Learn Swedish: De hade renderat dinosaurien som vi tittade på. - They had rendered the dinosaur that we were looking at.

Yes, rendera is borrowed from English, mostly used in computer graphics or IT. It is a regular Group 1 verb, which means it takes an -ar ending in the present tense, -ade in the past, and -at in the supine form used here with hade.

What is the base form of dinosaurien, and why does it end in -ien here?

The base form is en dinosaurie (a dinosaur). For en-words ending in -ie, we drop the final -e and add the standard -en suffix to make it definite, resulting in dinosaurien.

Why is the preposition på placed at the very end of the sentence?

Swedish allows preposition stranding at the end of relative clauses, just like English does. Because the relative pronoun som refers back to the dinosaur we were looking at, the preposition på belongs to the verb tittade but gets left at the end of the clause. Trying to force it earlier would sound highly unnatural.

Why use the past perfect hade renderat instead of just the past tense?