Romualdo Formation

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.

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.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 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.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 Dinosaurs of the Romualdo Formation Genus Species Presence Materials Notes Images AngaturamaWeishampel, 2004, pp. 563–570 A. limai Ceará Partial skull (rostralmost portion)."Table 4.1," in Weishampel, et al. (2004). Page 73. Possible junior synonym of Irritator challengeri. A spinosaurid. Aratasaurus A. museunacionali Ceará Partial right hindlimb A coelurosaur. Irritator I. challengeri Ceará Partial skull (posterior half); one of the most complete spinosaurid skulls known A spinosaurid Megaraptora indet Indeterminate Unknown Three sacral vertebrae, two caudal vertebrae, and a partial ilium A megaraptorid theropod. Originally identified as a possible oviraptorosaur. Mirischia M. asymmetrica Pernambuco Pelvis and partial left hindlimb A compsognathid Santanaraptor S. placidus Ceará Some caudal vertebrae, partial pelvis, most of both hindlimbs"Table 5.1," in Weishampel, et al. (2004). Page 114. 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 crocodyloformesCaririsuchusC. camposiRomualdo FormationA peirosaurid crocodyliform

Pterosaurs Pterosaurs of the Romualdo Formation Genus Species Presence Materials Notes ImagesAnhanguera A. araripensis A pterodactyloid pterosaur

A. blittersdorffi A complete skull A. piscator A nearly complete skeleton,A. robustusA. 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 specimens originally thought to have consisted of fragmented upper and lower jaws. May have been parts of the gills of an indeterminate, potentially amiid fish. Formerly classified as a ctenochasmatid pterosaur. May have been an indeterminate, potentially amiid ray finned fish. BarbosaniaElgin & Frey, 2011 B. gracilirostris An almost complete skeleton including the skull, that is partially articulated and uncompressedA 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 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 pterosaurSantanadactylus S. brasilensis ?S. pricei S. spixi Tapejara T. wellnhoferi Several holotypes consist 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 consist of a skull with mandibles, a partial mandible and skeleton with extensive elements of all body parts, except the tail and the lower hindlimbs. A tropeognathinae pterosaurTupuxuara T. deliradamus A skull A thalassodromid pterosaur T. leonardii T. longicristatus Unwindia U. trigonus A partial skull consisting of 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 turtleAraripemys barretoi type locality at Fossilworks.org Brasilemys B. josaiChapada do Araripe at Fossilworks.org Cearachelys C. placidoi A shell A bothremydinae pleurodiran turtleJuazeiro do Norte at Fossilworks.org Euraxemys E. essweini Crato at Fossilworks.org Santanachelys S. gaffneyi A protostegidae sea turtleSantanachelys gaffneyi at Fossilworks.org

Fish

Araripelepidotes temnurus Axelrodichthys araripensis Beurlenichthys ouricuriensisCasa de Pedra at Fossilworks.org Brannerion latum Dentilepisosteus laevis Calamopleurus cylindricusFara et al., 2005, p.152 Cladocyclus gardneriBuxéxé, Santana do Cariri at Fossilworks.org Enneles audaxEnneles audax Iemanja palmaIemanja palma Lepidotes wenzai Microdon penalvai Notelops brama Obaichthys decoratus Oshunia brevis Placidichthys bidorsalisPlacidichthys type locality at Fossilworks.org Rhacolepis buccalis Iansan beurleni Santanaclupea silvasantosi Tharrhias araripis Tribodus limae Vinctifer comptoni; V. longirostris; V. araripinensisZe Gomes at Fossilworks.org

Romualdo Formation

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