The developing bird pelvis passes through ancestral dinosaurian conditions
Christopher T Griffin1,2,3, João F Botelho1,2,4, Michael Hanson1,2
1Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA.
Nature
|July 27, 2022
Summary
Bird pelvis development reveals ancestral dinosaur traits transiently appearing during embryonic growth. This evolutionary pattern suggests a "terminal addition" mechanism in avian evolution.
Area of Science:
- Paleontology
- Developmental Biology
- Evolutionary Biology
Background:
- Living birds (Aves) exhibit significant anatomical modifications from their reptilian ancestors.
- The avian pelvis underwent substantial changes during the transition from early archosaurs to modern birds.
- While the fossil record documents evolutionary changes, the underlying developmental processes (ontogeny) are less understood.
Purpose of the Study:
- To investigate the three-dimensional morphogenesis of avian pelvic tissues using embryological imaging.
- To compare avian pelvic development with the fossil record of dinosaur-to-bird transitions.
- To understand the developmental basis for the evolution of the avian pelvis.
Main Methods:
- Utilized advanced embryological imaging techniques to examine pelvic tissue development in three dimensions.
- Performed quantitative analyses to compare avian pelvic ontogeny with phylogenetic sequences.
- Investigated phenotypic covariance within the pelvis across Archosauria.
Main Results:
- Ancestral dinosaurian pelvic features (e.g., forward-facing pubis, pubic 'boot') are transiently observed during early bird embryogenesis.
- Avian pelvic development follows a prenatal sequence that mirrors the evolutionary acquisition of traits from non-avian dinosaurs.
- Demonstrated phenotypic covariance in the pelvis, conserved across Archosauria, potentially explaining the retention of ancestral states.
Conclusions:
- Avian pelvic evolution likely occurred via "terminal addition," where new traits are added to the end of a developmental sequence, expressing ancestral states earlier.
- Phenotypic integration in the pelvis suggests a novel mechanism for terminal addition during evolution.
- The study highlights the importance of studying embryonic development to understand evolutionary transitions and the retention of ancestral traits.
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