Proeremotherium
| Proeremotherium | ||||||||||||
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two skulls from Proeremotherium , on the right the holotype |
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| Temporal occurrence | ||||||||||||
| Pliocene | ||||||||||||
| 5.333 to 2.588 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Proeremotherium | ||||||||||||
| Carlini , Brandoni & Sánchez , 2006 | ||||||||||||
Proeremotherium is an extinct genus of sloths from the Megatheriidae family. It lived in the Pliocene around 5 million years ago in northern South America. Two largely complete skulls have so far been recoveredthere in the Falcón Basin in Venezuela . The findings show the animals as medium-sized representatives of the ground-living sloths. In the skull structure, Proeremotherium is similar tothe later and huge Eremotherium . It is therefore assumed that the two members of the sloth are in a direct family relationship. The genus was introduced in 2006.
features
Proeremotherium was a medium-sized representative of the Megatheriidae and significantly smaller than the related Eremotherium . Two almost complete skulls of the genus have been handed down. These were 45.5 to 46.0 cm long and 16.0 to 16.8 cm wide in the area of the skull. The skull generally had a low and elongated shape with the greatest width at the anterior and posterior attachment of the zygomatic arch . Compared to the robust skull of Megatherium, that of Proeremotherium looked rather delicate. The forehead line was slightly arched in side view, which was particularly evident in the middle third. But there was a slight indentation on the nasal bone . Seen from above, the rostrum was clearly triangular in shape, which is not known from any other representative of the Megatheria. At the parietal bone is a strong rose head crest . This started differently in the two skulls, on the one hand at the front and on the other at the posterior zygomatic arch attachment. In front it dissolved into two temporal lines, which were straight or convex in shape. The occipital bone was formed as in eremotherium an angle of 90 °, wherein megatherium , it was considerably dull. The joint surfaces of the occiput for connection with the cervical spine protruded prominently to the rear and were hemispherical in shape. Analogous to Eremotherium, they sat relatively low on the skull just above the level of the palate , which differs from Megatherium or from Pyramiodontherium with their high-attached condyles , among other things . The base of the skull also formed a plane with the palate in accordance with Eremotherium , but also with Megathericulus . In Megatherium , the former was higher, which was caused by the stronger high-crowned teeth. The anterior zygomatic arch attachment was in the area of the second molar-like tooth. The front edge of the posterior palatal opening reached the fourth to fifth molar-like tooth in Proeremotherium , and further back in Eremotherium .
The teeth of Proeremotherium had the typical structure, as it is also known from other developed Megatheria. Each row of teeth consisted of five teeth at the top, which resembled molars in shape. Both rows ran more or less parallel to each other, the inner distance varied between 43 and 49 mm. The individual teeth of each row were close together, a diastema behind the first tooth, unlike most other sloths, was not formed. Typically, the teeth were square in outline with the exception of the last one, which was short and wide. The shape of the teeth corresponded to that of the other developed Megatheria, with more original members such as Megathericulus they still had a rectangular outline. They had the two sharp ridges characteristic of Megatheria, perpendicular to the longitudinal axis of the teeth, with a deep V-shaped indentation in between. The entire upper row of teeth reached a length of 16.9 cm, which corresponds to almost 37% of the length of the skull. The largest tooth was the third, 3.6 cm long and 3.2 cm wide.
Fossil finds
Two skulls from the Falcón basin in the north of Venezuela are available from Proeremotherium . In the Falcón Basin, a depression of around 36,000 km², deposits of the Urumaco sequence are exposed, which belong to the period from the Lower Miocene to the Pliocene and thus cover a period of around 20 million years. The sediments can be assigned to three geological rock units, the Socorro , Urumaco and Codore Formations . All three together form one of the most important fossil sites of northern South America from the Neogene . The Proeremotherium skull discovered first came from the Codore Formation about 1.5 km northwest of Cerro Chiguaje. The rock unit is formed from dark-colored, cross-layered sandstones and lighter limestones and was formed in the transition from the Upper Miocene to the Lower Pliocene about 6 million years ago. The deposits can be interpreted as the remains of a former river delta . Above all, the lower part of the layer, the El Jebe Member , is fossil-bearing. In addition to Proeremotherium , there are other sloths here, such as the genera Mirandabradys and Bolivartherium belonging to the Mylodontidae . In addition, remains of Glyptodontidae and birds have also been found.
A second skull was discovered in the San Gregorio Formation 12 km north-northwest of the city of Urumaco . With a formation period from the Upper Pliocene to the Lower Pleistocene , it no longer belongs to the Urumaco sequence. The main components of the rock unit consist of limestones with a small proportion of sandstones and conglomerates . It was created under tropical conditions in a savannah landscape interspersed with meandering rivers . A large part of the fossil finds of the San Gregorio Formation can be ascribed to the Vergel member , who is the oldest of a total of three layers. In addition to the skull of the sloth genus, remains of rodents such as guinea pig relatives came to light here, as well as armadillos , representatives of the Pampatheriidae and Glyptodontidae, as well as the South American ungulates . Further fauna components are formed by crocodiles.
Paleobiology
The two well-known skulls of Proeremotherium show individual variations in terms of the course of the temporal lines or the length of the crest, but also the zygomatic arch attachment and the orientation of the joints of the occiput. At the moment, however, it cannot be said whether it is a question of gender dimorphism , different age stages or taxonomic deviations.
Systematics
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Internal systematics of the Megatheriidae according to Varela et al. 2019
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Proeremotherium is a genus from the extinct family of Megatheriidae from the suborder of the sloths (Folivora). The species-poor group of sloths today showed a high diversity of forms in its phylogenetic past. Different lines of development can be distinguished within the sloth. The Megatheriidae together with the Megalonychidae and the Nothrotheriidae form a closely related group, the superfamily of the Megatherioidea . According to skeletal anatomical analyzes, the megatherioidea form, alongside the mylodontoidea, one of the two great lines of sloths. Opposite this classical view are molecular genetic and protein-based studies, which reveal an additional third line with the megalocnoid . According to the latter analyzes, the Megatherioidea also include the three-toed sloth ( Bradypus ) and thus one of the two species of sloth that still exist today.
The Megatheriidae produced the largest known representatives of the sloth, namely Megatherium and Eremotherium . Both came predominantly in the Pleistocene , the former was limited to the Pampas and Andean regions of South America, the latter reached the southern part of North America in the course of the Great American Faun Exchange . Due to the features of the skull, Proeremotherium is considered to be closely related to Eremotherium . Its phylogenetic precursor was unknown for a long time, but the greater adaptation to tropical climatic conditions suggested an origin in the more northern South America. The discovery of abundant sloth remains from the Middle to Upper Miocene and the Pliocene in northern South America, especially in the Urumaco sequence, supports this view, especially since representatives of the Megatheria are among them. Accordingly, Proeremotherium or another closely related form could have migrated north during the Pliocene to form the basis for the later Eremotherium . During the Pleistocene, Eremotherium again reached South America as part of a return migration. The same is assumed for Glyptotherium from the group of the Glyptodontidae .
The genus Proeremotherium was first scientifically described in 2006 by Alfredo A. Carlini and research colleagues . The basis was the skull from the Codore formation in the Falcón basin of Venezuela, which thus functions as a holotype (copy number AMU-CURS 126). The generic name with its part of the name Eremotherium and the Latin prefix pro ("for") indicates the presumed close relationship of the two genera. The only known species is P. eljebe , the specific epithet refers to the more precise find position in the El Jebe member of the Codore formation. The skull was mentioned two years earlier, but was assigned to the genus Plesiomegatherium .
literature
- Alfredo A. Carlini, Diego Brandoni and Rodolfo Sánchez: First Megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (Late Miocene) and Codore (Pliocene) Formations, Estado Falcón, Venezuela. Journal of Systematics Palaeontology 4 (3), 2006, pp. 269-278
- Alfredo A. Carlini, Diego Brandoni, Rodolfo Sánchez and Marcelo R. Sánchez-Villagra: A new Megatheriinae skull (Xenarthra, Tardigrada) from the Pliocene of Northern Venezuela - implications for a giant sloth dispersal to Central and North America. Palaeontologia Electronica 2018, S. 21.2.16A, doi: 10.26879 / 771
Individual evidence
- ↑ a b c d Alfredo A. Carlini, Diego Brandoni and Rodolfo Sánchez: First Megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (Late Miocene) and Codore (Pliocene) Formations, Estado Falcón, Venezuela. Journal of Systematics Palaeontology 4 (3), 2006, pp. 269-278
- ↑ a b c d Alfredo A. Carlini, Diego Brandoni, Rodolfo Sánchez and Marcelo R. Sánchez-Villagra: A new Megatheriinae skull (Xenarthra, Tardigrada) from the Pliocene of Northern Venezuela - implications for a giant sloth dispersal to Central and North America . Palaeontologia Electronica 2018, S. 21.2.16A, doi: 10.26879 / 771
- ^ Alfredo A. Carlini, Gustavo J. Scillato-Yané and Rodolfo: New Mylodontoidea (Xenarthra, Phyllophaga) from the Middle Miocene-Pliocene of Venezuela. Journal of Systematic Palaeiontology 4 (3), 2008, pp. 255-267
- ^ A b Alfredo A. Carlini, Alfredo E. Zurita, Gustavo J. Scillato-Yané, Rodolfo Sánchez and Orangel A. Aguilera: New Glyptodont from the Codore Formation (Pliocene), Falcón State, Venezuela, its relationship with the Asterostemma problem, and the paleobiogeography of the Glyptodontinae. Paläontologische Zeitschrift 82 (2), 2008, pp. 139–152
- ^ Stig Walsh and Rodolfo Sánchez: The first Cenozoic fossil bird from Venezuela. Paläontologische Zeitschrift 82 (2), 2008, pp. 105–112
- ↑ a b Omar J. Linares: Biostratigrafía de la fauna des mamíferos de las Formaciones Socorro, Urumaco y Codores (Mioceno Medio-Plioceno Temprano) de la región Falcón, Venezuela. Paleobiologia Neotropical 1, 2004, pp. 1-26
- ^ M. Guiomar Vucetich, Alfredo A. Carlini, Orangel Aguilera and Marcelo R. Sánchez-Villagra: The Tropics as Reservoir of Otherwise Extinct Mammals: The Case of Rodents from a New Pliocene Faunal Assemblage from Northern Venezuela. Journal of Mammalian Evolution 17 (4), 2010, pp. 265-273
- ↑ Mariela C. Castro, Alfredo A. Carlini, Rodolfo Sánchez and Marcelo R. Sánchez-Villagra: A new Dasypodini armadillo (Xenarthra: Cingulata) from San Gregorio Formation, Pliocene of Venezuela: affinities and biogeographic interpretations. Natural Sciences 101, 2014, pp. 77–86
- ↑ 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
- ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
- ↑ 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, 2019, 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, doi: 10.1038 / s41559-019-0909-z
