USING PHYLOGENETIC TREES AND 3D MORPHOMETRICS TO UNDERSTAND ECOLOGICAL CHANGE DURING THE LATE ORDOVICIAN MASS EXTINCTION AND RECOVERY

An organism’s morphology is the locus of interaction between ecological and evolutionary pressure. Morphological variation is controlled both by direct interactions between an organism and its environment (selection/ecology) and by historical constraints that exist due to previous changes within an organism’s clade (evolution/phylogenetics). For phylogenetic paleoecology to succeed as a subdiscipline, we must increase both the quantity and quality of morphological data sets. Placing geometric morphometric data within a phylogenetic framework allows us to assess the morphological variability of closely related taxa (clades) and gauge the impact that ecological or historical processes can have on morphological change.

For this project, we collected 3D morphological data from strophomenid brachiopods using the photogrammetry method Structure-from-Motion (SfM). This method creates a high-resolution 3D image from a series of overlapping 2D photographs. It has been used in other fields of geology, but has not yet been widely applied to paleontology. Unlike more complicated 3D techniques (e.g., CT scanning, laser scanning), SfM can be performed with photographs from any digital camera. This advantage makes SfM simple, inexpensive, and field-accessible, which is ideal for fossil organisms. Its simplicity and wide-applicability mean SfM can generate large datasets for robust statistical analysis of morphology. This sort of 3D data is particularly valuable for quantifying shell features (e.g., globosity, ribbing, texture) that can only be accurately captured in 3D.

We tested this method on well-preserved brachiopods from the Yale Peabody Museum and demonstrated that SfM can robustly resolve important external morphological characters in 3D. Preliminary results comparing these data to our previous phylogenetic character data illustrate the importance of considering historical components of geometric morphometric analyses across extinction and recovery events. The success of this method in the lab has motivated a field project to quantify change in brachiopod morphology within a stratigraphic section. This will allow us to place morphologic data in both a phylogenetic and stratigraphic context to better understand the relationship between phylogenetics and paleoecology.