Department of

Chemical and mechanical patterning of tortoise skin scales occur in different regions of the head.

Vertebrate skin appendages are diverse micro-organs such as scales, feathers, and hair. These units typically develop from placodes, whose spatial patterning involves conserved chemical reaction-diffusion dynamics. Crocodile head scales are a spectacular exception to this paradigm, as they instead arise from a mechanically dominated process of compressive folding driven by constrained skin growth. Here, we reveal that chemical versus mechanical processes pattern tortoise scales in different regions of their head. Indeed, we show that placode-derived scales emerge across the peripheral head surfaces while remaining absent from the central dorsal region where scales subsequently form through a mechanical folding process. Using light sheet microscopy, we build a three-dimensional mechanical model that qualitatively recapitulates the diversity of scale patterns observed in this central head region in different tortoise species. Overall, our analyses indicate that mechanical head-scale patterning likely arose before the divergence between Testudinata and Archosauria, and was subsequently lost in birds.

Alexandros Tsoupas wins the 2025 PSLS Annual Thesis Prize

His thesis, "Inferring Population Dynamics During Past Expansion Events Using Spatiotemporal Molecular Patterns", explores how genetic data distributed across space and time can reveal the demographic processes underlying past population expansions.

Understanding Architecture And Evolutionary Patterns In Haplolepidous Peristomes (Dicranidae, Bryophyta) Using Histology And Micro-Morphology

25.07.2023 14:00, Salle de conférence (Museum of Natural History)

Mathilde Ruche (Michelle Price's group).
hosted by: Michelle Price.