Lumbreratherium
| Lumbreratherium | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lower to Middle Eocene | ||||||||||||
| 56 to 37.3 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Lumbreratherium | ||||||||||||
| Herrera , Powell , Esteban & del Papa , 2017 | ||||||||||||
Lumbreratherium is an extinct genus of armadillos . She lived in the Lower and Middle Eocene 56 to 37 million years ago in what is now South America . So far, only a few finds are known that consist of a skull, parts of the body skeleton and some remains of the body armor. They come from the Lumbrera Formation in northern Argentina . Lumbreratherium ischaracterized byits set of teeth, which, unlike other armadillos, did not consist of uniformly shaped teeth reminiscent of molars, but rather had a canine-like tooth at the front. Further peculiarities can be found in the structure of the bone platelets of the back armor. It is believed that the animalsfedon insects , like most known armadillos. The genus was scientifically described in 2017.
features
Skeletal features
Lumbreratherium is a relatively original representative of the armadillos. So far, only the skull and the lower jaw as well as some elements of the body skeleton and bone plates of the shell are known of it. Only the left side of the skull has survived. The middle jaw bone is not preserved, the upper jaw had a smooth surface. The infraorbital foramen opened above the fourth molarenartigen tooth, the position corresponds approximately to the cabassous ( Cabasaous ), it is, however, significantly further moved forward as compared to the long-nose armadillo ( Dasypus ), the bristle belt animals ( Chaetophractus ) and the Sechsbinden- Armadillo ( Euphractus ). A shallow pit was formed in front of the infraorbital foramen. The maxillary foramen was located in the eye socket comparable to that of the bristle armadillos and the six-banded armadillo. In the long-nosed and bare-tailed armadillos, as well as in the giant armadillo ( Priodontes ), this is below the base of the zygomatic arch . The zygomatic arch itself was cylindrical and straight in Lumbreratherium , while in many of today's armadillos it has a curved course. The basioccipital had a broad shape, it was about twice as wide as the articular surfaces of the occiput . In contrast, the bare-tailed armadillos and the spherical armadillos ( Tolypeutes ) have a rather narrow basioccipital. A tympanic bladder was not formed, which in turn agrees with the long-nosed and spherical armadillos. The lower jaw was robust, it was stronger than in the long-nosed armadillos, but more graceful than in the bare-tailed, bristle and spherical armadillos and also in the dwarf armadillo ( Zaedyus ). The lower edge was largely straight, but bulged in the area of the teeth. The symphysis took up the entire anterior, toothless part of the lower jaw, in most of today's armadillos, with the exception of the long-nosed armadillos and the giant armadillo, it extends to the first or third molar-like tooth. In the Lumbreratherium there was a mental foramen between the end of the symphysis and the first molar-like tooth , which is unique within the armadillos. The crown process rose anteriorly at an angle of 56 °, but then became steeper. He had a short neck. The angular process was rounded, it lay below the line of the alveoli , while it is higher up in many other armadillos.
The Lumbreratherium dentition consisted of a total of 24 teeth, so there were a total of six teeth in the lower and upper row of teeth per half of the jaw. The foremost tooth had a canine-like shape ( caniniform ), the rest were molar-like ( molariform ). As a result, the teeth of Lumbreratherium did not have the strict homodontic shape as in other armadillos with their purely molar teeth, which is to be regarded as a unique feature. The caniniform tooth stood at a distance of 4.7 mm from the rear teeth ( diastema ). The molar-like teeth had more or less high crowns and were each equipped with two closed roots ( protohypsodont ). They did not stand in a closed row, but were separated from each other by short gaps between the teeth. The entire upper row of teeth measured 18.8 mm, excluding the canine-shaped tooth it was 12.3 mm.
The postcranial skeleton has so far been documented as the first cervical vertebra , five connected lumbar vertebrae, a caudal vertebra, numerous rib fragments plus a complete rib, the manubrium of the sternum , the upper part of the tibia and fibula , the ulna and some phalanges of fingers and toes. Only a few independent characteristics can be determined for Lumbreratherium .
Back armor
The back armor of Lumbreratherium consisted only of movable bands, which is a clear difference to today's armadillos. As a result, the osteoderms had a typically rectangular outline, their length varied from 6.1 to 8.4 mm, their width from 2.9 to 4.1 mm and their thickness from 1.7 to 1.9 mm. In armadillos, the bone platelets of the movable ligaments usually divide into an articulation surface, which is pushed under the neighboring bone platelet, and a surface that is visible from the outside. In addition, the Lumbreratherium osteoderms had stepped longitudinal edges, which resulted in additional connecting surfaces. As a result, each bone platelet steered with those of its own ligament as well as with those of the neighboring ligament. This characteristic design can be found among others in Pucatherium, another extinct representative of the armadillos. The articulation surface had three elevations in Lumbreratherium , which were separated by small dimples. With a few exceptions such as Pucatherium , this area is flat in other armadillos. The central pattern element of the externally visible surface formed a rectangular structure with rounded corners. This pattern was accompanied by five smaller elements, three at the end of the bone plate and one each on the long sides. These elements were separated by small grooves. There were three holes (foramina) in each of the two longitudinal grooves along the central pattern. In addition, further grooves and pits were formed on the inward-facing surface, all of which were at the edge.
Fossil finds
The previously known finds of Lumbreratherium were discovered in the north of Argentina in the province of Salta . They come from the lower layers of the Lumbrera Formation , which is exposed on the east side of the Andes in the Pampa Grande find region . The Lumbrera Formation is part of the parent Salta group , within which it belongs to the upper section (so-called Santa Barbara subgroup). In the outcrop area, the lower part of the Lumbrera formation is around 150 m thick. It consists of various sandstone formations as well as clay / silt stones , in which fossil soils are partially embedded. The deposits go back to a meandering river system that flowed through a flat landscape rich in vegetation. There is a discontinuous transition ( hiatus ) to the upper lumbrera formation . Based on the radiometric data obtained here on zirconium crystals, the age of the upper section is about 39.9 million years, which corresponds to the end of the Middle Eocene . The lower part of the Lumbrera Formation is therefore assigned to the Lower and Middle Eocene; locally stratigraphically it belongs to the Casamayorum . Both the lower and upper sections of the Lumbrera Formation are very fossil-rich. For example, crocodiles , lizards and mammals appear in the lower part, the latter including pouch hyenas , polydolopimorphia (original mammals) and numerous ungulates from the group of Meridiungulata , but also articular animals . The sedimentological hiatus is also evident in the fauna, as no representative of the lower Lumbrera formation reappears in the upper one. Here, however, Pucatherium, an armadillo form closely related to Lumbreratherium, is present.
Paleobiology
The set of teeth in Lumbreratherium differs from other armadillos and has a canine- shaped front tooth. Its function cannot yet be determined. The molar-shaped teeth are at a certain distance from one another and so do not form a closed row. In addition, the number of teeth is reduced compared to other armadillos. Both are typical of insectivorous animals. This is also supported by the lower jaw, which is somewhat more robust than that of the long-nosed armadillos, but much more delicate than that of the more omnivorous spherical armadillos and the six-banded armadillo.
Systematics
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Internal systematics of Dasypoda according to Herrera et al. 2017
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Lumbreratherium is an extinct genus from the group of armadillos (Dasypoda). These in turn include the armadillos living today, which form a total of two families , the Dasypodidae with the long-nosed armadillos and the Chlamyphoridae with all other representatives. The armadillos are characterized by their back armor with movable ligaments and their pin-like teeth. In terms of both skeletal anatomy and molecular genetics , the armadillos also belong to the extinct Glyptodontidae , which shared a rigid armor and lobed teeth for the consumption of plant-based food. Related to them for anatomical reasons are the Pampatheriidae , which in turn resembled the armadillos. The Dasypoda represent part of the order of the armored secondary articulated animals (Cingulata). Within this it is assumed that the Peltephilidae form the sister group of the Dasypoda. Lumbreratherium belongs to the basis of the development of the armadillos. According to phylogenetic studies, Pucatherium is the closest relative . This is also transmitted in northern Argentina via a partial skeleton from the Lumbrera Formation and additionally via isolated osteoderms from the Middle Eocene Casa Grande Formation . Both types are linked by the structure of the back armor, which consisted only of movable bands. In addition, the bone platelets show pronounced humps on the articulation side and on the lower surface as well as individual lateral protrusions, which resulted in a typical connection pattern with the respective neighboring osteoderms (the so-called "pucatheriine pattern").
The first scientific description of Lumbreratherium comes from a research team led by Claudia MR Herrera and was created in 2017. As a holotype (specimen number PVL 4262) they determined the previously existing find material from the Lumbrera formation. This was discovered by José Bonaparte in 1977. The generic name refers to the find area. The only known species was Lumbreratherium oblitum . The species name oblitum is of Latin origin and means something like "forgotten".
literature
- Claudia MR Herrera, Jaime E. Powell, Graciela I. Esteban and Cecilia del Papa: A New Eocene Dasypodid with Caniniforms (Mammalia, Xenarthra, Cingulata) from Northwest Argentina. Journal of Mammalian Evolution 24 (3), 2017, pp. 275-288, doi: 10.1007 / s10914-016-9345-x
Individual evidence
- ↑ a b c d e f g h i Claudia MR Herrera, Jaime E. Powell, Graciela I. Esteban and Cecilia del Papa: A New Eocene Dasypodid with Caniniforms (Mammalia, Xenarthra, Cingulata) from Northwest Argentina. Journal of Mammalian Evolution 24 (3), 2017, pp. 275-288, doi: 10.1007 / s10914-016-9345-x
- ↑ Cecilia del Papa, V. García and M. Quattrocchio: Sedimentary facies and palynofacies assemblages in an Eocene perennial lake, Lumbrera formation, northwest Argentina. Journal of South American Earth Sciences 15, 2002, pp. 553-569
- ↑ Cecilia del Papa, A. Kirschbaum, J. Powell, A. Brod, F. Hongn and M. Pimentel: Sedimentological, geochemical and paleontological insights applied to continental omission surfaces: A new approach for reconstructing an eocene foreland basin in NW Argentina. Journal of South American Earth Sciences 29, 2010, pp. 327-345
- ^ A b Claudia MR Herrera, Graciela I. Esteban, Martín R. Ciancio and Cecilia Del Papa: New specimen of Pucatherium parvum (Xenarthra, Dasypodidae), a singular dasypodid of the Paleogene (Eocene) of northwest Argentina: importance in the early evolution of armadillos. Journal of Vertebrate Paleontology 39 (4), 2019, p. 1670669, doi: 10.1080 / 02724634.2019.1670669
- ↑ Sergio F. Vizcaíno: The teeth of the “toothless”: novelties and key innovations in the evolution of xenarthrans (Mammalia, Xenarthra). In: Paleobiology 35 (3), 2009, pp. 343-366
- ↑ 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
- ↑ Frédéric Delsuc, Gillian C. Gibb, Melanie Kuch3, Guillaume Billet, Lionel Hautier, John Southon, Jean-Marie Rouillard, Juan Carlos Fernicola, Sergio F. Vizcaíno, Ross DE MacPhee and Hendrik N. Poinar: The phylogenetic affinities of the extinct glyptodonts. 26, 2016, pp. R141-R156
- Jump up ↑ Kieren J. Mitchell, Agustin Scanferla, Esteban Soibelzon, Ricardo Bonini, Javier Ochoa and Alan Cooper: Ancient DNA from the extinct South American giant glyptodont Doedicurus sp. (Xenarthra: Glyptodontidae) reveals that glyptodonts evolved from Eocene armadillos. Molecular Ecology, 25, 2016, pp. 3499-3508, doi: 10.1111 / mec.13695
- ^ Claudia M. Herrera, Jaime E. Powell and Cecilia Del Papa: Un Nuevo Dasypodidae (Mammalia, Xenarthra) de la Formación Casa Grande (Eoceno) de la Provincia de Jujuy, Argentina. Ameghiniana, 49 (2), 2012, pp. 267-271