Gutarra, S., Moon, B.C., Rahman, I.A., Palmer, C., Lautenschlager, S., Brimacombe, A.J. & Benton, M.J. 2019 Effects of body plan evolution on the hydrodynamic drag and energy requirements of swimming in ichthyosaurs . Proceedings of the Royal Society B 286: 20182786 doi:10.1098/rspb.2018.2786
As part of her PhD, Susana Gutarra has been modelling ichthyosaur hydrodynamics, investigating the effects of body morphology on their swimming ability. This was earlier a project that I started then gave to MSc student Alison Brimacombe, and Susana added lots of fluid dynamical knowledge and finesse.
Here we used 3D models, based on exceptionally preserved ichthyosaur specimens from throughout their phylogeny, in computational fluid dynamics simulations to explore how the changing shape of ichthyosaurs affect the amount of drag and lift generated.
We expected to see a clear trend where the later ichthyosaurs, traditionally considered to be better adapted to life in the oceans, had reduced the amount of drag generated, and so could put more of their effort into swimming forward.
However, the story is more complex. While morphology does have some minor effect on drag, what becomes more important is the ability to create thrust to overcome this. We therefore looked at the total cost of transport – how much effort do you have to put into going forwards. This did seem to reduce through ichthyosaur phylogeny, while also being heavily affected by the size of things.
Our summary was that getting bigger and swimming in a more efficient manner, like dolphins or tuna, are your best bets for reducing effort.