It is among those basic biological phenomena that underpin much of our understanding of evolutionary processes, ecological adaptation, and functional biology. If anything, the paleontologist is interested in how ancient organisms varied in form as providing a considerable insight into their evolutionary history and ecological role. This is especially true in studies of extinct organisms of complex morphology, where there is an increased need for appropriate, reproducible methods of shape variation analysis.
Now enters this new, exciting analytical method: geometric morphometrics, which, for the first time, allows researchers to study, quantify, and compare shapes in ways hitherto unimaginable. It has transformed morphological variation studies by scientists, not only in extant species but also in fossils where traditional analyses are compromised by incomplete, deformed, or otherwise compromised specimens.
In this blog, we take a closer look at how the method of geometric morphometrics serves as a tool in assessing morphological variation within the now-extinct group of brachiopods, Eublastoidea, which flourished during the Paleozoic era. We investigate methodologies and applications-what is this approach offering with regard to insights into the understanding of evolutionary history and diversity for this enigmatic group of organisms?
What is Geometric Morphometrics?
Geometric morphometrics represents a field that is on the very frontier of mathematics, statistics, and computational tools when it comes to the study of the shape and form of organisms. While traditional morphometrics remains mainly concerned with linear measures of length, width, or volume, geometric morphometrics extends this by analyzing the spatial configuration of landmarks that define the shape of an object.
In the general concept of it, geometric morphometrics rest on the basis of landmarks’ usage-that is, specific, repeated points on morphology. Examples include the tip of features, junctions, or centers of curves. When these points are identified and digitized, their relative positions can describe shape in a more holistic and multidimensional way.
Some important techniques in the realm of geometric morphometrics:
Procrustes superimposition: This is the statistical process that removes the size, position, and orientation-noise of the data so that only the shape variation is analyzed. It’s very important when your specimens may vary in size or orientation due to natural or taphonomic processes.
Principal Component Analysis (PCA): Commonly, once the Procrustes superimposition is performed, PCA will be followed through with the aim of reducing dimensionality of a data set to visualize the major axes of variation in shape. This course of action will grant the researchers the ability to identify which changes in shape account for most of the observed variation.
Thin-Plate Splines: A way of visualizing shape deformation by demonstrating landmark motion across the specimens or groups, thus presenting clear and graphical ways of depicting changes in shape.
Geometric morphometrics also allows the study of morphospace-a conceptual space in which different shapes are represented as points in multidimensional space. The method may also prove to be particularly useful when comparing how species or populations within a group such as Eublastoidea have evolved or adapted over time.
Why Apply Geometric Morphometrics to Eublastoidea?
The Eublastoidea was an extinct order of brachiopod brachiopods that occurred chiefly in the Paleozoic Era, although diverse in the Silurian and Devonian periods. They are marine organisms, usually having generally robust and highly complicated structures at times, but enormously variable in form on a range of species. This makes Eublastoidea an ideal subject for the application of geometric morphometrics, which enables researchers to quantify the variation in shell morphology and explore its relationship with evolutionary processes.
The study of Eublastoidea by means of geometric morphometrics enjoys several advantages:
Quantification of Complex Shape Variation: One of the challenges in paleontology is to accurately quantify morphological differences among extinct organisms. Often, fossil remains come in incomplete, deformed, or poorly preserved states. Many of these problems are overcome since the analysis of landmark configuration in geometric morphometrics can even be conducted on fragmentary specimens. This ascertains that paleontologists capture the essence of the organism’s shape, though the fossil may not be in a perfectly preserved state.
Overcoming Preservational Bias: The diversity of ways that the possible biases of preservation enter into a fossil record-in the taphonomic processes including, but not restricted to, compression, distortion, and fragmentation-finds inadequate controls via traditional means of analysis. Such biases, geometric morphometrics will be unusually resilient against. This works for landmarks that could already be cleaned up with regard to orientation and size, in order to adjust for a given object’s size or orientation, and for that caused by deformation resulting from fossilization itself.
Tracking Evolutionary and Ecological Adaptation: The various Eublastoidea shell shapes have included a wealth of information about the organism’s evolution regarding adaptation. Through the use of geometric morphometrics, changes in such shell morphologies that may indicate adaptations to various environmental parameters such as sedimentation, water depth, or ocean chemistry over time become identifiable and can thus be tracked.
Materials and Methods: Landmarking and Data Collection in Eublastoidea
First and foremost, geometric morphometric analyses of Eublastoidea require the acquisition of valid landmark data in fossil specimens. It is quite a meticulous process in which specific points on the surface of the shell are fixed, which are applicable to all specimens within a species or genus. Such features often include the umbo, or the raised generally central area of the shell.
Hinge line: the line at which the two valves of the shell meet. Anterior and posterior margins: the front and rear of the shell. Lateral edges: the sides of the shell. Any prominent ridges, folds, or other surface features that are stable and readily identifiable across specimens.
Once these are identified, then the next process is the digitization of its coordinates. These are done by either direct measurement-through the use of calipers-or, increasingly common nowadays, through 3D scanning technologies which produce a virtual model of the fossil specimens. The respective coordinates for each landmark are noted and documented in some sort of format accessible through a statistical software program.
After data collection, the landmark coordinates undergo Procrustes superimposition to align the specimens and remove the non-shape variation. The resulting dataset consists of a set of shapes that can be analyzed for morphological variation.
Analyzing Morphological Variation: Case Studies in Eublastoidea
Geometric morphometrics has been applied in various ways to the morphology of Eublastoidea. The main aspects examined include:
This could serve as an example of intraspecific variation in the shape of Eublastoidea shells, possibly with ontogenetic, allometric, or environmentally driven variations. Geometric morphometrics has succeeded in showing such variation, further helping the questions:
how does the shape change along the ontogeny? Does it have different morphometries among its populations from geographically or ecologically different environments?
Intergeneric differences: The several genera of this Eublastoidea group exhibit a variety of characteristic shapes that are in need of further investigation concerning shape variation and its possible implication through comparing geometric morphometric analyses for these genera. This would involve which shapes are more rounded, others more elongated, or even flat, possibly related to their ecological strategies such as burrowing versus surface-dwelling species.
Evolutionary Trends: Geometric morphometrics allow the restoration of the pattern of evolution of shell shapes in Eublastoidea through time. In such a way, taking fossil specimens across different time periods, morphological changes corresponding to major evolutionary events, such as changes in climate, marine ecosystems, or the development of new ecological niches, can be traced.
Challenges and Limitations of Geometric Morphometrics in Paleontology
While geometric morphometrics offers a long list of advantages, there are some problems related to its practice in paleontology: a. Errors of Landmarking: Geometric morphometric analyses are heavily dependent on the correctness of the location and identification of landmarks. Sometimes the process of landmarking is subjective, especially when the fossils happen to be partially damaged or incomplete. Variability in results arises due to the disagreement over landmark placement.
Taphonomic distortion: Although all the considerations of geometric morphometrics take into account some aspects of distortion, in certain instances, the taphonomic alteration could be quite significant; compression of the shell might occur. Therefore, other considerations or corrections in such studies need to be accounted for.
Size and Sample Biases: Rarely are more than a few specimens adequately preserved for analysis. Their comparative fewer numbers will reduce the strength of statistical analyses, particularly where preservation rates are very low in some species. Despite these, the advantages of geometric morphometrics far outweigh the limitations, particularly with new techniques and technologies continually evolving, such as improved 3D scanning.
Conclusion: The Future of Geometric Morphometrics in Paleontology
Geometric morphometrics has fully revolutionized the study of morphology in ancient organisms, putting into perspective a powerful framework for understanding shape variation, evolutionary patterns, and functional adaptations. In the case of one of the most interesting groups of brachiopods, the Eublastoidea, this technique opened new doors toward the understanding of the complexities of its form and function through time.
Further refinement of these methods, taken in conjunction with the development of new technologies, will enable the paleontologist of the future to address even more complex questions, such as how changes in the environment have influenced morphological diversity or what the phylogenetic relationships are among closely related extinct taxa. By accepting geometric morphometrics, the unraveling of the evolutionary history of Eublastoidea and other fossil groups goes on to complete such a detailed view of biodiversity rich in ancient seas covering the Earth.
