The Usili Formation is a

Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

. It preserves fossils of many terrestrial vertebrates from the Permian, including

temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carbo ...

s, pareiasaurs,

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

s and the

archosauromorph Archosauromorpha ( Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, l ...

Aenigmastropheus ''Aenigmastropheus'' is an extinct genus of early archosauromorph reptiles known from the middle Late Permian Usili Formation of Songea District, southern Tanzania. It contains a single species, ''Aenigmastropheus parringtoni'', known solely ...

''.

History of study

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 Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

to the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

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". In 1957, paleontologist Alan J. Charig described many more fossils from the upper bone beds in his Ph.D. thesis for the

University of Cambridge The University of Cambridge is a public collegiate research university in Cambridge, England. Founded in 1209 and granted a royal charter by Henry III in 1231, Cambridge is the world's third oldest surviving university and one of its most pr ...

.Charig, A. J. (1957). New Triassic archosaurs from Tanganyika, including ''Mandasuchus'' and ''Teleocrater'': Dissertation Abstracts. Cambridge University. 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 strata, 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

Manda Formation The Manda Formation (also known as the Manda Beds) is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the e ...

, and Charig's original Manda Formation has become a subunit of the formation called the Lifua Member. Six formations and one informal unit are currently recognized in the Songea Group (Ruhuhu basin) rocks range in age from Pennsylvanian to

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic ...

, including the Idusi (K1),

Mchuchuma Mchuchuma in south western Tanzania near Ludewa off the northern tip of Lake Nyasa, is the site of major coal deposits. There is also a thermal power station costing$612m. Recent studies indicate that Mchuchuma/ Ketewaka coal deposits should be c ...

(K2), Mbuyura (K3), Mhukuru (K4), Ruhuhu (K5), and Usili (K6) formations and the informal

Manda Beds The Manda Formation (also known as the Manda Beds) is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the e ...

, which include the Kingori Sandstone (K7) and Lifua Member (K8). Recent studies have described the Usili Formation as a thick fluvio-

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

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 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 South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

, as well as with the

Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most central point. Its neighbours are t ...

n Upper Madumabisa Mudstone ( ''Cistecephalus'' AZ). Comparison of Usili tetrapods with those of the lower

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underli ...

has suggested a broad

biostratigraphic Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...

correlation with the ''

Cistecephalus ''Cistecephalus'' is an extinct genus of dicynodont therapsid from the Late Permian of southern Africa (South Africa and Zambia). It was a small, specialised, burrowing dicynodont, possibly with habits similar to a modern mole. The head was flat ...

'', ''

Dicynodon ''Dicynodon'' ("two dog-teeth") is a genus of dicynodont therapsid that flourished during the Upper Permian period. Like all dicynodonts, it was herbivorous animal. This reptile was toothless, except for prominent tusks, hence the name. It proba ...

'', and '' Tropidostoma'' assemblage zones. Sidor ''et al.'' (2010) recognized only one undivided tetrapod faunal assemblage in the Usili Formation, which includes ''

'',

s, pareiasaurs,

gorgonopsia Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of sabre-toothed therapsids from the Middle to Upper Permian roughly 265 to 252 million years ago. They are characterised by a long and narrow skull, a ...

ns,

therocephalia Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their ...

ns, cynodonts, and

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typic ...

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. Sidor ''et al.'' (2010) and Sidor ''et al.'' (2013) noted that it is probable that the Chiweta Beds of Malawi and the Usili Formation of Tanzania represent the same rock unit, separated only by political boundaries and geologic faulting (being located on either side of

Lake Nyasa Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. It is the fifth largest fre ...

). Except for the

burnetiid Burnetiidae is an extinct family of biarmosuchian therapsids that lived in the Permian period whose fossils are found in South Africa and Russia. It contains ''Bullacephalus'', ''Burnetia'', '' Mobaceras'', ''Niuksenitia'', ''Paraburnetia'' and ...

MAL 240, which is unique to the Chiweta Beds, the Usili Formation hosts identical genera, including ''

Aelurognathus ''Aelurognathus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontologists Rober ...

'', ''

Dicynodontoides ''Dicynodontoides'' is a genus of small to medium-bodied, herbivorous, emydopoid dicynodonts from the Late Permian. The name ''Dicynodontoides'' references its “dicynodont-like” appearance (dicynodont = two-dog-tooth) due to the caniniform t ...

'', ''

Rhachiocephalus ''Rhachiocephalus'' is an extinct genus of dicynodont therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their orig ...

'', ''

Endothiodon ''Endothiodon'' (/ɛndoʊθiːoʊdɔːn/ "inner tooth" from Greek endothi (ἔνδοθῐ), "within", and odon (ὀδών), "tooth", most likely named for the characteristic of the teeth being placed internally to the maxillaBoos A. S., Schultz C ...

cf. E. bathystoma'', '' Oudenodon baini'', ''

Gorgonops ''Gorgonops'' (from el, Γοργών 'Gorgon' and 'eye, face', literally 'Gorgon eye' or 'Gorgon face') is an extinct genus of gorgonopsian therapsids, of which it is the type genus, having lived during the Late Permian (Wuchiapingian), about ...

? dixeyi'' and an indeterminate tusked

(SAM-PK-7862, SAM-PK-7863).

Paleobiota

Tetrapods

Temnospondyls

Parareptiles

Eureptiles

Therapsids

=Anomodonts

=Biarmosuchians

=Cynodonts

=Therocephalians

=Gorgonopsians

References

{{reflist Geologic formations of Tanzania Permian System of Africa Permian Tanzania Lopingian geology Sandstone formations Conglomerate formations Siltstone formations Mudstone formations Fluvial deposits Lacustrine deposits Permian southern paleotemperate deposits Paleontology in Tanzania Formations