| Proeremotherium Temporal range: Late Miocene-Early Pliocene (Huayquerian-Chapadmalalan) ~5.333–3.588 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ | |
|---|---|
| |
| Two skulls of Proeremotherium, holotype on the right | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Pilosa |
| Family: | †Megatheriidae |
| Genus: | †Proeremotherium Carlini et al. 2006 |
| Species: | †P. eljebe |
| Binomial name | |
| †Proeremotherium eljebe Carlini et al. 2006 | |
Proeremotherium is an extinct genus of megatheriine ground sloths in the family Megatheriidae. It lived during the Late Miocene and Early Pliocene of what is now Venezuela. So far, two largely complete skulls have been recovered in the Falcón Basin in Venezuela. The finds identify the animals as medium-sized representatives of the Megatheriidae. In the cranial anatomy, Proeremotherium resembles the later and giant Eremotherium. It is therefore assumed that the two ground sloths are directly related to each other.
Etymology
The genus name, Proeremotherium, is derived from the Latin prefix pro- meaning "before", and the genus Eremotherium in reference to the assumed close relationship between the two genera. The specific name refers to the locality where the holotype was discovered, in the El Jebe Member of the Codore Formation.
Description
Proeremotherium was a medium-sized member of the Megatheriidae and significantly smaller than the related Eremotherium. So far, two almost complete skulls have been assigned the genus. These were 45.5 to 46.0 cm long and 16.0 to 16.8 cm wide in the area of the cranium. The skull was generally low and elongated in shape, with greatest width at the anterior and posterior bases of the zygomatic arch respectively. Compared to the sturdy skull of Megatherium, Proeremotherium had a skull that looked rather graceful. The forehead line was slightly arched in side view, which was particularly evident in the middle third. On the nasal bone there was a slight dent. When viewed from above, the rostrum was clearly triangular in shape, which is not known from any other representative of the Megatheriidae. A strong crest rose at the parietal bone . This started differently in the two skulls, on the one hand at the front and on the other hand at the rear zygomatic arch. In front, it resolved into two temporal lines that were straight or convex in shape. The occipital bone formed an angle of 90° as in Eremotherium, in Megatherium was much more blunt. The joint surfaces of the back of the head for connection with the cervical spine stood out prominently to the rear and were hemispherical in shape. Similar to Eremotherium, they sat relatively low on the skull just above the palate level, which differs from Megatherium or Pyramiodontherium with their high-set condyles, among other things . The base of the skull formed a plane with the palate, also in agreement with Eremotherium, but also with Megathericulus. In Megatherium, the former was higher, which was caused by the more high-crowned teeth. The anterior zygomatic arch was in the area of the secondmolar-like tooth. The anterior edge of the posterior palatal hole reached the fourth to fifth molar-like tooth in Proeremotherium, and continued further back in Eremotherium.
The teeth of Proeremotherium had the typical structure, as it is also known from other megatheriids. 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 was not formed in contrast to most other sloths. Typically, the teeth were square in outline except for the last, which was short and broad. The shape of the teeth corresponded to that of other derived megatheriids, in more primitive members such as Megathericulus they still had a rectangular outline. They showed the two sharp ridges perpendicular to the longitudinal axis of the tooth, which are characteristic of Megatheria, 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 skull length. The largest tooth was the third at 3.6 cm long and 3.2 cm wide.
Discovery
Two Proeremotherium skulls are known from the Falcón Basin in northern Venezuela . In the Falcón Basin, an approximately 36,000 km² large depression, deposits of the Urumaco sequence are exposed, which date 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 the Codore Formations. All three together form one of the most important fossil deposits in the northern South America from the Neogene . The first Proeremotherium skull discovered is from the Codore Formation about 1.5 km northwest of Cerro Chiguaje. The rock unit is composed of dark-colored, cross-bedded sandstones and lighter-colored 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 . Especially the lower layer member, the El Jebe Member, is fossiliferous. Among other things, remains of representatives of the Glyptodontinae and birds are documented here. Besides Proeremotherium another sloth, Bolivartherium, was also found here, but it belongs to the Mylodontidae. On the other hand, fossil evidence of Urumaquia, a member of the Megatheriidae comes from older deposits of the Urumaco sequence. Pseudoprepotherium, Magdalenabradys, Eionaletherium and Urumacotherium have also been documented, all representing mylodontids, while Urumacocnus and Pattersonocnus belong to the Megalonychidae. With regards to the sloths, the Urumaco sequence forms a fossil site with a high level of diversity, comparable to sites of the same age from southern South America, such as the Pampas region or Mesopotamia.
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 Early Pleistocene, it no longer belongs to the Urumaco sequence. The main components of the rock unit are limestones with a small proportion of sandstones and conglomerates . It was created under tropical conditions in a savannah landscape interspersed with meandering rivers. Much of the fossil record of the San Gregorio Formation belongs to the Vergel Member attributed, which forms the oldest of a total of three layer members. In addition to the skull of the sloth genus, remains of rodents such as guinea pig relatives, but also armadillos, representatives of the Pampatheriidae and Glyptodontinae and South American ungulates were found here . Other faunal components are represented by crocodilians.
Paleobiology
The two known skulls of Proeremotherium show individual variations, such as the course of the temporal lines or the length of the crown crest, but also the insertion of the zygomatic arch and the orientation of the joints of the occipital bone. At the moment, however, it cannot be said whether this is due to sexual dimorphism, different age stages or taxonomic deviations.
Classification
Proeremotherium is a genus of the extinct Megatheriidae family from the suborder of sloths (Folivora). The group of sloths showed a high diversity of forms due to their phylogenetic past. Different lines of development can be distinguished within the sloths. The Megatheriidae thus form, together with the Megalonychidae and the Nothrotheriidae, a more closely related group, the superfamily of the Megatherioidea. Megatherioidea along with the Mylodontoidea are the two major lineages of sloths. This classic perspective is opposed to molecular genetic and protein-based investigations, which reveal an additional third lineage with the Megalocnoidea . According to the latter analyses, the Megatherioidea also include the three-toed sloths of the genus Bradypus and thus one of the two species of sloths that still exist today.
The genus Proeremotherium was first 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 acts as a holotype (specimen number AMU-CURS 126). The skull had already been mentioned two years earlier, but assigned to the genus Plesiomegatherium.
Below is a phylogenetic tree of the Megatheriidae, based on the work of Varela and colleagues (2019).
| Megatheriidae |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Palaeoecology
Proeremotherium lived in a tropical environment in an area of northern South America that was left relatively untouched by the Great American Interchange, the only non-native species of mammal known in the area of the Falcón Basin being the procyonid Cyonasua and Chapalmalania, and, potentially, a Camelidae still unassigned to a specific genus. Its environment was continental, an open, forested grassland area with rainforest elements, near freshwater. It coexisted with pampatheres such as Holmesina and Plaina, Proterotheriidae, the glyptodont Boreostemma, the Dasypodidae Pliodasypus and the notoungulate Falcontoxodon, as well as several species of caviomorph rodents such as Caviodon, Hydrochoeropsis, Marisela and Neoepiblema, and the crocodile Crocodylus falconensis.
References
- ^ Carlini, Alfredo A.; Brandoni, Diego; Sánchez, Rodolfo (2006). "First Megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (Late Miocene) and Codore (Pliocene) Formations, Estado Falcón, Venezuela". Journal of Systematic Palaeontology. 4 (3): 269–278. Bibcode:2006JSPal...4..269C. doi:10.1017/S1477201906001878. hdl:11336/80745. ISSN 1477-2019. S2CID 129207595.
- ^ Carlini, Alfredo A.; Brandoni, Diego; Sánchez, Rodolfo; Sánchez-Villagra, Marcelo R. (2018-05-05). "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. 21 (2): 1–12. doi:10.26879/771. hdl:11336/80208. ISSN 1094-8074.
- Alfredo A. Carlini, Alfredo E. Zurita, Gustavo J. Scillato-Yané, Rodolfo Sánchez und 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, S. 139–152
- Walsh, Stig; Sänchez, Rodolfo (2008). "The first Cenozoic fossil bird from Venezuela". Paläontologische Zeitschrift. 82 (2): 105–112. Bibcode:2008PalZ...82..105W. doi:10.1007/BF02988402. ISSN 0031-0220. S2CID 129314392.
- Carlini, Alfredo A.; Scillato-Yané, Gustavo J.; Sánchez, Rodolfo (2006-01-01). "New Mylodontoidea (Xenarthra, Phyllophaga) from the Middle Miocene-Pliocene of Venezuela". Journal of Systematic Palaeontology. 4 (3): 255–267. Bibcode:2006JSPal...4..255C. doi:10.1017/S147720190600191X. ISSN 1477-2019. S2CID 86701294.
- ^ Ortiz Jaureguizar, E. (1998-08-30). ""Bioestratigrafía de la fauna de mamíferos de las formaciones Socorro, Urumaco y Codore (Mioceno medio-Plioceno temprano) de la región de Urumaco, Falcón, Venezuela."". Estudios Geológicos. 54 (3–4). doi:10.3989/egeol.98543-4215. ISSN 1988-3250.
- Rincón, Ascanio D.; Solórzano, Andrés; McDonald, H. Gregory; Montellano-Ballesteros, Marisol (2019-03-04). "Two new megalonychid sloths (Mammalia: Xenarthra) from the Urumaco Formation (late Miocene), and their phylogenetic affinities". Journal of Systematic Palaeontology. 17 (5): 409–421. Bibcode:2019JSPal..17..409R. doi:10.1080/14772019.2018.1427639. ISSN 1477-2019. S2CID 90207481.
- McDonald, Greg (2020-01-01). "Reexamination of the Relationship of Pseudoprepotherium Hoffstetter, 1961, to the Mylodont Ground Sloths (Xenarthra) from the Miocene of Northern South America". Revista Geológica de América Central.
- Castro, Mariela C.; Carlini, Alfredo A.; Sánchez, Rodolfo; Sánchez-Villagra, Marcelo R. (2014-02-01). "A new Dasypodini armadillo (Xenarthra: Cingulata) from San Gregorio Formation, Pliocene of Venezuela: affinities and biogeographic interpretations". Naturwissenschaften. 101 (2): 77–86. Bibcode:2014NW....101...77C. doi:10.1007/s00114-013-1131-5. ISSN 1432-1904. PMID 24414134. S2CID 12924318.
- Sánchez-Villagra, Marcelo; Vucetich, M. (2010-01-01). "The tropics as reservoir of otherwise extinct mammals: the case of rodents from a new Pliocene faunal assemblage from Northern Venezuela".
{{cite journal}}: Cite journal requires|journal=(help) - Gaudin, Timothy J. (2004). "Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence". Zoological Journal of the Linnean Society. 140 (2): 255–305. doi:10.1111/j.1096-3642.2003.00100.x. ISSN 1096-3642. S2CID 38722942.
- Delsuc, Frédéric; Kuch, Melanie; Gibb, Gillian C.; Karpinski, Emil; Hackenberger, Dirk; Szpak, Paul; Martínez, Jorge G.; Mead, Jim I.; McDonald, H. Gregory; MacPhee, Ross D. E.; Billet, Guillaume (2019-06-17). "Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of Sloths". Current Biology. 29 (12): 2031–2042.e6. Bibcode:2019CBio...29E2031D. doi:10.1016/j.cub.2019.05.043. hdl:11336/136908. ISSN 0960-9822. PMID 31178321. S2CID 177661447.
- Presslee, Samantha; Slater, Graham J.; Pujos, François; Forasiepi, Analía M.; Fischer, Roman; Molloy, Kelly; Mackie, Meaghan; Olsen, Jesper V.; Kramarz, Alejandro; Taglioretti, Matías; Scaglia, Fernando (2019-06-06). "Palaeoproteomics resolves sloth relationships". Nature Ecology & Evolution. 3 (7): 1121–1130. Bibcode:2019NatEE...3.1121P. doi:10.1038/s41559-019-0909-z. ISSN 2397-334X. PMID 31171860. S2CID 174813630.
- Varela, Luciano; Tambusso, P Sebastián; McDonald, H Gregory; Fariña, Richard A (2018-09-15). "Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis". Systematic Biology. 68 (2): 204–218. doi:10.1093/sysbio/syy058. ISSN 1063-5157. PMID 30239971.
- ^ Carrillo, J. D.; Amson, E.; Jaramillo, C.; Sánchez, R.; Quiroz, L.; Cuartas, C.; Rincón, A. F.; Sánchez-Villagra, M. R. (2018). "The Neogene Record of Northern South American Native Ungulates". Smithsonian Contributions to Paleobiology. 101 (101): iv-67. doi:10.5479/si.1943-6688.101. S2CID 135113342.
- ^ Carrillo-Briceño, J. D.; Sánchez, R.; Scheyer, T.M.; Carrillo, J.D.; Delfino, M.; Georgalis, G.L.; Kerber, L.; Ruiz-Ramoni, D.; Birindelli, J.L.O.; Cadena, E.-L.; Rincón, A.F.; Chavez-Hoffmeister, M.; Carlini, A.A.; Carvalho, M.R.; Trejos-Tamayo, R.; Vallejo, F.; Jaramillo, C.; Jones, D.S.; Sánchez-Villagra, M.R. (2021). "A Pliocene–Pleistocene continental biota from Venezuela". Swiss Journal of Palaeontology. 140 (9): 9. Bibcode:2021SwJP..140....9C. doi:10.1186/s13358-020-00216-6. PMC 8550326. PMID 34721281.
| Taxon identifiers | |
|---|---|
| Proeremotherium | |