Extreme Ontogenetic Changes in a Ceratosaurian Theropod

Area of Science:

• Paleontology
• Evolutionary Biology
• Vertebrate Zoology

Background:

• Ontogenetic variation, or changes during an organism's life, is common in dinosaurs.
• Extreme ontogenetic changes are rare, especially in theropod dinosaurs.

Purpose of the Study:

• To investigate ontogenetic changes in the Jurassic theropod Limusaurus inextricabilis.
• To document the first fossil record of ontogenetic edentulism (tooth loss with age) in jawed vertebrates.

Main Methods:

• Analysis of 19 Limusaurus inextricabilis specimens across six ontogenetic stages.
• Utilized body size, histological data, and advanced imaging (Mi-CT and SR-μCT scanning).
• Examined jaw morphology, gastroliths, and stable isotopes.

Main Results:

• Identified 78 ontogenetic changes, including a shift from toothed jaws in juveniles to a toothless beak in adults.
• Confirmed gradual, complex ontogenetic tooth loss with evidence of dental alveolar vestiges.
• Phylogenetic analyses showed minimal impact of ontogenetic data on Limusaurus placement.

Conclusions:

• The tooth-to-beak transformation in Limusaurus inextricabilis suggests a dietary shift from omnivory to herbivory.
• This finding provides significant insights into the evolution of beaks in tetrapods, including birds.
• Ontogenetic edentulism is a previously undocumented phenomenon in the fossil record of jawed vertebrates.