Why are there dinosaurs in this 16th century painting?

In Pieter Bruegel the Elder's Suicide of Saul, you can clearly see what seem to be sauropods in the background. To my knowledge, dinosaurs would remain undiscovered for centuries. What are these things? They don't resemble anything other than Brontosauruses.
Source video: https://youtu.be/AYoE0BunkN4

Music: Intuit256 by Kevin MacLeod is licensed under a Creative Commons Attribution 4.0 license. https://creativecommons.org/licenses/by/4.0/

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