Donglei Chen

We are fascinated by the wonderful microscopic world hidden inside the fossils. Although the fossil remains of the earliest vertebrates are usually very fragmentary,

their histology can surprisingly be preserved with near-perfect nano-scale fidelity. With ultra-high-resolution phase-contrast synchrotron microtomography, we can visualise the 3D architecture of cell spaces, blood vessels, collagen fibres, etc. in the hard-tissue organs. Hard tissues (bony tissues and dental tissues) are among the key innovations of vertebrates. On the one hand, early vertebrates displayed a tremendous diversity of dental tissues, which has been lost in extant vertebrates. On the other hand, convergent evolution appears unexpectedly overwhelming: each type of hard tissue blinks on and off all over the vertebrate tree, with multiple times of loss and regain. How the diversity was achieved and what is the evolutionary relationship between the tissue types remain open questions. We look at the conundrums from a different angle and ask ‘Do any novelties have to evolve de novo? Is there a developmental continuum underlying the convergence?’ Therefore, our aim is to understand the mechanisms of tissue formation and interaction based on fossil materials by comparing with extant taxa.