A new index for quantifying the ornamentational complexity of animals with shells

Area of Science:

• Paleontology
• Evolutionary Biology
• Marine Biology

Background:

• Morphological complexity, particularly shell ornamentation, is vital for understanding animal function and evolution.
• Existing methods struggle to universally quantify shell ornamentation complexity due to variations in type, shape, and density.
• A standardized quantitative measure is needed for comparative studies of shelled organisms.

Purpose of the Study:

• To introduce and validate a novel Ornamentation Index (OI) for quantifying morphological complexity in shelled organisms.
• To demonstrate the OI's effectiveness across diverse species and geological time periods.
• To establish a tool for investigating evolutionary patterns and environmental influences on shell ornamentation.

Main Methods:

• Utilized 3D scanning technology to create virtual models of specimens.
• Developed a novel Ornamentation Index (OI) based on the extent of folding in shell ornamentation.
• Applied the OI to ammonites, bivalves, gastropods, and an echinoid, comparing it with fractal dimension, rugosity, and surface-volume ratio.

Main Results:

• The proposed Ornamentation Index (OI) effectively quantifies ornamentation complexity, irrespective of shape and size.
• The OI demonstrated superiority over traditional metrics like fractal dimension and rugosity.
• Measurements were successfully obtained for a range of fossil and modern shelled organisms.

Conclusions:

• The Ornamentation Index (OI) is a robust and versatile tool for characterizing shell ornamentation complexity.
• The OI can facilitate comparative analyses of morphological evolution in shelled organisms.
• This index offers potential insights into how environmental factors like ocean acidification and predation pressure influence shell evolution.