title: Palaeohistological Evidence for Ancestral High Metabolic Rate in Archosaurs.
abstract: Metabolic heat production in archosaurs has played an important role in their evolutionary radiation during the Mesozoic, and their ancestral metabolic condition has long been a matter of debate in systematics and palaeontology. The study of fossil bone histology provides crucial information on bone growth rate, which has been used to indirectly investigate the evolution of thermometabolism in archosaurs. However, no quantitative estimation of metabolic rate has ever been performed on fossils using bone histological features. Moreover, to date, no inference model has included phylogenetic information in the form of predictive variables. Here we performed statistical predictive modeling using the new method of phylogenetic eigenvector maps on a set of bone histological features for a sample of extant and extinct vertebrates, to estimate metabolic rates of fossil archosauromorphs. This modeling procedure serves as a case study for eigenvector-based predictive modeling in a phylogenetic context, as well as an investigation of the poorly known evolutionary patterns of metabolic rate in archosaurs. Our results show that Mesozoic theropod dinosaurs exhibit metabolic rates very close to those found in modern birds, that archosaurs share a higher ancestral metabolic rate than that of extant ectotherms, and that this derived high metabolic rate was acquired at a much more inclusive level of the phylogenetic tree, among non-archosaurian archosauromorphs. These results also highlight the difficulties of assigning a given heat production strategy (i.e., endothermy, ectothermy) to an estimated metabolic rate value, and confirm findings of previous studies that the definition of the endotherm/ectotherm dichotomy may be ambiguous.
authors.affiliation: Institut des Sciences de la Terre de Paris (ISTeP), Sorbonne Universités - Université Pierre et Marie Curie , 4 Place Jussieu, F-75005 Paris, France; lucasjlegendre@gmail.com.
authors.forename: Lucas J
authors.initials: LJ
authors.lastname: Legendre
authors.affiliation: Département de sciences biologiques, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Guénard
authors.affiliation: Karoo Palaeontology, National Museum, Bloemfontein 9300, South Africa; and.|Department of Zoology and Entomology, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Botha-Brink
authors.affiliation: Institut des Sciences de la Terre de Paris (ISTeP), Sorbonne Universités - Université Pierre et Marie Curie , 4 Place Jussieu, F-75005 Paris, France.
authors.forename: Jorge
authors.initials: J
authors.lastname: Cubo
mesh_terms: D000818:Animals; D001481:Basal Metabolism / Q000502:physiology*; D005075:Biological Evolution; D001717:Birds; D025061:Dinosaurs / Q000502:physiology*; D005580:Fossils; D008954:Models, Biological; D010163:Paleontology; D010802:Phylogeny
keywords: Archosaurs; bone histology; phylogenetic comparative methods; phylogenetic eigenvectors; resting metabolic rate; vertebrate palaeontology