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The '''Usili Formation''' is a ] ] in ]. It preserves fossils of many terrestrial vertebrates from the Permian, including ]s, ]s, ]s and the ] '']''.<ref name=Sidor&el13>{{cite journal | doi = 10.1073/pnas.1302323110 | title = Provincialization of terrestrial faunas following the end-Permian mass extinction | year = 2013 | last1 = Sidor | first1 = C. A. | last2 = Vilhena | first2 = D. A. | last3 = Angielczyk | first3 = K. D. | last4 = Huttenlocker | first4 = A. K. | last5 = Nesbitt | first5 = S. J. | last6 = Peecook | first6 = B. R. | last7 = Steyer | first7 = J. S. | last8 = Smith | first8 = R. M. H. | last9 = Tsuji | first9 = L. A. | journal = Proceedings of the National Academy of Sciences | volume = 110 | issue = 20 | pages = 8129–33 | pmid=23630295 | pmc=3657826 |
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The '''Usili Formation''' is a ] ] in ]. It preserves fossils of many terrestrial vertebrates from the Permian, including ]s, ]s, ]s and the ] '']''.<ref name=Sidor&el13>{{cite journal | doi = 10.1073/pnas.1302323110 | title = Provincialization of terrestrial faunas following the end-Permian mass extinction | year = 2013 | last1 = Sidor | first1 = C. A. | last2 = Vilhena | first2 = D. A. | last3 = Angielczyk | first3 = K. D. | last4 = Huttenlocker | first4 = A. K. | last5 = Nesbitt | first5 = S. J. | last6 = Peecook | first6 = B. R. | last7 = Steyer | first7 = J. S. | last8 = Smith | first8 = R. M. H. | last9 = Tsuji | first9 = L. A. | journal = Proceedings of the National Academy of Sciences | volume = 110 | issue = 20 | pages = 8129–33 | pmid=23630295 | pmc=3657826 |
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}}</ref><ref name=Aenigmastropheus>{{Cite journal | doi = 10.1371/journal.pone.0089165| title = The Origin and Early Evolution of Sauria: Reassessing the Permian Saurian Fossil Record and the Timing of the Crocodile-Lizard Divergence| journal = PLoS ONE| volume = 9| issue = 2| pages = e89165| year = 2014| last1 = Ezcurra | first1 = M. N. D. | last2 = Scheyer | first2 = T. M. | last3 = Butler | first3 = R. J. | pmid=24586565 | pmc=3937355}}</ref> |
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| doi-access = free }}</ref><ref name=Aenigmastropheus>{{Cite journal | doi = 10.1371/journal.pone.0089165| title = The Origin and Early Evolution of Sauria: Reassessing the Permian Saurian Fossil Record and the Timing of the Crocodile-Lizard Divergence| journal = PLOS ONE| volume = 9| issue = 2| pages = e89165| year = 2014| last1 = Ezcurra | first1 = M. N. D. | last2 = Scheyer | first2 = T. M. | last3 = Butler | first3 = R. J. | pmid=24586565 | pmc=3937355| doi-access = free}}</ref> |
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== History of study == |
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== History of study == |
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One of the first to study rocks of the Usili Formation was British geologist G. M. Stockley. In 1932, Stockley explored the geology of the Ruhuhu Basin in Tanzania. He called a series of layers dating from the ] to the ] of the Songea Series and divided it into eight units labelled K1-K8. Stockley was also the first to describe fossils from these rocks, naming an older layer the "Lower Bone Bed" and a younger layer the "Upper Bone Bed".<ref name=BBAG09/> |
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One of the first to study rocks of the Usili Formation was British geologist G. M. Stockley. In 1932, Stockley explored the geology of the Ruhuhu Basin in Tanzania. He called a series of layers dating from the ] to the ] of the Songea Series and divided it into eight units labelled K1-K8. Stockley was also the first to describe fossils from these rocks, naming an older layer the "Lower Bone Bed" and a younger layer the "Upper Bone Bed".<ref name=BBAG09/> |
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In 1957, paleontologist ] described many more fossils from the upper bone beds in his Ph.D. thesis for the ].<ref name=CAJ57>Charig, A. J. (1957). New Triassic archosaurs from Tanganyika, including ''Mandasuchus'' and ''Teleocrater'': Dissertation Abstracts. Cambridge University.</ref><ref name=NB12>{{Cite journal | last1 = Nesbitt | first1 = S. J. | last2 = Butler | first2 = R. J. | doi = 10.1017/S0016756812000362 | title = Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae | journal = Geological Magazine | pages = 225–238 | year = 2012 | volume=150| issue = 2 | url = https://semanticscholar.org/paper/7dfcd25c6aaa4e4d9a0a4a6bf024f5a43fe024c6 }}</ref> Subsequently, Stockley's units were renamed, Charig (1963) calling unit K6 the Kawinga Formation, K7 the Kingori Sandstones, and K8 the Manda Formation. Fossils were identified in many ], invalidating Stockley's division into two distinct bone beds. Since Charig's description, the Kawinga Formation has been renamed the Usili Formation, the Kingori Sandstones have become the Kingori Sandstone Member of the ], and Charig's original Manda Formation has become a subunit of the formation called the Lifua Member.<ref name=BBAG09>{{Cite journal | last1 = Butler | first1 = R. J. | last2 = Barrett | first2 = P. M. | last3 = Abel | first3 = R. L. | last4 = Gower | first4 = D. J. | title = A possible ctenosauriscid archosaur from the Middle Triassic Manda Beds of Tanzania | doi = 10.1671/039.029.0404 | journal = Journal of Vertebrate Paleontology | volume = 29 | issue = 4 | pages = 1022–1031 | year = 2009 }}</ref> Six formations and one informal unit are currently recognized in the Songea Group (Ruhuhu basin) rocks range in age from ] to ], including the ] (K1), ] (K2), ] (K3), ] (K4), ] (K5), and Usili (K6) formations and the informal ], which include the ] (K7) and ] (K8).<ref name=Sidor&el10>{{Cite journal | doi = 10.1080/02724631003758086| title = Tetrapod fauna of the lowermost Usili Formation (Songea Group, Ruhuhu Basin) of southern Tanzania, with a new burnetiid record| journal = Journal of Vertebrate Paleontology| volume = 30| issue = 3| pages = 696–703| year = 2010| last1 = Sidor | first1 = C. A. | last2 = Angielczyk | first2 = K. D. | last3 = Weide † | first3 = D. M. | last4 = Smith | first4 = R. M. H. | last5 = Nesbitt | first5 = S. J. | last6 = Tsuji | first6 = L. A. | url = http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1379&context=geosciencefacpub}}</ref> |
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In 1957, paleontologist ] described many more fossils from the upper bone beds in his Ph.D. thesis for the ].<ref name=CAJ57>Charig, A. J. (1957). New Triassic archosaurs from Tanganyika, including ''Mandasuchus'' and ''Teleocrater'': Dissertation Abstracts. Cambridge University.</ref><ref name=NB12>{{Cite journal | last1 = Nesbitt | first1 = S. J. | last2 = Butler | first2 = R. J. | doi = 10.1017/S0016756812000362 | title = Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae | journal = Geological Magazine | pages = 225–238 | year = 2012 | volume=150| issue = 2 | s2cid = 232175772 | url = https://semanticscholar.org/paper/7dfcd25c6aaa4e4d9a0a4a6bf024f5a43fe024c6 }}</ref> Subsequently, Stockley's units were renamed, Charig (1963) calling unit K6 the Kawinga Formation, K7 the Kingori Sandstones, and K8 the Manda Formation. Fossils were identified in many ], invalidating Stockley's division into two distinct bone beds. Since Charig's description, the Kawinga Formation has been renamed the Usili Formation, the Kingori Sandstones have become the Kingori Sandstone Member of the ], and Charig's original Manda Formation has become a subunit of the formation called the Lifua Member.<ref name=BBAG09>{{Cite journal | last1 = Butler | first1 = R. J. | last2 = Barrett | first2 = P. M. | last3 = Abel | first3 = R. L. | last4 = Gower | first4 = D. J. | title = A possible ctenosauriscid archosaur from the Middle Triassic Manda Beds of Tanzania | doi = 10.1671/039.029.0404 | journal = Journal of Vertebrate Paleontology | volume = 29 | issue = 4 | pages = 1022–1031 | year = 2009 | s2cid = 86267617 }}</ref> Six formations and one informal unit are currently recognized in the Songea Group (Ruhuhu basin) rocks range in age from ] to ], including the ] (K1), ] (K2), ] (K3), ] (K4), ] (K5), and Usili (K6) formations and the informal ], which include the ] (K7) and ] (K8).<ref name=Sidor&el10>{{Cite journal | doi = 10.1080/02724631003758086| title = Tetrapod fauna of the lowermost Usili Formation (Songea Group, Ruhuhu Basin) of southern Tanzania, with a new burnetiid record| journal = Journal of Vertebrate Paleontology| volume = 30| issue = 3| pages = 696–703| year = 2010| last1 = Sidor | first1 = C. A. | last2 = Angielczyk | first2 = K. D. | last3 = Weide † | first3 = D. M. | last4 = Smith | first4 = R. M. H. | last5 = Nesbitt | first5 = S. J. | last6 = Tsuji | first6 = L. A. | s2cid = 55397720| url = http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1379&context=geosciencefacpub}}</ref> |
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Recent studies have described the Usili Formation as a {{convert|260|m|ft}} thick ]-] succession made up of a lowermost conglomeratic interval that is approximately 5 meters thick, grading up into a trough cross-bedded, coarse-grained, sandstone-dominated interval that is {{convert|25|to|40|m|ft}} thick, overlain by massive nodular siltstone and laminated mudstone beds with minor ribbon sandstones forming the bulk of the succession. Since Parrington (1956), the Usili Formation became widely recognized as a Late Permian formation that correlates with the ] and ] formations of ], as well as with the ]n ] (]). Comparison of Usili tetrapods with those of the lower ] has suggested a broad ] correlation with the '']'', '']'', and '']'' assemblage zones. Sidor ''et al.'' (2010) recognized only one undivided tetrapod faunal assemblage in the Usili Formation, which includes '']'', ]s, ]s, ]ns, ]ns, ]s, and ]s, whose remains were collected from various localities. This suggests that several therapsid genera have unequal stratigraphic ranges and temporal durations in the Ruhuhu and Karoo basins.<ref name=Aenigmastropheus/><ref name=Sidor&el10/> |
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Recent studies have described the Usili Formation as a {{convert|260|m|ft}} thick ]-] succession made up of a lowermost conglomeratic interval that is approximately 5 meters thick, grading up into a trough cross-bedded, coarse-grained, sandstone-dominated interval that is {{convert|25|to|40|m|ft}} thick, overlain by massive nodular siltstone and laminated mudstone beds with minor ribbon sandstones forming the bulk of the succession. Since Parrington (1956), the Usili Formation became widely recognized as a Late Permian formation that correlates with the ] and ] formations of ], as well as with the ]n ] (]). Comparison of Usili tetrapods with those of the lower ] has suggested a broad ] correlation with the '']'', '']'', and '']'' assemblage zones. Sidor ''et al.'' (2010) recognized only one undivided tetrapod faunal assemblage in the Usili Formation, which includes '']'', ]s, ]s, ]ns, ]ns, ]s, and ]s, whose remains were collected from various localities. This suggests that several therapsid genera have unequal stratigraphic ranges and temporal durations in the Ruhuhu and Karoo basins.<ref name=Aenigmastropheus/><ref name=Sidor&el10/> |
One of the first to study rocks of the Usili Formation was British geologist G. M. Stockley. In 1932, Stockley explored the geology of the Ruhuhu Basin in Tanzania. He called a series of layers dating from the Late Carboniferous to the Middle Triassic of the Songea Series and divided it into eight units labelled K1-K8. Stockley was also the first to describe fossils from these rocks, naming an older layer the "Lower Bone Bed" and a younger layer the "Upper Bone Bed".
Recent studies have described the Usili Formation as a 260 metres (850 ft) thick fluvio-lacustrine succession made up of a lowermost conglomeratic interval that is approximately 5 meters thick, grading up into a trough cross-bedded, coarse-grained, sandstone-dominated interval that is 25 to 40 metres (82 to 131 ft) thick, overlain by massive nodular siltstone and laminated mudstone beds with minor ribbon sandstones forming the bulk of the succession. Since Parrington (1956), the Usili Formation became widely recognized as a Late Permian formation that correlates with the Teekloof and Balfour formations of South Africa, as well as with the Zambian Upper Madumabisa Mudstone (Cistecephalus AZ). Comparison of Usili tetrapods with those of the lower Beaufort Group has suggested a broad biostratigraphic correlation with the Cistecephalus, Dicynodon, and Tropidostoma assemblage zones. Sidor et al. (2010) recognized only one undivided tetrapod faunal assemblage in the Usili Formation, which includes Aenigmastropheus, temnospondyls, pareiasaurs, gorgonopsians, therocephalians, cynodonts, and dicynodonts, whose remains were collected from various localities. This suggests that several therapsid genera have unequal stratigraphic ranges and temporal durations in the Ruhuhu and Karoo basins.
Tanzania