| Romualdo Formation | |
|---|---|
| Stratigraphic range:Early Albian ~111–108 Ma | |
 Fossils ofAnhanguera (top) andSantanadactylus (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°12′S39°18′W / 7.2°S 39.3°W /-7.2; -39.3 |
| Approximate paleocoordinates | 12°12′S10°42′W / 12.2°S 10.7°W /-12.2; -10.7 |
| Region | Pernambuco,Piauí &Ceará |
| Country |  Brazil |
| Extent | Araripe Basin |
 Extent of the Santana Group, to which the Romualdo Formation belongs, in blue | |
TheRomualdo Formation is a geologicKonservat-Lagerstätte in northeasternBrazil'sAraripe Basin where the states ofPernambuco,Piauí andCeará come together. The geological formation, previously designated as the Romualdo Member of theSantana Formation, named after the village ofSantana do Cariri, lies at the base of theAraripe Plateau. It was discovered byJohann Baptist von Spix in 1819. Thestrata were deposited during theAptian stage of theEarly Cretaceous in alacustrinerift basin with shallow marine incursions of theproto-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 diversefossil faunal assemblage. Some 25 species offossil fishes are often found with stomach contents preserved, enabling paleontologists to studypredator–prey relationships in this ecosystem. There are also fine examples ofpterosaurs,reptiles andinvertebrates, andcrocodylomorphs. Even dinosaurs are represented (Spinosauridae,Tyrannosauroidea,Compsognathidae). The unusualtaphonomy of the site resulted inlimestoneaccretions 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 thetransfer 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, theweathering of Romualdo Formation rocks has contributedsoil conditions unlike elsewhere in the region. TheAraripe 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 theChapada do Araripe soils formed ultimately from Romualdo Formation rocks.
TheCrato 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 sedimentstrata 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 theAptian-Albian boundary, about 112 million years ago. Nevertheless, aCenomanian 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]
Indeterminate remains of non-aviantheropods,avialans,ornithischians, and possiblyoviraptorosaurs have been found in Ceara state, Brazil.[5] The oviraptorosaurian remains have been re-identified asmegaraptoran fossils.[6]
| Dinosaurs | ||||
|---|---|---|---|---|
| Genus | Species | Presence | Notes | Images |
| Angaturama[5] | A. limai | Ceará | Spinosauridae. Partial skull (rostralmost portion).[7] Possible junior synonym ofIrritator challengeri. |  |
| Aratasaurus[8] | A. museunacionali | Ceará | Acoelurosaur. Partial right hindlimb. |  |
| Irritator[5][9] | I. challengeri | Ceará | Spinosauridae. Partial skull (posterior half); one of the most complete spinosaurid skulls known. |  |
| Mirischia[5] | M. asymmetrica | Pernambuco | Compsognathidae. Pelvis and partial left hindlimb. |  |
| Santanaraptor[5] | S. placidus | Ceará | A possibletyrannosauroid. Some caudal vertebrae, partial pelvis, most of both hindlimbs.[10] |  |
| 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 theAmerican Museum of Natural History. |  |
| Caririsuchus | C. camposi | Romualdo Formation | Apeirosaurid crocodyliform. | |
| Pterosaurs | |||
|---|---|---|---|
| Genus | Species | Presence | Images |
| Anhanguera |
|  | |
| Araripedactylus | A. dehmi | ||
| Araripesaurus | A. castilhoi | ||
| Barbosania[11] | B. gracilirostris | ||
| Brasileodactylus | B. araripensis | ||
| Cearadactylus | C. atrox |  | |
| "C."ligabuei[12] | |||
| Kariridraco | K. dianae |  | |
| Maaradactylus | M. kellneri |  | |
| Santanadactylus |
| | |
| Tapejara | T. wellnhoferi |  | |
| Thalassodromeus | T. sethi |  | |
| Tropeognathus | T. mesembrinus |  | |
| Tupuxuara |
|  | |
| Unwindia | U. trigonus | ||
| Turtles | ||||
|---|---|---|---|---|
| Genus | Species | Presence | Notes | Images |
| Santanachelys | S. gaffneyi | [13] |  | |
| Cearachelys | C. placidoi | [14] |  | |
| Araripemys | A. barretoi | [15] |  | |
| Euraxemys | E. essweini | [16] | ||
| Brasilemys | B. josai | [17] | ||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
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