While reading his description of the Germanic tribes clothes I found this paragraph particularly interesting-
"They choose certain wild beasts, and, having flayed them, diversify their hides with many spots, as also with skins of monsters from the deep, such as are endangered in the distant ocean and in seas unknown"
What monster of the deep is he referring to? If I understand the geography correctly he must be referring to creatures from the North Sea, right? What sea creatures do we have on the fossil record from that area and time period that no longer exist?
That's a... strange translation. The original text is:
Eligunt feras et detracta velamina spargunt maculis pellibusque beluarum, quas exterior Oceanus atque mare gignit.
I would translate that as "they choose the animals carefully and trim the flayed hides with patches/spots and fur from animals who are brought about by the outer Ocean and the unknown seas".
Beluarum are the animals, or wild beasts, but Tacitus here doesn't refer to any animals of the deep like a Kraken, that are brought about (quas gignit) - or engendered? Maybe that's a typo by the translator here - by the distant, i.e. northern Ocean, on the outer edge of Roman knowledge at the time. 'Monsters from the deep' is translating it a bit loosely. Belua usually refers to large or monstrous animals, also to the wolf - beluae pellis is the hide of the wolf. But Tacitus is referring to animals used for their fur, which came from the lands around the 'outer' or northern ocean, the Baltic Sea area and Northern Europe in general. So it could be better understood as 'fur from animals from across the Northern Sea', or who live on the edges of the Northern sea. That could include seals, who are often used for their fur and do have spotted hides but I don't think we need to strain the interpretation that far.