THREE-DIMENSIONAL CHANGES IN MORPHOLOGICAL DIVERSITY OF BRACHIOPODS ACROSS THE RICHMONDIAN INVASION, LATE ORDOVICIAN

Invasive species are a major driver of extinction in modern taxa. However, because anthropogenic invasion events are relatively recent geologically, the long-term impacts of invasions are unclear. Understanding the effects of invasion events over geologic and evolutionary timescales requires us to use the ancient invasion events preserved in the fossil record. We focus on the Richmondian Invasion, which occurred during the Late Ordovician when a set of related invaders arrived in the Illinois Basin from the Bighorn Basin resulting in major changes in community composition.

Here, we investigate morphological diversity of brachiopods across the Richmondian Invasion. Changes in morphological diversity can be measured by ordinating shape data from different time intervals and exploring the changes in ordination space. This is important because a decrease in the morphological diversity of a species may decrease its ability to resist extinction. Understanding morphological diversity also helps link changes in ecology to evolution. This is especially useful in sessile brachiopods, which primarily interact with their environment through the shape of their shell.

To measure changes in shell shape we use the Structure-from-Motion (SfM). SfM uses 2D photographs taken from different angles around an object reconstruct its 3D shape. We developed a set of methods to collect high quality 3-dimensional data of fossil specimens in the field to use with 3D geometric morphometrics. This allows us to create a large dataset of 3D brachiopod shapes quickly and inexpensively. We photographed external valves of specimens in the field in 360 degrees (approximately 24 photos per specimen) and used the software ‘Photoscan’ to make 3D models of the specimens. We export these models into R and use the package ‘morpho’ to generate a set of semi-landmarks across the surface of the shells. We collected brachiopod photographs of endemic taxa from the C2 sequence (before the Richmondian Invasion) and C5 sequence (after the Richmondian Invasion) and are currently building the 3D models. We expect that morphological diversity will decrease after the introduction of invasive taxa as they compete for space and resources.