Romualdo Formation

Romualdo Formation
Stratigraphic range: Early Albian
~111–108 Ma

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Romualdo Formation; Stratigraphic range: Early Albian; ~111–108 Ma PreЄ Є O S D C P T J K Pg N ↓
	Fossils of Anhanguera (top) and Santanadactylus (bottom) from the Romualdo Formation
Type	Geological formation
Unit of	Santana Group
Underlies	Exu & Arajara Formations
Overlies	Crato & Ipubi Formations
Thickness	2–10 m (6.6–32.8 ft)
Lithology
Primary	Mudstone
Other	Limestone, shale
Location
Coordinates	7.2°S 39.3°W
Approximate paleocoordinates	12.2°S 10.7°W
Region	Pernambuco, Piauí & Ceará
Country	Brazil
Extent	Araripe Basin
	; Extent of the Santana Group, to which the Romualdo Formation belongs, in blue

The Romualdo Formation is a geologic Konservat-Lagerstätte in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piauí and Ceará come together. The geological formation, previously designated as the Romualdo Member of the Santana Formation, named after the village of Santana do Cariri, lies at the base of the Araripe Plateau. It was discovered by Johann Baptist von Spix in 1819. The strata were deposited during the Albian stage of the Early Cretaceous in a lacustrine rift basin with shallow marine incursions of the proto-Atlantic. At that time, the South Atlantic was opening up in a long narrow shallow sea.

The Romualdo Formation earns the designation of Lagerstätte due to an exceedingly well preserved and diverse fossil faunal assemblage. Some 25 species of fossil fishes are often found with stomach contents preserved, enabling paleontologists to study predator–prey relationships in this ecosystem. There are also fine examples of pterosaurs, reptiles and invertebrates, and crocodylomorphs. Even dinosaurs are represented (Spinosauridae, Tyrannosauroidea, Compsognathidae). The unusual taphonomy of the site resulted in limestone accretions that formed nodules around dead organisms, preserving even soft parts of their anatomy. In preservation, the nodules are etched away with acid, and the fossils often prepared by the transfer technique.[1]

Local mining activities for cement and construction damage the sites. Trade in illegally collected fossils has sprung up from the decade of 1970, driven by the remarkable state of preservation and beauty of these fossils and amounting to a considerable local industry. An urgent preservation program is being called for by paleontologists.[2]

In addition, the weathering of Romualdo Formation rocks has contributed soil conditions unlike elsewhere in the region. The Araripe manakin (Antilophia bokermanni) is a very rare bird that was discovered only in the late 20th century; it is not known from anywhere outside the characteristic forest that grows on the Chapada do Araripe soils formed ultimately from Romualdo Formation rocks.

Geology and dating

Outcrop and interpretation of the Romualdo Formation

Outcrop of the Romualdo and Ipubi Formations

The Crato Formation was previously considered the lowest member of the then Santana Formation, but has been elevated to a formal formation. The Crato Formation is the product of a single phase, where complicated sequence of sediment strata reflect changeable conditions in the opening sea. The age of the Romualdo Formation, formerly known as the Romualdo Member of the Santana Formation, has been controversial, though most workers have agreed that it lies on or near the Aptian-Albian boundary, about 112 million years ago. Nevertheless, a Cenomanian age cannot be ruled out.[3][4]

The extent of the Crato unit and its relationship to the Romualdo Formation had long been ill-defined. It was not until a 2007 volume on the unit by Martill, Bechly and Loveridge that the Crato Formation was given a formal type locality, and was formally made a distinct formation separate from the Romualdo Formation, which is about 10 Ma younger.[3]

Fossil content

Archosaurs

Indeterminate remains of non-avian theropods, avialans, ornithischians, and possibly oviraptorosaurs have been found in Ceara state, Brazil.[5] The oviraptorosaurian remains have been re-identified as megaraptoran fossils.[6]

Dinosaurs

Dinosaurs
Genus	Species	Presence	Notes	Images
Angaturama[5]	A. limai	Ceará	Spinosauridae. "Rostral portion of [a] skull."[7] Junior synonym of Irritator challengeri.
Irritator[5][8]	I. challengeri	Ceará	Spinosauridae, "partial skull"
Mirischia[5]	M. asymmetrica	Ceará	Compsognathidae
Santanaraptor[5]	S. placidus	Ceará	A tyrannosaurid dinosaur. "Partial postcranium"[9]

Crocodylomorphs

Crocodylomorphs
Genus	Species	Presence	Notes	Images
Araripesuchus	A. gomesii	Romualdo Formation	Type specimen 423-R is a single skull articulating with part of a lower jaw. A more complete specimen, AMNH 24450, is at the American Museum of Natural History.

Pterosaurs

Pterosaurs
Genus	Species	Presence	Images
Anhanguera	* A. blittersdorffi A. santanae A. araripensis A. robustus A. piscator A. spielbergi		Anhanguera
Araripedactylus	A. dehmi
Araripesaurus	A. castilhoi
Barbosania[10]	B. gracilirostris
Brasileodactylus	B. araripensis
Cearadactylus	C. atrox
Cearadactylus	C. ligabuei
Maaradactylus	M. kellneri
Santanadactylus	S. brasilensis ?S. pricei S. spixi
Tapejara	T. wellnhoferi
Thalassodromeus	T. sethi
Tropeognathus	T. mesembrinus
Tupuxuara	T. deliradamus T. leonardii T. longicristatus
Unwindia	U. trigonus

Turtles

Turtles of the Romualdo Formation
Genus	Species	Presence	Notes	Images
Santanachelys	S. gaffneyi		[11]
Cearachelys	C. placidoi		[12]
Araripemys	A. barretoi		[13]
Euraxemys	E. essweini		[14]
Brasilemys	B. josai		[15]

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.

Fish

References

Maisey et al., 1991, pp.99–103
Gibney, Elizabeth (6 March 2014). "Brazil clamps down on illegal fossil trade". Nature. 507 (7490): 20. Bibcode:2014Natur.507...20G. doi:10.1038/507020a. ISSN 0028-0836. PMID 24598620.
Martill et al., 2007
Martill, 2007
Weishampel, 2004, pp. 563–570
Aranciaga Rolando, Alexis M.; Brissón Egli, Federico; Sales, Marcos A.F.; Martinelli, Agustín G.; Canale, Juan I.; Ezcurra, Martín D. (2018). "A supposed Gondwanan oviraptorosaur from the Albian of Brazil represents the oldest South American megaraptoran". Cretaceous Research. 84: 107–119. doi:10.1016/j.cretres.2017.10.019. ISSN 0195-6671.
"Table 4.1," in Weishampel, et al. (2004). Page 73.
Martill, D. M.; Cruickshank, A. R. I.; Frey, E.; Small, P. G.; Clarke, M. (1 February 1996). "A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil". Journal of the Geological Society. 153 (1): 5–8. Bibcode:1996JGSoc.153....5M. doi:10.1144/gsjgs.153.1.0005. ISSN 0016-7649.
"Table 5.1," in Weishampel, et al. (2004). Page 114.
Elgin & Frey, 2011
Santanachelys gaffneyi at Fossilworks.org
Juazeiro do Norte at Fossilworks.org
Araripemys barretoi type locality at Fossilworks.org
Crato at Fossilworks.org
Chapada do Araripe at Fossilworks.org
Casa de Pedra at Fossilworks.org
Fara et al., 2005, p.152
Buxéxé, Santana do Cariri at Fossilworks.org
Enneles audax
Iemanja palma
Placidichthys type locality at Fossilworks.org
Ze Gomes at Fossilworks.org

Bibliography

Cavalcanti Duque, Rudah Ruano, and Alcina Magnólia Franca Barreto. 2018. Novos Sítios Fossilíferos da Formação Romualdo, Cretáceo Inferior, Bacia do Araripe, Exu, Pernambuco, Nordeste do Brasil - New Fossiliferous Sites of the Romualdo Formation, Lower Cretaceous, Araripe Basin, Exu, Pernambuco, Northeast of Brazil. Anuário do Instituto de Geociências, UFRJ 41. 5–14. Accessed 2018-10-06.
Elgin, Ross A.; Frey, Eberhard (20 April 2011). "A new ornithocheirid, Barbosania gracilirostris gen. et sp. nov. (Pterosauria, Pterodactyloidea) from the Santana Formation (Cretaceous) of NE Brazil". Swiss Journal of Palaeontology. 130 (2): 259. doi:10.1007/s13358-011-0017-4. ISSN 1664-2384.
Fabin, Carlos E.; Osvaldo J. Correia Filho; Márcio L. Alencar; José A. Barbosa; Tiago S. de Miranda; Virgínio H. Neumann; Igor F. Gomes, and Felipe R. de Santana. 2018. Stratigraphic Relations of the Ipubi Formation: Siliciclastic-Evaporitic Succession of the Araripe Basin. Anais da Academia Brasileira de Ciências 90. 2049–2071. Accessed 2018-10-05.
Fara, Emmanuel; Antônio Á.F. Saraiva; Díogenes de Almeida Campos; João K.R. Moreira; Daniele de Carvalho Siebra, and Alexander W.A. Kellner. 2005. Controlled excavations in the Romualdo Member of the Santana Formation (Early Cretaceous, Araripe Basin, northeastern Brazil): stratigraphic, palaeoenvironmental and palaeoecological implications. Palaeogeography, Palaeoclimatology, Palaeoecology 218. 145–160. Accessed 2018-10-06.
Maisey, J.G.; I. Rutzky; S. Blum, and W. Elvers. 1991. Laboratory Preparation Techniques. In Maisey, j:G. (ed): Santana Fossils: An Illustrated Atlas, 99–103. Tfh Publications Inc.. ISBN 0866225498
Martill, David M.; Günter Bechly, and Robert F. Loveridge. 2007. The Crato Fossil Beds of Brazil: Window into an Ancient World, 236. Cambridge University Press. Accessed 2018-10-06. ISBN 978-1-139-46776-6
Martill, D.M. 2007. The age of the Cretaceous Santana Formation fossil Konservat Lagerstätte of north-east Brazil: a historical review and an appraisal of the biochronostratigraphic utility of its palaeobiota. Cretaceous Research 28. 895–920. Accessed 2018-10-06.
Weishampel, David B. et al. 2004. Dinosaur distribution (Early Cretaceous, South America) in: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 563–570. Berkeley: University of California Press. ISBN 0-520-24209-2