The Usili Formation is a

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

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, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...

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

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Per ...

s, therapsids 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) than to lepidosaurs (such as tuataras, lizards, a ...

'' Aenigmastropheus''.

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 or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...

to the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

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 university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...

.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 In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

, 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?) Formation (stratigraphy), geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassi ...

, 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 Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, on the International Commission on Stratigraphy, ICS geologic timesc ...

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

, including the Idusi (K1), Mchuchuma (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 often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

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. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

, as well as with the

Zambia Zambia, officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa. It is typically referred to being in South-Central Africa or Southern Africa. It is bor ...

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 under ...

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 Biology ...

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 fla ...

'', ''

Dicynodon ''Dicynodon'' (from Ancient Greek '' δίς'' "two" and '' κυνόδους'' "canine teeth", often translated to "two canine-teeth" or "two dog-teeth") is a genus of dicynodont therapsid that lived in southern and eastern Africa during the Lat ...

'', and ''

Tropidostoma ''Tropidostoma'' is a medium-sized herbivorous oudenodontid dicynodont therapsid that lived during the Late Permian (Lopingian) period in South Africa. The first ''Tropidostoma'' fossil was described by Harry Govier Seeley in 1889. Later two su ...

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

gorgonopsia Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of Saber-toothed predator, sabre-toothed therapsids from the Middle Permian, Middle to the Upper Permian, roughly between 270 and 252 million years ago. ...

ns,

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

ns,

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s, and

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

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 fourth largest ...

). 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, Zambia and Russia. It contains '' Bondoceras'', ''Bullacephalus'', ''Burnetia'', '' Mobaceras'', '' Niuksenit ...

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 and Zambia. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontol ...

'', ''

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 Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means ' ...

'', ''

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 maxilla) is an extinct genus ...

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

Gorgonops ''Gorgonops'' (from 'Gorgon' and 'eye, face', literally 'Gorgon eye' or 'Gorgon face') is an extinct genus of gorgonopsian therapsid, of which it is the type genus. ''Gorgonops'' lived during the Late Permian (Wuchiapingian), about 260–254 ...

? dixeyi'' and an indeterminate tusked

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

Paleobiota

Tetrapods

Temnospondyls

Parareptiles

Eureptiles

Therapsids

=Anomodonts

=Biarmosuchians

=Cynodonts

=Therocephalians

=Gorgonopsians

References

{{reflist 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