The Yerrapalli Formation is a

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

rock formation A rock formation is an isolated, scenic, or spectacular surface rock (geology), rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock Geological formation, formation ...

consisting primarily of

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s that outcrops in the Pranhita–Godavari Basin in southeastern India. The Yerrapalli Formation preserves fossils of freshwater and terrestrial vertebrates as well as

trace fossil A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

s of invertebrates.Yerrapalli Formation
at

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.org The

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

fauna includes

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 ...

amphibians, archosauromorph reptiles, and dicynodonts.

Geology

Most of the Yerrapalli Formation consists of red mudstones. The mudstones were deposited across a

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

during the

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 ...

stage of 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 ...

. Smaller

lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

represent ephemeral streams that branched off from the larger channels that were the source of the floodplain sediments. The climate of the region during the time is thought to have been monsoonal with both wet and dry seasons. The Yerrapalli Formation overlies the Kamthi Formation, underlies the Bhimaram Formation, and is conformable with both formations. Two

members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

of the Yerrapalli Formation have been recognized; a lower member consisting of layers of red and purple clay with lenses of pale green clay and an upper member consisting of alternating layers of clay and fine-grained sandstone.

Paleobiota

The paleobiota of the Yerrapalli Formation is similar to that of the overlying Maleri Formation, which also preserves fossils of temnospondyls and archosauromorphs. The main difference between the Yerrapalli and the Maleri faunae is the presence of dicynodonts in the former. The discovery of dicynodont fossils in the Pranhita-Godavari Basin in 1964 was one of the earliest indications that the Yerrapalli Formation represented a distinct paleofauna. Before this discovery, Yerrapalli strata were grouped within the Maleri Formation. The dicynodonts of the Yerrapalli Formation are similar to those of the Ntawere Formation in Zambia, which also dates back to the Anisian. During the Middle Triassic, what is now India and southern Africa formed one continuous landmass as part of the supercontinent

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

Synapsids

Reptiles

Amphibians

Fish

References

{{reflist Geologic formations of India Triassic System of Asia Triassic India Anisian Stage Mudstone formations Fluvial deposits Paleontology in India Geology of Andhra Pradesh Formations