The start of this video has had 9 million views on TikTok: https://www.tiktok.com/@mamlambofossils/video/7067243212762647809

The crab is around 12 million years old, from the middle Miocene, and it lived in deep water. I found the round rock on a beach in New Zealand and could tell there was a crab inside by the leg holes visible on each side. The rock was removed using an air scribe. I then created a 3D model of the crab using photogrammetry which is shown on the carousel. The 3D models have been made available so everyone can print their own crab using a 3D printer.

The two questions I try and answer in this video:

1. Why did the crab not get eaten by another animal when it died?
2. How did it get into the rock?

Question 1: The crab was probably covered in mud / sediment by a landslide, turbidity current or some other geological event. This stopped it from being eaten by other crabs. I used some lego crabs to show how a landslide could potentially bury a colony of crabs in an instant.
Question 2: Using Blender (3D application), I created a 3D model showing one theory of how the crabs became trapped in the rocks. The decomposing crab releases fatty acids (black see-thru sphere) which provides the carbon for the next part of the reaction. The carbon reacts with the calcium (red spheres) in the sea water and form calcium carbonate which cements the mud together into a concretion.

The concretion is harder than the surrounding rock so they get eroded out and then end up on the beach where they get washed around by the waves.

The species of crab is a Tumidocarcinus giganteus which is now extinct.


The rock is called a concretion and is made up of calcium carbonate (CaCO3).

All 3D models and footage in the video was created by myself, Mamlambo Fossils.
Music: https://www.bensound.com/royalty-free-music