A geometric morphometric protocol to correct postmortem body arching in fossil fishes

Area of Science:

• Paleontology
• Ichthyology
• Geometric Morphometrics

Background:

• Postmortem body curvature is a common taphonomic process affecting fossil fish.
• This curvature introduces significant error into morphometric data analysis.
• Existing methods for correcting curvature in living fish may not be suitable for fossils.

Purpose of the Study:

• To evaluate mathematical approaches for correcting postmortem body curvature in fossil fish.
• To determine the most effective method for correcting geometric morphometric data from fossil specimens.
• To assess the influence of factors like taxon, morphology, and size on body curvature in fossils.

Main Methods:

• Two mathematical approaches, multivariate regression and "unbending functions," were tested.
• The methods were applied to exceptionally preserved gonorynchiformes fossil fishes (Rubiesichthys gregalis and Gordichthys conquensis).
• Geometric morphometric data from 2D fossil specimens were analyzed to assess curvature correction efficacy.

Main Results:

• Both multivariate regression and "unbending functions" successfully corrected body curvature in fossil fish.
• The "unbending functions" method, focusing on correcting specimen arching, yielded the best results for 2D fossil data.
• Body curvature's effect is largely taxon-independent, with morphological diversity mitigating its impact.
• Larger fossil individuals exhibited less pronounced curvature.

Conclusions:

• Mathematical correction of postmortem body curvature is crucial for accurate fossil fish morphometrics.
• The "unbending functions" approach is recommended for correcting 2D fossil fish geometric morphometric data.
• Size is a significant factor influencing the degree of body curvature in fossil specimens.