The Isalo III Formation is a geological formation in Madagascar, off the eastern coast of Africa. It dates back to the Middle Jurassic.[1] 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.[2] 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.[3] 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.[2] The formation is found in the northwest and in the southeast of the country and has provided a variety of fossils.
Isalo III Formation | |
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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°36′S 47°00′E / 16.6°S 47.0°E |
Approximate paleocoordinates | 23°54′S 25°06′E / 23.9°S 25.1°E |
Region | Mahajanga & Fianarantsoa Provinces |
Country | Madagascar |
Extent | Mahajanga Basin |
Taxon | Species | Presence | Remains | Notes | Images |
---|---|---|---|---|---|
Lapparentosaurus[1] | L. madagascariensis | Faritany Majunga[1] | "More than [four] partial skeletons lacking skulls and teeth"[4] | Considered a titanosauriform by Mannion (2010),[5] Suggested to be a Cetiosaurid by Raveloson et al (2019)[6] | |
Narindasaurus | N. thevenini[7][8] | Ankinganivalaka | Right tibia, left pubis, caudal vertebrae, right fibula | Turiasaurian sauropod | |
Archaeodontosaurus | A. descouensi | Ambondromamy, Majunga | Teeth and mandible | ||
"Bothriospondylus" [1] | "B." madagascariensis | Faritany Majunga[1] | Type:"NHM R2598: mid‐dorsal vertebra." Referred: "NHM R2596–2615, R16588, R16589 dorsal, sacral and caudal vertebrae; elements of the pectoral and pelvic girdles; a partial humerus; fragments of the hindlimbs. Material represents a minimum of three individuals, based on duplication of elements and size differences."[5] | Non‐neosauropod eusauropod, distinct from Lapparentosaurus, also formerly referred to by the same name.[5] | |
Theropoda | Indeterminate | IIIb | MSNM V6234 "a large, serrated tooth crown"[9] MSNM V5804 vertebra, isolated teeth representing 8 morphotypes[10] | ||
Ceratosauria | Indeterminate | IIIb | MSNM V6235 Pedal ungual[9] | ||
?Diplodocoidea[11] | Indeterminate | IIIb | Teeth | ||
?Titanosaurifomes[11] | Indeterminate | IIIb | Teeth |
Taxon | Species | Presence | Notes | Images |
---|---|---|---|---|
Razanandrongobe[3] | R. sakalavae | IIIb | Notosuchian |
Taxon | Species | Presence | Notes | Images |
---|---|---|---|---|
Ambondro | A. mahabo | IIIb | A member of Australosphenida[12] |
Pterosaur teeth referred to Rhamphorhynchoidea are known from the formation.[13]