The Crato 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 amphibians, invertebrates (particularly insects), and plants. Even dinosaurs are represented: a new maniraptor was described in 1996. The unusual taphonomy of the site resulted in limestone accretions that formed nodules around dead organisms, preserving even soft parts of their anatomy.
History
Fish fossils in the area were noted in 1823. When they were first methodically published, in 1993, the Crato Formation limestones provided a new site for pterosaurs, one that also preserved insects that fell into a brackish lagoon and semionotid fish preserved in phosphatized nodules. The fossils are usually compacted and preserved in layers of limestone. Fossil Odonata (dragonflies) and damselflies are especially rich in the Crato lagerstätte: currently 384 specimens have been recovered, 264 adults and 120 larvae. Hemiptera (true bugs) and Orthoptera (grasshoppers and crickets) are also abundant in number of species and in number of specimens. There are also plant remains.
Local mining activities for cement and construction damage the sites. Trade in illegally collected fossils has sprung up in the last decade, 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 Crato and Santana 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 Crato and Santana Formation rocks.
The Crato Formation has often historically been considered the lowest member of the Santana Formation (or, alternatively, the Araripina Formation) of the Araripe Group,[2] later redefined as the Romualdo Formation of the Santana Group.[3][4] The Crato Member is the product of a single phase, where complicated sequence of sediment strata reflect changeable conditions in the opening sea. The age of this strata has been controversial, though most workers have agreed that it lies on or near the Aptian-Albian boundary, about 112 million years ago.[5]
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 Santana, which is about 10 Ma younger.[5] The Crato Formation is considered time equivalent with the Paracuru Formation.[6]
Fossil content
Insects
(Note: Many more insects have been described than are present in the table below)
Isolated tooth listed in a book appendix.[5] It has later been suggested that the lithostratigraphic provenance of this specimen might have been incorrect.[26]
^ abcdefghBáez et al., 2009. Retrieved 2018-10-06.
^Ismar de Souza Carvalho; Federico Agnolin; Mauro A. Aranciaga Rolando; Fernando E. Novas; José Xavier-Neto; Francisco Idalécio de Freitas; José Artur Ferreira Gomes de Andrade (2019). "A new genus of pipimorph frog (Anura) from the Early Cretaceous Crato formation (Aptian) and the evolution of South American tongueless frogs". Journal of South American Earth Sciences. 92: 222–233. Bibcode:2019JSAES..92..222C. doi:10.1016/j.jsames.2019.03.005. hdl:11336/123956. S2CID134070810.
^Federico Agnolin; Ismar Souza Carvalho; Alexis M. Aranciaga Rolando; Fernando E. Novas; José Xavier-Neto; José Artur Ferreira Gomes Andrade; Francisco Idalécio Freitas (2020). "Early Cretaceous neobatrachian frog (Anura) from Brazil sheds light on the origin of modern anurans". Journal of South American Earth Sciences. 101: Article 102633. Bibcode:2020JSAES.10102633A. doi:10.1016/j.jsames.2020.102633. S2CID218957427.
^Caetano, João Marcus Vale; Delcourt, Rafael & Ponciano, Luiza Corral Martins de Oliveira (March 2023). "A taxon with no name: Ubirajara jubatus (Saurischia: Compsognathidae) is an unavailable name and has no nomenclatural relevance". Zootaxa. 5254 (3): 443–446. doi:10.11646/zootaxa.5254.3.10. PMID37044710.
^Ismar de Souza, Carvalho Vale; Leonardi, Giuseppe; Rios-Netto, Aristoteles de Moraes; Borghi, Leonardo; Freitas, Alexandre de Paula; Andrade, José Artur & Freitas, Francisco Idalécio (2021). "Dinosaur trampling from the Aptian of Araripe Basin, NE Brazil, as tools for paleoenvironmental interpretation". Cretaceous Research. 117: 104626. Bibcode:2021CrRes.11704626C. doi:10.1016/j.cretres.2020.104626.
Aparecida dos Reis Polck, Márcia; Sardenberg Salgado de Carvalho, Marise; Miguel, Raphael; Gallo, Valéria (2015). Guia de identificação de peixes fósseis das Formações Crato e Santana da Bacia do Araripe. Serviço Geológico do Brasil (CPRM). pp. 1–74.
Ribeiro, Alexandre Cunha; Ribeiro, Guilherme Cunha; Varejão, Filipe Giovanini; Battirola, Leandro Dênis; Pessoa, Edlley Max; Simões, Marcello Guimarães; Warren, Lucas Veríssimo; Riccomini, Claudio; Poyato-Ariza, Francisco José (May 2021). "Towards an actualistic view of the Crato Konservat-Lagerstätte paleoenvironment: A new hypothesis as an Early Cretaceous (Aptian) equatorial and semi-arid wetland". Earth-Science Reviews. 216: 103573. Bibcode:2021ESRv..21603573R. doi:10.1016/j.earscirev.2021.103573. S2CID233924513.
Weishampel, David B.; et al. (2004). Dinosaur distribution (Early Cretaceous, South America) in: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria. Berkeley: University of California Press. pp. 563–570. ISBN0-520-24209-2.