Henry Gee

Now, some creatures such as jellyfish and hydra, they have one opening that leads to a bag-like gut.

So everything that goes in comes out the same way.

And it's usually a kind of dissolved wash process.

of stuff, but a major innovation was the through gut, where there's a mouth at one end and an anus at the other end.

Now, of course, biology loves its exceptions.

There are these amazing things called cone jellies, ctenophores.

They have four anuses, which is amazing.

But we'll forget about them.

They're another, like chickens are another whole thing.

But so there was a mouth at one end and an anus at the other.

And so animals, for the first time, had a direction of travel.

So animals started doing things that they hadn't done before.

Most of the time, previously, they just stayed in the same place, waving tentacles in the air.

I mean, Ediacaran animals were rather like that.

They just stayed in the same place.

They started burrowing.

Now, as we've talked about, the origin of the Cambrian is marked when burrowing.

burrowing animals happened.

There's a particular kind of burrow called treptichmus that was made by a burrowing animal.

Now, there are many ways to burrow.