Chewing or not? Intraoral food processing in a salamandrid newt

Area of Science:

• Comparative anatomy
• Evolutionary biology
• Vertebrate paleontology

Background:

• Food processing, or mechanical breakdown before swallowing, is crucial for digestion across gnathostomes.
• Chewing, involving jaw and tongue movements, is common in chondrichthyans, actinopterygians, lungfishes, and amniotes.
• The evolution of amniote chewing is linked to tetrapod terrestrial adaptation, but lissamphibian processing remains poorly understood.

Purpose of the Study:

• To investigate intraoral food processing mechanisms in lissamphibians, specifically the salamandrid newt, *Triturus carnifex*.
• To compare newt feeding behaviors with those of fish and amniotes to understand the evolution of food processing.
• To explore the potential of salamanders as models for reconstructing early tetrapod feeding evolution.

Main Methods:

• High-speed fluoroscopy to visualize jaw and tongue movements during feeding.
• Anatomical reconstructions to study the feeding apparatus.
• Stomach content analysis to determine diet and processing outcomes.

Main Results:

• Newts exhibit cyclic head bobbing coordinated with rhythmic jaw and tongue movements.
• Prey is processed by rasping against the palate's dentition using a loop motion of the tongue, without mandibular jaw involvement.
• This processing mechanism shares characteristics with both fish and amniote feeding strategies.

Conclusions:

• Salamanders possess a derived intraoral food processing mechanism distinct from typical chewing.
• Newt food processing provides insights into ancestral tetrapod feeding and the fish-tetrapod transition.
• Salamanders are valuable models for understanding the evolution of intraoral processing mechanisms.