The Isalo III Formation is a geological formation in

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

, off the eastern coast of Africa. It dates back to the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

.Weishampel et al., 2004, pp.542-543 The use of the term "Isalo III" is somewhat controversial as the two prior units Isalo I and II are

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 ...

cross-bedded In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original ...

sandstone units that form a continuous depositional sequence, while the "Isalo III" sandstones are not part of the same depositional sequence, and were deposited considerably later. and are perhaps better treated as part of several separate formations.Geiger et al., 2004 It is traditionally divided into two subunits the lower,

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonia ...

aged Isalo IIIa unit also known as the Beronono Formation and the upper,

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

aged Isalo IIIb unit also known as the Sakaraha Formation or Sakahara Formation. The Sakaraha Formation consists of

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 ...

marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...

s and

carbonates A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group . ...

and represents a coastal plain environment, and is laterally equivalent to the predominantly carbonate

Bemaraha Formation The Bemaraha Formation is a Middle Jurassic (early Bajocian to early Bathonian) geological formation of the Morondava Basin of Madagascar. The lime mudstones, grainstones and limestones of the formation were deposited in lagoonal and reefal enviro ...

, which represents a coastal barrier lagoon complex. The formation is found in the northwest and in the southeast of the country and has provided a variety of fossils.

Fossil content

Pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...

teeth referred to

Rhamphorhynchoidea The Rhamphorhynchoidea forms one of the two suborders of pterosaurs and represents an evolutionary grade of primitive members of flying reptiles. This suborder is paraphyletic unlike the Pterodactyloidea, which arose from within the Rhamphorhync ...

are known from the formation.Dal Sasso C. & Pasini G., 2003 - First record of pterosaurs (Pterosauria, Archosauromorpha, Diapsida) in the Middle Jurassic of Madagascar. Atti della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano, 144 (II): 281-296.

Dinosaurs

Sauropods

Theropoda

Crocodyliformes

References

Bibliography

* * * * * * {{cite journal , last=Thevenin , first=A , year=1907 , title=Paléontologie de Madagascar. IV Dinosauriens , url=https://paleoglot.org/files/Thevenin_07.pdf , journal=

Annales de Paléontologie ''Annales de Paléontologie'' is a peer-reviewed scientific journal covering paleontology. It is published by Elsevier. According to the ''Journal Citation Reports'', its 2020 impact factor is 0.702. The journal is abstracted and indexed in BIOSI ...

, volume=2 , pages=121–136