Bishop Bell's dinosaur

For those who don't know, this is an engraving on Bishop Bell’s tomb-brass in Carlisle Cathedral (UK). It shows a pretty clear image of something that couldn't be something else than a dinosaur. Here is a link: http://storiesfromthediogenesclub.blogspot.ca/2007/07/strange-beasts-on-bishop-bells-tomb.html

Nobody explained how could a dinosaur appear in a 15th century image, we only found about them much later. All the explanations that I found are ridicule at best, including the one from that link. What do you think?