Romualdo Formation
Brazilian geologic formation
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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 Aptian 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.
| Romualdo Formation | |
|---|---|
| Stratigraphic range: Early Albian ~ | |
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 |
  Romualdo Formation (Brazil) | |
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
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 of the Romualdo Formation | |||||
|---|---|---|---|---|---|
| Genus | Species | Presence | Materials | Notes | Images |
| Angaturama[5] | A. limai | Ceará | Partial skull (rostralmost portion).[7] Possible junior synonym of Irritator challengeri. | A spinosaurid. |  |
| Aratasaurus[8] | A. museunacionali | Ceará | Partial right hindlimb. | A coelurosaur. |  |
| Irritator[5][9] | I. challengeri | Ceará | Partial skull (posterior half); one of the most complete spinosaurid skulls known. | A spinosaurid. |  |
| Megaraptora indet.[10] | Indeterminate | Unknown | Three sacral vertebrae, two caudal vertebrae, and a partial ilium. | A megaraptorid theropod. Originally identified as a possible oviraptorosaur. | |
| Mirischia[5] | M. asymmetrica | Pernambuco | Pelvis and partial left hindlimb. | A compsognathid. |  |
| Santanaraptor[5] | S. placidus | Ceará | Some caudal vertebrae, partial pelvis, most of both hindlimbs.[11] | A possible tyrannosauroid. |  |
Crocodylomorphs
| Crocodylomorphs of the Romualdo Formation | |||||
|---|---|---|---|---|---|
| Genus | Species | Presence | Materials | 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. | A uruguaysuchid crocodyloformes |  |
| Caririsuchus | C. camposi | Romualdo Formation | A peirosaurid crocodyliform. | ||
Pterosaurs
| Pterosaurs of the Romualdo Formation | |||||
|---|---|---|---|---|---|
| Genus | Species | Presence | Materials | Notes | Images |
| Anhanguera | A. araripensis | A pterodactyloid pterosaur |          | ||
| A. blittersdorffi | A complete skull | ||||
| A. piscator | A nearly-complete skeleton, | ||||
| A. robustus | |||||
| A. santanae | |||||
| A. spielbergi | |||||
| Araripedactylus | A. dehmi | A single wing bone | A pterodactyloid pterosaur of uncertain affinities | ||
| Araripesaurus | A. castilhoi | A partial wing, including distal fragments of the radius and ulna, carpals, all metacarpals and several digits | An ornithocheirid pterosaur | ||
| Bakiribu | B. waridza | Two specimen consists of fragmented upper and lower jaws | A ctenochasmatid pterosaur | ||
| Barbosania[12] | B. gracilirostris | An almost complete skeleton including the skull, that is partially articulated and uncompressed | A targaryendraconian pterosaur | ||
| Brasileodactylus | B. araripensis | Several specimen consists of amandible, and the front of a snout and mandible. More complete fossils include, a fragmentary skeleton, and a skull, with mandible and proximal left wing | An anhangueria pterosaur | ||
| Cearadactylus | C. atrox | ||||
| "C." ligabuei[13] | |||||
| Kariridraco | K. dianae | A fairly complete skull, including the lower jaws, and the first four neck vertebrae | A thalassodromid pterosaur | ||
| Maaradactylus | M. kellneri | A skull | An anhanguerid pterodactyloid pterosaur | ||
| Santanadactylus | S. brasilensis | ||||
| ?S. pricei | |||||
| S. spixi | |||||
| Tapejara | T. wellnhoferi | Several holotypes consists of a partial skull, a partial mandible (lower jaw), and an anterior (front) cervical (neck) vertebra | A tapejarid pterosaur | ||
| Thalassodromeus | T. sethi | A large skull | A large thalassodromid pterosaur | ||
| Tropeognathus | T. mesembrinus | Several holotypes conists of a skull with manidles, a partial mandible, and skeleton with extensive elements of all body parts, except the tail and the lower hindlimbs | A tropeognathinae pterosaur | ||
| Tupuxuara | T. deliradamus | A skull | A thalassodromid pterosaur | ||
| T. leonardii | |||||
| T. longicristatus | |||||
| Unwindia | U. trigonus | A partial skull consisting only the fused premaxillae and maxillae, some teeth and parts of the palate | A pterodactyloid pterosaur | ||
Turtles
| Turtles of the Romualdo Formation | |||||
|---|---|---|---|---|---|
| Genus | Species | Presence | Marterials | Notes | Images |
| Araripemys | A. barretoi | A shell | An araripemydidae turtle [14] |  | |
| Brasilemys | B. josai | [15] | |||
| Cearachelys | C. placidoi | A shell | A bothremydinae pleurodiran turtle [16] |  | |
| Euraxemys | E. essweini | [17] | |||
| Santanachelys | S. gaffneyi | A protostegidae sea turtle [18] |  | ||
Color key
|
Notes Uncertain or tentative taxa are in small text; |
Fish
- Araripelepidotes
- Axelrodichthys araripensis.[19]
- Beurlenichthys ouricuriensis[20]
- Brannerion[21]
- Calamopleurus[21]
- Cladocyclus[21][22]
- Enneles audax[23]
- Iemanja palma[24]
- Lepidotes wenzai[15]
- Microdon penalvai[15]
- Notelops[21]
- Obaichthys[15]
- Oshunia brevis[15]
- Placidichthys bidorsalis[25]
- Rhacolepis[21]
- Iansan beurleni[15][26]
- Santanaclupea silvasantosi
- Tharrhias[21]
- Tribodus limae[15]
- Vinctifer[21][27]