Fossil site reveals giant arthropods dominated the seas 470 million years ago
https://www.exeter.ac.uk/news/research/title_953405_en.htmlQuoteDiscoveries at a major new fossil site in Morocco suggest giant arthropods – relatives of modern creatures including shrimps, insects and spiders – dominated the seas 470 million years ago.
Early evidence from the site at Taichoute, once undersea but now a desert, records numerous large "free-swimming" arthropods.
More research is needed to analyse these fragments, but based on previously described specimens, the giant arthropods could be up to 2m (6.56 feet) long.
Still this needs further research before we can confirm gigantism was widespread back then.
We still have the gigantic sea scorpions (eurypterids), trilobites and anomalocardids. Ironically the largest arthropod to have ever existed was a land bound one, Arthropleura was roughly the size of a crocodile.