I apologize if this has been proposed before (my searches didn't find it), but I think that Shinovar is the last remnant of Roshar's original, Earthlike ecology. My theory is as follows:
Once, the Rosharan super-continent was Earthlike, with Shinovar at its eastern end. Then Odium sent the Everstorms, which began to erode the western part of the continent. In response, Honor sent the Highstorms, which laid down crem, creating new lands to the east. Over the course of the millennia, the original continent was eroded away up to Shinovar, while a new continent was created. Meanwhile, sea creatures began to migrate onto the new land (possibly with help from Honor or Cultivation) and, with the help of magic, evolved into chulls, axehounds, skyeels, and the rest. Now Shinovar is all that remains of the planet's original ecology.
In addition to geology and the storms, this theory is supported by the fact that most of the non-Shinovaran wildlife of Roshar does not seem physically possible without the help of magic. In real life, a large land invertebrate like a chull would be crushed by the weight of its own exoskeleton, even in a lower-gravity environment like Roshar's (remember the square-cube law). Brandon has confirmed that chasmfiends require spren to survive, and I suspect that something similar is going on with the more mundane greatshells. Thus, these life forms must postdate all of the ambient magic that currently exists on Roshar. Moreover, there's Hoid's comment about the orphaned etymology in the term "axehound", which seems to imply that hounds once existed on Roshar but have been forgotten.
