The Isalo III Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

, off the eastern coast of Africa. It dates back to the Middle Jurassic.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 ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

cross-bedded 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 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stra ...

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

Bathonian In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. Str ...

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

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, marls and

carbonates A carbonate is a salt of carbonic acid (H2CO3), 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 g ...

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 env ...

, 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.

Vertebrate fauna

Dinosaurs

Crocodyliformes

Mammals

Pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is 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 ...

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 Rhamphorhynch ...

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.

References

Bibliography

* * * * * * {{cite LSA , last=Thevenin , first=A , year=1907 , title=Paléontologie de Madagascar. IV Dinosauriens , url=https://paleoglot.org/files/Thevenin_07.pdf , journal= Annales de Paléontologie , volume=2 , pages=121–136

* É. Buffetaut. 2005. A new sauropod dinosaur with prosauropod-like teeth from the Middle Jurassic of Madagascar. Bulletin de la Société Géologique de France 176(5):467-473 * S. Maganuco, C. Dal Sasso, and G. Pasini. 2006. A new large predatory archosaur from the Middle Jurassic (Bathonian) of Madagascar. Atti della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 147(1):19-51 * J. J. Flynn, J. M. Parrish, B. Rakotosamimanana, W. F. Simpson, and A. R. Wyss. 1999. A Middle Jurassic mammal from Madagascar. Nature 401:57-60 * A. Ogier. 1975. Etude de Nouveaux Ossements de ''Bothriospondylus'' (Sauropode) d'un Gisement du Bathonien de Madagascar tudy of New Bones of Bothriospondylus (Sauropod) from a Locality from the Bathonian of Madagascar Sciences Naturelles, Université de Paris VI 1-111 * M. Collignon. 1954. Decouverte de dinosauriens a Tsinjorano, district d'Ambato-Boeni iscovery of dinosaurs at Tsinjorano, Ambato-Boeni district Bulletin de l'Académie Malgache 31:59-61 Geologic formations of Madagascar Jurassic System of Africa Middle Jurassic Africa Jurassic Madagascar Bajocian Stage Bathonian Stage Sandstone formations Shale formations Marl formations Paleontology in Madagascar Formations Formations