Vertebral morphometrics and lung structure in non-avian dinosaurs

Area of Science:

• Paleontology
• Comparative Anatomy
• Vertebrate Physiology

Background:

• The unique lung-air sac system of modern birds has long been a subject of evolutionary debate.
• Determining the origin of avian respiratory systems in dinosaur ancestors is challenging due to limited osteological evidence.
• Axial morphology offers a novel approach to inferring lung structure from skeletal remains.

Purpose of the Study:

• To investigate the presence of avian-style respiratory structures in non-avian dinosaurs and basal dinosauriforms.
• To use vertebral shape as a direct osteological correlate for lung structure.
• To understand the physiological capabilities of dinosaurs, particularly their aerobic and metabolic potential.

Main Methods:

• Geometric morphometrics was employed to quantify vertebral shape in birds, crocodilians, and diverse dinosaur taxa.
• Axial morphology was analyzed as a direct osteological correlate of lung structure.
• Comparative analysis was conducted across avian and non-avian lineages.

Main Results:

• Non-avian dinosaurs and basal dinosauriforms exhibited bird-like costovertebral joints and a furrowed thoracic ceiling.
• These features indicate immobilization of the lung's dorsal surface, a prerequisite for efficient gas exchange.
• Fully avian lungs were determined to be a later evolutionary innovation.

Conclusions:

• The respiratory system of non-avian dinosaurs was structurally adapted for enhanced gas exchange.
• These adaptations likely supported high aerobic and metabolic activity, contributing to dinosaur success.
• The study provides quantitative evidence for bird-like respiratory mechanics in dinosaurs, predating fully avian lungs.