Ferrobeast is not just a species, it's a category of a wide variety of species which have a common set of ancestors.
In the early interuniverse era, scientific institutions were given vast amounts of resources to conduct experiments in parallel universes which were far higher on the entropy scale, which also meant time passed at a relatively much faster rate compared to our universe.
Initially, computational experiments were carried out but it was eventually concluded that the greatly increased energy consumption including the various energy leaks that characterize the environment of such space, hindered any significant advantage an increased relative time for calculations would result in.
One thing however that could handle such an unusual environment was life itself.
Biological and accelerated evolutionary experiments could be carried out with rapid results in these relative time-dilated-space-time universes.
Inside one of the dead planets in high entropy space, an enormous complex was dedicated to a new branch of biological research: incorporating a large amount of metals into biological life, in hopes of making them highly resilient to the harsh environments that were beyond the realistic possibilities of space colonization.
These lifeforms could serve as initial prospectors and workers even before terraforming completes, and they would be much more versatile and adaptive than even robots.
After the experiments started with evolution-accelerating techniques and the huge artificial caverns were established, the evolutionary process was set loose on its own, including a complete ecosystem of life from ferro-microbes to ferrobeasts.

Scientists would send in expedition teams every month through the huge time-dilation difference entrance, "the ramp", spend one week inside, then return outside to normal space, where a fraction of an hour has passed.
Inside, in this one month time frame between expeditions, thousands of years would have passed in the experiment's varied caverns.
The entrance was guarded by a guardian A.I. whose purpose was to secure the entrance, make sure the systems of the place were not penetrated by the creatures, but wasn't under any circumstances allowed to mass exterminate them.
The creatures proved to be more and more of a danger even to the advanced combat robots manufactured by the factory modules at the A.I.'s disposal.
The scientists, returning from their later expeditions about a decade after the experiment started, reported outstanding success in this evolutionary experiment, even with the looming danger of how formidable the creatures started to become.

And then, war broke out in our space.
With the frontline steadily approaching the lowspace base, the scientists and the military force defending the outer structure has no better choice, but to do one last expedition, then seal the entrance indefinitely.
The station lay abandoned throughout the war and afterwards, for 29 years of normalspace time.
What happened inside and what the now uncontrolled evolution would produce inside was an unknown to the dwellers of the worlds outside, but one thing was for sure: whatever lived inside evolved to survive and fight against an endless combat-robot army and other creatures of similar capabilities, in a struggle longer than any advanced species' entire recorded history.