Macroevolution Unit
The Macroevolution Unit (PI: Lauren Sallan) is a theory-driven research group focused on explaining how biological diversity is generated, constrained, and reorganized across space and deep time. We ask two linked questions: what actually happened in evolutionary history, and why? Answering the first requires reliable primary evidence - taxonomy, specimens, fossil occurrences, traits, phylogenies, biogeography, and observations of living communities. Answering the second requires causal tests using comparative analysis, developmental mechanisms, biomechanics, field ecology, and generative models.
Our work is converging in an emerging Diversity–Reset Framework for asking when processes observed at one biological scale become persistent macroevolutionary structure, and when extinction or other disruption changes the rules. Across projects, the same mismatches recur: variation is not realized form, survival is not radiation, local ecological advantage is not necessarily long-term evolutionary success, and taxonomic turnover need not expand functional space.
We therefore ask when local effects persist, repeat, propagate, or sort lineages strongly enough to shape biodiversity at larger scales. Reset and recovery are one part of this problem: extinction and environmental disruption can redistribute ecological opportunity and alter which developmental, functional, ecological, and geographic filters act on subsequent evolution.
Macroevolution refers to evolution above the level of populations and species: the origin, diversification, and extinction of lineages; the construction of ecosystems; and long-term patterns in diversity and form across deep time.
Our lab uses fishes as a primary model system, not as an endpoint, but as a mechanism-rich window into general evolutionary dynamics. Hydrodynamics and biomechanics tightly couple form, performance, and ecology in aquatic vertebrates, making fishes an unusually powerful system for linking organismal design to macroevolutionary pattern
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Systems and approaches
Projects in the Unit address one or more of four linked questions:
Reset & Reassembly - How does disruption change the course of evolution?
Lineage Fate - Why do some lineages radiate while others persist or disappear?
Ecology Across Scales - When do local ecological processes influence macroevolution?
Form, Function & Exceptions - Why do organismal solutions recur, improve, or defy expectations?
We integrate fossils, phylogenetics, taxonomy and systematics, biomechanics, development, population genomics, field ecology, comparative trait data, and theoretical modeling. Different projects supply different kinds of evidence, but together they allow us to connect the generation of variation, functional viability, ecological filtering, geography, lineage history, and deep-time persistence.
Many of the datasets needed to answer macroevolutionary questions do not already exist at the necessary scale or consistency. At vertebrate and deep-time scales, occurrence and trait datasets may require years of assembly from primary literature and specimen records, taxonomic reconciliation, and standardization across tens of thousands of observations before comparative analysis is possible. Building reliable primary evidence is therefore part of the research itself, not merely preparation for analysis.
Okinawa provides a complementary living system in which species identities, distributions, traits, genomes, performance, and community structure can be measured at much higher resolution. We use this evidence to test mechanisms that can then be compared with the incomplete historical record preserved by fossils.
Our research asks:
• when extinction and environmental disruption alter subsequent evolutionary trajectories;
• why similarly aged lineages differ so strongly in diversification and persistence;
• when ecological interactions, habitat and geography scale into clade-level patterns; and
• how development and biomechanics constrain which apparently possible forms actually evolve and recur.
Current projects include diversity-dependent diversification, lineage imbalance in phylogenies and ecosystems, functional and biomechanical constraints in early and modern vertebrates, the influence of mass extinction, ecological factors, and key innovations on fish evolution through time, models of emergence and divergence of phenotypic novelty, alpha taxonomy and speciation in clupeiform and other fishes, and genomic biogeography and community assembly in Indo-Pacific systems.
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Join the lab
We welcome applications from students, postdoctoral researchers, and interns from a wide range of scientific backgrounds, including biology, physics, engineering, mathematics, computer science, and earth sciences.
We treat macroevolution as a complex system shaped by ecological interaction, physical constraint, and deep time. Applicants drawn to theory, organismal biology, and integrative research are especially encouraged.
PhD students will pursue an individual research project, which will be based on their interests within the Unit.
Postdoctoral researchers bring deep expertise and build independent research directions within the scope of the Unit.
Interns contribute to ongoing projects and may develop supervised side projects.
Interns are eligible for authorship on resulting publications, including lead authorship where appropriate, and may continue projects after their internship.
We are not a field-monitoring, conservation, or survey-oriented lab. Fieldwork and taxonomy support hypothesis-driven macroevolutionary research.
Primary Study Groups
Fishes
Our primary model system for connecting form, function, ecology, diversification, and lineage history. Their 500-million-year fossil record can be integrated with living diversity, biomechanics, development, genomics, and ecology to test general macroevolutionary hypotheses across scales.
Early Vertebrates
Early vertebrates provide natural experiments in the origins of major body plans, ecological strategies, and functional systems, and a window on the initial diversification of major clades. Their fossil record lets us test how developmental and biomechanical possibilities were realized, how extinction reorganized evolutionary opportunity, and why some forms persisted while others disappeared.
Aquatic Ecosystems
Living and fossil aquatic communities allow us to test when local ecological processes scale into long-term evolutionary structure. We study habitat association, competition, dispersal, community assembly, biogeography, and turnover to ask when ecological effects persist, repeat, propagate, or sort lineages across space and time.
Macroevolution Unit Logo
Lab logo
The Macroevolution Unit logo (painted by John Megahan) features two fishes that bracket the evolutionary and conceptual scope of the lab.
The jawless Paleozoic fish Sacabambaspis represents early vertebrate evolution, the origin of skeletal systems, and deep-time ecological structure. The modern reef fish Pterocaesio diagramma (gurukun / タカサゴ), Okinawa’s prefectural fish, represents contemporary biodiversity, community assembly, and functional ecology in Indo-Pacific systems.
Although separated by ~460 million years, the two species are similar in adult size and feeding mode (zooplanktivory), highlighting a central theme of our work: ecological roles and functional designs recur across deep time even as lineages turn over. The pairing reflects the lab’s focus on constraint, repetition, and reset in vertebrate macroevolution.
