Baraguatherium
| Baraguatherium | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lower Miocene | ||||||||||||
| 18.27 to 17.21 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Baraguatherium | ||||||||||||
| Rincón , Solórzano , McDonald & Flores , 2017 | ||||||||||||
Baraguatherium is an extinct genus from the Mylodontidae family, a line of large, ground-dwelling sloths that is also extinct today. It has comedown to uson the basis of only a few finds from northwestern Venezuela and, with a dating of the layersleading tothe find, to the Lower Miocene and 18 to 17 million years ago represents the oldest representative of its family in the northern part of South America . The structure of the teeth suggests that the genus represents a more basal form within the Mylodonts. In contrast to other Mylodonts, who preferred more open grasslands, Baraguatherium livedin a tropical rainforest that was rich in rivers and near the coast. The genus was scientifically introduced in 2016.
features
Baraguatherium is a medium-sized member of the Mylodontidae . Its body weight was estimated to be around 495 to 765 kg on the basis of a thigh bone that has not been entirely preserved . In addition to the long bone, there is also a fragmented right branch of the lower jaw with the three remaining rear teeth and some isolated teeth of the upper jaw. The lower jaw lacks the front section and the upper part of the ascending branch. The fragment is 12.3 cm long in total. The lower jaw itself was massive and wide. Reconstructed, the two rows of teeth were probably parallel to each other, which differs from most other Mylodonts, which had diverging rows of teeth due to their ready snouts. The symphysis reached up to the second molar-like ( molar-shaped ) tooth and was rather narrow. The lower edge of the lower jaw was straight. The transition to the ascending joint branch was rounded at the upper edge, it started directly behind the last tooth. The lower jaw corresponded to that of the other Mylodonts with an anterior canine-like ( caniniform ) tooth and three posterior molar-shaped teeth. In Baraguatherium, only the alveolus of the anterior caniniform tooth has so far been occupied, but in contrast to numerous other mylodonts there was no diastema to the posterior teeth . All three molars were characterized by a bilobate chewing surface structure with raised margins and a shallow depression in between. On the last molar-like tooth, the anterior lobe was significantly wider than the posterior. Inside , the teeth had a core made of vasodentin , a softer component of the dentin , which was encased in orthodentin , a harder variant. The outer layer was made of dental cement , but it was thinner in the Baraguatherium than in other Mylodonts. As with all sloths, the enamel was missing here too . The length of the molar row was 6.8 cm. The second molar-like tooth was the largest tooth at 2.1 cm in length and 1.7 cm in width, but all teeth were similar in their dimensions.
The thighbone is around 35 cm long, which corresponds to around 60 to 70% of the total length. Reconstructed, it should have been between 41 and 46 cm long. The shaft showed a board-like, flattened shape, characteristic of large ground sloths. The joint head and the large crescent are not recorded, the third cusp (third trochanter) was located in the middle of the shaft and pointed backwards. The knee joint was characterized by a larger inner (middle) and smaller outer (side) joint role.
Fossil site
The previously known remains of Baraguatherium come from the Castillo Formation , which is exposed in the Falcón Basin in northwestern Venezuela . The Falcón Basin lies on the border between the Caribbean and the South American Plate . Here an almost complete deposition sequence has been handed down that extends from the Eocene to the Pliocene and is partly very rich in fossils. The most important and well-known finds so far come from the Urumaco sequence of the Middle and Upper Miocene . The Castillo Formation is stratigraphically older and covers the north-west to south-west edge of the Falcón Basin in a semicircle. It was first studied and named in the 1960s. One of the most important outcrops is that of Cerro la Cruz near the village of La Mesa around 20 km north of Carora in the Venezuelan state of Lara . It lies on the southern flank of the Serranía La Baragua and consists of a series of sediments at least 360 m high over an area of around 2 km². The sequence is made up of different layers of clay / silt stones , in which individual layers of lime and sandstone are embedded, in addition, limonites and conglomerates are added locally . A total of four units (A to D from bottom to top) can be distinguished. Above all, the three lower units contain numerous fossil material, which increases again sharply in sections B and C. The fossil wealth was first noticed in the transition from the 20th to the 21st century. Overall, marine organisms predominate in the fossil record , including crustaceans , mollusks , fish , turtles , manatees, and whales . Some forms, such as the genus Portunus belonging to the decapods, suggest waters close to the coast. There are also freshwater forms such as the Black Pacu or the genus Mylossoma as representatives of the fish, as well as members of the snake-necked turtle . In the middle section of unit C, remains of land-living vertebrates were also recovered. Among other things, some members of the South American ungulates and the articular animals , including the remains of baraguatherium, should be emphasized here . In this area, which is informally also called valle de los vertebrados ("Valley of the vertebrates"), in addition to tree trunks, numerous bioturbations in the form of trace fossils can be detected, for example from Gyrolithes , a possibly crustacean-like creature that dug corkscrew-like duct structures in the coastal soil. Based on the geological and palaeontological findings, it can be assumed that the coastal landscape was formerly mangrove-lined and probably only existed for a short time. Dating with the help of strontium isotopes resulted in an age of 19.27 to 17.21 million years for the Castillo formation, which corresponds to the Lower Miocene, the section that also contains the terrestrial vertebrates is probably younger than 18.27 million years be. The isolated molars of Baraguatherium were already presented in a scientific article in 2004, but their exact taxonomic assignment was uncertain. In another publication from 2014, the authors referred the lower jaw to the more primitive sloth family of the Orophodontidae .
Paleobiology
Due to the large thigh bone, it can be assumed that Baraguatherium belonged to the ground-dwelling sloths and moved on quadrupeds. The geological-palaeontological findings refer to a coastal tropical rainforest as habitat , which was crossed by numerous rivers. In this point Baraguatherium differed from other Mylodonts, which preferred more open grasslands.
Systematics
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Internal systematics of the Mylodontoidea according to Varela et al. 2019
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Internal systematics of the Mylodontoidea according to Boscaini et al. 2019
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Baraguatherium is a genus from the extinct family of the Mylodontidae within the suborder of the sloths (Folivora) and the order of the tooth arms (Pilosa). The sloths today comprise two genera of smaller, tree-dwelling animals, in the geological past they were very rich in shape and varied. Within the subordination , two main lines can be distinguished in a classical view, determined by skeletal anatomical investigations: the Mylodontoidea with the Mylodontidae, the Scelidotheriidae and the Orophodontidae (partly the Scelidotheria and Orophodont are included in the rank of subfamilies in the Mylodontidae) and the Megatherioidea . With reference to molecular genetic and protein-based analyzes, the megalocnoidea should be added as a third line. According to the latter studies, the Mylodontoidea with the two-toed sloth ( Choloepus ) also contain one of the two still existing genera. The Mylodontidae form a very diverse group, which are characterized by high-crowned teeth with a lobate chewing surface structure, which is generally understood as an adaptation to grassy food in open landscapes. The foremost tooth, on the other hand, has a canine-like design and is separated from the rear molar-like teeth by a gap. The group has been detectable since the Oligocene , one of the oldest finds is Paroctodontotherium from Salla-Luribay in Bolivia . It is possible that the Mylodonts, like many other groups of secondary arthropods (Xenarthra), have their origin in the southern part of South America .
With an age of 19 to 17 million years, Baraguatherium is the oldest known representative in northern South America. Its age corresponds to the finds from the important Santa Cruz Formation in the south of today's Argentina . The Mylodonts handed down there, such as Nematherium or Analcitherium, are significantly smaller than Baraguatherium, with a body weight of less than 100 kg . The formation of three bilobed molars clearly represents Baraguatherium in the Mylodonts. What is noticeable, however, is the vasodentin core of the teeth, which only occurs in very original forms, but not in more modern genera such as lestodon or paramylodon . For this reason, some authors place baraguatherium at the base of the development of the Mylodonts. Others, however, see the form embedded within a group of other representatives of northern South America and some archaic forms. The discovery of Baraguatherium shows that the northern part of South America had a similarly high diversity of sloths as the southern part and was of comparable importance for the development history of this group. Since the beginning of the 21st century alone, several new forms have been discovered among the Mylodonts and their other relatives, including Eionaletherium , Bolivartherium or Mirandabradys .
The first scientific description of Baraguatherium was made by a collective of authors around Ascanio D. Rincón in 2017. The basis was formed by the lower jaw and the thigh bone from the valle de los vertebrados of Cerro la Cruz in the Venezuelan state of Lara . The former also represents the holotype (copy number IVIC -P-1828), it is kept in Caracas. The name Baraguatherium is made up of the name Baragua for the Serranía La Baragua (also Sierra de La Baragua), a mountain range in northern Venezuela, on the southern flank of which the site of Cerro la Cruz is, and the Greek word θηρίον ( thērion ) for "animal " together. The only known species is called Baraguatherium takumara . The specific epithet refers to the word takumará of the Ayamanes Indian group, in whose language it means “sloth”.
literature
- Ascanio D. Rincón, Andrés Solórzano, H. Gregory McDonald and Mónica Núñez Flores: Baraguatherium takumara, Gen. et Sp. Nov., the Earliest Mylodontoid Sloth (Early Miocene) from Northern South America. Journal of Mammalian Evolution 24 (2), 2017, pp. 179-191, doi: 10.1007 / s10914-016-9328-y
Individual evidence
- ↑ a b c d e f g Ascanio D. Rincón, Andrés Solórzano, H. Gregory McDonald and Mónica Núñez Flores: Baraguatherium takumara, Gen. et Sp. Nov., the Earliest Mylodontoid Sloth (Early Miocene) from Northern South America. Journal of Mammalian Evolution 24 (2), 2017, pp. 179-191
- ↑ Marcelo R. Sánchez-Villagra, RJ Burnham, RM Feldmann, ES Gaffney, RF Kay, R. Lozsán, R. Purdy and GM Thewissen: A new near shore marine fauna and flora from the Early Neogene of Northwestern Venezuela. Journal of Paleontology 74 (5), 2000, pp. 957-968
- ^ A b Marcelo R. Sánchez-Villagra, Robert J. Asher, Ascanio D. Rincón, Alfredo A. Carlini, Peter Meylan and Robert Purdy: New faunal reports for the Cerro La Cruz Locality (Lower Miocene, Northwestern Venezuela). In: Marcelo R. Sánchez-Villagra and JA Clack (eds.): Fossils of the Miocene Castillo Formation, Venezuela: contributions on neotropical palaeontology. Special Papers in Palaeontology 71, 2004, pp. 105-116
- ↑ Marcelo R. Sánchez-Villagra, Orangel A. Aguilera, Rodolfo Sánchez and Alfredo A. Carlini: The Fossil Vertebrate Record of Venezuela of the Last 65 Million Years. In: Marcelo R. Sánchez-Villagra, Orangel A. Aguilera and Alfredo A. Carlini (Eds.): Urumaco and Venezuelan Paleontology, The Fossil Record of the Northern Neotropics. Indiana Press University, 2010, pp. 19-51
- ↑ a b Ascanio D. Rincón, Andrés Solórzano, Mouloud Benammi, Patrick Vignaud and H. Gregory McDonald: Chronology and geology of an Early Miocene mammalian assemblage in North of South America, from Cerro La Cruz (Castillo Formation), Lara State, Venezuela : implications in the 'changing course of Orinoco River' hypothesis. Andean Geology 41 (3), 2014, pp. 507-528, doi: 10.5027 / andgeoV41n3-a02
- ↑ a b c Luciano Varela, P. Sebastián Tambusso, H. Gregory McDonald and Richard A. Fariña: Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis. Systematic Biology 68 (2), 2019, pp. 204-218
- ↑ a b Alberto Boscaini, François Pujos and Timothy J. Gaudin: A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths. Zoologica Scripta, 2019, doi: 10.1111 / zsc.12376
- ↑ Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross DE MacPhee, Guillaume Billet, Lionel Hautier and Hendrik N. Poinar : Ancient mitogenomes reveal the evolutionary history and biogeography of sloths. Current Biology 29 (12), 2019, pp. 2031-2042, doi: 10.1016 / j.cub.2019.05.043
- ↑ Samantha Presslee, Graham J. Slater, François Pujos, Analía M. Forasiepi, Roman Fischer, Kelly Molloy, Meaghan Mackie, Jesper V. Olsen, Alejandro Kramarz, Matías Taglioretti, Fernando Scaglia, Maximiliano Lezcano, José Luis Lanata, John Southon, Robert Feranec, Jonathan Bloch, Adam Hajduk, Fabiana M. Martin, Rodolfo Salas Gismondi, Marcelo Reguero, Christian de Muizon, Alex Greenwood, Brian T. Chait, Kirsty Penkman, Matthew Collins and Ross DE MacPhee: Palaeoproteomics resolves sloth relationships. Nature Ecology & Evolution 3, 2019, pp. 1121-1130, doi: 10.1038 / s41559-019-0909-z
- ^ H. Gregory McDonald and Gerardo de Iuliis: Fossil history of sloths. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 39-55
- ↑ Bruce J. Shockey and Federico Anaya: Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands / Savannas in South America. Journal of Mammal Evolution 18, 2011, pp. 101-115
- ^ Néstor Toledo, Guillermo Hernán Cassini, Sergio F. Vizcaíno and M. Susana Bargo: Mass estimation of Santacrucian sloths from the Early Miocene Santa Cruz Formation of Patagonia, Argentina. Acta Palaeontologica Polonica 59 (2), 2014, pp. 267-280
- ↑ Luciano Brambilla and Damián Alberto Ibarra: Archaeomylodon sampedrinensis, gen. Et sp. nov., a new mylodontine from the middle Pleistocene of Pampean Region, Argentina. Journal of Vertebrate Paleontology 2018, p. E1542308, doi: 10.1080 / 02724634.2018.1542308
- ^ Alfredo A. Carlini, Gustavo J. Scillato-Yané and Rodolfo Sánchez: New Mylodontoidea (Xenarthra, Phyllophaga) from the middle Miocene – Pliocene of Venezuela. Journal of Systematic Palaeontology 4, 2006, pp. 255-267
- ↑ Ascanio D. Rincón, H. Gregory McDonald, Andrés Solórzano, Mónica Núñez Flores and Damián Ruiz-Ramoni: A new enigmatic Late Miocene mylodontoid sloth from northern South America. Royal Society Open Science 2, 2015, p. 140256, doi: 10.1098 / rsos.140256