Release the robotic Pleurocystites!

Speaking of paleobiology, here's a fun story that crossed my desk recently...

If you've ever seen a fossil of Pleurocystites or its ilk, you've probably wondered what the heck it was doing in life (and perhaps how disturbing it may have looked while doing it). What once was confined to the realm of speculation now takes a step, or more accurately a kind of thrash, into the 21st century with the "Rhombot", a robotic pleurocystitid detailed in Desatnik et al. (2023).

The rhombots use the basic form of a pleurocystitid: central capsular body (theca), two short appendages (brachioles) at one end, one long appendage (stem) at the other end. The body plan is scaled-up in comparison to the real thing, and, of course, it is made of various artificial materials (many of which are not rigid, hence the "soft robotics" tag) rather than pleurocystitid stuff.

Pleurocystitids, thrashing their way from Ordovician seafloors to the modern day via the rhombot (Figure 1, Desatnik et al. 2023) (CC BY-NC-ND-4.0).

Granted, a rhombot is not a direct replica of a Pleurocystites. Assuming the living thing did indeed use its stem for propulsion, what can we gather from a robotic equivalent? First off, the rhombot was much more efficient with the stem moving it from behind rather than pulling it along. (This seems like a common-sense conclusion on first principles, so it's good to see it confirmed.) The stem also was more effective when used with a stiff sweep, rather than working with a sinuous motion. Finally, there was an optimal length for the stem (Desatnik et al. 2023). I encourage you to go to the linked article and see the movies of rhombots in action; they are not the most graceful robots, but pleurocystitids were probably not the most graceful animals.

References

Desatnik, R., Z. J. Patterson, P. Gorzelak, S. Zamorad, P. LeDuca, and C. Majidi. 2023. Soft robotics informs how an early echinoderm moved. Proceedings of the National Academy of Sciences 120(46):e2306580120. doi: https://doi.org/10.1073/pnas.2306580120.