Question: When you find an embryo, is it ever hard to notice what type of animal it is?

Ceri-Wyn Thomas answered on 16 Jun 2010:

Cool question!! Yes it’s basically impossible to guess what sort of animal a fossil embryo came from because the fossil embryos I work on are at such an early stage of development (they’re just balls of cells in a little round envelope) that we have no clues as to what sort of animal they could be. They’re not found with any adults that may have produced them and they are from a period in Earth’s history when animals were only beginning to evolve anyway! Our guess is that they came from a sort of pre-animal- an ancestor from which the animals that we know and love evolved. However, if you go a little further ahead in time to the Cambrian period (542-488 million years ago) we’ve found embryos that look exactly like the embryos modern jellyfish produce!

If I was working on real embryos from living animals (which I’ve also done) then hopefully I would always know because you need the adults there in the first place. The embryology of many organisms is very well known and embryos from different animals can look quite different even when they’re all just balls of cells- they can be different sizes and colours and have different ways of dividing up into more cells as they grow.