title: Was dinosaurian physiology inherited by birds? Reconciling slow growth in archaeopteryx.
abstract: BACKGROUND
  Archaeopteryx is the oldest and most primitive known bird (Avialae). It is believed that the growth and energetic physiology of basalmost birds such as Archaeopteryx were inherited in their entirety from non-avialan dinosaurs. This hypothesis predicts that the long bones in these birds formed using rapidly growing, well-vascularized woven tissue typical of non-avialan dinosaurs.
  
  
  RESULTS
  We report that Archaeopteryx long bones are composed of nearly avascular parallel-fibered bone. This is among the slowest growing osseous tissues and is common in ectothermic reptiles. These findings dispute the hypothesis that non-avialan dinosaur growth and physiology were inherited in totality by the first birds. Examining these findings in a phylogenetic context required intensive sampling of outgroup dinosaurs and basalmost birds. Our results demonstrate the presence of a scale-dependent maniraptoran histological continuum that Archaeopteryx and other basalmost birds follow. Growth analysis for Archaeopteryx suggests that these animals showed exponential growth rates like non-avialan dinosaurs, three times slower than living precocial birds, but still within the lowermost range for all endothermic vertebrates.
  
  
  CONCLUSIONS
  The unexpected histology of Archaeopteryx and other basalmost birds is actually consistent with retention of the phylogenetically earlier paravian dinosaur condition when size is considered. The first birds were simply feathered dinosaurs with respect to growth and energetic physiology. The evolution of the novel pattern in modern forms occurred later in the group's history.
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, USA. gerickson@bio.fsu.edu
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Erickson
authors.forename: Oliver W M
authors.initials: OW
authors.lastname: Rauhut
authors.forename: Zhonghe
authors.initials: Z
authors.lastname: Zhou
authors.forename: Alan H
authors.initials: AH
authors.lastname: Turner
authors.forename: Brian D
authors.initials: BD
authors.lastname: Inouye
authors.forename: Dongyu
authors.initials: D
authors.lastname: Hu
authors.forename: Mark A
authors.initials: MA
authors.lastname: Norell
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D001842:Bone and Bones / Q000033:anatomy & histology*; D025061:Dinosaurs / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D005241:Feathers / Q000033:anatomy & histology / Q000254:growth & development; D005426:Flight, Animal / Q000502:physiology; D005580:Fossils; D008953:Models, Anatomic; D008954:Models, Biological; D010163:Paleontology / Q000379:methods; D010802:Phylogeny