Hello! Do you have any information on ancient jellyfish? many thanks (:
Hey! Yes I do, although I had kinda forgotten about them up until now (so thanks for reminding me).
Jellyfish first appear back in the fossil record back in the Mid-Cambrian, 505 million years ago. On one hand, this is to be expected, as most major animal groups appear at this time. But on the other hand, jellyfish are soft and squiggy - soft and squiggy things don’t tend to get preserved in the fossil record. For ease, I am going to take “jellyfish” to mean all members of the Medusozoa clade, which includes true jellyfish, box jellyfish, blue bottles, stalked jellyfish - even though most people probably would associate all members as “jellyfish”, e.g. hydra.
Cartwright et al. (2007), wrote a cool paper describing the oldest known jellyfish fossils. The fossils have a lot in common with modern jellyfish, suggesting that he Medusozoa clade diversified in the Cambrian, and then remained relatively the same ever since.
Scale bar = 5mm. The tentacles around the hood/bell/“jelly” bit is a trait common in Hydrozoa (e.g. Portuguese man o’ war).
Scale bar = 5mm. The square shape of this jellyfish suggests it may have been an early Cubozoa (i.e. box jellyfish), further supported by the thickening at the tops of the tentacles (lebelled “ped”), which are interpreted to be early pedalia.
Scale bar = 5mm. This fossil is just the top of the jellyfish (i.e. the hood/bell/“jelly” bit), and shows the muscles that enable the jellyfish to swim around and are characteristic of Scyphozoa (i.e. true jellyfish).