Various animal sources can actually provide significant vitamins to a diet, especially vitamin D and especially in offal.

From the abstract to this article:

The published data show that the highest values of vitamin D are found in fish and especially in fish liver, but offal also provides considerable amounts of vitamin D. The content in muscle meat is generally much lower. Vitamin D concentrations in egg yolks range between the values for meat and offal. If milk and dairy products are not fortified, they are normally low in vitamin D, with the exception of butter because of its high fat content.

Hiya! You may be interested in a few earlier posts on this question

• How were the indigenous people of the Great Plains able to ingest enough vitamin C to avoid scurvy? - despite the post title, /u/Gargatua13013 does comment on vitamin sources in Inuit diets

• What did earlier(Before current refrigeration) Northern peoples eat instead of citrus? - /u/AshkenazeeYankee makes a brief comment on vitamins in northern diets in general; I provide a bunch o' links to more posts on the causes of scurvy and dietary sources of vitamins

It often used to be asserted (even in my own history class) that Aboriginals in the far north could make some of their own vitamins due to an adaptation in response to vitamin deficiencies, we now know that the sea life of which their diet was comprised of actually did provide the full suite of nutrients due to them not discarding parts of the animal that other societies might discard as offal.