Most genetically modified, human-derived species in the Orion's Arm Civilisation have retained at least a baseline-level intelligence. However high intelligence comes with a price; the human brain requires a lot of energy to operate (which quite often requires processed or cooked food to obtain), and high intelligence and self-awareness are not absolute requirements when designing a successful species. The well known Abdicator clade, Homo epimetheus, is an example of a humanoid post-intelligent species. On the planet Bullseye the famous gengineer, Jintre Fo-La, has created a post-intelligent non-humanoid (but still largely human-derived) species, intended to potentially last for hundreds of millions of years without evolving significantly. This species is the Snark.
A Snark is an amphibious crocodile-like creature, with a smooth but resilient pinkish-grey skin and streamlining similar to a dolphin. In fact the Snark clade incorporates many genes from the sentient dolphin race, as well as from merhuman types found around the Orion Arm. Most of the Snark genome is human, although some is indeed derived from crocodile sources.
Creatures which develop intelligence have to devote a significant amount of their energy and resources simply to support their large brains. Intelligence is an adaptation which confers many advantages, but also can cause increased stress on a population. Compared with a successful, long-established species like a shark or a crocodile, the human species has a short history. If a species of human descendant could be developed which was as well-adapted to its environment as the crocodile or the shark, then it could thrive on a suitable planet for hundreds of millions of years without sentience and all the strife that attends that condition. The Snark was not the first attempt at such a post-sentient adaptationist solution, but so far it is one of the most successful.
The Snark is mostly an ambush hunter, leaping out of creeks to catch large quadrupeds or from hiding to surprise fish in the shallow seas. The species has a dual metabolism, capable of switching to poikilothermy when required to conserve energy. Such a metabolism could not support an over-large brain, so Snarks rely on instinct most of the time in their hunting behaviour. The set of behaviours instilled into the Snark species was derived from many successful predators throughout the Orion Arm, from Earth and elsewhere.
Since the development of the Snark clade on Bullseye the baseline human population of that world has declined until the world is almost deserted, except for the post-sentient beasts in the rivers and seas. On the other hand Snarks or similar post-sentient species have been introduced into an increasing number of worlds throughout the Orion Arm. Snarks are in fact a relatively dangerous species, and hundreds of thousands of fatalities have been caused by Snark attacks over the last millennium alone. The satisfied smile of a Snark after eating a modosophont victim is something many witnesses have remarked upon.
One factor which has contributed to the popularity of this option is that in general, when a Snark is augmented back into sophonce by artificial means, the creature expresses great contentment with eir former lifestyle and often requests to be returned to a state of unthinking innocence.