title: Exceptional preservation reveals gastrointestinal anatomy and evolution in early actinopterygian fishes.
abstract: Current knowledge about the evolutionary morphology of the vertebrate gastrointestinal tract (GIT) is hindered by the low preservation potential of soft tissues in fossils. Exceptionally preserved cololites of individual †Saurichthys from the Middle Triassic of Switzerland provide unique insights into the evolutionary morphology of the GIT. The GIT of †Saurichthys differed from that of other early actinopterygians, and was convergent to that of some living sharks and rays, in exhibiting up to 30 turns of the spiral valve. Dissections and literature review demonstrate the phylogenetic diversity of GIT features and signs of biological factors that influence its morphology. A phylogenetically informed analysis of a dataset containing 134 taxa suggests that body size and phylogeny are important factors affecting the spiral valve turn counts. The high number of turns in the spiral valve of †Saurichthys and some recent sharks and rays reflect both energetically demanding lifestyles and the evolutionary histories of the groups.
authors.affiliation: Paleontological Institute and Museum, University of Zurich, 8006 Zurich, Switzerland.
authors.forename: Thodoris
authors.initials: T
authors.lastname: Argyriou
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland.
authors.forename: Marcus
authors.initials: M
authors.lastname: Clauss
authors.affiliation: Stuttgart State Museum of Natural History, 70191 Stuttgart, Germany.
authors.forename: Erin E
authors.initials: EE
authors.lastname: Maxwell
authors.affiliation: Paleontological Institute and Museum, University of Zurich, 8006 Zurich, Switzerland.
authors.forename: Heinz
authors.initials: H
authors.lastname: Furrer
authors.affiliation: Paleontological Institute and Museum, University of Zurich, 8006 Zurich, Switzerland.
authors.forename: Marcelo R
authors.initials: MR
authors.lastname: Sánchez-Villagra
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005399:Fishes / Q000033:anatomy & histology* / Q000145:classification; D005580:Fossils; D041981:Gastrointestinal Tract / Q000033:anatomy & histology*; D010802:Phylogeny