Isalo III Formation

Isalo III Formation
Stratigraphic range: Bajocian-Bathonian ~
Type	Geological formation
Sub-units	Isalo IIIa or Beronono Formation Isalo IIIb or Sakaraha Formation
Overlies	Isalo II Formation (unconformity)
Lithology
Primary	Sandstone
Other	Claystone, marl
Location
Coordinates	16.6°S 47.0°E / -16.6; 47.0
Approximate paleocoordinates	23.9°S 25.1°E / -23.9; 25.1
Region	Mahajanga & Fianarantsoa Provinces
Country	Madagascar
Extent	Mahajanga Basin

The Isalo III Formation is a geological formation in Madagascar, off the eastern coast of Africa. It dates back to the Middle Jurassic. The use of the term "Isalo III" is somewhat controversial as the two prior units Isalo I and II are Triassic 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. It is traditionally divided into two subunits the lower, Bajocian aged Isalo IIIa unit also known as the Beronono Formation and the upper, Bathonian aged Isalo IIIb unit also known as the Sakaraha Formation or Sakahara Formation. The Sakaraha Formation consists of sandstones, marls and carbonates and represents a coastal plain environment, and is laterally equivalent to the predominantly carbonate Bemaraha Formation, 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

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Dinosaurs

Sauropods

Sauropods of the Isalo III Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Archaeodontosaurus	A. descouensi	Ambondromamy, Majunga		Teeth and mandible	A eusauropod sauropod
Lapparentosaurus	L. madagascariensis	Faritany Majunga		"More than [four] partial skeletons lacking skulls and teeth"	A cetiosaurid sauropod
Narindasaurus	N. thevenini	Ankinganivalaka		Right tibia, left pubis, caudal vertebrae, right fibula	A turiasaurian sauropod
?Diplodocoidea Indet	Indeterminate	IIIb	Teeth
?Titanosaurifomes Indet	Indeterminate	IIIb	Teeth

Theropoda

Theropods of the Isalo III Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Theropoda Indet.	Indeterminate	IIIb		MSNM V6234 "a large, serrated tooth crown" MSNM V5804 vertebra, isolated teeth representing 8 morphotypes
Ceratosauria Indet.	Indeterminate	IIIb		MSNM V6235 Pedal ungual

Crocodyliformes

Crocodyliformes of the Isalo III Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Andrianavoay	A. baroni	IIIb			A machimosaurine thelattosuchian
Razanandrongobe	R. sakalavae	IIIb			A notosuchian

Ichthyosaurs

Ichthyosaurs of the Isalo III Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images

Plesiosaurs

Plesiosaurs of the Isalo III Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images

Mammals

Mammals of the Isalo III Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ambondro	A. mahabo	IIIb			A henosferid australosphenidan

Pterosaur teeth referred to Rhamphorhynchoidea are known from the formation.

See also

• List of dinosaur-bearing rock formations
• List of fossiliferous stratigraphic units in Madagascar
• Geology of Madagascar

References

Bibliography

• Royo Torres, Rafael; Cobos, Alberto; Mocho, Pedro; Alcalá, Luis (2021). "Origin and evolution of turiasaur dinosaurs set by means of a new 'rosetta' specimen from Spain". Zoological Journal of the Linnean Society. 191: 201–227. doi:10.1093/zoolinnean/zlaa091.
• Bindellini, Gabriele; Sasso, Cristiano Dal (2019). "Sauropod teeth from the Middle Jurassic of Madagascar, and the oldest record of Titanosauriformes". Papers in Palaeontology. 7: 137–161. doi:10.1002/spp2.1282. S2CID 203376597.
• Dal Sasso, Cristiano; Pasini, Giovanni; Fleury, Guillaume; Maganuco, Simone (2017). "Razanandrongobe sakalavae, a gigantic mesoeucrocodylian from the Middle Jurassic of Madagascar, is the oldest known notosuchian". PeerJ. 5: e3481. doi:10.7717/peerj.3481. PMC 5499610. PMID 28690926.
• Geiger, Markus; Clark, David Norman; Mette, Wolfgang (2004). "Reappraisal of the timing of the breakup of Gondwana based on sedimentological and seismic evidence from the Morondava Basin, Madagascar". Journal of African Earth Sciences. 38 (4): 363–381. Bibcode:2004JAfES..38..363G. doi:10.1016/j.jafrearsci.2004.02.003.
• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka, eds. (2004). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 1–880. ISBN 9780520941434.
• Thevenin, A (1907). "Paléontologie de Madagascar. IV Dinosauriens" (PDF). Annales de Paléontologie. 2: 121–136.

Further reading

• 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 [Study 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 [Discovery of dinosaurs at Tsinjorano, Ambato-Boeni district]. Bulletin de l'Académie Malgache 31:59-61