Nucula specimen data used for: Testing the ‘Plus ça Change’ model: A comparison of Nuculid bivalve evolution across contrasting broad-scale climatic regimes

Slattery, Joshua 1 ; Harries, Peter2 ; Jarrett, Matthew3; Sandness, Ashley4

Research facility: University of South Florida

Published May 29, 2025 on Dryad. https://doi.org/10.5061/dryad.sqv9s4ndb

Data files

May 29, 2025 version files 159.93 KB

README.md

3.33 KB
Slattery_Supplemental_Material_Figure_1.pdf

72.86 KB
Supplemental_Data_Table_1.csv

82.05 KB
Supplemental_Data_Table_2.csv

924 B
Supplemental_Data_Table_3.csv

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Abstract

Documenting patterns of evolution and stasis has been a major focus of paleobiology. However, despite substantial knowledge gleaned on this topic, many questions related to the underlying environmental processes that determine the dynamics of evolution and stasis remain unresolved. Therefore, this study focuses on examining these evolutionary patterns framed within an environmental context. Specifically, we test Sheldon’s (1996) ‘Plus ça Change’ model, which predicts that morphological change is associated with more stable environments, such as in tropical latitudes or greenhouse climates, whereas stasis is linked to less stable environments, like those found in temperate latitudes or during icehouse climates. We examine the role that broad-scale climatic variation exerts on evolutionary dynamics by documenting morphological change among nuculid bivalves in shallow shelf settings from three different climate regimes: 1) the stable Late Cretaceous greenhouse climate; 2) the moderately stable Neogene transitional climate; and 3) the less stable Quaternary icehouse climate. Morphological changes over time were assessed using both bivalve size and outline shape. Comparison among changes in size and outline-shape patterns for Late Cretaceous and Neogene–Quaternary Nucula indicates that morphological change over time and stasis, respectively, dominated these different time intervals. In all cases, morphological change over time coincided with the more stable and less climatically variability greenhouse conditions, whereas stasis was associated with the more variable regimes characteristic of icehouse climates. These data provide strong support for the need to consider broad environmental factors – in this case climate – when assessing evolutionary modes. Furthermore, it points to the relevance of the ‘Plus ça Change’ model to explain patterns of evolution and stasis.

https://doi.org/10.5061/dryad.sqv9s4ndb

Description of the data and file structure

A total of 887 right and left valves of Cretaceous and Neogene–Quaternary Nucula specimens were analyzed for this study, including 141 valves of Cretaceous Nucula percrassa and 746 Neogene–Quaternary Nucula valves. Specimens are housed in the Mississippi Museum of Natural Science, Florida Museum of Natural History, and Yale Peabody Museum of Natural History.

To examine evolutionary patterns, size and outline shape data were collected. Specimens were photographed against a black background using a macro-enabled camera mounted on a copy stand to ensure consistent scaling. Images were converted to black-and-white silhouettes in GIMP to facilitate shape extraction and cleaned to remove artifacts.

Shape data were obtained using the FIJI image processing program, where shell outlines were traced, and xy-coordinates were extracted. Centroid sizes, representing shell size, were calculated from these outlines using a 10-mm scale for reference. These methods ensure precise measurements and minimize distortion in the analysis.

Files and variables

Table 1: Nucula Specimen Data
- Taxon Name: The species or taxonomic group of each specimen.
- Valve Side: Indicates whether the specimen is a right (R) or left (L) valve.
- Museum Catalog Number: Unique identifier for each specimen, linked to the respective museum collection (Florida Museum of Natural History, University of Florida (UF), Mississippi Museum of Nature and Science (MMNS), Yale Peabody Museum of Natural History (YPM), or personal collection of the author).
- Locality: Geographical location where the specimen was found.
- Formation/Age: Geological formation and the age of the specimen.
- Size Data: Centroid size data, calculated as the sum of squared distances between landmarks on the valve and the centroid.
Table 2: Summary Data for Nucula Log Size Boxplots
- Log Size Data: The log-transformed size data of Nucula specimens, linked to the boxplots in Figure 6.
Table 3: Summary Data for Principal Component Scores and Disparity
- PC1 and PC2 Scores: Scores from the first and second principal component analyses of shape data, linked to Figures 10, 11, and 12.
- Disparity Values: Measures of the variation in shape data across the specimens.
Figure 1: Examples of Shape Rotation and Analysis
- A: Example of an unrotated shape, the first elliptical Fourier ellipse, and the calculation of rotation angle for shape alignment.
- B: Examples of shapes scaled and rotated using procrustes superimposition.
- C: Example of shape rotation and alignment using the method described by Jarrett (2016), showing the improved fit between outlines.

Each data file and its associated variables are integral to understanding the morphometric analysis, allowing comparisons of size and shape patterns among Nucula species across different climatic regimes.

Code/software

No special code is needed. To view the files you need a PDF reader.