title: Heart fossilization is possible and informs the evolution of cardiac outflow tract in vertebrates.
abstract: Elucidating cardiac evolution has been frustrated by lack of fossils. One celebrated enigma in cardiac evolution involves the transition from a cardiac outflow tract dominated by a multi-valved conus arteriosus in basal actinopterygians, to an outflow tract commanded by the non-valved, elastic, bulbus arteriosus in higher actinopterygians. We demonstrate that cardiac preservation is possible in the extinct fish Rhacolepis buccalis from the Brazilian Cretaceous. Using X-ray synchrotron microtomography, we show that Rhacolepis fossils display hearts with a conus arteriosus containing at least five valve rows. This represents a transitional morphology between the primitive, multivalvar, conal condition and the derived, monovalvar, bulbar state of the outflow tract in modern actinopterygians. Our data rescue a long-lost cardiac phenotype (119-113 Ma) and suggest that outflow tract simplification in actinopterygians is compatible with a gradual, rather than a drastic saltation event. Overall, our results demonstrate the feasibility of studying cardiac evolution in fossils.
authors.affiliation: Department of Pharmacology, University of Campinas, Campinas, Brazil.|Brazilian Biosciences National Laboratory, Campinas, Brazil.
authors.forename: Lara
authors.initials: L
authors.lastname: Maldanis
authors.affiliation: Brazilian Biosciences National Laboratory, Campinas, Brazil.|Department of Zoology, Biosciences Institute, University of São Paulo, São Paulo, Brazil.
authors.forename: Murilo
authors.identifier: http://orcid.org/0000-0001-6881-5271
authors.initials: M
authors.lastname: Carvalho
authors.affiliation: Institute of Chemistry, University of Campinas, Campinas, Brazil.
authors.forename: Mariana Ramos
authors.initials: MR
authors.lastname: Almeida
authors.affiliation: Geopark Araripe, Crato, Brazil.
authors.forename: Francisco Idalécio
authors.initials: FI
authors.lastname: Freitas
authors.affiliation: National Department of Mineral Production, Ministry of Mines and Energy, Crato, Brazil.
authors.forename: José Artur Ferreira Gomes
authors.initials: JA
authors.lastname: de Andrade
authors.affiliation: Brazilian Synchrotron Light Laboratory, Campinas, Brazil.
authors.forename: Rafael Silva
authors.initials: RS
authors.lastname: Nunes
authors.affiliation: Heart Institute, InCor, University of São Paulo, São Paulo, Brazil.
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Rochitte
authors.affiliation: Institute of Chemistry, University of Campinas, Campinas, Brazil.
authors.forename: Ronei Jesus
authors.initials: RJ
authors.lastname: Poppi
authors.affiliation: Brazilian Synchrotron Light Laboratory, Campinas, Brazil.
authors.forename: Raul Oliveira
authors.initials: RO
authors.lastname: Freitas
authors.affiliation: Institute of Chemistry, University of São Paulo, São Paulo, Brazil.
authors.forename: Fábio
authors.initials: F
authors.lastname: Rodrigues
authors.affiliation: Department of Chemistry, Materials, and Surfaces, SP Technical Research Institute of Sweden, Borås, Sweden.
authors.forename: Sandra
authors.initials: S
authors.lastname: Siljeström
authors.affiliation: Brazilian Synchrotron Light Laboratory, Campinas, Brazil.
authors.forename: Frederico Alves
authors.initials: FA
authors.lastname: Lima
authors.affiliation: Brazilian Synchrotron Light Laboratory, Campinas, Brazil.
authors.forename: Douglas
authors.initials: D
authors.lastname: Galante
authors.affiliation: Departamento de Geologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Ismar S
authors.identifier: http://orcid.org/0000-0002-1811-0588
authors.initials: IS
authors.lastname: Carvalho
authors.affiliation: Brazilian Synchrotron Light Laboratory, Campinas, Brazil.
authors.forename: Carlos Alberto
authors.identifier: http://orcid.org/0000-0003-4284-3148
authors.initials: CA
authors.lastname: Perez
authors.affiliation: Department of Zoology, Biosciences Institute, University of São Paulo, São Paulo, Brazil.
authors.forename: Marcelo Rodrigues
authors.initials: MR
authors.lastname: de Carvalho
authors.affiliation: Brazilian Nanotechnology National Laboratory, Campinas, Brazil.
authors.forename: Jefferson
authors.initials: J
authors.lastname: Bettini
authors.affiliation: European Synchrotron Radiation Facility, Grenoble, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Fernandez
authors.affiliation: Brazilian Biosciences National Laboratory, Campinas, Brazil.
authors.forename: José
authors.identifier: http://orcid.org/0000-0003-4648-789X
authors.initials: J
authors.lastname: Xavier-Neto
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005399:Fishes / Q000033:anatomy & histology*; D005580:Fossils; D006321:Heart / Q000033:anatomy & histology*; D055114:X-Ray Microtomography
keywords: Cretaceous; cardiac; development; ecology; evolution; evolutionary biology; fishes; fossils; genomics; none