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Kathleen Ritterbush

Title: Associate Professor
College: Mines & Earth Sciences
School / Department: Geology & Geophysics
Mentoring Philosophy:

Research Scope

I explore the roles of animal life in our dynamic Earth system through time. My research uses field, computation, microscopy, and experimental work to discover practical animal-environment interactions that underpinned marine ecosystems in deep time.

Biomechanics in the Fossil Record

Fossils reveal radical changes in animal biodiversity, distribution, and abundance, but we cannot reconstruct past ecosystems without accurate biomechanics. Earth’s history of catastrophic global mass extinctions is written in the fossilized remains of our oceans’ once-ubiquitous squid-like residents, the ammonites.

  • Found on every continent as fossilized spiral seashells, ammonoids flourished at sea for four hundred million years until their demise alongside large dinosaurs.
  • But to reconstruct shifting marine ecosystems we must know what ammonoids could do – could they swim, chase, escape, dive, lurk, or merely float? – and how this varied as different lineages took over our seas.
  • My research team at the University of Utah has shown that ammonites’ biomineralized parts absolutely would allow them to swim – and to twirl, dart, jet, or cruise – depending on the shape and size of their shell (e.g., Ritterbush & Hebdon in press; Peterman & Ritterbush in press).


We have three windows into ammonoid ecosystems.

First, we observe fossils and living relatives, which tell us how size, shape, diversity, and abundance of these open-ocean animals weathered boom-and-bust evolution cycles (Ritterbush et al. 2014; Ritterbush 2015). I do this work in the field (collecting new specimens); in museums (with curated fossils; Pietsch et al. 2019) and with big data (paleobiology database; Foote, Ritterbush, Miller 2016). Determining the ecologic consequences of ammonoid shell morphological evolution is one of the primary goals of my career. Paleontologists had no explanation for why wildly-successful post extinction ammonites of the Early Jurassic presented such simply coiled “serpenticone” shells which ought to be terrible at swimming (Ritterbush & Bottjer 2012), but some day we would have the tools to test these fundamental animal-environment relationships.

Second, we create computer models and simulations to test hydrodynamic consequences of each component of shell shape (Hebdon et al. Integrative & Comparitive Biology 2020). I established the Ammonite Motility Modeling Laboratory (AMMLab) and recruited first-generation college graduate Nicholas Hebdon (BS ’15 Rochester) to drive its computational development. Nick chose engineering software (Ansys Fluent) for his simulations; published a groundbreaking methods paper (Hebdon et al. Paleo. Electronica 2020); mentored undergraduates via UROP and ACCESS; and produced results that we presented to paleontologists in Morocco, physicists in Seattle, and the public at well-attended DinoFest events. These early results were vital to my successful NSF CAREER proposal, and were well-received across disciplines. Now finished (PhD ’21), Nick is building undergraduate-accessible training and workflows for steady-state fluid simulations, and pushing ahead into dynamic flow simulations.


We discovered that the very features thought to hamper swimming in simply-coiled serpenticone ammonites – their large exposed “hubcap” coils – actually could help these animals escape predators and travel efficiently.

  • The shell’s narrow profile allows quick acceleration on par with much smoother, streamlined species; once at speed, water trapped along the indented flanks should add virtual mass to keep their momentum.
  • Intriguing as a possible selective pressure during rapid evolution, this exemplifies a more fundamental discovery: Individual ammonite animals essentially spent their lives toggling between laminar and turbulent flow.
  • Morphological innovation to overcome this constant challenge may have contributed to the ammonoids’ radical diversification rates (i.e., Ritterbush & Foote 2017).

Third, we build physical experiments to test how hydrostatics, hydrodynamics, and jet propulsion determine real-world ammonoid-environment interactions (Peterman et al. WY GeoAssociation Special Issue 2020). Our capabilities expanded by helping experimentalist David Peterman (also a first-generation college graduate) earn a NSF Postdoctoral Fellowship.

  • With facilities limited by COVID, we designed experiments in rain barrels, home 3D print labs, and swimming pools public (Peterman et al. Scientific Reports 2020;Schultz 1846682574).
  • I nixed a plan to build permanent (and high-maintenance) flume equipment on campus in favor of mobile observation rigs. From our specs, David built portable underwater frames for triangulated high-speed cameras. We use machine learning to track specimen motion, velocity, etc.
  • We learned how helically-spiraled torticone ammonites twirl up and down through the water – good for patiently collecting microscopic food; while dagger-like orthocones dart – good for playing chicken with bigger, toothier predators.