Head size, weaponry, and cervical adaptation: Testing craniocervical evolutionary hypotheses in Ceratopsia

Area of Science:

• Paleontology
• Vertebrate Anatomy
• Evolutionary Biology

Background:

• The anterior cervical vertebrae connect the skull and body in tetrapods, influencing head and neck function.
• The neoceratopsian syncervical, a fusion of three anterior cervical vertebrae, is a highly modified structure in vertebrates.
• Previous hypotheses suggested the syncervical evolved to support large skulls or for combat in ceratopsids.

Purpose of the Study:

• To test functional/adaptive hypotheses for the origin of the neoceratopsian syncervical within a phylogenetic framework.
• To critically examine methods for quantifying relative head size in the fossil record.
• To investigate the evolutionary pressures shaping the atlas-axis complex in ceratopsians.

Main Methods:

• Phylogenetic analysis of ceratopsian dinosaurs.
• Quantitative assessment of cranial size and weaponry.
• Comparative anatomical study of the atlas-axis complex.

Main Results:

• Neither the evolution of cranial weaponry nor large head size correlates with the origin of cervical fusion in ceratopsians.
• The study rejects the hypotheses that the syncervical evolved for skull support or combat.
• Cervical fusion has evolved independently in multiple amniote lineages.

Conclusions:

• The adaptive hypotheses for the origin of the ceratopsian syncervical are rejected.
• The evolutionary basis for cervical fusion in Neoceratopsia requires further investigation, potentially through studies of extant groups.
• Understanding the evolution of cervical fusion in dinosaurs may benefit from comparative research on modern animals.