Quantifying shell patterning helps identify species of Trionychidae

Area of Science:

• Paleontology
• Herpetology
• Quantitative Morphology

Background:

• Softshell turtles (Trionychidae) possess unique shell sculpturing patterns.
• Previous attempts to use sculpturing for fossil classification were limited by qualitative methods and intraspecific variation.
• The potential for reliable, quantitative taxonomic traits from shell sculpturing remains underexplored.

Purpose of the Study:

• To quantitatively assess trionychid shell sculpturing patterns using topographic measurements.
• To determine the accuracy of these topographic metrics for species identification.
• To explore the utility of these methods for classifying fossilized shell fragments.

Main Methods:

• Obtained carapaces from extant specimens of Apalone ferox, Apalone spinifera, and Amyda cartilaginea.
• Created digital shell fragments from 3D scans.
• Quantified topographic features using Dirichlet Normal Energy (DNE), Relief Index (RFI), and Orientation Patch Count Rotated (OPCR).

Main Results:

• A nested MANOVA indicated significant variation in sculpturing at species, individual, and carapace location levels.
• Linear discriminant analysis correctly predicted species identity from DNE, RFI, and OPCR with 75.2% accuracy.
• Topographic measurements revealed informative patterns in shell sculpturing.

Conclusions:

• Quantitative topographic measurements provide a reliable method for distinguishing softshell turtle species.
• This approach shows potential for identifying fossilized shell fragments currently classified as Trionychidae indet.
• Further research should include more species and account for ontogenetic changes.