How do paleontologists "reconstruct" an entire animal from just a small portion of its bones. e.g. I just read this wikipedia page:

https://en.wikipedia.org/wiki/Purussaurus

>Purussaurus is an extinct genus of giant caiman that lived in South America during the Miocene epoch, from the Colhuehuapian to the Montehermosan in the SALMA classification. It is known from skull material found in the Brazilian and Peruvian Amazon, Colombian Villavieja Formation, Panamanian Culebra Formation and the Urumaco and Socorro Formations of northern Venezuela.

How can you surmise what a whole crocodilian looks like by just looking at skull fragments?