The Romualdo Formation is a geologic Konservat-Lagerstätte in northeastern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

's Araripe Basin where the states of

Pernambuco Pernambuco () is a state of Brazil, located in the Northeast region of the country. With an estimated population of 9.6 million people as of 2020, making it seventh-most populous state of Brazil and with around 98,148 km², being the ...

Piauí Piaui (, ) is one of the states of Brazil, located in the country's Northeast Region. The state has 1.6% of the Brazilian population and produces 0.7% of the Brazilian GDP. Piaui has the shortest coastline of any coastal Brazilian state at 66 ...

and

Ceará Ceará (, pronounced locally as or ) is one of the 26 states of Brazil, located in the northeastern part of the country, on the Atlantic coast. It is the eighth-largest Brazilian State by population and the 17th by area. It is also one of th ...

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 The Chapada do Araripe, also known as the Serra do Araripe, is a '' chapada'' (plateau) in northeastern Brazil. The chapada forms the boundary of Ceará and Pernambuco states, and forms the watershed between the Jaguaribe River of Ceará, which flo ...

. It was discovered by

Johann Baptist von Spix Johann Baptist Ritter von Spix (9 February 1781 – 13 March 1826) was a German biologist. From his expedition to Brazil, he brought to Germany a large variety of specimens of plants, insects, mammals, birds, amphibians and fish. They constitute ...

in 1819. The

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

were deposited during the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ag ...

stage of the

Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

in a

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

rift basin In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

with shallow marine incursions of the

proto-Atlantic The Iapetus Ocean (; ) was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the pale ...

. 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 A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

faunal assemblage. Some 25 species of fossil fishes are often found with stomach contents preserved, enabling paleontologists to study

predator–prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

relationships in this ecosystem. There are also fine examples of

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the Order (biology), order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cre ...

s, reptiles and

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s, and crocodylomorphs. Even dinosaurs are represented ( Spinosauridae, Tyrannosauroidea, Compsognathidae). The unusual

taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremo ...

of the site resulted in

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

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.Maisey et al., 1991, pp.99–103 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. In addition, the

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movemen ...

of Romualdo Formation rocks has contributed

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

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

Romualdo Formation - outcrop and interpretation

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

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

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± ...

boundary, about 112 million years ago. Nevertheless, a Cenomanian age cannot be ruled out.Martill et al., 2007Martill, 2007 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.

Fossil content

Archosaurs

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

Dinosaurs

Crocodylomorphs

Pterosaurs

Turtles

Fish

* '' Araripelepidotes'' * '' Beurlenichthys ouricuriensis'' * ''

Brannerion ''Brannerion'' is an extinct genus of prehistoric bonefish. Fossils of the genus were found in the Romualdo Formation of the Santana Group, Araripe Basin, northeastern Brazil.Calamopleurus''Fara et al., 2005, p.152 * '' Cladocyclus'' * '' Enneles audax'' * '' Iemanja palma'' * '' Lepidotes wenzai'' * '' Microdon penalvai'' * ''

Notelops ''Notelops'' is an extinct genus of prehistoric ray-finned fish. See also * Prehistoric fish * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizatio ...

'' * '' Obaichthys'' * '' Oshunia brevis'' * '' Placidichthys bidorsalis'' * ''

Rhacolepis ''Rhacolepis'' is an extinct genus of ray-finned fish from the Cretaceous Santana Formation of Brazil. Complete fossilised hearts from this species have been recovered. References Crossognathiformes Prehistoric ray-finned fish ...

'' * '' Rhinobatos beurleni'' * '' Santanaclupea silvasantosi'' * '' Tharrhias'' * '' Tribodus limae'' * ''

Vinctifer ''Vinctifer'' is an extinct genus of prehistoric bony fish erected by David Starr Jordan in 1919. Fossil record This genus is known in the fossil record from the Late Jurassic (Kimmeridgian) to the Aptian stage of the Early Cretaceous epoch (a ...

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Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org

References

Bibliography

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