Research Interests
I study macroevolution and how the interactions between an organism’s physical and biotic environment, development, and resultant morphologies lead to long-term evolutionary consequences.
I work primarily with marine mollusks, especially turritellid gastropods.
Principle Areas of Research:
1) Biotic responses of marine mollusks to environmental changes
2) Macroevolutionary dynamics in marine mollusks- extinction dynamics and life history evolution
3) The origin of molluscan morphological features- heterochronic processes and functional morphology
Representative cases are given below, but see Publications & CV for additional examples.
Techniques commonly employed in my research:
Phylogenetic paleoecology: incorporating ecological information into a phylogenetic framework. I generate and work with both molecular and morphological data for my study systems
Collections-based ecological data: I work with large datasets derived from analysis and measurement of museum specimens to study evolution and assemblage changes through time
Isotopic sclerochronology: the study of how shells record seasonal variation as they grow
Raman spectroscopy: A non-destructive technique for evaluating fossil mineralogy
nano/microCT and SEM imaging: Many aspects of morphology of molluscs, including shell microstructure and larval shell characters are best studied through non-destructive imaging techniques.
CT scan of Turritella montanitensis PRI 68717 Agua Clara Fm. (early Miocene), Falcon, Venezuela
Vermicularia recta, UF 123499, Macasphalt Shell Pit, Sarasota County, Florida, Plio–Pleistocene. Anderson and Allmon 2023
Turritellids
Turritellids are some of the most common macrofossils in the fossil record and can be extremely abundant in both live and fossil communities. Turritellids occur worldwide in the fossil record and are currently represented by around 150 living species. They have also been important sources of paleoenvironmental data through examination of the isotopes used in the construction of their shells as they are fast growing and can provide data on seasonal ranges of variation. Many turritellids are referred to the genus “Turritella”, but in most cases this is due to the inability to specify what genus is appropriate for a given species. By employing molecular techniques I have worked to establish which traits are more likely to be associated with clade membership so more fossils can be assigned to genera that have biological meaning.
Much of my PhD thesis was spent working on Vermicularia, a genus of turritellids which evolved to be uncoiled, often cementing to hard surfaces or living inside of sponges. Some even intercoil with each other and form reef masses, which can be stratigraphically significant.
Mollusks and Environmental Change
Isotopic data in mollusk shells can document marine conditions
Anderson et al. 2017; showing how turritella dominated assemblages are related to upwelling in the Gatun Formation
Mollusks also respond to environmental changes in a variety of ways including extinction, migration, diversification and within-lineage evolution.
Sang et al. 2019; Showing how after the closure of the Central American Seaway protoconch size became larger in the western Atlantic, a change associated with reduced nutrient availability.
Macroevolutionary Dynamics in Mollusks
Some traits of organisms, such as larval mode (feeding or non-feeding), may have consequences for speciation and extinction rates. Placing these data into phylogenetic context can reveal whether trends emerge due to biases in direction of change or variation in net-speciation rates, or are the result of chance.
Figure from Friend et al. 2021
Aggregating data from multiple species we can examine whether there are macroevolutionary trends exhibited by clades over time and what environmental or biological processes may have influenced their evolution.
Figure from Pietsch et al. 2023, Showing Turritellid gastropod body size has been in stasis since the Cretaceous.
Origins of Morphological Features
Some morphological features of shells have not been well documented, and may have a variety of evolutionary origins. Septa in turritellids (left image) may be evolutionary spandrels, secondary byproducts of shell thickening, while the hollow newel state (absence of columella; right image) may facilitate the development of large body size.
Figures from Anderson and Allmon, 2018 and Friend et al. 2024.
Very large body size in Caviturritella abrupta was the result of both longer than typical lifespan and retention of relatively fast growth rates in the first year of life, as indicated by isotopic sclerochronology. A series of environmental changes affecting carbonate saturation state and nutrient availability caused their geographic range to contract, and ultimately this species’ extinction.
Figure from Anderson and Allmon, 2020