Subsequent work has begun to reveal a greater diversity and complexity of life history strategies among these Mesozoic clades than previously understood. However, many initial studies of bone histology in Mesozoic avialans concluded that stem-group birds were either moderately more slow-growing (as in ornithuromorphs ( Chinsamy, Chiappe & Dodson, 1995 Bell et al., 2010)), or drastically slower (as in the case of enantiornithines and Archaeopteryx ( Chinsamy, Chiappe & Dodson, 1994 Cambra-Moo et al., 2006 Erickson et al., 2009 O’Connor et al., 2014)). Modern birds are extremely fast-growing animals ( de Ricqlès et al., 1991 Starck & Ricklefs, 1998 Erickson et al., 2009 Wilson & Chin, 2014), as were many non-avialan dinosaurs. The description and evolution of osteohistological structures and characteristics of avian adult bone have been a subject of scientific investigation for decades, particularly following the discovery of the dinosaurian ancestry of birds. Small size is achieved by truncating the period of fast growth manipulation of the timing of offset of bone growth is therefore an important factor in changing growth trajectories to alter adult body size. Thus, while the OCL is indicative of a cessation of appositional growth it is not always indicative of cortical maturity (that is, maximum organization of bony tissue for a given taxon). The outer circumferential layer (OCL) also appears at earlier growth stages in small-bodied taxa. Large-bodied birds have cortices of fibrolamellar bone, but organization of tissue increases and vascularity decreases with diminishing body size. Bone tissue in adults exhibited unexpected variation, corresponding to differences in body size. We did not find evidence to support hypotheses that precocial chicks exclusively have thicker cortices and more mature bone in the femur than the humerus at time of hatching instead, this is a characteristic of nearly all taxa (regardless of developmental mode), suggesting deep evolutionary origins and the effects of developmental channeling.
The tissue of precocial chicks is relatively more mature at hatching than in altricial, but other categories along the developmental spectrum were less easy to distinguish, thus we were unable to identify a definitive histological proxy for developmental mode. Across taxa, the femoral and humeral tissue of neonates can be broadly characterized as highly-vascularized, disorganized woven bone with great variation in cortical thickness (inter-and intrataxonomically, within an individual specimen, and within a single section). Our goals were to: (1) describe the microanatomy of each individual (2) make inter-and intra-taxonomic comparisons (3) assess patterns that correspond with developmental mode and (4) to further parse out phylogenetic, developmental, and functional constraints on avian osteological development.
In this study, we describe microanatomical characteristics of the humerus and femur in partial growth series from 14 crown group birds representing ten major clades (Struthioniformes, Galliformes, Apodiformes, Columbiformes, Charadriiformes, Accipitriformes, Strigiformes, Psittaciformes, Falconiformes, and Passeriformes). PeerJ 9: e12160 īone histology of crown-group birds is a research topic of great interest, permitting insight into the evolution of remarkably high growth rates in this clade and variation across the altricial-precocial spectrum. A histological survey of avian post-natal skeletal ontogeny. Cite this article Atterholt J, Woodward HN. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited. 3 Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, Tulsa, Oklahoma, United States DOI 10.7717/peerj.12160 Published Accepted Received Academic Editor David Ferrier Subject Areas Developmental Biology, Evolutionary Studies, Zoology, Histology Keywords Post-natal development, Aves, Osteohistology, Altricial-precocial spectrum, Bone growth Copyright © 2021 Atterholt and Woodward Licence This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed.