[nudephil (OP)]

Our latest question comes from one of our younger listeners, five-year-old Johan...

Why is a crocodile's skin bumpy and not smooth?

Can anyone chip in?

[alancalverd]

Several possibilities occur. One is camouflage: a broken and mottled outline merges better with the natural debris when the animal is on land. Another is hydrodynamic advantage: rather like a dimpled golf ball, the bumpy surface gives better boundary layer adhesion at high speeds (simply put, water flows easily over a turbulent layer rather than dragging on a smooth hydrofoil), and counterintuitively allows the crocodile to swim faster and manoeuver more vigorously than a smooth skin.

Zillions of years of evolution have optimised the shape and distribution of the bumps for rapid acceleration and turning.

[evan_au]

The osteoderms (boney skin) on a crocodile's back and sides acts as armour -
- Defensive: Pressure from an attacking animal is spread over a large area
- Offensive: Pressure from a large area is concentrated on a small area of a prey animal.

Note that a crocodiles belly is actually quite smooth.
See: https://en.wikipedia.org/wiki/Osteoderm

[Bored chemist]

Why is a crocodile's skin so bumpy?
Have you ever tried to iron one?

[alancalverd]

Not sure which species (other than handbags) prey on crocodiles. I think the smooth belly is a compromise - difficult to drag a washboard through mud!

[Bored chemist]

Not sure which species (other than handbags) prey on crocodiles.

Some of the big cats will take on an adult croc.
Baby crocs are prey for just about any decent sized carnivore or omnivore.

[EvaH]

Asked and answered on the show!

https://www.thenakedscientists.com/podcasts/question-week/why-do-crocodiles-have-such-bumpy-skin