Tooth replacement patterns in the Early Triassic epicynodont Galesaurus planiceps (Therapsida, Cynodontia)

Area of Science:

• Paleontology
• Vertebrate Zoology
• Evolutionary Biology

Background:

• Cynodonts, particularly Galesaurus planiceps, are crucial for understanding early mammal evolution.
• Dental replacement patterns provide insights into ontogeny and life history strategies.
• Previous studies on cynodont dental development have highlighted variations within the group.

Purpose of the Study:

• To investigate the patterns of dental replacement and development in Galesaurus planiceps across various ontogenetic stages.
• To compare the dental development of Galesaurus planiceps with other cynodonts, specifically Thrinaxodon.
• To analyze the functional morphology of canine roots in mature Galesaurus planiceps specimens.

Main Methods:

• Micro-computed tomography (micro-CT) scanning of 16 Galesaurus planiceps specimens.
• Analysis of dental replacement in incisors, canines, and postcanines.
• Measurement of basal skull length to correlate with developmental stages.
• Examination of canine root morphology in mature individuals.

Main Results:

• Incisors and postcanines showed continuous replacement, even in the largest specimens.
• Canine replacement ceased upon reaching skeletal maturity (~90 mm basal skull length).
• Open-rooted canine morphology was observed in mature Galesaurus planiceps, a novel finding for Mesozoic theriodonts.
• An alternating replacement pattern was noted in maxillary and mandibular postcanines, with increasing tooth number correlating with skull length.
• Galesaurus planiceps differed from Thrinaxodon in retaining mesial-most postcanines, contributing to a longer postcanine series.

Conclusions:

• Galesaurus planiceps possessed a finite number of canine replacement cycles, distinct from continuous replacement in incisors and postcanines.
• The dental development and replacement strategies of Galesaurus planiceps show significant divergence from Thrinaxodon.
• The observed open-rooted canine morphology in mature Galesaurus planiceps represents a unique adaptation within Mesozoic theriodonts.