, such as the high lower jaw and the teeth, which are more complex than those of the armadillos. In contrast to the Pampatherien, the Glyptodonts had rigid armor on their backs. Both families together form the superordinate taxon Glyptodonta .
Compared to the extremely rich in shape glyptodonts, the pampatheria are considered to have very few variants and are rather conservative. So far, only around a dozen genera are known. Their earliest confirmed occurrence dates back to the Middle Miocene around 14 to 15 million years ago from northern South America . The most important and well-known representatives are Pampatherium and Holmesina from the Upper Pleistocene , the former is an endemic form of South America, the latter also occurred in North America . With the extinction of the two genera in the transition to the Holocene , the entire line of the Pampatheria also became extinct.
With Tonnicinctus a third representative of the Pampatherien in the Pleistocene is now proven, whose presence remains limited for the time being to the Pamparegion . Originally, the finds from the two sites were pampatherium , more precisely Pampatherium typum . In a revision of Pampatherien as part of a dissertation by Flávio Góis but the numerous discrepancies were detected with the previously known forms. Góis then described the new genus Tonnicinctus together with some research colleagues in 2015 . The part of the name Tonni honors the Argentine paleontologist Eduardo P. Tonni , who made a great contribution to the study of the geological past of his homeland. The Latin word cinctus means "belt" or "girdle" and refers to the movable ligaments. With Tonnicinctus mirus only one type known. The specific epithet is also of Latin origin and means "wonderful" or "amazing". It was chosen because of the special ornamentation of the bone plates. The holotype (copy number MLP 54-III-16-1, 27 ) comprises the finds from La Plata , in whose museum it is kept. The single osteoderm from the Río Salado represents the paratype .
Individual evidence
- ↑ a b c d e Flávio Góis, Laureano Raúl González Ruiz, Gustavo Juan Scillato-Yané and Esteban Soibelzon: A Peculiar New Pampatheriidae (Mammalia: Xenarthra: Cingulata) from the Pleistocene of Argentina and Comments on Pampatheriidae Diversity. PlosOne 10 (6), 2015, p. E0128296 doi : 10.1371 / journal.pone.0128296
- ↑ Timothy J. Gaudin and John R. Wible: The Phylogeny of Living and Extinct Armadillos (Mammalia, Xenarthra, Cingulata): A Craniodental Analysis. In: MT Carrano, TJ Gaudin, RW Blob and JR Wible (eds.): Amniote Paleobiology. Chicago / London: University of Chicago Press, 2006, pp. 153-198
- ↑ Juan-Carlos Fernicola, Serdio F. Vizcaíno and Richard a. Fariña: The evolution of armored xenarthrans and the phylogeny of the glyptodonts. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 79-85
- ↑ Esteban Soibelzon, Ángel Ramón Miño-Boilini, Alfredo Eduardo Zurita and Cecilia Mariana Krmpotic: Los Xenarthra (Mammalia) del Ensenadense (Pleistoceno inferior a medio) de la Región Pampeana (Argentina). Revista Mexicana de Ciencias Geológicas 27, 2010, pp. 449-469
