Maevarano Formation

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Maevarano Formation
Stratigraphic range: Maastrichtian
~70–65.8 Ma
↓
TypeGeological formation
Sub-unitsMasorobe, Anembalemba & Miadana Members
UnderliesBerivotra Formation
Overlies
Thickness>105 m (344 ft)
Lithology
PrimarySandstone
OtherClaystone, siltstone
Location
Coordinates15°54′S 46°36′E / 15.9°S 46.6°E / -15.9; 46.6Coordinates: 15°54′S 46°36′E / 15.9°S 46.6°E / -15.9; 46.6
Approximate paleocoordinates30°06′S 38°24′E / 30.1°S 38.4°E / -30.1; 38.4
RegionMahajanga Province
Country Madagascar
Extent
Type section
Named for
Named bySalètes
Year defined1895
Maevarano Formation is located in Madagascar
Maevarano Formation
Maevarano Formation (Madagascar)

The Maevarano Formation is a Late Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age,[1] and records a seasonal, semiarid environment with rivers that had greatly varying discharges. Notable animal fossils recovered include the theropod dinosaur Majungasaurus, the early bird Vorona, the paravian Rahonavis, the titanosaurian sauropod Rapetosaurus, and the giant frog Beelzebufo.

Description[]

The Maevarano Formation is well exposed in the , in particular near the village of Berivotra near the northwestern coast of the island where its outcrops have been heavily dissected by erosion. At the time it was being deposited, its latitude was between 30°S and 25°S as Madagascar drifted northward after splitting from India about 88 million years ago. It is composed of three smaller units or members. The lowest is the Masorobe Member, which is usually reddish and is at least 80 metres (260 ft). Its rocks are mostly poorly sorted coarse-grained sandstones with some finer-grained beds. It is separated by an erosional disconformity from the next member, the Anembalemba Member. The lower portion of the Anembalemba Member is fine to coarse clay-rich sandstone, whitish or light grey in color, with cross-bedding. The upper portion of this member is made of poorly sorted clay-rich sandstone, light olive-grey in color, that lacks cross-bedding. Most vertebrate fossils come from the Anembalemba Member, especially from the upper portion. The Miadana Member, the third and uppermost member, is not always present, and is up to 25 metres (82 ft) in some places. Elsewhere, it is replaced by the marine Berivotra Formation. The Miadana Member is made up of claystone, siltstone, and sandstone, lacks cross-bedding, and has several colors of rock. The Maevarano Formation as a whole is underlain by the Marovoay beds and capped by the Berivotra Formation.[1]

The age of the Maevarano Formation has been debated; the Berivotra Formation, which is partially contemporaneous with the upper portions of the formation, shows that at least the upper part of the Maevarano is Maastrichtian in age. There is no evidence that it is Campanian,[1] despite previous reports to that effect.[2] The Berivotra Formation appears to include near its top a magnetic reversal, interpreted as the shift from Chron 30N to Chron 29R, which occurred approximately 65.8 million years ago (about 300,000 years before the Cretaceous–Paleogene boundary and associated Cretaceous–Paleogene extinction event. This suggests that Maevarano organisms also lived shortly before (geologically speaking) the extinction event.[1]

History of exploration[]

The Maevarano Formation was first explored by French military physician Dr. Félix Salètes and his staff officer Landillon in 1895, and fossils and geologic data were sent to paleontologist Charles Depéret.[3] He briefly described the formation and named two dinosaurs from the remains (Titanosaurus madagascariensis and Megalosaurus crenatissimus, now Majungasaurus).[4] Similar collections were made throughout the 20th century, yielding mostly fragmentary fossils;[3] one such specimen, a rough partial skull roof, became the holotype of supposed pachycephalosaur (bonehead dinosaur) Majungatholus in 1979.[5] (This specimen was later shown to be part of the skull ornamentation of a Majungasaurus.) Large-scale expeditions (seven to date), under the banner of the Mahajanga Basin Project, began in 1993. These expeditions, conducted jointly by Stony Brook University and the University of Antananarivo, have greatly expanded knowledge of this formation and the organisms that lived while it was being deposited.[3]

Paleoenvironment[]

The Maevarano Formation is interpreted as a low-relief alluvial plain that over time was covered by a marine transgression. Broad, shallow rivers flowed to the northwest from central highlands; evidence for debris flows suggests that the discharges of the rivers varied greatly, with periods of dilute water flow, and periods of rapid erosion dumping sediment into the channels. Paleosols are reddish and include root casts. The paleosols and other sedimentologic evidence indicate well-drained floodplains with abundant vegetation adapted to a relatively dry climate, strongly seasonal (rainy and dry seasons) and at times semiarid (not unlike the present climate of the area).[1]

Vertebrate paleofauna[]

Majungasaurus crenatissimus,
top land predator of the formation

Animals found in the formation include frogs (including Beelzebufo ampinga),[6] turtles, snakes, lizards, at least seven species of crocodyliforms (including species of Mahajangasuchus and Trematochampsa), abelisaurid theropods Majungasaurus, noasaurid Masiakasaurus, two types of titanosaurian sauropods (Rapetosaurus and Vahiny), and at least five species of bird-like dinosaurs, including Rahonavis. The 6 to 7 metres (20 to 23 ft) long Majungasaurus was likely the apex predator in the terrestrial environment. Crocodyliforms were very diverse and abundant.[1]

Amphibians[]

Amphibians
Genus Species Location Stratigraphic position Material Notes Images
Beelzebufo Beelzebufo ampinga locality MAD98-25[7] A large frog
Beelzebufo BW.jpg

Dinosaurs[]

Indeterminate Lithostrotia remains formerly attributed to the titanosauridae. Undescribed Lithostrotia form. Indeterminate Enantiornithes remains. Possible indeterminate spinosaurid remains.[citation needed] A rich avifauna with several undescribed taxa are known, including pengornithid enantiornithes and putative omnivoropterygids.[8]

Dinosaurs
Genus Species Location Stratigraphic position Material Notes Images
Falcatakely[9] F. forsterae "Partial skull" A member of Enantiornithes
Majungasaurus[10] M. crenatissimus[10] "Scattered remains leading to nearly most of the animal."[11] An abelisaur
Majungasaurus head BW.jpg
Masiakasaurus[10] M. knopfleri[10] "Disarticulated remains of at least 6 individuals," as well as other isolated fossils.[12] A noasaurid abelisaur
Masiakasaurus BW.jpg
Rahonavis[10] R. ostromi[10] "Partial postcranial skeleton"[13] A paravian of unclear phylogenetic placement
Rahonavis NT.jpg
Rapetosaurus[10] Rapetosaurus krausei[10] "[Three] skulls, at least [one] postcranial skeleton."[14] A titanosaur
Rapetosaurus BW.jpg
Stegosaurus[10] S. madagascariensis[10] "Teeth"[15] Possibly an indeterminate ankylosaur. [16]
Titanosaurus[10] T. madagascariensis[10]
Vahiny[17] Vahiny depereti[17] "Partial braincase"[17] A titanosaur
Vorona[10] V. berivotrensis[10] "Partial hindlimbs"[18] An ornithuromorph

Crocodylomorphs[]

Crocodylomorphs
Genus Species Location Stratigraphic position Material Notes Images
Mahajangasuchus M. insignis A peirosaurid
Mahajangasuchus BW.jpg
Miadanasuchus M. oblita Formerly known as Trematochampsa oblita
Simosuchus S. clarki A chimaerasuchid
Simosuchus.jpg
Araripesuchus A. tsangatsangana A notosuchian
Araripesuchus wegeneri.jpg

Squamates[]

Squamates
Genus Species Location Stratigraphic position Material Notes Images
Kelyophis K. hechti A snake
K. mahalana A cordylid lizard
Madtsoia M. madagascariensis A madtsoiid snake
Menarana M. nosymena Vertebrae and rib fragments A madtsoiid snake

Turtles[]

Turtles
Genus Species Location Stratigraphic position Material Notes Images
Kinkonychelys K. rogersi A side-necked turtle
Sahonachelys S. mailakavava A sahonachelyid side-necked turtle
Sokatra S. antitra A sahonachelyid side-necked turtle
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.

Mammals[]

Vintana, a large sized gondwanathere mammal

The mammal fauna known from the Maevarano Formation is dominated by gondwanatheres, a lineage of herbivorous multituberculates. These include Lavanify miolaka, Vintana sertichi, Adalatherium hui and at least one undescribed taxa.[19] Some taxa are particularly large sized herbivores, exemplifying the diversity of Mesozoic mammals.[20]

Other mammal remains include the broken tooth UA 8699, which has been interpreted both as metatherian and as eutherian, a non-gondwanathere multituberculate tooth fragment, a non-gondwanathere multituberculate femur,[21] and a yet undescribed mammal known from an articulated skeleton.[22]

See also[]

References[]

  1. ^ Jump up to: a b c d e f Rogers et al., 2007
  2. ^ Weishampel et al., 2004
  3. ^ Jump up to: a b c Krause et al., 2007b
  4. ^ Depéret, 1896
  5. ^ Sues & Taquet, 1979
  6. ^ Evans, Susan E.; Jones, Marc E. H.; Krause, David W. (2008). "A giant frog with South American affinities from the Late Cretaceous of Madagascar". Proceedings of the National Academy of Sciences of the United States of America. 105 (8): 2951–2956. Bibcode:2008PNAS..105.2951E. doi:10.1073/pnas.0707599105. PMC 2268566. PMID 18287076.
  7. ^ Evans et al., 2014, p.5
  8. ^ O'Connor and Forster, 2010. A Late Cretaceous (Maastrichtian) avifauna from the Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology. 30(4), 1178-1201.
  9. ^ Patrick M. O’Connor; Alan H. Turner; Joseph R. Groenke; Ryan N. Felice; Raymond R. Rogers; David W. Krause; Lydia J. Rahantarisoa (2020). "Late Cretaceous bird from Madagascar reveals unique development of beaks". Nature. 588 (7837): 272–276. Bibcode:2020Natur.588..272O. doi:10.1038/s41586-020-2945-x. PMID 33239782. S2CID 227174405.
  10. ^ Jump up to: a b c d e f g h i j k l m n "83.2 Faritany Majunga, Madagascar; 3. Maevarano Formation," in Weishampel et al., 2004, p.605
  11. ^ "Table 3.1," in Weishampel et al., 2004, p.50
  12. ^ "Table 3.1," in Weishampel et al., 2004, p.49
  13. ^ "Table 11.1," in Weishampel et al., 2004, p.211
  14. ^ "Table 13.1," in Weishampel, et al. (2004). Page 270.
  15. ^ "Table 14.1," in Weishampel, et al. (2004). Page 326.
  16. ^ Maidment, Susannah; Norman, David; Barrett, Paul; Upchurch, Paul (2008). "Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia)". Journal of Systematic Palaeontology. 6 (4): 367–407. doi:10.1017/S1477201908002459. S2CID 85673680.
  17. ^ Jump up to: a b c Rogers & Wilson, 2014
  18. ^ "Table 11.1," in Weishampel et al., 2004, p.212
  19. ^ Krause et al, 2014
  20. ^ Krause et al., 2020
  21. ^ Krause, David W.; Hoffmann, Simone; Werning, Sarah (December 2017). "First postcranial remains of Multituberculata (Allotheria, Mammalia) from Gondwana". Cretaceous Research. 80: 91–100. doi:10.1016/j.cretres.2017.08.009.
  22. ^ Krause, David W.; O'Connor, Patrick M.; Rogers, Kristina Curry; Sampson, Scott D.; Buckley, Gregory A.; Rogers, Raymond R. (23 August 2006). "Late Cretaceous terrestrial vertebrates from Madagascar: Implications for Latin American biogeography". Annals of the Missouri Botanical Garden. 93 (2): 178–208. doi:10.3417/0026-6493(2006)93[178:LCTVFM]2.0.CO;2. JSTOR 40035721.

Bibliography[]

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